PCB Fabrication

Evaluating a PCB Assembler

The flood of printed circuit board (PCB) service providers in the market makes it very difficult for OEMs to decide the most suitable fabricator or assembler for their product. Rush PCB is hereby offering some guidelines on how to evaluate and select the PCB house that can be a perfect fit for a long-term cooperation.

Although PCB manufacturers offer several references and links justifying their suitability, and OEMs should inspect them carefully, the main consideration hinges on three aspects:

  • PCB Types Handled—Industries Served, Quality, and Cost
  • Engineering Capabilities—Certifications and Technology used
  • Services Offered—Lead Time and Responsiveness

PCB Types Handled

The types of PCBs handled by manufacturer gives a broad view of their overall capabilities. With so many industries using PCBs, OEMs should look at specific industries the PCB house serves, preferably with strict and special requirements. PCB manufacturers can at best serve only a few industries at a time, as they will be proficient for certain industries and not so proficient for others. If the PCB manufacturer is serving industries similar to that of the OEM, then they could be a suitable choice, provided they meet other criteria.

Rush PCB supplies boards to Google, NASA, Nvidia, Fairchild, Linear Technology, Fitbit, GE, Intersil, and many others. Visit our website for more information.

Quality of the PCBs is an important factor to consider. The OEM must look for evidence of the use of Statistical Process Control (SPC) during the manufacturing process. They should also have implemented an overall quality administration improvement program such as TQM or QCC. Other things to look for may include equipment calibration, ESD implementation, BOM preservation, file administration, AQL level, SMT yield rate, material inspection record and administration, and whether they administer Engineering Change Order (ECO), as all of them affect the quality of PCBs.

One of the biggest elements driving the choice of a PCB assembler is their cost of operation. While this may not be directly visible without a financial audit, it does reflect in their quotations. OEMS should look for an integral quotation that includes all aspects of the PCB manufacturing, and does not have some hidden factors that they will reveal at a later period. Most reputed PCB manufacturers also offer some discounts on reorders. The discount comes mainly from non-recurring tooling costs, and manufacturers apply such strategies to form a long-term cooperation.

For a comprehensive quote, simply send your BOM to Rush PCB. We provide breakup of price for bare boards, components, and labor.

Engineering Capabilities

PCB quality is closely linked to the engineering capabilities of the manufacturer or assembler. It is usual for them to demonstrate these capabilities in two ways—through certifications and through technology they use. Manufacturer earn their certifications based on their manufacturing capabilities and their proven adherence to international standards such as ISO 9001:2008 or ISO 9001:2015, RoHS, UL, and more, to demonstrate the high quality of their products.

Rush PCB certifications include ISO 9001:2015, UL, IPC, RoHS. Please visit our website for more information.

OEMs can gain insight into the technological capabilities of the PCB manufacturer by looking for the in-house presence and use of machinery and processing capabilities pertaining to their requirement. For instance, if the OEM needs BGA processing capabilities, the manufacturer must own a BGA IC repair capability. Other important things to look for are capabilities such as panel processing, storage life administration, solder paste temperature and thickness monitoring, moisture sensitivity level monitoring, RoHS implementation. The manufacturer must also have the capability of reviewing circuits, providing DFM service, and the capability of soldering and repairing SMDs as small as 0201 or 01005.

OEMs should also look for up-to-date equipment when selecting a PCB manufacturer or assembler. This includes equipment for fabrication, assembly, and testing, such as for solder paste inspection, SMT pick and place, X-ray inspection, Automated optical inspection, and In-Circuit inspection. For some equipment, it is also important to check their accuracy, such as SMT pick and place machines, especially when they are to handle tiny components such as 0201 and 01005.

Rush PCB manufactures all types of PCBs including FR-4, multi-layer, flex, rigid-flex, and HDI. We undertake military and aerospace PCB assembly. Our website has more information, please visit.

Services Offered

Manufacturers may offer a number of added services that benefit OEMs. Total turnkey PCB assembly service is one such where the manufacturer takes the responsibility of manufacturing the PCB, procuring the components, assembling and testing them, and finally delivering the completed PCB. However, before submitting to such a service, OEMs should look for proper component sourcing capabilities.

Crucial component sourcing capabilities should include sourcing qualified components from leading global component distributors. It would be advantageous if the assembler accepted components supplied by the OEM, and if they stock surplus components for future projects.

Lead time, or the time the manufacturer takes from receipt of order to actual delivery of PCBs, is an important factor, as it affects the time to market for the OEM. Therefore, the OEM should always check whether the lead time is compatible with their requirements, and whether the manufacturer is able to maintain the delivery times.

Read About: Requirements for PCB Assembly Drawing

Responsiveness to the customer’s needs and requirements is another factor that seriously affects long-term association. The manufacturer should be able to react to new orders quickly. This may include fast reactions towards a change in the project before or during production, expanding manufacturing capabilities for urgent orders, and providing practical solutions during emergencies.

Rush PCB offers full turnkey solutions for PCB assembly. We accept all orders, including prototype, small production orders, or large-scale and continuous production orders.

Conclusion

Detailed investigation can lead to making an informed decision about the suitability of the PCB house in providing adequate and long-term services for the requirements of the OEM.

PCB Assembly Reliability

Ensuring PCB Assembly Success

Although there is a distinct difference between PCB manufacturing and PCB assembly, Rush PCB has experienced personnel to handle both. We ensure that you get a quality solution, whether you get your PCBs fabricated by us, allow us to assemble components on your PCBs, or both.

At Rush PCB, we make sure the solution to your problem is both cost-effective as well as high in quality. We make this possible by paying due attention to our processes, acting as a consultant to our customers, and offering effective suggestions both for assembly as well as for other aspects such as design and best practices.

PCB Fabrication and Assembly

The process of PCB assembly comes after the PCB fabrication is over. However, Rush PCB recommends customers begin their consultations with their PCB assembly partner early in the process. This is necessary because the PCB assembler can provide important inputs before and during the design stage, as they have accumulated vast experience and expertise. Not consulting them in the early stages may require incorporating these modifications later, a step that could prove not only expensive, but also delay you from going to market.

Selecting an Assembler

Therefore, Rush PCB recommends customers to choose their PCB assembler wisely. It is always wise to look for multiple suppliers who can assemble your PCB, so that you have a backup in case your assembler discontinues production for whatever reason.

Offshore vs. Onshore

While an offshore PCB assembler can be cheaper than an onshore supplier, the former may have several hidden costs. A delay in delivery or receiving low quality products can easily offset the low initial cost, forcing you to factor them in your product pricing.

File Formats

It is important that the PCB assembler understands the file formats you will be sending over to them—not all assemblers use all file formats. This is one more reason Rush PCB recommends customers to begin consulting their assembler at the early stages of design. Making sure the PCB assembler is comfortable with the file formats you are using can help avoid wastage of time.

Consulting Begins Early

At Rush PCB, experienced personnel can help you with the initial design and schematic creation. This has the advantage of not having issues at the later stage of assembly. Having to redo the prototype at this late stage can not only prove to be very expensive, but also the customer will lose out on precious time.

Importance of DFM

Rush PCB also recommends a Design for Manufacturing or DFM review before sending the design for a PCB assembly. A DFM review checks whether the design is easy to manufacture, and identifies issues such as those of component polarity and inadequate spacing between components. Pointing out such discrepancies at the start of the design instead of at the end saves time and a lot of expenses.

Special Requirements

Listing the special qualities of the board in the beginning helps the assembler as well as the manufacturer. A key requirement of your board may be its high current handling capability, very high frequency capability, or strong signal transmission. Keeping this requirement in view helps the design achieve it better. Of course, during the design, there may be some trade-offs that are inevitable. But enumerating the special requirement in the beginning ensures meeting the final expectations without discrepancies. The PCB assembler may also offer their recommendations.

Lead Time Factors

Both the design phase and the assembly phase will have their own lead times. Designers need to factor in these lead times to arrive at the final time to market. In addition, designers will also need to add the testing time that the PCB assembler will need to test the boards after completing the assembly Rush PCB recommends factoring in these lead times as it offers the customer as well as the assembler adequate confidence in defining the quality of the product.

Rush PCB offers dedicated PCB manufacturing and assembly, SMT PCB assembly, LED PCB assembly, Prototype PCB assembly, Mixed PCB assembly, and more services as per requirements and specifications of our customers.

For any inquiries and questions, please feel free to contact us via email or phone.

PCB Assembly

PCB Layout and Assembly for EV Charging Stations

With people all over the world endeavoring to give up use of fossil fuels, electric vehicles (EV) are beginning to take over the roads from vehicles using internal combustion engine. This is causing numerous charging stations to come up every day to help charge EVs. Rush PCB is driving innovations in such car charging stations by providing expert Printed Circuit Board (PCB) layouts, PCB manufacturing, and assembly solutions.

How EV Charging Stations Operate

Plug-in Electric Vehicles (PEVs) function with a battery in the vehicle driving an electric motor. As the battery charge depletes, periodically, it becomes necessary to recharge it from EV charging stations. This is possible to do by plugging in the vehicle to a wall outlet, which an EV charging station provides.

EV Charging Requirements

Although battery technology is still progressing, electric vehicle owners demand fast charging of the battery, as they must spend the minimum amount of time at the charging station. This is forcing the electronic industry to come up with innovative solutions for car charging stations to provide them with fast and high efficiency chargers. While the electronic industry is developing new and more efficient components for achieving better charging methods, Rush PCB offers their expertise in PCB manufacturing for improved layouts, manufacturing, and assembly techniques.

Contact Rush PCB for the latest types of PCBs for your EV charging station requirements.

Types of EV Charging Stations

Rush PCB offers high quality PCB prototypes using the latest technology. Manufacturers make EV charging stations for homes, commercial, or for public use, and Rush PCB caters to all types of PCB requirements with multi-functionality features. Depending on your requirement of a new type of customized solution for a pedestal charging structure, a wall mounted type of charging station, or a curve/ball type of charging platform, Rush PCB has the necessary solution to offer.

Commercial EV Charging Stations

Commercial EV charging stations usually demand a robust vandal resistant unit, typically providing one-way or two-way plug-in facility with customized fast-charging features. Rush PCB provides charging station manufacturers with innovative solutions for security including c/w hatch lock, overload protection, and fault current monitoring.

Challenges to PCB Manufacturing

Apart from automatic charging capabilities, commercial EV charging stations also require auto plug-in and payment facilities. These requirements are an additional challenge to the PCB manufacturer, as they require the presence of an embedded controller within the system offering Near Field Communication (NFC) and Internet capabilities for mobile payments. Rush PCB offers all the above at nominal cost of production, based on their highly efficient technology for manufacturing and assembling PCBs.

Commercial EV charging stations also require control centers with a dual facility—for optionally selecting pay-to-use or free-to-use car charging service. Additionally, one control center must manage multiple local EV charging points. Once a vehicle comes in and parks at a certain EV charging point, the control center automatically initiates the charging procedure. Rush PCB offers high quality PCBs for manufacturers of control centers, compatible with multiple charging stations.

Rush PCB Customized Design and Layout solutions

Rush PCB provides customized PCB design and layout solution for the EV charging station designer and manufacturer. We have a dedicated team of technical experts to provide an effective PCB layout for your project, and follow it up with unique assembly solutions. For realizing your market objectives, Rush PCB offers you the consigned and complete turnkey solution.

Rush PCB Customized Assembly Solutions

Rush PCB offers its customized PCB assembly using state-of-the-art techniques and machinery. We offer compact and multi-featured PCBs for the automobile industry using the latest Surface Mount Technology (SMT), but we also offer Through Hole Technology according to customer requirements. For the high-tech control systems that the EV charging stations use, we offer a complete PCB turnkey solution. If you require any type of consultation, we offer the services of our experienced technical personnel.

Contact Rush PCB Now

The main strength of Rush PCB lies in our extensive experience and our offer of quality PVB design and manufacturing solutions. Let us know of your requirements through email, or give us a call. We will solve all your queries, and we will give you a quote. Visit our website for more insight into our capabilities of PCB layout, manufacturing, assembly, and prototyping services.

Read About: Requirements for PCB Assembly Drawing

pcb assembly

Determining Inspection Methods for PCB Assembly

Rush PCB suggests implementing inspection for Printed Circuit Boards (PCBs) at various stages during manufacturing and assembly processes to eliminate surface defects and ensuring they are of high quality and reliability. As a renowned PCB manufacturer and assembler, Rush PCB has professional inspectors capable of exposing leading defects prior to the PCB going for electrical tests.

Circuit boards consisting of surface mount devices (SMDs) assembled on them present a higher requirement for inspection, as solder joints for SMDs need to withstand greater stress than those with through hole components do. Adequate solder is usually not present for anchoring SMDs to the board, which leads to SMDs facing higher structural loads. That means, long-term reliability of boards with SMDs assembled on them depends to a large extent on the structural integrity of the solder joints of its components, thereby necessitating PCB assembly inspections.

Methods of inspection vary tremendously depending on the technology and defects the assemblers expect. Usually, manufacturers classify these into two broad categories:

  • Visual Inspection
  • Structural Process Tests

Visual Inspection

Manufacturers place visual inspection stages between specific processes during PCB assembly, and select the equipment according to the inspection necessary at that stage. Such visual inspection stages may be:

Assembly StageTools UsedDefects Checked
After Solder Paste PrintingNaked Eyes/Magnifying GlassPrinting defects and contamination
After Component PlacementNaked Eyes/Magnifying GlassMissing components, misplaced components, disoriented components
After ReflowNaked Eyes/Magnifying Glass, Light SourceSolder bridges, open joints, tombstoning, etc.

 

Structural Process Tests

By automating video capture in real time and digitizing the process of analysis, manufacturers can speed up the inspection process and improve the quality and reliability of the inspection process.

Depending on the volume of inspection and the speed required, Rush PCB suggests automated optical inspection (AOI) methods. These usually require multiple light sources, cameras, and computers with programs for detecting defects. Automated inspection methods are more expensive than manual visual inspection methods are, but much faster.

Complexity of modern PCBs with higher component density and specialized component structures such as BGA is leading manufacturers use different types of test systems with laser beams and X-rays, rather than visible light. Structural process tests usually do not need physical contact with the circuit board, and provide very high repeatability, while eliminating subjectivity from measuring defects.

Selecting the Method of Inspection to Use

OEMs usually are undecided on the proper method of inspection they want for their boards. To help in picking the inspection method most appropriate for our customers, Rush PCB has prepared the following guide. Prior to deciding whether to go with AOI or X-ray inspection, we suggest that our customers consider three elements:

  • Cost of Inspection
  • Defect Type
  • Inspection Speed

Designers need to consider the expenditure for inspection in relation to the cost of their boards. There is not much merit in conducting an expensive inspection procedure for a low-cost PCB.

The type of defects the designer is expecting in a PCB should define the choice of the inspection method. For instance, if the designer is concerned only about components missing or with wrong polarity, and simple solder joint defects, visual inspection would be enough to detect these defects in small volumes of PCBs.

On the other hand, if the volume of PCBs under production is large, detection of the above defects may require deployment of Automated Optical Inspection.

Additionally, if the PCB assembly consists of BGA and or fine pitch components, the designer may have to decide on X-ray inspection. Computerized X-ray inspection methods may be necessary if the production volume is very high and high inspection speed is the target.

Cost of inspection usually increases with requirements of speed and complexity of the method. For instance, while the cost of inspection is lowest for manual methods, it is higher for low speed inspection involving AOI methods, and the highest for automated X-ray methods for high speed inspection.

Inspection MethodDefect TypesSpeed of InspectionCost of Inspection
Manual OpticalPrinting defects and Contamination,

Missing components, Misplaced components, Disoriented components,

Solder bridges, Open joints, Tombstoning, etc.

SlowLow
Automated OpticalPrinting defects and Contamination,

Missing components, Misplaced components, Disoriented components,

Solder bridges, Open joints, Tombstoning, etc.

MediumMedium
Automated X-raySemiconductor packaging, BGA and fine-pitch solder defects,

Voids in joints,

Internal defects in multi-layer PCBs

HighHigh

Conclusion

Defining the proper inspection method for the PCB assembly can result in enormous cost-savings for the OEMs. On one hand, this defines the expenditure incurred by the OEM for the inspection method, and on the other, it serves to bring down the rejection level and improve the quality and reliability of the PCB assembly. Rush PCB suggests following the above method for selecting the optimum way of inspecting PCB assemblies.

pcb assembly

Requirements for PCB Assembly Drawing

Rush PCB assembles Printed Circuit Boards (PCBs) for their customers. To achieve an acceptable final product, we must faithfully follow the customer’s instructions, which in turn, must be complete and legible.

PCB assembly drawings are necessary as the person assembling the board is not the same person who has designed it. The PCB manufacturer needs the drawings to interpret how to assemble the board.

This document is an introduction to designers who have never created an assembly drawing before. It is necessary designers understand different elements of an assembly drawing and how their PCB layout tools can help in generating these documents.

Different manufacturers accept assembly drawings in several formats. It is necessary for the designer to communicate with their manufacturer to understand the form and nature of the document most suitable to them. However, there are some basic elements that all manufacturers will require when accepting assembly drawings for PCBs.

Basic Elements of Assembly Drawings

Format: Most CAD systems now generate the drawing format automatically. However, some may require the designer to create it as a separate library format. In either case, the designer will need to combine that format with their design database for building their drawing.

Outline of the Board: For fabrication, the manufacturer will require a display of the board outline of the PCB. The designer may scale the drawing to make it more presentable or show greater detail.

Mechanical Parts: The manufacturer will also require information about any mechanical part that the designer wants mounted on the PCB, along with details of the mounting hardware. Non-electrical parts may not have a regular footprint, and the designer may have to provide the drawing of the shape separately. Although some non-electrical mechanical parts may not appear on the schematic, the designer must include them in the bill of materials and in the assembly drawing.

Electrical Parts: All electrical parts that the designer wants mounted and soldered on the PCB, they must display the part shapes along with their reference designators. The designer must also list the parts in the bill of materials and reference them with their unique designators.

Notes for Assembly: Designers must offer instructions for details of basic assembly, with reference to industry specifications and standards where applicable. The notes must also contain the details and location for any special features present on the board.

Bill of Materials: This is a list of all items that the PCB will hold, along with their unique identifying reference designators. The list should also mention the manufacturer and the type number of the components.

Location of the Identification Label: PCBs often require an identification label in the form or a tag or bar code. The manufacturer will need a drawing indicating the position of the label on the board and a reference to the specific label.

Additional Drawing Views: PCBs may have components on both sides. In such cases, the manufacturer will need a view of the back side of the board along with the view of its front side. While the designer may use additional drawings for larger boards, they may include both views in a single drawing for smaller boards. For greater clarity on mounting some mechanical parts, the designer may also add drawings showing the side view of the board.

Cut-Away or Expanded Views: The designer may include expanded views of areas they want to show in greater detail for clarity of the manufacturer. They can scale the cut-away view to provide more clarity, while indicating its position on the main board with a pointer.

For further details, please contact Rush PCB.

Creating Assembly Drawings using Layout Tools

Earlier, designers had to use separate drafting tools for creating assembly drawings. However, almost all modern PCB CAD tools have the functionality to generate all the required assembly drawings in detail.

Using modern PCB CAD tools, designers can import board outlines along with parts information, and rotate, mirror, or scale them as necessary. They can compose or import assembly instructions from an external file, and add them to the drawing. It is also possible for these tools to display detailed cut-away views of the necessary area of the assembly.

After compiling all the necessary drawings, the PCB CAD tool can also convert all the drawing to the electronic format and include them with the manufacturing output files.

Conclusion

Rush PCB recommends designers provide good PCB assembly drawings to manufacturers to help in smooth manufacturing. Providing more details helps the manufacturer complete the assembly without confusion and delay.

PCB

PCB Assembly Fabrication Methods

PCB or Printed Circuit Board assembly at Rush PCB UK Ltd involves combining the bare PCB, electronic components, and other accessories effectively to allow the assembly to function as the designer intended. Broadly, the fabrication methods involve a number of major steps:

  • Component placement
  • Soldering
  • Cleaning
  • Inspection
  • Testing

However, depending on the nature of the PCB undergoing the assembly, above steps may involve further activities.

Component Placement

Methods of placing components on the PCB depend on several factors such as:

  • Single or double side component placement
  • SMD components only
  • Through-hole (TH) components only
  • Mix of SMD and through-hole components

A PCB may have components present only on one of its sides or on both, although assembling a PCB with through-hole components on both sides is a rare occurrence. Single side component placement with either all SMDs or all through-hole components is more common, while single sided PCBs with a mix of SMDs and through-hole components is also to be found.

For assemblies requiring SMDs on both sides of the PCB or a mix of SMD and through-hole components on the top and only SMDs on the bottom, the PCB assembly process must be broken up into several intermediate steps, and the assembler needs to take special precautions for each of them.

Single-Side Component Placement

This type of PCB may have only SMDs, only TH components, or a mix of both. If it is only SMDs, the necessary steps for assembly are:

  • Solder paste printing
  • SMD placement
  • Reflow soldering
  • Manual Inspection
  • Electrical and Functional Testing

When the PCB has only TH components, solder paste printing is not necessary, in place of SMD placement, there is either manual placement or machine placement of the TH components, and wave soldering replaces reflow soldering. For a mix of both components, the assembler places TH components after anchoring the SMDs to the underside using adhesive and follows it up by wave soldering. This is because SMD components at the bottom of the board require to be held in place, while component leads extending on the underside of the PCB are undergoing wave soldering.

Double-Side Component Placement

Similar to the single sided PCBs, double sided PCBs may have SMDs alone, TH components alone, or a mix of SMD and TH components. Although it is usual to mount SMD components on both sides, mounting TH components on both sides is not feasible. However, it is possible to have a mix of SMD and TH components on top, and only SMDs on the bottom side of the PCB.

With both sides of the PCB holding components, multiple steps are necessary for the placement and soldering of the individual sides. SMDs on the underside need anchoring to the bottom side of the PCB to prevent them from falling away. Assemblers use a glue dispenser or a glue stencil to deposit a small drop of glue at the coordinate where the pick-n-place machine will deposit the SMD on the bottom side of the PCB. Baking is necessary to allow the SMD to permanently stick to the board before the soldering process.

The top side of the board may have only SMDs, only TH components, or a mix of the two. If the board has only TH components on its top side, the assembler inserts them and sends the board for wave soldering. However, if there are only SMDs on the top or a mix of SMDs and TH components, the assembler mounts the SMDs first, solders them with reflow, mounts the TH components and then wave solders the bottom side of the PCB.

Soldering

Soldering is the process of joining two dissimilar metals using a molten filler metal alloy. The molten metal alloy enters the joint, and as it cools and solidifies, bonds with the adjoining metals. Primarily, there are three common ways of soldering:

  • Manual Soldering
  • Wave Soldering
  • Reflow Soldering

Manual Soldering

Manual soldering requires the use of a soldering iron whose tip is heated either by gas or electricity. The pcb assembler applies the hot tip to the component lead and pad to heat them up. Solder held on the heated junction melts and solidifies to form a joint. The assembler may apply flux to the surfaces to help the process of soldering.

Wave Soldering

Wave soldering is a bulk soldering method. The PCBs to be soldered pass over a bath of molten solder. The bath has a pump to create a wall of solder that washes the underside of the PCB as it passes over the wall, effectively soldering the components to the underside of the PCB.

Temperature of the molten solder in the bath and the time the PCB is exposed to the solder are the two important parameters governing the quality of the solder joints formed. It is also necessary to preheat the board mounted with components to allow proper wetting. Although wave soldering is primarily effective for TH components, it can solder SMD components anchored with adhesive on the underside of the PCB.

Reflow Soldering

Assemblers use reflow as the most common method for soldering SMD components to the top side of the PCB. However, before they can solder the components, they must deposit solder paste and mount the components in place. The sequence they follow are:

  • Solder Paste Printing
  • Mounting SMD Components in place
  • Passing the assembly through a Reflow Soldering Oven

The assembler first deposits solder paste using a prefabricated stencil onto the pads of the PCB. Instead of using solid solder, SMD assemblers use a paste of solder and flux, which they draw with a squeegee over a stencil placed on the PCB. Appropriate cutouts in the stencil allow the solder paste to deposit onto the pads. On removing the stencil, the pads that will hold the components only retain the solder paste.

A pick-n-place machine then places respective SMDs onto their locations on the PCB. A pre-assigned program on the machine allows it to pick a specific SMD component from reels or cassettes and position it on a predefined position on the solder paste.

This assembly of PCB, solder paste, and components then passes through an oven on a conveyor belt, where heat melts the solder paste, effectively soldering the SMDs to the board. The speed of the board through the oven and the oven temperature are very important settings for achieving a good quality of solder joints.

Cleaning

After soldering is over, some flux residue may remain on the printed circuit board. Over time, this can turn acidic, and corrosively damage solder joints. The flux residue can also attract fingerprints and make the PCB look unclean.

For cleaning and removing flux residue, Rush PCB UK Ltd prefers washing the PCB assembly with high-pressure deionized water. A quick drying cycle with compressed air removes all traces of water, and the PCBs are ready for inspection and testing.

Manual Inspection

Inspection is necessary at various stages of assembly. For instance, one stage of inspection is necessary when the operator has stuffed TH components into the board, and again once the assembly has undergone wave soldering.

Likewise, for reflow soldering, inspection is necessary once after solder paste printing is over, then again after mounting the SMD components, and once again after the boards have exited the reflow oven.

Also Read: PCB Assembly Compatibility with In-Circuit Testing

Inspectors in both cases above look for missing components, wrong components, wrong polarity, solder bridges, excess solder, inadequate solder, dry joints, and many more defects. For minor faults, a touch up station is enough to rectify them, but for more severe and persistent faults, a change in process parameters is the solution.

AOI & X-Ray Inspection

For large batches of PCB assembly, the manual inspection process may be too slow. A faster process is the Automatic Optical Inspection or AOI process. AOI machines have video cameras to capture images of the PCB, the components, and the solder quality, and they can compare the images with standard images in the machine’s memory. The AOI machines work at high speed processing a large number of PCBs within a relatively short time.

Fine pitch components such as BGA conceal the solder joints under the component body, preventing manual or automatic inspection. The only way to assess the quality of solder joints hidden under such components is by passing the board through an X-Ray machine, capturing the images on camera, and examining the results.

Electrical & Functional Testing

Electrical testing may be necessary after the assembly has passed through the above stages, to test whether the assembly functions as intended by the designer. This may involve programming the board, or calibrating certain components before the actual testing can begin.

Electrical and functional testing involves applying specific voltage/voltages to the circuit on the PCB and looking for normal/abnormal behavior at predefined outputs. Some tests may require a voltmeter and ammeter, while others may need more sophisticated instruments such as an oscilloscope or a waveform analyzer to complete the testing.

Conclusion

PCB assembly is a complicated process involving several technical processes with important setup parameters. Eminent assemblers such as Rush PCB UK Ltd are always careful with these setup parameters to allow the final product achieve the desired quality

PCB

Importance of PCB DFM Checks — Steps Involved

PCB assembly at Rush PCB involves several steps and processes, as we want to make sure in advance that our customers’ boards will not have any issues with manufacturing. Therefore, Rush PCB employs Design for Manufacturing or DFM checks to ensure we manufacture all PCB assemblies properly.

PCB DFM checks are totally cost-effective, as the system in use at Rush PCB is entirely automated for both DFM and DFA. Our system rapidly scans the manufacturing issues that may prohibit the PCB manufacturing process. Therefore, the application of this DFM/DFA check is beneficial to our customers, as it saves the PCB lead time while lowering the PCB cost.

It can become very expensive for the customer when they find errors in the fabrication or assembly process during the final stages of delivering the product to market. Anything may have gone wrong—PCB layout, material used, difference between prototype and original manufacturing files, and so on. By going through DFM checks it is possible to solve these problems before the Contract Manufacturer or CM starts fabricating and assembling their PCB.

Who Handles DFM?

Often, OEM design teams tend to look at DFM as something their CM should handle. In fact, most CMs perform DFM analysis prior to taking up production for identifying and fixing issues. This is a vulnerable step if the manufacturer does not share the changes they make with the design team and make the changes without a proper understanding of the requirements of the design and circuit performance. Any new revision by the design team will result in total chaos and probable failure of the PCB and finished devices.

Rush PCB recommends the design team performs their own DFM analysis prior to the prototyping stage to detect and weed out the issues, allowing them to incorporate the changes in the PCB design. This ensures the OEM lowers the cost by maintaining their design intent, and ensure the follow-on builds also work properly.

Involving the CM in the early stages of design works to the advantage of the OEMs. The CM, when reviewing the design, will match the parts on the board with their master component vendor inventory database, offering real-time recommendations on the availability of parts.

Design engineers at the CM will also review the design for its functional performance. They make recommendations for material the board should use and changes necessary at layer stackups for impedance control, suggesting routing changes for improvements. They may also suggest changes in component placement and routing for improving signal integrity.

Working closely at the early stages of the design is a win-win situation for both the OEM and the CM, resulting in smooth operation for the production of a successful and working PCB assembly, ready for market deployment.

Implementing DFM Checking Systems

It is easy to set up DFM checking systems as software packages are readily available. These packages work along with the CAD system for PCB design including schematic drawing and PCB track layout. The DFM system can detect errors that normally remain undetected during the reworking of the design. CAD systems often overlook issues such as acid traps, starved thermals, insufficient annular rings, slivers, and so on, but which can be disastrous during manufacturing. DFM software is usually equipped with fabrication analysis for detecting such issues.

Most DFM checking packages include easy-to-use PCB manufacturing analysis technology for identifying specific design issues that could be detrimental to PCB fabrication. DFM checking software, therefore, helps to reduce scrap, improve yield, while preventing setbacks from expensive time to market issues.

Major Issues Covered in DFM Checking

Major issues that DFM checking systems detect during design are:

  • Formation of Acid Traps
  • Possibility of sliver and island formation
  • Formation of solder bridges between pads
  • Paste mask openings for heat sinking
  • No solder connection or cold solder joints
  • Non-inclusion of test points
  • Proximity of copper to board edge
  • Optimization of drill size
  • Incorrect pad sizes
  • Component spacing
  • Component location and rotation

Formation of Acid Traps

Acute or odd angles of copper features on the PCB can form acid traps. These are areas where acid can remain trapped during the PCB etching process, and sometimes even cleaning chemicals are unable to clean them completely. The residual acid gradually erodes the nearby copper features, creating a smaller width of traces than intended, or even creating a discontinuity in the trace.

PCB designs with 4-5 mil traces are quite common today. Trapped acid can easily erode and open these thin traces. Designers can avoid such acid traps by not placing incoming traces at acute or odd angles to pads. Rush PCB advises keeping the angles of traces at 45 or 90 degrees to the pad, and the DFM software can flag non-conformances.

Possibility of Sliver and Island Formation

While designing, many plane layers can have slivers and islands or free-floating copper, which can create serious problems during etching. These freely floating copper specks can cause several issues as they find their way to other portions of the panel creating a short between closely spaced traces. Slivers may also cause noise and other interference as it is floating copper and may behave as an antenna does.

The only way to make sure there are no slivers or islands created is to check manually or let the DFM software detect them.

Also Read:  How to Detect Circuit Board Faults?

Formation of Solder Bridges Between Pads

With designers using fine-pitch components more commonly than before, it is essential they also include solder mask in between adjacent pads. Excluding this essential solder mask can allow excess solder on pads to join during reflow, creating a solder bridge and an unwanted electrical short.

To get around this issue, designers need to check the alignment and spacing of solder mask from pads to neighboring shapes. They should also consult their CM for the minimum webbing space and alignment they allow in a design. The DFM system software can easily flag issues such as non-existing solder mask between adjacent pads, and if solder mask covers a pad.

Paste Mask Openings for Heat Sinking

A heat sink is essential for absorbing and dissipating heat from an electronic component. The thermal contact is usually through a metal base that attaches to a large copper surface on the PCB. For proper heat transfer, the electronic component is also soldered to the copper surface. However, a large opening in the paste mask allows deposition of a substantial amount of solder paste, allowing the component to float off the pads during reflow.

To prevent the above, designers must limit the amount of solder paste the paste mask can deposit on the copper pads. Rather than have a single large paste mask opening, the designer can break it up into several smaller openings, thereby preventing the component from floating away during the reflow process.

Rush PCB suggests designers should consult their CM for the proper size of the paste mask opening. Essentially, DFM systems check for proper paste mask openings.

No Solder Connection or Cold-Solder Joints

Vias placed within pads can create an issue, as the via can allow molten solder to flow down the opening and leave the pad with too little solder to form a strong joint. This forms a no solder connection or a cold-solder joint. The DFM software checks if the percentage of the via within the pad is within permissible limits or else flags it for plugging.

Non-Inclusion of Test Points

Inclusion of test points in the PCB during design allows testing the board after assembly and in the field. This allows an easy way to tell whether the board functions as intended. DFM systems allow checking test points for clearance from components, their pad size, placement along a grid, and so on, to allow a fixture to locate them easily.

Designers must Include test points in the PCB during the initial layout phase of the design. Adding test points later on could lead to creating noise and crosstalk in sensitive circuits. The primary requirement of test points is they are easily accessible and not hidden below components. Their spacing must also be adequately apart to allow test pins to access them.

Proximity of Copper to Board Edge

Manufacturers prefer making boards in panels, as it is cost effective to make multiple boards simultaneously. They separate the individual boards from the panel by various means such as shearing, breaking along a V-cut and other methods. Essentially, a minimum gap must exist between the edge and the copper surfaces on the board, to prevent the copper from damage when the fabricator separates the boards.

Another reason exists for maintaining a proper distance between the copper on the board and the board’s edge. Motorized transport must grip the boards properly during the various processes. For instance, the etching process requires application of electric current to the panel, and presence of copper too close to the edge of the board can create shorts.

Designers must consult their CM for various equipment they use and the spacing they require. The DFM system checks for and flags the issue if it finds the spacing inadequate.

Optimization of Drill Size

Designers often use several drill sizes for their boards. Changing drills during board manufacturing not only wastes time, it increases the expense for board fabrication. The DFM software checks for drill sizes in the board and flags the designer to consolidate them to an optimum number.

Incorrect Pad Size

Sometimes the designer may overlook a wider trace leading to different sized pads for an electronic component. While reflow, the different size of pads can lead to uneven heating of the component, resulting in the chip component lifting up on one of its ends, a condition known as tombstoning. DFM systems check for and flag instances of incorrect or mismatched pad sizes.

Component Spacing

Pick-n-place machines need a minimum gap between components to enable proper placement. The designer must consult their CM to know the minimum their machines need. While placing components during layout, if the designer places components too close, the CM will have a problem during assembly, as the pick-n-place machine may not function optimally. DFM systems check for this spacing and flags if it finds the spacing inadequate.

Component Location and Rotation

Placing smaller components very close to large ones may cause soldering problems during reflow. The larger components absorb more heat leaving the smaller components not hot enough for proper soldering. DFM systems predict this shadow effect and warn designers.

Conclusion

It is not only frustrating but also expensive for the customer to detect failure when getting ready to enter the market. According to Rush PCB, one of the ways of avoiding such failures is by planning for the future by designing for manufacturing. The availability of several good DFM software packages makes it easy to implement such checks and prevent failures from cropping up. Although it is always possible to manually identify and resolve such issues, the DFM software systems make checking independent of the human.

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PCB Assembly Compatibility with In-Circuit Testing

RUSH PCB UK Ltd wants all its clients to be assured that we ship all products from our production facility only after testing them to be in perfect working condition. For this we have a variety of strict quality control procedures at each stage of our PCB assembly process. This includes not only standard services such as visual inspection and automated optical inspection, but also advanced test procedures such as X-ray inspection, and functional circuit testing or FCT. Although each method has its own advantages, for the most meticulous testing method, RUSH PCB UK Ltd recommends In-Circuit Testing or ICT.

In Circuit Testing (ICT)

Working at component levels, ICT allows localizing issues that may be present on the board under test. For instance, ICT can point to a specific device as the cause of the problem. With ICT, it is possible to test the individual voltage and current levels on the PCB, while including a step-by-step program execution.

The above helps in troubleshooting complex boards where the board is still a prototype and the design is not totally verified. Boards not passing the test may need reworking at component level to potentially save the batch. When this happens, our test engineers generate a Design for Assembly (DFA) recommendation to the client.

At RUSH PCB, we work closely with our clients and provide them flexible services tailored to their individual requirements. We have an engineering team to review the specific test requirements for a project, recommend the necessary equipment, and develop the test workflow. We even design test jigs if necessary. We have equipment to handle any type of project.

One of the advantages of using ICT is its speed of test. For instance, a few seconds is all it takes to test a complicated board. Therefore, projects involving large volumes of PCBs benefit exclusively from ICT. Apart from the speed of testing, detection of faults at component levels makes the diagnosis process faster and at the same time, does not involve a skilled operator.

However, for the ICT to be effective and accurate, the process requires a dedicated test fixture and a program. In addition, the PCB design must also allow the test machine and fixture to interface properly with the assembly. To maximize the test coverage and find the maximum number of potential faults, our clients must consider some points when designing the layout for their PCB assemblies. This not only reduces the redesign steps necessary at the prototype stage, it also helps in producing boards that perform right at the first attempt.

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Making PCB Assembly Compatible with ICT

Test Pads—have a test pad on each electrical network on the PCB, including on unused IC pins. It should be possible to connect to the test pad via a spring-actuated test pin in the test fixture. For through-hole technology, the test pin can engage the component leg on the solder side.

It is usual to place 0.05-inch (1.27 mm) diameter test pads on a 0.1-inch (2.54 mm) grid, with the test pads spaced 0.1 inch (2.54 mm) from any component, and 0.125 inches (3.18 mm) away from the edge of the PCB. The above dimensions allow using long-lasting standard test pins. RUSH PCB UK Ltd does not recommend using test pads of reduced diameters, as thinner test pins are generally more expensive, requiring more frequent replacements.

Probing—place all test pads ideally on the solder side of the PCB to allow the test pins on the jig to access them from the bottom side. While it is possible to place test pads on the top, the construction of the test jig will become more complicated and expensive as it will require additional transfer probes and wiring.

Solder-Side Components—it is preferable to have no components on the solder side, other than small SMDs. Test fixtures usually have a vacuum plate to hold the PCB assembly from the bottom. It may be necessary to mill the vacuum plate for accommodating components on the bottom side. As milling is an expensive process, it is necessary to restrict the milling for bottom components to only a few millimeters.

Locating Holes—add locating or tooling holes to the PCB (not in the panel), to allow the test jig to locate the PCB in the fixture. Preferably use non-plated holes of 3 to 4 mm diameter. Locating two tooling holes in diagonally opposite corners will allow the test jig to accommodate the PCB unambiguously. Keeping a free space of 5 mm around each hole will ensure the tooling pins of the fixture will not cause shorting of components or tracks during the test.

Pull-Up Resistors—use pull-up or pull-down resistors on all floating pins, rather than connecting them directly to the power rails. For pins that hold other devices to a reset state or high impedance state, the presence of these resistors allows the test jig to control the pins. Tying the pins through pull-up or pull-down resistors also helps in product functioning, as the circuit can reject spurious signals. These resistors also help the test jig in isolating individual components when locating a fault.

Space for Pusher Rods—these are necessary to push down on the PCB when testing. ICT jigs usually have fixtures with 2 mm diameter pusher rods and necessary space should be available between components on the top-side of the PCB under test. Spacing them evenly around the PCB helps the jig manufacturer locate individual positions for the pusher rods.

Programming Devices—although capable of programming devices such as EEPROMs during testing by ICTs, the cycle time per board may go up. RUSH PCB UK Ltd recommends pre-programming such devices before assembly, and allowing the ICT to control them during testing.

Batteries—preferably, fit batteries only after the testing is over. As an alternative, use a removable link to connect/disconnect them during the testing.

Review—reviewing the design to ensure proper functioning is important before committing to a fixture. Moving test pads or components on a PCB can mean a new fixture, leading to time and cost overruns, as an ICT jig can be expensive and take some time to prepare.

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Conclusion

We at the Electronic Manufacturing Services (EMS) from RUSH PCB UK Ltd offer advice to our clients on the above points and help them to design their PCB properly for compatibility with ICT. However, once the design meets DFA requirements, ICT provides fast and accurate testing, making the returns worth the investment.

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Printed Circuit Board (PCB)

Embedding Components within the PCB

The rise of the mobile industry on one hand and the increasing demand for wearables on the other, combined with the increasing use of IoT in the industry, has led to the complexity and density of electronic designs to increase substantially in the last two decades. Simultaneously, these demands have also increased the challenges for designers of printed circuit boards (PCBs) tremendously. One of the ways PCB designers are coping with the issue is by embedding electronic components within the PCB substrates. This is fast becoming a feasible step for eminent board manufacturers such as RUSH PCB UK LTD.

Advantages of Embedding

Before starting the design, it is imperative to understand the advantages that embedding components brings, while at the same time considering the drawbacks of adding the fabrication steps leading to the embedding. In fact, there are potential effects on cost and production yield that the design team must factor in when considering embedding components within PCBs. Some of these advantages are:

  • Reduction in size and cost
  • Minimizing electrical path lengths
  • Decreasing parasitic capacitance and inductance
  • Reducing EMI effects
  • Improving thermal management

For RUSH PCB UK LTD, innovation in PCB technology comes basically from reduction in size and cost. Embedding components within the PCB substrates help to reduce the size of the board assembly. For complex products, a PCB embedded with components can potentially reduce the manufacturing costs.

High-frequency circuits are highly susceptible to the parasitic effects of long electric path lengths during PCB design. Embedding components within the PCB helps in minimizing electrical path lengths, thereby reducing the parasitic effects to a large extent.

Such reduction in path lengths when connecting embedded passive components to the pins of an IC can decrease the parasitic capacitance and inductance, thereby reducing load fluctuations and noise within the system. For instance, it is possible to place embedded passive components directly underneath the pins of an IC. This not only reduces the via inductance, but also minimizes potential negative parasitic effects, and improves device performance. In fact, embedding components within the substrates of a board allows reduction of path lengths over surface mounting.

It is possible to integrate an electromagnetic Interference shield around an embedded component. For instance, simply adding PTH all around the component can reduce noise coupling from outside. In certain applications, this may even eliminate the need for any additional surface-mounted shield.

It is also possible to add heat-conducting structures to an embedded component for improving thermal management. For instance, embedding thermal micro-vias to be directly in contact with the embedded component can help it to dissipate the heat to a thermal plane on an external layer. Adding thermal micro-vias also reduces thermal resistance, as the amount of heat traveling through the PCB substrate reduces.

One of the major concerns when embedding components within a PCB is the long-term reliability of the design. Solder joints on embedded components formed and placed within the laminates of a PCB can be affected when the PCB undergoes soldering processes such as reflow during assembly of surface mount devices. Embedded components can be an additional problem after manufacturing, as they cannot be easily tested or replaced once they have failed.

What Components can be Embedded?

RUSH PCB UK LTD considers two main categories of components fit for embedding into PCB laminates—passive and active. They are used in different ways and for different applications. As a large majority of embedded components are of the passive category, embedded resistors and capacitors are the most popular.

However, an embedded passive component does not mean that a discrete resistor or capacitor is placed inside a cavity within the substrate of a board. Rather, it is the selection of a specific layer material to form the resistive or capacitive structure of an embedded passive.

Benefits such as listed above make embedded components an alternative to discrete surface-mount passive components. Applications such as series termination resistors benefit from this technology tremendously, a huge number of transmission lines terminate at dense memory devices and ball-grid array (BGA) ICs.

Embedding Chips

RUSH PCB UK LTD can embed a chip within a PCB, but steps for other manufacturers may vary. Typically, the fabricator has to create space for the body of the IC, and this takes the form of a cavity. Approaches to chip embedding technology may take the following approaches:

CIP or Chip in Polymer: this involves embedding thin chips when building up dielectric layers of the PCB, rather than integrating them within the core layers. The fabricator can use standard laminated substrate materials.

ECBU or Embedded Chip Buildup: this involves mounting chips on polyimide films and building up interconnect structures thereon.

EWLP or Embedded wafer-level package: this involves performing all technology steps at the wafer level. IO area available is limited to the footprint size of the chip, as this technology essentially requires fan-in.

IMB or Integrated module board: this involves aligning the components and placing them within a cavity and using controlled-depth routing to place the cavity within a core laminate. Filling the cavity with molding polymer ensures chemical, electrical, and mechanical compatibility to the substrate. Impregnation of isotropic solder in the polymer helps to form reliable solder joints while laminating the embedded part into the stack.

Component Design Considerations for Embedding

RUSH PCB UK LTD considers layout of components and their physical orientation as important factors when designing for embedded purposes. It is also necessary to select proper substrate materials and compatible components, as this reduces the chances of failure during PCB fabrication.

Selecting specific materials is the key to determine the electrical properties of embedded passives. For instance, an embedded resistor is simply a sheet of resistive film, its dimensions defining the value of the resistance. The resistance of such material is dependent on the resistivity of the material, its length, and its cross-sectional area. Resistive film materials vary in their resistivity, and this directly influences the final resistance value. Therefore, selection of the material is critical to the design and the manufacturing process.

Manufacturers make embedded capacitors by arranging properly dimensioned copper cladding to act as plates, and placing suitable dielectric material in between. Designers calculate capacitance based on the dielectric constant of the material, the permittivity of free space, distance between the plates, and the area of the plates. The final capacitance value increases with an increase in the dielectric constant of the chosen material, an increase in the area of the plane, and decreases with an increase in the plane-to-plane distance in the board layers. Manufacturers use special material for maintaining dielectric strength, with a thin but dimensionally stable dielectric layer for creating embedded capacitors for power supply decoupling.

For making other active components such as ICs, manufacturers and designers select materials that provide substrate durability and long-term reliability of components within cavities. CTE or coefficient of thermal expansion defines the manner in which the material will change during high-temperature events such as reflow soldering of surface-mount components. It is highly imperative for the designer to select substrate material and polymer with matched CTE for filling cavities to maintain the integrity of the board structure.

RUSH PCB UK LTD has two ways of aligning and placing embedded components in cavities—face-up and face-down, with face-down being the preferred process. For a face-down alignment, the cavity depth needs to match the package height, and therefore, the manufacturer can embed chips of different thicknesses on the same layer. This allows for good thickness control for the dielectric material, and accurate component placement during assembly.

Manufacturing Processes for Embedding Components

Individual manufacturers will vary their fabricating processes for embedding depending on the type of PCB and the available equipment at their disposal. Broadly, manufacturing process at RUSH PCB UK LTD for embedding components follow two methods—one, aligning component and placing them within cavities, and the other, molding components into the substrates, building up additional structures thereon.

Manufacturers use different manufacturing and configuration techniques to make cavities in PCBs. Advancement in technology has led to better and more efficient methods of developing cavities for embedding active components. The new methods offer additional benefits such as higher production yields and improved reliability.

Drilling cavities with lasers offers the highest positional accuracy and precision of all methods, as it is possible to control a laser beam precisely for achieving uniform depth and wear as it removes dielectric material. Using a longer wavelength prevents the laser from penetrating copper layers, thereby forming a distinct stop layer. After forming the cavity, the fabricator adds an anisotropic conductive adhesive before placing a component inside the cavity. Application of heat and certain amount of pressure helps to melt the solder particles in the adhesive material, thereby forming reliable solder bonds.

More conventional methods use milling for creating cavities, as milling is more cost-effective than lasers are. Although improved technology allows making miniature milling tools, there is a practical limit to using milling and routing for cavity creation. Even so, milling is more popular as compared to lasers.

Some manufacturers prefer using thin wafer packages, integrating them directly into dielectric layers during the buildup, rather than drilling or routing cavities into the core material. The fabricator begins by die-bonding the thin chip to the substrate, following it up with a layer of liquid epoxy or an application of a laminated RCC or resin-coated copper film as a dielectric. He/she then applies a heated press lamination process, optimizing it to embed the chip without void formation.

Documentation Requirements

Any design with embedded components will require proper documentation for reducing manufacturing time and cost. As the process of embedding components combines component assembly, packaging, and PCB manufacturing into a single manufacturing process, necessary documentation requires layer stack diagrams, NC drill files, fabrication notes, pick-n-place files, and assembly notes for effective PCB fabrication.

Conclusion

Market demand is pushing for high-density, low-profile electronic devices. Manufacturers are complying to this demand with the technology for embedding passive and active components within the board substrate. RUSH PCB UK LTD has successfully broken through potential barriers of reliability concerns and risks to production yields and cost.

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Integrity of the Signal in HDI Circuits

With rise-times of signals on the printed circuit boards (PCBs) continuing to drop, the age-old concerns related to signal integrity is always at the forefront of (PCB) Printed circuit board design. However, with the increasing quantities of printed circuits in high-density interconnect or HDI technology, there are some interesting new solutions.

Signal integrity analysis in PCBs has five major areas of concern:

  1. Reflection
  2. Cross-talk
  3. Simultaneous Switching
  4. Electromagnetic Interference (EMI)
  5. Interconnect Delays

Although HDI does offer improvements and alternatives for all the concerns above, it does not provide all the solutions. Signal integrity depends on the materials the PCB uses, and the materials the HDI technology uses, together with the PCB design rules and dimensional stack-up helps the electrical performance including signal integrity. Likewise, miniaturization of the PCB using the HDI technology is a major improvement for signal integrity.

HDI Benefits Signal Integrity

With new electronic components such as ball grid arrays and chip-scale packaging achieving widespread use, designers are creating PCBs with new fabrication technologies to accommodate parts with very fine pitches and small geometries. At the same time, clock speeds and signal bandwidths are becoming increasingly fast, and this is challenging system designers to reduce the effect of RFI and EMI on the performance of their products. Moreover, the constant demand for denser, smaller, faster, and lighter systems are compounding the problems with restrictions placed on cost targets.

With HDI incorporating microvia circuit interconnections, the products are able to utilize the smallest, newest, and fastest devices. With microvias, PCBs are able to cover decreasing cost targets, while meeting stringent RFI/EMI requirements, and maintaining HDI circuit signal integrity.

Advantages of Using Microvia Technology in HDI Circuits

Microvias are vias of diameter equal to or less than 150 microns or 6 mils. Designers and fabricators use them mostly as blind and buried vias to interconnect through one layer of dielectric within a multi-layer PCB. High-density PCB design benefits from the cost-effective fabrication of microvias.

Microvias offer several benefits from both a physical and an electrical standpoint. In comparison to their mechanically created counterparts, designers can create circuit systems with much better electrical performance and higher circuit densities, resulting in robust products that are lighter and smaller.

Along with reductions in board size, weight, thickness, and volume, come the benefits of lower costs and layer elimination. At the same time, microvias offer increased layout and wiring densities resulting in improved reliability.

However, the major benefits of microvias and higher density go to improving the electrical performance and signal integrity. This is mainly because the HDI technology and microvias offer ten times lower parasitic influence of through-hole PCB design, along with less reflections, fewer stubs, better noise margins, and less ground bounce effects.

Along with higher reliability achieved from the thin and balanced aspect ratio of microvias, the board has ground planes placed closer to the other layers. This results in lowering the surface distribution of capacitance, leading to a significant reduction in RFI/EMI.

HDI PCBs use thin dielectrics of high Tg and this offers improved thermal efficiencies. Not only does this reduce PCB thermal issues, it also helps the designer in streamlining thermal design PCB.

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Improved Electrical Performance of HDI Circuits

The designer can place more ground plane around components, as they implement via-in-pad with microvias. The increase in routabilty offers better RFI/EMI performance due to the decrease in ground return loops.

As HDI circuits offer smaller PCB design along with more closely spaced traces, this contributes to signal integrity improvements. This helps in many ways—noise reduction, EMI reduction, signal propagation improvement, and lowers attenuation.

The improved reliability of HDI circuits with the use microvias also helps in PCB thermal issues. Heat travels better through the thin dielectrics. Streamlining thermal design PCB helps remove heat to the thermal layers. Several manufacturers make complex enhanced tape BGAs of thin, laser-drilled polyimide films to take advantage of PCB design with HDI.

The physical design of the microvia helps in reducing switching noise. The reason for this decrease is due to decrease in inductance and capacitance of the via, since it has a smaller diameter and length.

Signal termination may not be necessary in HDI circuits as devices are very close together. Since the thickness of the layers is also small, the designer can utilize the backside of the interconnection effectively as well.

Just as the signal path is important in PCB design, so is the return path. Moreover, the return path also influences the resistance, capacitance, and inductance experienced by the signal. As the signal return current takes the path of minimum energy, or the least impedance, the low frequencies follow the path minimizing the current loop.

Miniaturization from using HDI technology provides interconnections with shorter lengths, meaning signals have to traverse shorter distances from origin to destination. Simply by lowering the dielectric constant of the HDI material system, the designer can allow a size reduction of 28%, and still maintain the specified cross-talk. In fact, with proper design, the reduction in cross-talk may reach even 50%.

Conclusion

HDI PCB design not only helps in improving the integrity of signals, but the presence of thin dielectric helps with the PCB thermal issues as well. In fact, HDI technology helps with all the five major areas of concern related to signal integrity.

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