How do Circuit Boards Work

How do Circuit Boards Work?

How do Circuit Boards Work?

Whatever electronic equipment or device you are using, there is likely to be a circuit board inside. Most of us use our equipment or device without any thoughts or considerations about what lies under the hood, or how the computer circuit board works. In this blog, Rush PCB UK explains the basics of the circuit board or printed circuit board (PCB), the components on it and their functioning, to give you a better idea of the PCB electronics you are using regularly.

You can consider the electronic circuit board as the heart of an equipment. Basically, the simple circuit board is made of glass fibers with copper tracks and pads on one or both sides. The copper tracks act as conductors of electricity between tiny PCB components mounted and anchored on pads on the board. If you look closely, a grey-colored material known as solder anchors the components in place.

circuit board

PCB Construction

A glass fiber board with copper tracks on one side forms the PCB construction. A slightly more complex type of PCB electronics can have copper tracks on both sides, while still more complex boards can consist of multiple layers, with copper tracks on each layer.

A designer uses a computer and a special program like a PCB CAD for designing the PCB electronics. Depending on the complexity, the PC-Board may be single-, double-, or multi-layered. Once complete, the designer outputs the entire design in the form of a standard file format, commonly, the Gerber format. The designer sends the Gerber file to the PCB manufacturer.

The manufacturer fabricates the printed circuit board design following the Gerber files. They build the PCB in layers with copper traces on each layer. Vias make the interconnections between the layers. A green mask covers the two outermost layers, thereby insulating and protecting the copper from tarnishing. The pads remain exposed as they are necessary for mounting the components. However, a layer of surface finish protects them from tarnishing, until soldering. To help and guide operators mounting components, a silkscreen printing displays the part number of each component in white.

Electronic Components

A multitude of circuit board components are available for use on PCBs, depending on their individual functions. Some of the most circuit board parts are:

Switch: Allows two circuits to interconnect electrically or remain isolated. Once interconnected, a switch allows current to flow.

Battery: Supplies the circuit with electrical energy at a defined voltage level.

Resistor: Controls the amount of current flow in a circuit by offering electrical resistance.

Capacitor: These components store and release charge as necessary

Inductor: These also store and release charge, but in an opposite manner to that by capacitors.

Diodes: These components allow current to flow only in one direction, blocking it in the other.

LEDs: These are diodes that can emit light in many colors.

Transistors: Active components with ability to amplify charge

ICs: Integrated Circuits are active components with multiple functionalities.

PCB Assembly

A PCB assembly consists of mounting and anchoring circuit parts on the PCB, with machines doing most of the work. A solder paste dispensing machine places small amounts of solder paste on the pads of the PCB. Next, a pick-and-place machine takes the surface mount components from reels and places them at specific places on the PCB. This combination of components and PCB then passes through a reflow oven where heat melts the solder paste and anchors the components on the PCB. After testing for shorts and opens, the PCB assembly is ready for use in a device.


We, at Rush PCB UK, have presented only a very brief overview of PCB circuits and how do circuit boards work with components. Although the basic principles remain the same, the complexity increases with the size and number of layers of a PCB, and the type of components it uses.

Call Rush PCB today or visit our website for all your PCB requirements.

Make Your PCBs More Reliable with Vias

Make Your PCBs More Reliable with Vias

Make Your PCBs More Reliable with Vias

The electronic industry uses printed circuit boards (PCBs) with multiple layers to reduce the physical size the board occupies. This increases the component density on the top layer of the board, and it also splits the space available for routing traces onto different inner layers, with vias being the only way to electrically connect between different layers. Although this makes vias an essential part of board design, they also affect solderability and introduce weaknesses, leading to a lower reliability of the board. However, by following good design practices offered by Rush PCB, you can make your PCBs more reliable even with vias.

Types of Via

A via is a hole in the PCB, spanning a single layer or multiple layers, with the fabricator plating the hole with copper forming a barrel. The ends of this barrel connect to specific traces on the respective layers, forming electrical contact between two layers. If the via spans multiple layers, the inner layers may also connect to it, provided the circuit requires it to do so. Primarily, there are three types of vias, through-hole, buried, and blind.

A through-hole via traverses the entire thickness of the PCB, beginning at the top layer and ending at the bottom-most layer. The fabricator may plate the through hole via or leave it without plating, depending on the requirement. A plated through hole via has the advantage that other inner layers may connect to it, if the circuit demands.

A buried via spans two or more inner layers and is not visible either at the top or the bottom layer. The layers a buried via spans may connect to it, if the circuit requires. A blind via begins either at the top layer or the bottom layer, and finishes at an inner layer. On the way, a bind via may span several inner layers, and they may connect to it if necessary.

High Density Interconnect (HDI) PCBs and flex PCBs use another type of vias known as micro-via. These are very small, and fabricators drill them using laser beams. Each micro-via spans only one layer, and the fabricator can stack them on other layers to function as through-hole vias, blind, and buried vias.

Via Size

The bigger the diameter of the via, the stronger it is. This is because a large via has greater mechanical strength, and higher electrical and thermal conductivity. However, a large via subtracts from the already scarce PCB real estate that could be useful for routing traces. Rush PCB recommends vias with a minimum drill width of 20 mils, an annular ring of 7 mils, and a minimum aspect ratio of 6:1.

Thermal Considerations

When a PCB heats up, whether during processing or in the work environment, the difference of the coefficient of thermal expansion (CTE) between the copper and laminate can lead to issues. The structural latticework of the PCB laminate limits expansion in the horizontal direction (along the plane), but can freely contract or expand significantly in the vertical direction (perpendicular to the plane).

For instance, FR-4 laminates can contract or expand at four times the rate at which copper can. Therefore, the copper barrel in a via hole is under tremendous strain every time the board heats up. If the thickness of the copper barrel is not adequate, and the PCB too thick, the board will expand to the point where the copper may break. For a drill width of 20 mils, a pad diameter of 34 mils will work adequately with a maximum board thickness of 120 mils.

Solder Wicking

Positioning a via is as important as its size. Locating a via very close to a solder pad may cause several problems to arise, foremost among them being the effect of solder wicking.

As the via and the solder paste on the pad heat up, capillary action in the via draws solder from the solder pad into the via. The solder travels through the via and collects on its bottom side, leaving the pad deficient or entirely free of solder. A larger via will wick more solder more quickly, and the joint will likely be mechanically weak and electrically resistive. Rush PCB recommends three ways for preventing this, and any one of them is effective:

Solder Mask Barrier: a barrier of solder mask placed between the via and the solder pad will prevent solder from moving into the via hole. However, to place an adequately wide solder mask barrier, the designer may have to move the via farther from the pad. This may not be possible if the board is already crowded, or the board handles high-frequency signals.

Tented Via: If it is not possible to move the via away from the pad and put a solder mask barrier in between, masking the via pad totally may help. Completely sealing the via does prevent solder from flowing into it, but it also prevents using the via as a test point. It is possible that some contaminant may enter the via and corrode the copper barrel.

Filled Via: It is also possible to fill up a via entirely with a conducting or non-conducting material before tenting it. Totally sealing a via with filler material has the advantage of providing a better barrier against contamination.


Rush PCB recommends undertaking Design for Reliability studies as a valuable process for improving reliability, lowering costs, reducing time to market, and improving customer satisfaction. Implementation of Design for Reliability requires a proper combination of personnel, tools, and time limitations.

Call Rush PCB today or visit our website for all your PCB requirements.


Selective Coating for PCBs

Selective Coating for PCBs

Printed circuit boards (PCBs) often need protection from damaging external environments, for which, Rush PCB coats them with a thin layer of protective finish such as casting resin or similar during the process of conformal coating. Although sealing the entire circuit board with the conformal coating is the norm, Rush PCB can also cover only sections or individual components on the substrate. For this, we have developed several methods such as flip-chip under-fill, dam and fill, and glob top for the purpose.

A protective finish is necessary with all industries now using PCBs as the most frequent carrier and connecting component for all types of electronic components. These industries include medical, security, communications, household, airspace, transportation, and computers. The protective finish helps in permanently protecting the intricate electronics on a PCB against ingress of chemicals, dirt, moisture, and other damaging influences such as impact. Although potting does help to achieve most of the protection necessary, Rush PCB UK has developed methods depending on the specific electronic components (sensors and processors, etc.) on the board, or specific potting functions the application demands.

Generic Conformal Coating

Typically, a conformal coating is the application of potting compounds or special coatings on the PCB to protect the onboard components. Depending on the application, PCB assemblers can apply the coatings manually using brush painting or by spraying then on. With PCBs growing more sophisticated, it is necessary to apply conformal coatings with high precision and reproducibility. Therefore, Rush PCB frequently opts for robot-controlled or automated applications using suitable metering heads.

Flip-Chip Under-fill

Rush PCB has developed the flip-chip under-fill process specifically for mechanically stabilizing flip chips. After mounting, a thin gap is normally present between the flip-chip and the substrate, which can lead to stress and even deformation. Filling this gap with a low-viscosity material, an under-fill, reduces the stress on the chip. Once applied, capillary action forces drawing the under-fill within the narrow gap, until it fills completely with the casting resin.

Dam and Fill

Rush PCB has developed this selective process for enabling potting of individual areas on the PCB, and without affecting the surrounding components and surfaces. This process is also known commonly as frame and fill. The process involves making a dam or frame with a high viscosity material by dispensing it around the area of the board that needs the protection. This creates a cavity, which the assembler proceeds to fill with a liquid casting resin until they have completely covered the particular structure.

We use this dam and fill procedure for optical bonding as well. For this, we first dispense a dam on the substrate, thereby forming a gap between the display or touchscreen and the cover glass. We then fill the dam with an optically clear adhesive. We have improved the process for achieving better heat dissipation, greater stability, and superb display readability.

Glob Top

Rush PCB has an additional option for protecting selective and sensitive areas on the PCB. This is the glob top process, with the potting compound being the only difference between this and the dam and fill process. In the glob top process, we dispense a viscous casting resin on the semiconductor chip, thereby fully encapsulating it and its wire bonding contacts. The viscous casting resin we use for this process does not flow so easily, and it does not contaminate adjacent components or coat areas of the PCB that need to remain uncovered. These are the main considerations for choosing the type of casting resin and for determining its quantity as a potting compound.

Read About: Printed Circuit Boards and AI

Dispensers for Protective Finish

Rush PCB generally uses two types of dispensers based on the application. These are gear pump dispensers and volumetric piston dispensers. While gear pump dispensers are ideally suitable for under-fill applications, volumetric pump dispensers are great for dam and fill and glob top applications. Gear pump dispensers have an optional swivel needle for providing precise and fast material dispensing even when the PCB has highly complex component geometries.

Volumetric piston dispensers are a cost-effective alternative, depending on the requirement and material. We precisely tailor the dispensing cylinders in these dispensers to the volume necessary, or to the specific mixing ratio, thereby ensuring maximum process reliability.

Thermal Management

As applying a conformal coating affects the natural cooling process on the PCB, it is necessary to consider effective thermal management aspects as well while potting. Rush PCB is increasingly selecting materials with thermal interface properties. For such applications of liquid thermal interface materials, the volumetric piston dispenser is most suitable.

Rush PCB also uses a compact and complete solution for dispensing liquid thermal interface materials. We pre-configure and parameterize the system for thermal management applications. This ensures short delivery times and fast start of production, while offering an attractive price-performance ratio.

Read About: How Important is DFMA for PCBs

Potting SMD Boards

It is important to select potting materials with low coefficients of thermal expansion when potting circuit boards with SMD. Rush PCB recommends this to prevent risking shrinkage of material at low temperatures, as this can damage soldered connections. Another consideration should be the glass transition temperature of the potting material must be above the temperature at which the board operates.

pcb solder

What is Solder Thieving?

What is Solder Thieving?

Soldering is a key process in the electronic industry, where it enables electrical connectivity and mechanical stability. Solder bonds the leads of electronic components to copper pads on the printed circuit board (PCB), thereby not only helping them to stay in place, but also providing the components the necessary electrical connection to the rest of the circuit. Rush PCB recognizes solder thieving as a major problem during the soldering process.

However, solder thieving is not to be confused with copper thieving. Although both are related to PCB design, solder thieving occurs only during the soldering process, while copper thieving is a process to allow uniform copper plating in via holes. In copper thieving, designers add copper dots to the outer layers of the PCB, creating a uniform distribution of copper across the board surface. A non-uniform copper distribution can cause heavy plating in areas with little exposed copper, while areas with connector pins or BGA pads will not plate properly.

The presence of copper dots helps by stealing part of the plating current, preventing it from concentrating on sparse features, and spreading it more uniformly in areas with dense features. Rush PCB uses copper thieving on all types of PCBs, including FR-4, flex, and rigid-flex.

Mechanism of Solder Thieving

During soldering, it is very essential that the amount of solder at the joint is adequate. If the amount of solder is too little, the joint will have inadequate mechanical strength, and the component’s thermal and electrical connectivity to the PCB will suffer. Via-in-pad designs suffer from this problem of solder thieving occasionally, as the molten solder wicks down the untented via leaving very little solder for the joint itself. Unprotected copper areas and via-near-pads may also cause problems of solder thieving.

Preventing Solder Thieving

Presence of plated holes within or near pads along with missing solder-mask boundaries allow molten solder to flow away from the pad. While solder fills the via cavity, very little of it remains on the pad to form the inter-metallic bond between the part and the pad. Rush PCB suggests design options to prevent solder thieving in PCBs by:

  • Filling the via with Conductive materials
  • Filling the via with Non-Conductive materials
  • Plugging the via
  • Tenting the via

Conductive Via-filling: Conductive via-fill materials generally use silver coated copper particles in epoxy to fill the via hole. After the fill cures, the material provides some electrical and thermal conductivity. Conductive via-fill materials may vary in finished coefficient of thermal expansion (CTE) because of the overall particulate size they contain.

Non-Conductive Via-filling: Non-Conductive via-fills also use epoxy, but do not have any conductive material. They provide a better CTE match with standard PCB laminates.

Via-Plugging: In this process, the manufacturer uses solder mask or any other non-conductive media to plug the via hole. Next, they apply LPI mask over the plug, to guarantee covering all vias on the PCB.

Via-Tenting: While tenting vias, the mask data layer has no apertures, and the solder mask therefore covers the via pads and covers the hole. However, Rush PCB does not recommend this procedure, as it may create entrapment and lead to lowering the board reliability.

Solder Thieving as a Solution

Just as solder thieving can cause problems of inadequate solder for joints, it can also be useful for removing excess solder. While soldering, molten solder tends to accumulate in certain locations on the PCB, where it may cause solder bridging. For reflow soldering processes, this may be because of the congregation of several surface mount components on a single copper land that has inadequate solder masking. For wave soldering processes, solder accumulation is usually at joints with several component leads close by.

The wave soldering process causes molten solder to flow across the surface of the circuit board. Although this allows soldering the board with speed, solder bridges may form between pads of ICs. Typically, the bridge forms between the last two pads of a sequence of a row of pads. Earlier, the distance between adjacent pads was large enough to prevent bridges during soldering.

However, with increasing circuit densities, the pin spacing in ICs is becoming smaller, and the potential for bridge formation is also increasing. In such cases, designers are using solder thieving is a solution.

By providing the circuit board surface with additional pads, designers reduce the tendency of solder bridges to form. The additional pads act as solder thieves that draw off the excess solder preventing the formation of any bridge.

The designer places an approximately rectangular shaped pad touching the edge of the last pad of a sequence of pads, orienting the length of the pad in the direction of the flow of solder. The dimensions of the solder thief are such as to enable the pad to spontaneously wick the excess solder away from the nearest two pads, thereby preventing a solder bridge from forming between them.

Designers use the same process for preventing formation of solder bridging on SMT pads that undergo wave soldering. To prevent solder from forming clumps on the extra pads, the design of solder thieves includes two pads separated from each other but adjacent to the last pad such that they wick solder away from the last pad. By distributing the excess solder between two thieving pads, designers prevent clumps of solder from interfering with automated test equipment probes.

Read About: Role of Solder & Paste Masks in PCBs


Although solder thieving can be a problem for the soldering process, design methods are available to counter it. On a similar note, designers use solder thieving techniques to prevent formation of solder bridges.

Smart pcb manufacturing

What is Smart Manufacturing for PCBs?

What is Smart Manufacturing for PCBs?

The world over, manufacturers of electronic products continue to struggle to meet market demands. These are caused mainly by the requirement of rapid new product introduction to keep ahead of the competition, customization/personalization, expectations of quality, internet connectivity, and more. To meet these product demands and more, Rush PCB recommends using Smart Manufacturing for printed circuit boards (PCBs).

So far, electronic manufacturers have applied one or more solutions of applied digitalization to their processes during product development. These include:

  • PCB contract manufacturing through supplier collaboration
  • Advanced part and mold manufacturing through model-driven processes
  • Product optimization through integrated simulation and layout
  • Production ramp-up, process verification, virtual design, test management, and execution
  • Box builds and shop floor connections through manufacturing execution system
  • PCB assembly and test through integrated planning and management

With digitization, manufacturers can plan better and validate production alternatives faster. This helps to increase the performance and effectiveness of manufacturing operations. However, according to extensive studies, digitalization has not helped in creating the anticipated bottom-line impact.

Rush PCB recognizes that digitalization requires a new manufacturing/operating model, an integrated platform—one that unites all the domains necessary to engineer, manufacture, and deliver better quality PCBs. At Rush PCB, we call this Smart Manufacturing. For this, Rush PCB follows steps like:

  • Validating manufacturability of PCBs
  • Virtual design, simulation, and optimization of production processes
  • Managing manufacturing operations and materials
  • Using manufacturing data to generate business value

Validating Manufacturability of PCBs

Rush PCB uses Design for Manufacturing (DFM) analysis for fabrication, assembly, test, and reliability checks to asses issues affecting performance. We assess the PCB design and the placement of components for ease of manufacturing and assembly with the goal of making a better product at a lower cost. We do this by suggesting simplification, optimization, and refinement of the PCB design. For this we examine five principles during a DFM exercise:

  • Material
  • Design
  • Process
  • Environment
  • Compliance/Testing

Rush PCB recommends DFM in the early stages of the PCB design process, even before we begin the tooling process. Ideally, DFM requires the participation of all stakeholders, including designers, engineers, manufacturer, and material supplier. This cross-functional DFM exercise ensures optimization of the design.

Read About: Past and future trends in PCB design

Virtual Design, Simulation, and Optimization of Production Processes

At Rush PCB, we plan the fabrication and assembly processes to enable a smooth flow. The planning helps in preparing the process while identifying the impact of design changes on fabrication and assembly lines while delivering updated work instructions.

By validating processes, we visualize and analyze the entire assembly operation, thereby discovering issues related to human and machine assembly, while ensuring adherence to best practices.

The major advantage of the above exercise is a substantial improvement in capital investments planning and operating expenses prediction. This way of optimizing production leads to maximization of utilization and reduction of costs.

Managing Manufacturing Operations and Materials

At Rush PCB, we use materials management tools to ensure just-in-time delivery of materials to the fabrication and assembly line. This eliminates excess work-in-process, while improving inventory turnover.

Our comprehensive solution for electronic preproduction, production, and execution helps to manage data from all resources such as operators, tools, and machines to build complete traceability. We integrate this solution seamlessly with our product life-cycle management and enterprise resource planning systems.

Read About: PCB Routing Requirements

Using Manufacturing Data for Generating Business Value

All our manufacturing processes generate data, such as those on material consumed, process flow, quality, and more. This real-time, normalized manufacturing data helps us in driving intelligent, decision-making business analytics solutions, root-cause analysis, prediction of future performance, and cost and quality trends, thereby helping to improve our business value.

Advantages of Smart Manufacturing

With Smart Manufacturing, Rush PCB is on its way to eliminate disconnected systems, silos of information, and mounds of paper-based work instructions. This helps us to manage a continuous integrated work flow starting from design, to planning, to production, to delivery.

At every stage of PCB fabrication and assembly, a difference is eminently visible between Rush PCB’s Smart Manufacturing and the earlier piece-meal digitization strategy. Major differences include:

  • Designs are more reliable and manufacturable
  • Design, engineering, and manufacturing departments collaborate better
  • Data redundancy is lower
  • Shop floor planning mistakes are fewer
  • Manual data entry is less error-prone
  • Inventory and use of materials are more optimized
  • Best practices of manufacturing are better enforced
  • Work instructions are more accurate and up-to-date
  • Key performance indicator monitoring is through real-time data collection
  • Root-cause identification is faster
  • Higher product mix capability without loss of factory performance

To the customers of Rush PCB, its Smart Manufacturing strategy offers several advantages, namely:

  • Lower product development time, leading to faster time-to-market, with the advantage of frequent new product introduction. The quality improvement through DFM exercises improves the design for a longer life-cycle of the product.
  • With Smart Manufacturing, Rush PCB can quickly follow up with manufacturing, as soon as the design is complete. This allows for better product personalization and customization.
  • With more informed decision-making through manufacturing data, there is better visibility into analysis and manufacturing.
  • Smart Manufacturing at Rush PCB is improving the efficiency of our manufacturing processes and materials. This not only reduces overall manufacturing costs, it makes our PCBs more affordable to our customers.

For all your PCB requirements, please contact Rush PCB, or visit our website today.

pcb glue

PCB – Precision Glue Dosing

PCB – Precision Glue Dosing

Rush PCB understands that high quality products require highly precise component placements on their printed circuit boards (PCBs). However, in traditional PCB assembly, there is typically a high amount of wastage because of fluctuations in glue viscosity, inconsistent height of the dispensing needle, and variable amounts of glue.

The effect of this variability is that assemblers often have to scrap expensive components, resulting in slowing production lines that hit the bottom line. Additionally, these variables also make the gluing process rather operator-intensive, further adding to the production time and costs.

Problems with Glue-Dosing

There can be several problems with glue-dosing. One of the most common issues is constant dripping of glue. Usually, there are three causes for this—very thin glue, large air pressure, large needle diameter.

Very thin glue may drip constantly, and the solution is to replace it with a thicker glue. A large air pressure may also force the glue to drop continuously, and this can be solved by reducing the pressure.

It is very important to use the correct diameter for the dispensing needle. If the diameter is too large, the glue can drip continuously. On the other hand, with a small diameter needle, the valve may start dripping once it is closed. This is because the small diameter needle causes a back pressure to build up. Rush PCB recommends using a tapered oblique needle to reduce back pressure.

Read About: How Does Prototyping Help?

Precision Glue-Dosing Solutions

To eliminate most of the above variables from their production environment, Rush PCB uses fully automated turnkey glue-dosing solutions. Driven by precise vision and motion systems, the turnkey solution is self-calibrating as it applies an identical amount and pattern of glue to every component. Not only does this process simplify the operator’s tasks, it also ensures repeatability, while reducing scrap. In turn, we at Rush PCB, transfer the cost reduction to the customer, resulting in lower quotes.

One of the biggest challenges during PCB assembly is applying microscopic amounts of epoxy glue efficiently in precise parallel lines. Irrespective of production cycles being short or long, there is a high possibility that the regular process of glue application may turn inconsistent or go wrong.

For instance, there are chances that the alignment or positioning of the surface mount devices (SMDs) might change slightly, there may be too much glue, the dispensing needle may be somewhat lower, higher, or offset from the previous PCB, there may be inadequate glue, the glue may be of a different viscosity, and so on.

To reduce the impact of the above variables, we at Rush PCB have installed an automated system in our production environment. This ensures a perfect alignment of the plate and glue-dispensing needle, while keeping them the same distance apart all the time.

The automated system consists of two high-resolution vision camera systems, and a mechanism for imparting precise motion, operating on smart software. The combination helps to keep the distance between the plate and the glue-dispensing needle to within ±5 microns on the three axes. Additionally, a volumetric glue-dispensing system ensures that only the required volume of glue dispenses to each part.

The system also has a recipe handler that helps with product changeovers. It allows the operator to reconfigure the system quickly by simply entering the new value such as glue type, speed, start/stop positions, and height.

Read About:Printed Circuit Boards and AI

Benefits of Precision Glue-Dosing

There are several advantages to Rush PCB when using an automated system for precision glue-dosing. As the entire system is fully automated, the process is entirely operator independent. Moreover, the system ensures a repeatable operation providing uniform product quality and takt time.

The turnkey glue-dosing system being self-calibrating, it does not require the operator to intervene periodically, thereby eliminating time-consuming stoppages. Moreover, the operator does not require training in calibrating the system.

The automatic dosing system dispenses glue volumetrically, ensuring application of precise amounts of glue.

Applications of Precision Fluid-Dosing Systems

Apart from attaching SMDs to PCBs for quality assembly, Rush PCB uses the precision glue-dosing system in other applications involving fluid dispensing. These involve applications such as:

Large IC Failure Protection with Underfill

While assembling large ICs such as PoP, BGA, and CSP, it is necessary to underfill them to prevent failure. Densely populated boards require tight keep-out zones with small, narrow fillets. A high degree of precision is necessary with applying underfill to these components to augment quality, speed, and productivity.

Adhesives for Thermal Management

Several components dissipate heat when operating, and require thermal management to keep them within safe operating temperatures. Most such components use heatsinks with heat-conducting adhesives in between the heat-producing IC and the heatsink. The heat-conducting adhesive helps to transfer the heat from the component to the heatsink. For proper application, the fluid-dosing system must dispense the heat-conducting adhesive in exact volumes and in a thin profile. The automated system helps in dispensing the adhesive in the right consumable combinations and speed.

Please contact Rush PCB for all your precision assembly requirements. Please visit the Rush PCB website, or call now for an instant quote.

pcb solder

Role of Solder & Paste Masks in PCBs

Role of Solder & Paste Masks in PCBs

For improving the quality of soldering on printed circuit boards (PCBs), the electronic industry uses two types of masks—solder and paste masks. As the names are very similar, it is easy for newcomers to the industry to be confused about the usefulness and functioning of the two. In reality, the industry uses the two essential masks for entirely different purposes. In this article, Rush PCB explains their individual functioning, and the advantages of using them.

Solder Mask for PCBs

As the name implies, the solder mask creates the soldermask on the PCB, allowing soldering on selected areas of a PCB, while masking the others. Most commonly, the soldermask appears on the PCB as a green layer on its two outer surfaces. The green layer covers most of the PCB surface, except for copper pads that will accept component leads for soldering. Therefore, if a copper trace or pad is under the green soldermask, it will not be possible to make solder adhere to it.

Copper traces and pads on a PCB, if left uncovered, readily tarnish when they encounter air. The tarnish is due to the formation of copper oxide, a compound that does not conduct electricity, and does not allow soldering. Moreover, the presence of Sulphur in air causes the formation of copper sulphate, a corrosive substance. The net result, for a PCB with exposed copper on it, is a degradation of its quality when stored for some time.

To get over this problem, Rush PCB takes recourse to two processes. The first is to cover those parts of the PCB that will not undergo soldering with a green soldermask, and the other, to apply surface treatment to the exposed copper. The two processes ensure no copper surface on the PCB encounters air, while making it is easier to solder components on the PCB during assembly. With a soldermask present and surface treatment on the PCB, Rush PCB ensures the possibility of storing bare boards for a longer time, without any damage, until it is time to assemble them.

The common implement to apply the green soldermask on a PCB is the solder mask. The actual mask is a negative or complement of the green soldermask, and therefore, covers all the copper areas that will undergo soldering. When applying, the green color penetrates the open areas of the mask, and deposits on the PCB, covering the areas the mask exposes.

Paste Mask for PCBs

This mask or stencil is applicable to the use of solder paste, controlling the amount of paste the assembler dispenses to each solder pad on a PCB. Applying the proper amount of solder paste using a paste mask is an important process during assembly, since the presence of excess solder paste may cause solder to overflow, thereby creating shorts during reflow soldering, while inadequate solder paste may create dry soldering on some components.

Rush PCB prefers making paste masks or stencils of stainless steel, although it is possible to make them with other materials as well. For accuracy, the openings in the stencil must be laser cut and the surface finished with chemical etching. This creates a smooth inner surface in the openings, allowing for a smooth deposition and no sticking of paste on the stencil walls.

The thickness of the paste mask determines the volume of solder paste the process deposits on the copper pads. For dense PCBs, it is essential to have a thin stencil to adequately control the amount of solder paste deposition. For good quality of soldering, it is essential to accurately register the stencil on the PCB.

Advantages of Solder Mask and Paste Mask

Rush PCB uses both solder and paste masks on PCBs to ensure the quality of soldering. We need the solder mask while fabricating the board, and use the paste mask while assembling it. Both are indispensable for ensuring high quality. For instance, in HDI boards, we use the solder mask to create soldermask dams in between closely spaced pads, thereby preventing molten solder from overflowing and bridging neighboring pads during reflow soldering.

For PCBs using fine-pitch components, such as BGAs and gull-wing ICs, the pitch between neighboring pads may not be enough to allow placing a soldermask dam. For such PCBs, Rush PCB recommends using soldermask defined pads. While the pads are of a larger dimension, a smaller soldermask opening defines the opening for the solder paste.

Designing a paste mask or a stencil is an involved subject, and eminent PCB manufacturers such as Rush PCB have evolved their own special techniques for fabricating them.

Please consult Rush PCB with your design today, and get expert advice on the type of solder and paste masks necessary. Visit our website, or give us a call for a free quote.


What is Electrodeposition Photoresist?

What is Electrodeposition Photoresist?

At Rush PCB, we are always at the forefront of technologies for the development of printed circuit boards (PCBs). This involves facing numerous challenges such as improving the density of PCBs, miniaturizing them, and searching of ways to make them suitable for the high speeds our customers want. All this means we must explore beyond the traditional methods of manufacturing technology to meet the newer requirements for these PCBs.

Traditional PCB Manufacturing

Traditional double-sided PCB manufacturing begins with blanking the copper clad laminate and cleaning the copper surface. The fabricator then drills the board according to the drilling information in the Gerber files, and plating the entire panel to create plated through holes. The fabricator then coats both copper surfaces with a photoresist, covers them with negative patterns of the traces, and exposes the board to a specific wavelength range of UV light. This helps to polymerize the exposed photoresist.

The fabricator then removes the negative patterns and proceeds to develop the photoresist, a process that removes the unexposed photoresist from the board, leaving the exposed photoresist as a hard layer on the copper. The fabricator then proceeds to plate the exposed copper with a thin layer of copper and tin.

In the next stage, the fabricator strips off the hard resist layer and removes the exposed copper by etching. He/she then removes the tin layer, exposing and retaining only the required copper traces. The rest of the process then follows, namely, solder mask printing and surface treatment.

Disadvantages of Traditional PCB Manufacturing Techniques

The major disadvantage of the traditional methods of PCB manufacturing is they do not allow fabrication of very thin and closely spaced traces as modern PCBs demand. It is difficult for the fabricator to control the etching process to create evenly spaced traces when the trace and space width is below a certain level. For instance, Rush PCB makes High Density Interconnect (HDI) boards with trace widths and spacing of less than 100 µm, which is very difficult to achieve by the traditional methods of PCB manufacturing. For making HDI boards, Rush PCB uses modern techniques such as electrodeposition photoresist.

Electrodeposition Photoresist

Electrodeposition is a popular electrochemical process that the industry uses to coat a substance with another material. To form the patterned traces on a PCB, Rush PCB electroplates copper into micro-cavities on HDI circuit boards.

Compared with spin and spray coating techniques, electrodeposition photoresist has several advantages for HDI boards requiring high reliability, high density, high capacity, lightweight, and micromation. Therefore, electrodeposition photoresist is the most suited technique to pattern traces with a smaller line width, when combined with the advantages of UV curable photoresist and electrodeposition.

The fabricator at Rush PCB begins the process by coating the laminate with a thin layer of copper seed layer. Next, the surface of the PCB undergoes a coating with a photoresist using the photolithography technique. The fabricator then exposes the resist to ultraviolet light through a patterned photomask and dissolves the exposed areas. This results in a patterned insulating film on the PCB surface exposing the seed layer on the bottom of the pattern.


The fabricator then subjects the PCB to an electroplating process by submerging it into an electroplating bath using copper anodes. As the seed layer is the cathode, passing an electric current through the system results in copper depositing on the seed layer. The thickness of the deposited layer depends on the current density at various positions on the seed layer over time. This way, solid copper fills the cavities in the patterned photoresist, while the fabricator maintains the plating rate by controlling the current density.

After the board attains the requisite thickness of copper, the fabricator strips away the remaining photoresist and etches away the thin seed layer to isolate the plated copper traces from each other.


Rush PCB has made several improvements to the above technique to optimize the process so that it is comparable or cheaper than the regular process when making HDI boards.

For example, the current density is usually higher at the edges of the board, resulting in unacceptable plating thickness variation along the surface. Rush PCB uses an insulating shield with an opening positioned between the anodes and the PCB within the electroplating bath. Optimizing the size of the opening and judiciously placing the shield in the bath results in a plating with uniform thickness. Rush PCB uses simulations to minimize the thickness variation of the plating across the PCB.

Using simulation along with a dummy aperture before the actual process of electrodeposition allows minimizing the manufacturing costs by optimizing the process for the best results. This helps Rush PCB run the actual process at the highest possible rate, while still achieving the necessary thickness specifications.

Advantages of Electrodeposition Photoresist Technique

By using electrodeposition photoresist technique for making HDI boards, Rush PCB gains several advantages. Some of these are:

  • Suitable for thin and high-density boards
  • Suitable for multi-layer board production of very high quality
  • Suitable for forming fine line resolutions (up to 0.25 mm)
  • Operation times can be short
  • Production process is simple
  • Low costs


Rush PCB is a pioneer in the electronic industry, making different types of high-density boards, suitable for applications in high-technology fields such as medical and aerospace.

Visit Rush PCB website, or call for a quick quote for all your PCB requirements now.

PCB Assembly

The Importance of V-Scoring in PCBs

The Importance of V-Scoring in PCBs

Rush PCB recommends using V-scoring in Printed Circuit Boards (PCBs) for easily removing individual boards from a circuit board array. V-scoring a board array requires a precision scoring tool with a pair of top and bottom cutting blades. The PCB manufacturer either runs the cutting blades across the panel in a straight line or pulls the panel through the blades to create the scoring.

For separating parts from a completed PCB assembly panel, Rush PCB offers V-scoring as a great cost saving and a highly efficient way. Our customers consider our offer of V-scored PCBs as a great value add.

V-Scoring and Jump-Scoring

Very often designers and manufacturers place a set of smaller boards together in an array to make the assembly process more efficient. After assembly is over, the assembler manually separates the individual boards from the array. To make it easier for separating the boards without damage, the manufacturer scores a v-shaped breaking line along the intersection between individual boards using a precision cutting tool. The idea behind scoring the PCB is to provide a solid structure for the board assembly, while allowing for application of minimal pressure to separate the assembled boards. Rush PCB follows some rules for V-scoring PCBs:

The Importance of V-Scoring in PCBs

  • Only straight scoring lines
  • Vertical and horizontal scoring lines allowed
  • Scoring lines from one outer edge to other outer edge, except in jump-scoring
  • Scoring recommended only above minimum PCB thickness of 1 mm
  • For PCB thicknesses 0.8 to 1.0 mm, one-sided scoring possible

During V-scoring, the manufacturer cuts a v-shaped groove on the top and the bottom sides of a circuit board, while leaving a small amount of material in place to make the PC boards stay in place. The general practice is to cut the grooves to a depth of 1/3rd the board thickness on the top and bottom, leaving a thickness of 1/3rd in the middle.

Read About: Printed Circuit Boards and AI

For thin laminates or when the board has heavy components, scoring lines from one outer edge to the other may be problematic during assembly. In such cases, unscored waste rails are necessary to maintain the strength of the array to prevent the individual parts from falling apart before the assembly is over. Manufacturers get over this problem by lifting the scoring blades off the PCB surface before they get to the end of the panel. As the blades need to jump over some parts of the PCB, manufacturers call this process jump-scoring.

Rush PCB has the state-of-the-art V-scoring equipment for creating PCBs with V- and jump-scoring. Contact us for your requirements.

V-Scoring Equipment

At Rush PCB, we have the latest V-scoring equipment with programmable blades. We can program the blades to lift off the panels at the appropriate location. We have experienced personnel who know how to jump-score properly, as errors in jump-scoring can affect the quality of assembled PCBs.

Timing the jump-scoring is important, as allowing the blades to cut into the waste rails could weaken the panels leading to problems of separation before assembly. On the other hand, if the blades jump too early, it can reduce the V-scoring depth, and the assembler will find it more difficult when separating individual boards from the array.

V-Scoring Requirements

Designers must be careful with V- and jump-scoring to indicate accurately and define the parameters on the design drawing. The positional and alignment accuracy of the top and bottom grooves is critical for a clean separation and to minimize the post-separation smoothing for the board edges.

IPC-2222 Section 5.3.1 defines the alignment tolerance for V-scoring to ±80 µm. It is possible to have 90-degree groove or a 30-degree one. Whatever the angle, the designer must maintain a track routing distance of at least 1 mm from the scoring edge top, to prevent damage during de-paneling. Rush PCB recommends that the designer and the fabricating shop collaborate on the V-scoring angle options available.

Read About: Key Steps in Designing Printed Circuit Board Layouts

Disadvantages of V-Scoring

  • Difficulty in breaking individual parts from the array
  • Poor scoring due to dull blades
  • Not suitable for low-tolerance PCBs

If the two grooves on the PCB are not deep enough or do not align properly, the assembler may have difficulty in breaking individual parts from the array. This may cause the forces placed on the assembly to create a haloing along the parting edge. This may result in fracturing the PCB laminate such that the separation happens outside the v-scoring channel, resulting in uneven breaks along the board edge.

Dull cutting blades of the v-scoring equipment may result in offset v-score, or excess material between two board sections. This causes uneven and difficult separation of individual boards.

Although the excess material remaining along the edges of boards separated by v-scoring is too minute to affect in fitting, boards with very low tolerance for unit fit may face an issue.

Contact Rush PCB for all your PCB needs, including V-scored PCBs. Call us or visit our website today.


How Important is DFMA for PCBs

How Important is DFMA for PCBs

In this highly competitive market, where OEMs continually develop new products for widening their customer base, they must also remain vigilant about the quality of their products. Properly planning is necessary before they can develop high quality products in less time at lower production costs, which ultimately translates into more sales and greater customer loyalty. Design for manufacturing and assembly (DFMA) is an important step in this direction, and Rush PCB offers simple guidelines for their customers to follow for PCBs.

Why Design for Manufacturing and Assembly

One of the most important advantages of following the DFMA methodology is reduction of the time-to-market. By eliminating multiple revisions and design changes that typically occur during PCB design, DFMA techniques help produce designs that are more comprehensive and efficient to produce, while being able to meet the customers’ requirements the first time. In turn, a shorter time-to-market results in lowering the development costs. By applying DFMA methods for PCBs, our customers can:

  • Shorten PCB assembly times
  • Lower PCB assembly costs
  • Eliminate process waste
  • Increase PCB reliability

Performing Design for Manufacturing and Assembly

Rush PCB recommends integrating the DFMA methods through design and manufacturing teamwork. In practice, two different classifications make up DFMA—DFM or Design for manufacturing, and DFA or Design for assembly—with slightly different goals for each.

The techniques of DFM focus more on reducing or eliminating expensive, unnecessary, and complex features, which would make them difficult to manufacture.

The techniques of DFA focus on standardization and reduction of parts, sub-assemblies, and assemblies, with the aim of reducing the assembly time and cost.

Rush PCB recommends integrating DFM and DFA into DFMA, as combining them prevents one from causing negative effects on the other. For instance, the designer may be able to reduce assembly steps by combining parts. However, if the part is difficult or expensive to manufacture, the process will not produce any gain. The goal must be to work together to:

  • Simplify the PCB design
  • Design the PCB for ease of fabrication
  • Design within known process capabilities
  • Use common parts and materials
  • Mistake proof the design for assembly
  • Design the PCB for ease of assembly
  • Reduce flexible parts and interconnections
  • Design PCB for automation

Simplifying the PCB Design

Boards with a complicated contour take more time to fabricate, and therefore, introduce extra cost. Rush PCB recommends designers should follow simple contours for their boards, unless necessary.

Design the PCB for Ease of Fabrication

Fitting an electronic circuit within a small board may require fabricating it in multiple layers to allow accommodating all interconnections between on-board components. However, this may increase the complexity of fabricating the board as interconnecting multiple layers may require introduction of vias, and therefore, additional steps during fabrication.

Designing Within known Process Capabilities

Rush PCB strongly recommends early discussions with the fabricator if the designer is contemplating incorporating special features in the PCB. A mismatch of process capabilities at the fabricator with the designer’s requirements will lead to a time loss.

Using Common Parts and Materials

Unless required by the application, Rush PCB recommends designers to use commonly available parts and materials for their PCBs. For instance, metal backed PCBs are more expensive than regular PCBs, and designers should use metal backed PCBs only when they need heat removal from components on the board.

Mistake Proof the Design for Assembly

Rush PCB recommends designers should follow best practices for making their boards mistake proof during assembly. This involves using proper orientation and labels for diode and LED orientation, as a simple example.

Design the PCB for Ease of Assembly

Consulting with the assembler regarding the tools and equipment they will use for assembly is an important step the designer must consider beforehand. It is important the designer avoids multiple reorientation or set-ups during the assembly process, as this creates wasted movements and time. Moreover, it is important to allow for adequate tool clearance with no obstruction to tool movement.

Read About: PCB Assembly Fabrication Methods

Reduce Flexible Parts and Interconnections

Considering the usage and environment in which the PCB must operate, the designer must use components parts robust enough to the application. For instance, a designer must avoid using fragile ribbon cables that could become brittle over time and break with vibration.

Designing PCBs for Automation

Although cost-effective for low volumes of production, manual assembly is a time-consuming and error-prone process for larger quantities of production. Designing the PCB for automated assembly processes not only reduces assembly time, but also reworking costs.


The steps presented above for designers to follow for implementing DFMA is only for representation, and Rush PCB recommends designers to explore more about the methodology by visiting our website and or calling us. Rush PCB has personnel who are experienced and customers can get all guidance for their requirements.