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Importance of Stiffeners for Flex PCBs

Importance of Stiffeners for Flex PCBs

As printed circuit boards (PCBs) evolve, they are gradually changing over from rigid boards to flexible types. Its demand is increasing in medical field. Additionally,  military, aerospace, and industrial markets, manufacturers are gearing up to produce flexible circuits board along with rigid ones. Rush PCB has the technology and expertise in place for producing various types of flexible boards to meet the market demands.

The major advantage flexible circuits offer designers is the capability to outfit products with a suitable circuit when the design of the product will not admit using a rigid circuit board. That makes flexible circuits invaluable to several applications in the electronics industry.

Although flexibility may be a desirable feature in most applications, some parts of the circuit may need to be stiff as well. For instance, if the area where a connector needs soldering on the PCB is not stiff, there is a potential risk of damage to the PCB with the insertion and removal of the connector. As the board is soft and flexible, the force of insertion and removal of the connector falls on the soldered pads. Also, it causes them to lift off the board, thereby damaging it. With a stiff board, the force distributes itself over the entire area. Furthermore, it does not damage the solder joints on the circuit.

The necessity for PCB Stiffeners

Rush PCB UK adds stiffeners in flexible circuits to reinforce areas containing components and where rigidity is necessary, but not in areas where the board will flex. There are various instances where a flexible circuit needs to have rigid areas. These include:

  • Presence of components near a flex zone
  • Increasing the abrasion resistance of the flex circuit
  • Specific areas of the board need mechanical strengthening
  • Maintaining the required thickness in the flex circuit
  • Supporting components and connectors on the PCB
  • Constraining flexibility to parts of the circuit that require it
  • Enabling better handling of the flexible board
  • Keeping specific areas of the flexible circuit stable and flat
  • Improving heat dissipation and providing strain relief
  • Meeting Zero Insertion Force (ZIF) connector specifications
  • Increasing and constraining the bend radius at the intersection of flex and rigid parts of the circuit — for avoiding stress on the flex part during repeated bending operations.

The basic reason for the use of stiffeners is when the flexible circuit requires a rigid area as protection against damage maybe from connectors or components attached to it. As the stiffener does not allow the circuit to bend, it protects the integrity of the solder joints in the area.

One may not need to use stiffeners if the flex circuit only has small SMD components that do not exert too much strain on the flexible part. Also, if there are no components mounted on the PCB in the flex region, the designer may decide not to use any stiffener.

Materials for Stiffeners

Although FR4 is the most common material Rush PCB uses for making stiffeners. Furthermore, they also use Polyimide, Aluminum, and Stainless Steel as the application demands. FR4 and Polyimide stiffeners may also have additional features such as pads, plated through holes, along with mounted components.

Although stiffener thickness may range from 8 mil to 59 mil (0.008”-0.059”), manufacturers prefer to use them in standard thicknesses. Generally, it is of 20 mil (0.020”), 31 mil (0.031”), 39 mil (0.039”), and 59 mil (0.059”). The requirement for a specific thickness of the stiffener depends on the application. In general, thicker the stiffener, better the support it offers the flexible PCB.

For instance, a ZIF connector requires the area of the flex circuit that plugs into it to be stiff. Manufacturers achieve this by using Polyimide stiffeners at the contact fingers. Typically, the PCB thickness requirement for ZIF connectors is between 0.2 and 0.3 mm. Allowing for the thickness of the actual flex PCB material, the stiffener thickness at the contact fingers can vary between 2 mil and 8 mil (0.002” and 0.008”).

Certain applications demand higher stiffness and manufacturers use Aluminum or Stainless-Steel stiffeners for the purpose. Metal stiffeners have the added advantage of acting as a heat sink if necessary. However, adding metal stiffeners increases the cost of the flexible circuit considerably.

Read Also:  New Configurations for Rigid-Flex PCBs

Application of Stiffeners

It is possible to use stiffeners for components requiring plated through holes (PTH). Rush PCB recommends using the stiffener on the side of the flex board on which the components will mount. This will allow access to solder pads on the flex circuit, making assembly easier. Designers should always enlarge holes on the FR4 stiffener to about 0.3 mm larger than those on the flex circuit. This will definitely ensure good alignment.

Rush PCB also recommends making flex circuits in the form of arrays, while including FR4 stiffeners all along the array border. This helps to make the array rigid enough to allow it to run through the automated assembly processes. It doesn’t require any additional tooling plates.

Manufacturers typically attach stiffeners to the circuit using heat and pressure. However,  Rush PCB recommends attaching stiffeners using pressure sensitive adhesives. Among the several varieties of such adhesives available to meet specific performance requirements. Two of the more popular types are thermally bonded adhesives and pressure sensitive adhesives.

Manufacturers select the type of adhesive to use depending on the location and configuration of the stiffener. For instance, if the stiffener size does not extend beyond the flexible board outline, pressure sensitive adhesive will be the best method for attaching it to the circuit. The manufacturer decides the specific pressure sensitive adhesive to use. It is mainly based on whether the flex PCB will undergo automated an automated reflow cycle, and or to what material it will finally adhere. Stiffeners often require their own prepreg lamination cycle, with certain stiffener materials requiring additional lamination cycles as well.

Bonding Between Rigid and Flex Circuits

Manufacturers prefer to use no-flow prepreg as the typical material for bonding flex and rigid material.It is most common in standard FR4 or Polyimide material. Depending on the application, a manufacturer may attach stiffeners to only one side or to both sides of the flex PCB. When attaching stiffeners to both sides, Rush PCB recommends a review by the designer to avoid complications at PCB assembly stages.

A single flex circuit design may require multiple stiffener thicknesses. This type of design has some limitations, and may need a thorough review of the PCB supplier for their capabilities.

Strain Relief for Stiffeners

Although designers add stiffeners to certain areas of a flex circuit to relieve the strain on the flexing part, the stiffener itself may need strain relieving. It’s needed more specifically where the circuit extends beyond the stiffener. Rush PCB recommends filleting the transient edge with a resilient adhesive or epoxy.  They can better relief such strains. Providing strain relief at the edge of a stiffener helps to prevent stress risers from occurring at transition areas such as from the flex to the rigid.

Conclusion

Stiffening some part of a highly flexible circuit may seem contrary to its functionality. However, the ability to do so helps the durability and reliability of the fragile circuit in many ways. Rush PCB recommends that designers use a stiffener. The suggestion is to relieve the strain on the flex circuit at a specific area. Mainly, it is the best way to extend its working life.

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Introduction to Semi-Flex Circuit Boards

Influence of IoT on PCBs

Polyimide is the typical base material for making flex printed circuit boards (PCBs). However, for some applications, OEMs find flex printed circuit boards (PCBs) made from Polyimide more expensive than their budgets allow. This may be because their application does not require the PCB to bend in a small angle, or bend repeatedly. In such cases, Rush PCB recommends the use of semi-flex boards.

Semi Flex Circuit Board

As the name suggests, a semi-flex board is partly flexible. It is possible to bend the semi-flex board only a limited number of times, typically about four to six times. It needs to be done before it develops a potential problem. Products with several circuit boards mounted at different angles to each other, without the requirement of ongoing flexibility, find semi-flex boards suitable. The OEM bends the circuit board only once during assembly, after which the board does not undergo any more flexing.

Semi-flex boards have all the advantages that a flex circuit offers. Just as in a flex circuit, there are no fragile wire interconnects or connectors in semi-flex boards. Over time, connector contacts can oxidize, leading to poor connections, compromising the reliability and safety of the product. Absence of connectors also implies a reduction in the number of solder joints, leading to an improvement in reliability. Flex and semi-flex boards simplify the production process, as there is no longer any requirement of manufacturing looms for special interconnect cables, and install them manually.

Semi-Flex Circuit Construction

Rather than use Polyimide, which is expensive, semi-flex circuits instead use a thin layer of standard FR4 material, with a lamination of copper layer on both its sides. Even without any special treatment, this thin FR4 layer can bend a few times without failure. The manufacturer uses four available copper layers for the rigid portion of the semi-flex board, with the flexible part consisting of the core or the thin FR4 layer with copper layers on both sides. Therefore, a two-layer circuit board forms the flexible connection between the two four-layer rigid circuit boards. The FR4 material defines the angle and radius that the flexible circuit can make.

For instance, the central core layer of the semi-flex PCB is a layer of FR4, with a thickness of 100 µm, and a layer of copper foil on its two sides with a thickness of 35 µm. This is how the manufacturer puts the flexible part in between, while continuing to build on the core, which continues through the entire circuit board. For the rigid parts, the manufacturer creates a double layer of prepreg on the inner two layers. The prepreg layer has a total thickness of 126 µm. A layer of FR4 material of 0.51 mm thickness and a layer of copper of 18 µm follows on the prepreg layer. Processing of the outer layers can follow the same methods as that for any ordinary four-layer circuit board. As the construction is symmetrical, the resulting semi-flex circuit board is stable and robust.

Limitations of Semi-Flex Circuits

An alternative less-robust method of construction process uses controlled depth routing or deep milling of specialized FR4 layers. This method helps to achieve a bending/flexing section within the traditional rigid FR4 construction. This is a typical inexpensive flex-to-fit solution for specific applications. It is suitable only for static operations, with the bend typically just for installation. The rigid sections may have up to 12 layers, with the bending performance going up to 50 bend cycles of 0°-90°-0°.

While designing the PCB, the designer must take into account the limitations of a semi-flex circuit:

  • Bend radius should not be less than 5 mm
  • Bend angle should not exceed 180°
  • Length of semi-flex part should not be less than 15.7 mm
  • Radius of corners should not be less than 1 mm
  • No holes, slots, or cut-outs should be present in the semi-flex part

Best Practices for Semi-Flex Circuits

Rush PCB recommends following some best practices for effective utilization of semi-flex circuits. For instance, designers should preferably plan copper layers of 35 µm thickness on both sides of the semi-flex part. They must surrounding the print traces with copper polygons.

According to Rush PCB UK, it is best to have a selective chemical Ni/Au (ENIG) final finish on the non-flexible part of the PCB. Manufacturers also offer alternative surface finishes such as HASL (SnPb), LF HASL (SnNiCu), OSP, Immersion Tin, Immersion Silver, and Electrolytic Gold. The designer can follow the same process for screen prints, slots, and cut-outs as a regular PCB requires, along with a green solder mask.

The designer can follow advanced production techniques such as peel-off mask, round edge plating, PTH on board edges, and copper up to the board edges. Some manufacturers offer options of carbon pads and gold edge connectors. As the semi-flex boards are less flexible as compared to flex circuits, manufacturers prefer to supply them in panels to avoid damage during transport and assembly.

Variants of Semi-Flex Circuits

Although the symmetrical configuration is most common for semi-flex circuits, manufacturers also make asymmetrical configurations according to demand and application.

For instance, it is possible to have an asymmetrical deep-milled semi-flex portion with a single layer or two layers of copper. Likewise, it is possible to have a built-up PCB with an asymmetrical configuration of the semi-flex portion with a single or two layers of copper.

Advantages of Semi-Flex Circuits

One of the major advantages of semi-flex PCBs over flexible circuits is the former is much cheaper. Although semi-flex circuits are only moderately more complex to manufacture than rigid circuits are. The main reasons for lower costs involve the use of FR4, rather than the more expensive Polyimide material.

In contrast to conventional flex and rigid-flex circuits, semi-flex circuits do not require the use of Polyimide foils. Therefore, the manufacturing process can omit the complex preparation of prepregs and cover foils. Additionally, the requirement for the usual tempering or annealing of the Polyimide material before beginning the soldering process is also not necessary for semi-flex circuits. Other advantages of a semi-flex circuit are:

  • Saves the cost of traditional connecting material between two rigid PCBs, i.e. cables or wires, crimps, connectors, binders, labels, including their individual cost of assembly
  • Improves the reliability offered by cables and connectors, especially as this is the most frequent cause of detect
  • Eases the assembly process and integration into boxes and housing
  • Applicable in cost-challenging applications, especially as replacement for rigid-flex
  • Applicable as angled connectors on large PCBs
  • Fits easily into boxes and housing
  • Possibility of semi-flex portions on both sides of the PCB
  • Reduces the product’s weight and volume
  • Allows designing in 3 dimensions
  • Easy to define characteristic impedance of the circuit systems on the printed circuit

 

Also Read: The Future of Flexible Circuits

 

IPC Standards for Semi-Flex Circuits

Semi-flex circuits follow the same IPC standards applicable to flex and rigid-flex boards. For designers and engineers, the most important among them are:

  • IPC 2223C
  • IPC-6013C
  • IPC-4202
  • IPC-4203
  • IPC-4204

The IPC 2223C is the Sectional Design Standard related to flex printed boards. It provides guidance on selecting adhesive materials as well as on connecting flex and rigid PCBs, providing specific and comprehensive tips for creating flex and rigid PCBs.

The IPC-6013C provides the Qualification and Performance Specifications in relation to flexible printed boards. It covers the qualification and performance requirements of single and multi-layered flexible and rigid-flex PCBs.

The IPC-4202 standard defines the base dielectrics that flexible printed Circuits can use.

The IPC-4203 standard defines the adhesive coated dielectric films and the flexible adhesive bonding films that flexible printed circuits can use as cover sheets.

The IPC-4204 standard defines the flexible metal-clad dielectrics that flexible printed circuits can use in their fabrication.

Summary

Rush PCB estimates semi-flex circuits to be approximately three times cheaper than an equivalent rigid-flex PCB combination. Compared to a system of rigid PCBs interconnected with cables, an equivalent semi-flex circuit can be up to 30% cheaper on the total cost.

rigid-flex PCB

New Configurations for Rigid-Flex PCBs

New Configurations for Rigid-Flex PCBs

Rigid-flex PCBs comprise both rigid as well as flexible board materials, and they consist of layers of flexible substrates attached to rigid boards. With rigid-flex circuit boards, designers can have more options, while eliminating the need for expensive, unreliable wires connecting the rigid substrates.

Ensuring the integrity of the boards and successful manufacturing requires attention to detail. Rush PCB, the largest rigid-flex printed circuit board (PCB) manufacturer, manages four vital design parameters when configuring their PCBs and creating them.

Stack Management

The stackup for the PCB design needs an impeccable template for the finished product to work flawlessly. For this, designers must use appropriate software and create the rigid-flex layers of the PCB. Delays and issues related to PCB performance will surely result from improper communication with the fabricator, inefficient management, and flaws with the rigid-flex stackup.

Rush PCB recommends proper ECAD software and related tools for designing rigid-flex PCBs. The board design requires fine-tuning for region-specific stack up. The software must have board specific tools for altering the board outline, rather than making multiple complicated changes when designing the stackup.

Integration tools between ECAD and MCAD can save time when designing precise stackup for configuring rigid-flex boards. ECAD programs that support 3-D design is most suitable for rigid-flex design especially as it helps with verifying the placement and integrity of sensitive components and bends.

Ground Plane Management

The configuration for the rigid-flex PCB depends on whether it will be a flex-to-install or a dynamic-flex type. Flex-to-install PCBs need bending only once when the OEM places it in the product during assembly. On the other hand, a dynamic-flex PCB needs to bend and fold repeatedly whenever the device using it is active. Ground planes in a dynamic-flex PCB are under constant stress as it bends, and therefore, need more attention during design.

The key concern during the design of a dynamic-flex PCB is the integrity of the signals and that of the ground planes surrounding them. The designer must place emphasis on the reliability of the materials and substrates the PCB uses.

For instance, using solid copper ground planes in a dynamic-flex PCB may result in cracking and failure. Some designers prefer using annealed copper on the flexible parts. Others prefer reinforcement of Gold and Nickel plating on the ground planes. However, both the above increase the cost of the PCB while reducing flexibility.

Also Read:  Material and Methods for High Quality Rigid-Flex PCBs

Rush PCB recommends using cross-hatched polygon rather than solid copper for ground planes. Although this does increase flexibility while reducing the possibility of cracking during repeated flexing, it impacts high-speed signals negatively. The recommendation is to add solid copper return paths below the high-speed traces. Making the return paths 5-10 times wider than the signal traces helps improve signal integrity.

Bend Management

Designers have several concerns when the rigid-flex PCB must bend. Apart from ground and power planes in the bend area, pads for SMDs and through holes are also at risk when present in the area of the PCB that will bend. Designers often resort to anchoring pads using additional coverlay and plating for through holes to strengthen the PCB.

Rush PCB recommends not using components or vias very close to bends in a rigid-flex PCB. When designing bends, the recommendations are to:

  • Reduce material thickness at bends
  • Avoid bends that are too tight
  • Avoid stretching of bend material

Mechanical stresses at the bend area will repeatedly stretch the outer layers while compressing the inner layers as the PCB bends. Unless the designer has properly configured the materials at the bend, the PCB is likely to fail prematurely.

Trace Management

Rush PCB UK recommends routing traces perpendicular to the bend during the design. In a rigid-flex design, the perpendicular routing helps reduce the stress on the traces when they bend. For double-sided flex design, the recommendation is to offset the traces. Staggering the traces on the top and the bottom layers makes the PCB stronger, enabling it to withstand repeated bending.

When bending traces, it is best to avoid a 90-degree bend, as the corners of the trace will be under greater stress than straight traces or curved traces. Therefore, using a gradual curve when bending the traces or using piece-wise linear curves reduces the chance of traces delaminating during bends.

Likewise, using tear-drop pads rather than round pads improves the reliability of rigid-flex boards significantly. For further copper adhesion to the flexible substrate, designers provide pads with anchor stubs.

For signal integrity, it is necessary the impedance of the high-speed signal path remains constant for the entire length of the trace. As the impedance may change as the track passes from the rigid to the flexible parts (and vice-versa) of the PCB, the ECAD tools should have the provision for altering the width of the trace to accommodate the change in impedance.

Rigid-Flex PCB Construction — Standard

Although manufacturers use several combinations and configurations for rigid-flex construction, some advanced constructions use odd layer count construction, varying flex layer counts, asymmetrical construction, air-gap flex layer constructions, blind and buried vias, multiple rigid area thicknesses, integrated ZIF constructions, shielded flex layers and more.

The standard method of constructing rigid-flex PCBs has the flex layers in the center of the construction with both the flex and rigid areas containing even layer counts. There is an even layer count in the thicker regions, and these are the rigid areas. The layer count may vary from four to eighteen layers or even more. The distinguishing feature of the standard design is that the construction sandwiches the flexible layers in its center.

Rigid-Flex PCB Construction — Odd Layer Counts

Among rigid board designs, layers with even counts are more common. However, designs with odd layer counts do exist, and have their own benefits. Similarly, rigid-flex boards may have an odd layer count.

For instance, it is possible to have a nine-layer rigid board along with three flexible circuit layers. Designs that necessitate two-sided shielding primarily use the odd layer construction. Stripline type impedance control mostly drives such requirements of two-sided shielding. The layers of flex consist of the ground + signal + ground construction, aimed at controlling RF and EMI. It is also possible to guide numerous interconnects between the rigid sections. This type of design offers a high amount of flexibility while reducing the cost.

The odd layer count construction is applicable to both the rigid and the flex parts of the PCB, but may also be independent of each other. For instance, it is possible that one side has an even layer count while the other end has an odd layer count, should the application demand such a design. The primary advantage provided by this configuration is an improved mechanical bend reliability due to improved flexibility, brought about by minimizing the flex area thickness.

Rush PCB recommends keeping bend reliability and constructions compliant with IPC 2223C. This will ensure all parts of the PCB have a high degree of reliability. To some extent, the odd layer-count configuration cuts down the cost of the design as it minimizes the final number of flex layers.

Rigid-Flex PCB Construction — Asymmetrical Design

The necessity for complex impedance usually drives asymmetric designs of rigid-flex PCBs. These designs require dielectric thickness to vary widely within the design. Constructions with asymmetrical design also improves reliability and manufacturability of the PCB by allowing a reduction of the aspect ratio of blind vias in the PCB.

However, asymmetric design may require fixtures to hold down the arrays during transportation for assembly. This is due to the introduction of warps and twists because of the unbalanced build of the PCB.

For instance, in an asymmetrical construction, the location of the flex layer may no longer be at the center of the design. Rather, the location of these layers may shift up towards the top or towards the bottom. In general, an asymmetric rigid-flex PCB design does not have any significant manufacturing concerns other than introduction of a few warps and twists.

Rigid-Flex PCB Construction — Varying Flex Layer Count

A varying flex layer count design is also common for rigid-flex PCB construction, where the layer count of the flex part varies between the rigid sections. As an example, if a PCB has three rigid sections, the second and third sections may have one or two flex layers joining them, with three or four layers joining the first to the second—this type of construction may have large variations in the configurations.

Rush PCB recommends using a construction with air-gaps in the flex layer for a varying flex layer count design to meet the IPC 2223C guidelines. Although the extra flex layers may run into the rigid section for routing, they may not surpass between the other sections. The reduction in the flex section, therefore, allows it greater flexibility and bend capability, which is the primary advantage of this design.

Rigid-Flex PCB Construction — Integrated ZIF Tail Construction

A ZIF tail integration within a rigid-flex construction is a common occurrence for the stackup. Such a construction eliminates the need for a flex circuit with a separate rigid section with a ZIF connector mounted on it. Therefore, the construction actually reduces the requirements of real-estate of the rigid area. The design also helps when the PCB is a high-density type with real-estate at a premium or a very thin design where it is not possible to incorporate the height of the ZIF connector.

The integrated ZIF tail construction actually improves the reliability of the PCB, as it eliminates the rigid section, the connector, and the associated interconnect points. The ZIF tail may require an additional stiffener using Polyimide, mainly to achieve the specified thickness requirements of the finger contact area of ZIF connector. If there are multiple layers in the flex part, the stiffener may not be necessary. However, more than four layers may make it difficult to achieve the ZIF thickness requirements. Rush PCB recommends limiting the integrated ZIF tail constructions to one and or two-layer flex configurations.

Rigid-Flex PCB Construction — Blind and Buried Vias

Rigid-flex PCB constructions may also utilize blind and buried vias, just as rigid circuit boards do. The necessity for using blind and buried vias arises from high-density applications, such as those for BGA and fine-pitch component mounting that may require via-in-pad designs. In case the blind vias require interconnects to the layers of the flexible circuits, it may be necessary for the designer to utilize an asymmetrical construction.

The number of sequential lamination cycles required by the design may limit the configuration. Typically, rigid-flex PCBs with multiple layers accommodate only a specific number of cycles of lamination, before the manufacturing methods and the dimensional tolerance of the materials prevent layers form registering effectively to one another. Again, just as in rigid PCBs, applications requiring via-in-pads can use capping and via fill.

Rigid-Flex PCB Construction — Air-Gap Construction

In rigid-flex PCBs with air-gap construction, manufacturers use isolated independent pairs of flex layers to substantially improve the flexibility. Rush PCB recommends constructions with two or more layers of flex to use this method, especially as using this method with four or more layers allows the design to conform to the guidelines of IPC 2223C.

Using air-gap construction precludes the use of any flexible adhesives within the rigid areas, ensuring the reliability of via structures within them. This method of construction also offers a very high degree of reliability and ensures a long-term operational life of the PCB.

Rush PCB recommends using coverlay on both sides of each flex pair, followed by a tiny air gap. All subsequent pairs follow a similar construction.

If the manufacturer constructed the design with bonding together of all layers, there would be significant issues of via reliability, and the flex section would have limited flexibility, to the extent of being almost non-flexible. Additionally, this construction would not meet IPC 2223C requirements.

Rigid-Flex PCB Construction — Multiple Rigid Area Thickness

Although a complex construction, some designs need rigid-flex PCB designs with multiple rigid areas of different thicknesses. Rush PCB recommends reviewing alternative options because of the manufacturing complexities that the design involves. In practice, manufacturers limit the construction to a maximum of two rigid area thicknesses, mainly due to the materials they require for the construction. The stackup is expensive, as the design is similar to manufacturing two boards at the same time.

In this design, one of the rigid sections may be considerably thicker than the other rigid section. Both sections may have plated hoes and vias. However, the manufacturer may have to limit the final thickness of the thinner section as there would be some commonality of materials between the two sections. For instance, the prepreg thickness on both rigid sections need to be the same. Presence of any extra core on one side would need mirroring it on the other side as well.

For instance, the manufacturer may start the construction as a four-layer stackup, encompassing layers two through five. They will run through all the manufacturing processes in sequence, leaving out creation of the outer profile. At this time, the manufacturer will have to start from the beginning again to add layers one and six, proceeding with all the manufacturing sequence once again, finally adding the outer profile. Unless the application demands following this process of multiple rigid area thickness, the process is an expensive one.

Rigid-Flex PCB Construction — Shielded Flex layers

Applications that require FR or EMI shielding use this method of construction, where manufacturers use specialized films in place of copper layers for shielding. Using these films saves on the expense of copper layers as well as allowing the flex construction to be thinner and hence improving its flexibility, along with an effective RF and EMI shielding.

Coverlays on the flex area can have selective multiple openings that expose the ground circuit. Electrically conductive adhesives on the films allow them to bond to the uncovered ground when laminated, thereby grounding the shield layers.

Summary

Combining the rigid PCB to the flex circuits technology allows adding a significant level of creativity, the overall reduction in packaging, and design integration. Rush PCB combines several specific constructions described above to create endless numbers of rigid-flex circuit configurations for their customers.