Collaboration optimizes flex circuit assembly and module designs for manufacturing.

It wasn’t long ago that OEMs had PCB design, production, and assembly in-house. I remember seeing those teams produce great results by working together to optimize designs for manufacturing and to solve problems before volume ramp. These same great results can be achieved with integrated flexible printed circuits and assemblies. Today, I see OEM designers and flex printed circuit/assembly applications engineers (AEs) collaborating and leveraging the flex manufacturer’s experience in materials, fabrication, assembly, module integration and test.

I see the best results when OEMs and flex manufacturers connect early in the design phase; that is when production risks evaporate and time to volume-ramp shrinks. This collaborative approach also generates continuous improvements and co-innovation to meet future technology capabilities. It is something that OEMs just don’t get from even the best “build to print” flexible printed circuit and assembly vendors.

So why does this work? Because flex circuit and assembly designs often require human interpretation and action in addition to the design-rule checks performed by automated design tools. This is even more critical in differentiated technology solutions in which component assembly on a flex circuit is further integrated into a module. Experienced AEs from flex companies with a keen understanding of how components, packaging and interconnect requirements achieve the desired fit and function have the added value of being intimately attached to the breadth of manufacturing process and materials their companies offer.

Here are five areas where I see regular opportunities for OEM designers effectively collaborating with experienced AEs at the module level to create an optimum design for manufacturability that meets the functionality requirements at competitive costs.

Material selection. Depending on the fit and function, an experienced AE not only recommends appropriate materials options, including stiffeners, PSA, shielding, coverlay and solder mask, but also highlights key tradeoffs in selecting those materials to meet mechanical and electrical requirements, while ensuring the end result is mass-producible.

Let’s take controlled-impedance requirements as an example. I have seen AEs help designers come to a decision on the balance between trace widths and dielectric thicknesses, and the tradeoffs between ground-plane cross-hatching compared to filled-copper all to address signal integrity required for the application.

I have seen engineers use simulations to suggest appropriate EMI versus copper shielding materials as an optimum solution to meet the mechanical and electrical requirements of a device in both high-speed-flex designs, as well as dynamic and tight-bending applications.

Padstack. While pad sizes, solder-mask openings, registration tolerances, surface finishes, and stiffener types are generally determined by component type and footprint, an experienced AE might recommend a padstack using coverlay, as opposed to using solder mask typically used for PCBs.

For example, I saw an engineer suggest a board-to-board connector padstack, where the tips of the pads are extended to be captured under gang-opening coverlay, and suggest compensating for adhesive squeeze out on the coverlay opening to meet the component footprint requirement.

Surface finish. AEs also help deciding between a universal or a combination of surface finishes to accommodate SMT and other electrical interconnect requirements. For example, ENIG (electroless nickel immersion gold) can be used as a universal surface finish for SMT components and contact areas (i.e., keypads), whereas ENIG for SMT components might be used in combination with electrolytic hard gold for contact areas that require plating bar connections. Another solution is to use ENEPIG (electroless nickel electroless palladium immersion gold) as a universal surface finish for SMT assembly and contact areas versus OSP (organic solderability preservative) and ENIG or electrolytic hard-gold plating.

Module integration. Module integration requires collaboration at the early design stage to ensure that all mechanical fit, electrical and functional performance requirements are met. Collaboration on the test strategy is also vital to get a functionally tested, flex-assembly module. This is especially important when performing three-dimensional assembly of flex circuits to a plastic or metal chassis, where properly accounting for the spring-back force is important to prevent the flex circuit from peeling away from the chassis.

For example, AEs with experience integrating flex assemblies into chasses have great insights for designers on how different conductor and dielectric thicknesses impact spring-back forces. Where substrate material choices are narrow, an experienced AE might suggest different bend configurations and higher bond-strength PSA. This usually adds up to the OEM getting a more reliable flex-assembly module design faster.

Design data package review. Although we’ve been talking about early collaboration, I don’t want to understate the importance of a thorough design data package review, because it’s critical to releasing a design to manufacturing. Although there’s less true collaboration, flex AEs work with OEM designers to quickly resolve any issues that arise from DRCs.

Here, the AE’s expertise in manual design verification is a key differentiator in ensuring a design’s manufacturability because automated DRCs for flex circuits and assemblies may not catch all known issues.

Many OEM designers have learned to leverage their flex manufacturer’s AEs – many of whom are dedicated to a particular OEM – to optimize today’s designs and innovate for tomorrow’s. This collaboration paves the way for packaging flex assemblies into modules, chassis and other super sub-assemblies in new, differentiated ways, while maintaining or enhancing manufacturability.

Jay Desai is director of marketing at MFLEX (mflex.com); This e-mail address is being protected from spambots. You need JavaScript enabled to view it .