Flex Rigid PCBs Affect Assembly Yield Rates

Rigid flex PCBs enable the assembly of multiple components and circuits within an integrated rigid-flex design without using connectors or wires. This simplifies the design, reduces component costs and improves electrical performance compared to traditional rigid PCBs. Rigid flex PCBs are also more durable, even in harsh environments like shock and vibration. However, they’re more delicate during manufacturing and field operation than a rigid PCB, making them susceptible to damage in handling and assembly, ultimately impacting the yield rate of the resulting boards. This directly affects the overall cost of the finished product.

To avoid this, it’s important to optimize your flex rigid pcb for manufacturing and assembly by ensuring that your designs are properly configured during the design stage. This includes using a specialized design-for-manufacturing software tool, working with integrated MCAD and ECAD flexible design tools, defining your bending region and more. By combining these tools in a single software application, it’s easy to design your flex circuit for maximum manufacturing success, reducing your total production costs.

When it comes to the assembly of a rigid-flex board, one of the most critical factors is the number of layers. A high layer count adds complexity and increases lamination times, which in turn leads to higher costs. Choosing the right conductor material is another factor that can influence your production costs. Copper is the most common material for rigid-flex PCBs, but it’s not the only option. Conductor materials with varying thermal, chemical and mechanical properties are available as well. It’s important to choose the right material for your application, balancing price with reliability and other criteria.

How Do Flex Rigid PCBs Affect Assembly Yield Rates?

Rigid-flex boards require special attention when it comes to their interface region, the area where the rigid and flexible portions of the circuit meet. This area is more delicate than the rest of the design and requires careful consideration. Best practices for this include avoiding vias, mounting holes and slots proximate to the area where the flex and rigid portions meet (typically less than 2.5mm), and designing your circuits to use a coverlay that extends throughout the rigid portion.

Finally, the choice of adhesive for the rigid-flex assembly is a crucial decision that impacts assembly yield rates. Epoxies are the most popular type of adhesive used in rigid-flex PCB assembly, offering a high degree of flexibility and excellent bond stability. They also provide good temperature and solvent resistance. But if your circuit board will be exposed to extreme conditions, you may need a more durable adhesive, such as a polyimide or fluoropolymer.

Rigid-flex boards are also prone to moisture absorption, which can cause delamination during the assembly reflow process. This is especially true for polyimide rigid-flex circuits. Moisture that absorbs into the foils can transform into steam when the PCBs are heated during reflow, which in turn can weaken or crack the laminate layers. To prevent this, your flex circuit should be pre-baked immediately before assembly to ensure that it’s 100% moisture-free.