Epec's Blog | Electronics Manufacturing Solutions

When developing a flex PCB based design, one of the most common early decisions is whether a flex circuit with stiffener(s) will meet the design requirements or if a rigid-flex construction is necessary or more effective. While there is some overlap between the two methodologies, there are significant capability, performance, and cost differences that require review to ensure a successful design.

Integrating flex circuits with rigid PCBs in a rigid-flex configuration helps address common design challenges by combining the mechanical advantages of flex circuitry with the functionality of rigid circuit board sections.

Stiffeners are a critical element in flex circuit design and directly influence the performance, reliability, and manufacturability of the finished product. Properly specified stiffeners provide support for component and connector areas, help meet ZIF connector requirements, address mechanical bend constraints, and can assist with heat dissipation. Complete and accurate documentation is essential to ensure the finished flex circuit meets design requirements.

Many of today’s rigid-flex circuit designs utilize the same high-density components found in rigid PCB designs. This requires the use of blind and or buried vias to allow the signal lines to be routed out from within the high-density components or the high-density areas of the design. The most common component that we see driving this today is the 0.4mm pitch BGA package.

The flex PCB stack-up documentation is an important component of the data set of a flexible printed circuit board design. It consists of a description of a flex or rigid-flex circuit board that defines in detail the specific material requirements and construction of the design.

Many electronics assemblies that utilize flexible printed circuit boards are sensitive to either absorbing or emitting electromagnetic interference (EMI). If EMI is left uncontrolled it can negatively impact the performance of the design and in extreme cases completely prevent it from functioning.

Pre-baking polyimide-based flex PCBs immediately prior to assembly is required to prevent moisture-driven delamination during reflow. Polyimide materials naturally absorb moisture, which expands into steam under high temperatures and separates layers. Removing this moisture just before assembly is the only reliable way to avoid failures.

When ordering flex circuit boards online, quick turn order delivery timelines can incur setbacks if the data set is either incomplete or if the design has technical issues. Technical issues can be related to either manufacturability or the end use of the parts. These issues then often require multiple communications to resolve and in some worst-case scenarios, extensive design revision. Any of these issues will of course delay the delivery of the finished parts.

Flex circuit suppliers vary widely in experience, capabilities, and financial stability. Choosing the right partner is critical to the success of your application.

A structured vetting process helps ensure that your supplier can support design requirements, manufacturing constraints, and long-term production goals. The following five questions identify the most important areas to evaluate when selecting a flex circuit supplier.

Flexible circuits share some characteristics with rigid printed circuit boards, but the manufacturing approach is fundamentally different. The thinness and lack of reinforcement in flex materials introduce unique challenges that affect handling, processing, and dimensional control.