By Gordon Vinther, Ardent Concepts -- In the design phase of next generation small electronic handheld devices, designers are often faced with the challenge of mating relatively small parallel printed circuit boards (PCBs). In many cases, engineers employ flex circuit cables to accomplish this task.
There are many benefits to using flex PCBs in some applications -- weight and dynamic flexing capability are two -- but they are not without inherent risks. A flex circuit is typically soldered to one PCB, wrapped around back over itself, and connected to another PCB via some small COTS (commercial of the shelf) connector. In many cases, it may be more efficient in the end to replace the flex PCB and connector set with one custom compression connector which connects the two PCB’s to replace those components.
Here’s why: Flex circuits can be relatively expensive, and there are a limited number of COTS connectors to attach them which are not precisely suitable for each individual application. Many engineers discover after extended research that in order to design in the sufficient number of leads needed to accomplish the interconnect task, the flex connector options in the market are limited to larger and/or bulkier form factors, which eat into precious real estate in the device.
Also, in some cases, yield issues on flex connectors can delay production times. Furthermore, COTS flex connectors can be difficult to mate within a tiny assembly, adding to the cost of manufacturing. And finally, once installed, the reliability of the COTS flex connector can often become the weak link in a design due to inherent issues with durability in shock and vibration environments, which are the natural habitats of handheld devices. Flimsy, ill-fitting connectors holding tiny pieces of flex are a potential pitfall of performance over time for many mobile applications.
One alternative to the flex and COTS connector methodology is to design a simple custom spring loaded connector. One side of the connector may be tooled and rigidly fixed to on PCB, allowing for the addition of the second PCB -- easily added further down the assembly line. The spring loaded connector allows the necessary relative translation between the PCBs, while still providing a robust current path from one PCB to the other. The cost of the custom connector may often be the same or less than the flex circuit and its COTS connector together. Simply put, use of a spring loaded connector adds a level of robustness to the system and eases manufacturability, two common concerns in the mobility market.
Mobile devices, with their inherent complexity and real estate limitations, represent a substantial drain on the bandwidth of design engineers who seek to understand the trade-offs between manufacturability and field performance over time. The use of a simple, easy to design and build spring loaded connector is a recipe for gains on both fronts.
Gordon Vinther is a connector expert and entrepreneur. He can be reached at Gordon@ardentconcepts.com.
