In the evolving landscape of electronic engineering, the quest for reliability in electronic components has never been more critical. At the heart of this pursuit lies the concept of reliability — the ability of an apparatus or system to consistently perform its required function without degradation or failure.
This principle is particularly paramount in applications where failure is not an option: military, aerospace, life-supporting medical devices, and increasingly, in the automotive industry. Reliability engineering studies have illuminated a crucial vulnerability in electronic components: the point of interconnection, which is often the genesis of failure.
The Cost Benefits of Reliability
Beyond the imperative of operational integrity, reliability in electronic design introduces significant cost advantages. Enhanced final assembly yields and the elimination of latent in-the-field failures not only reduce product return and replacement expenses but also foster customer loyalty through consistent product performance. This financial efficiency can counterbalance the initial higher costs associated with advanced solutions like rigid-flex PCBs.
The initial cost of rigid-flex PCBs tends to remain high, due to the need to essentially build what would be a build process for two circuit boards, only to produce one board. The way this offsets overall costs involves the long term, by introducing a part with higher reliability that replaces multiple boards with interconnects, reducing the number of avenues of failure and allowing full confidence in the final assembly’s reliability. While this can sound risky, hedging an increased cost for an increase in reliability, the benefits in the long term can far outweigh the perceived risk of a rigid-flex design replacing existing assemblies.
Rigid-flex circuit board with multiple rigid-to-flex transition zones.
Reducing the frequency of replacing parts can also lead to cost savings in many ways such as: no longer needing to replace failed interconnects, no longer needing to replace other circuit boards that may have failed and require assembly, or in the most extreme scenario, no longer needing to replace or repair entire assemblies. These cost savings are the primary drivers of the increasing usage of rigid-flex PCB designs as time goes on.
The Mechanical Reliability of Rigid-Flex PCB Designs
Rigid-flex PCBs represent a paradigm shift in design philosophy, integrating flexibility and rigidity into a singular, cohesive unit. This innovation eliminates the traditional points of interconnect, thereby reducing potential failure sites inherent in older designs. The seamless integration of flex and rigid layers through standard plated through vias ensures a reliability comparable to traditional rigid printed circuit board, but with added benefits in design flexibility and durability.
The construction of rigid-flex PCBs allows for a reduction in assembly errors, as the design dictates the assembly process, leaving little room for deviation. Moreover, the shock and vibe performance of these PCBs surpasses that of wired solutions due to their lighter weight and the inherent ductility of flex materials like polyimide. This material excellence extends to bend capabilities, where rigid-flex PCBs can achieve tighter bends with reduced stress, enhancing their application in space-constrained environments. This can allow for designs to fit where standard wire harnesses and cabling cannot, not only improving reliability, but have the side effect of greater numbers of applications by going in radii and bends that wires may not be able to.
The Durability Advantage
The choice of polyimide as a core material for flex sections of rigid-flex PCBs is no accident. It’s remarkable durability against a wide array of chemical, thermal, and mechanical stresses makes it an unparalleled choice for challenging environments. Polyimide's high dielectric strength ensures reliable electrical insulation, vital for maintaining performance in high-voltage applications. This same durability is shared in the coverlay as well, with coverlays typically made from polyimide, like the cores, allowing an external facing layer of protection against the many varieties of stresses a board may take on.
Beyond the material’s resistance to chemicals and thermal excursions, the mechanical properties of all materials used in the flexible portions allow for many use cases that the alternatives cannot compete with, ranging from some tight bends in static cases, to less tight, but still thin bends for dynamic cases. In some uses, the flexible sections can even be creased, allowing for scenarios where almost all connection types cannot compete.
Summary
The transition to rigid-flex PCB design is not merely a trend but a strategic evolution towards more reliable, durable, and efficient electronic components. The inherent advantages of this design approach address the critical vulnerability at the point of interconnection, offering a robust solution that meets the demanding requirements of today's high-reliability applications.
As we continue to push the boundaries of what's possible in electronic design, the adoption of rigid-flex circuit boards stand as a testament to the engineering commitment to excellence, reliability, and the relentless pursuit of innovation.
