The history of electronics is one of massive reductions in size and increasing power for several decades. Yet, as the pace of manufacturing improvements and technological advancements have slowed, electronic design has had to accommodate new challenges, namely fitting electronic systems into enclosures and designs that would be impossible with traditional rigid boards. While flex offers unparalleled bending, some stackups need to find a middle ground between the density of rigid boards and the mechanical abilities of flex. As a rigid-flex PCB manufacturer, VSE offers a best-of-both-worlds scenario for printed circuit manufacturing.
Rigid-Flex PCB Manufacturer
Advantages and Disadvantages of Rigid-Flex Printed Circuits
Why Rigid Flex?
Rigid-flex boards are a hybrid between standard PCBs and flex printed circuits, offering advantages at the cost of a highly intricate manufacturing process. In terms of operations, rigid boards are the go-to option when design factors are not limiting, making the board production routine and predictable, while flex offers improvements to the thickness and applicability (i.e., wearables) of printed circuits; in comparison, rigid-flex combines the flexibility of latter with the stabilization of the former. There’s an inherent difficulty in matching flex and rigid materials’ physical and electrical characteristics, mainly as the transition between the material types results in significant manufacturing hurdles.
Comparing Rigid, Flex, and Rigid-Flex Constraints
Rigid
- Requires balancing (a symmetrical arrangement of board materials layer-by-layer about the center)
Materials Management
- Limit to flex layer thickness due to bending action can complicate routing
- Component keepouts
Rigid-Flex
- Stress accumulation at the junction of rigid and flex materials requires novel solutions (fillets, pad support, etc.)
Also worth observing is the general increase in complexity with rigid-flex as the layer count increases. While a rigid PCB can easily reach layer counts well into the double digits, multilayer rigid-flex becomes a much more daunting production. Multiple breakout routes are one method to meet the high-density requirements of a rigid-flex while still maintaining manufacturability. In these designs, the rigid-flex is more akin to a wire harness with discrete layers or layer groupings used to route connections between different system areas physically. For example, the rigid section of the board may account for layer pairs on the top and bottom sides of the stackup, with inner flex layer pairs routed to a corresponding system area. While this is technically a multilayer stackup (and relatively complex in its own right), realizing rigid-flex designs of this caliber is much more reasonable.
How a Rigid-Flex PCB Manufacturer Accommodates Design Constraints
The thickness of the conductor layers will also play a significant role in the long-term functionality of the flex portion of the circuit. As thickness in the flexible region grows, flexibility decreases; the ideal solution for sections of the flex circuit meant to undergo repeated, dynamic flexing during its surface life is a single conductive layer. Static bends are less stressful on the material and can accommodate a greater thickness, provided an appropriate bend radius supports the flex material. Prototyping is essential to stress-test the materials according to the design parameters of the circuit; designers can abide by a flex bend radius “rule of thumb” to ballpark these values.
| Bend Radii By Thickness | |
|---|---|
| Metal Layers | Bend Radius |
| 1 | 3~6x thickness |
| 2 | 7~10x thickness |
| Multilayer | 15~20x thickness |
| Dynamic flex (single layer) | 20~40x thickness |
Drilling is more feasible in the rigid sections of the board, but flex drilling is possible. While some manufacturers may recommend avoiding flex drilling due to long-term reliability concerns, design intent may be the final judge. For enhanced reliability, VSE adds anchoring to the pads, providing additional surface contact for the weak adhesion between the conductor and outer flex layers. Like a sequential lamination for microvias, flex drilling will require supplementary and separate drill-then-plate steps; as a result, per-board fabrication costs and processing time will increase appreciably.
Your Contract Manufacturer Prioritizes Flexibility in Design
Rigid-flex PCB manufacturers provide a novel solution to many issues rigid boards or flex-printed circuits face. However, the fabrication requires additional considerations (not to mention cost) that make the decision nontrivial. As always with DFM, we encourage designers to speak with us at the project outset and determine the best path for meeting design intent while optimizing cost. Here at VSE, we’re a team of engineers committed to building electronics for our customers that satisfy all performance requirements while maintaining long-term reliability. We’ve been realizing life-saving and life-changing devices with our manufacturing partners for over 40 years.
If you are looking for a CM that prides itself on its care and attention to detail to ensure that each PCB assembly is built to the highest standards, look no further than VSE. Contact us today to learn more about partnering with us for your next project.