Electromechanical Variables Impact Design – When you design rigid-flex PCBs, think in terms of electromechanical factors which affect both flex circuit and the rigid board. As you build your design, focus on the ratio of bend radius to thickness. With flex circuits, tight bends or even an increased thickness at the bend area boost the chances for failure. Fabricators recommend keeping the bend radius at the very least of ten times the thickness of the flex-circuit material and building a “paper doll” of the circuit to find out where bends occur.3,6
You ought to avoid stretching the flex circuit along its outer bend or compressing it over the inner bend. Increasing the bend angle beyond 90° increases stretching at some time and compression at another point on the rigid flex pcb stackup. Another key issue in rigid-flex reliability is the thickness and kind of conductor based in the bend region. It is possible to decrease thickness and mechanical stress by reduction of the quantity of plating on the conductors and ultizing pads-only plating. The usage of heavy copper, gold, or nickel plating decreases flexibility in the bend and allows mechanical stress and fracturing to happen.
Rigid-Flex PCB Design Requires Teamwork – New PCB design tools give your design team the opportunity to manage multiple layer stacks, visualize 3D electromechanical designs, check design rules, and simulate the operation of flex circuits. Despite having these power tools at hand, the successful style of a rigid-flex PCB depends upon teamwork in between your team and fabricators. Teamwork must begin at the earliest stages in the project and continue through the design process and hinges on consistent communication.
A Printed Circuit Board Is Not Always a “Board” – Once the term “PCB” is used, many individuals think of a rigid PCB (printed circuit board). However, the term PCB can make reference to either a rigid PCB or even a flexible PCB. Flexible PCBs are definitely more often called flex circuits, however they are also known by other names including flex boards, flexible circuit boards, flexible printed circuit boards and, more officially, flexible electronics. Flex circuits have recently gained huge popularity because of the fact that they can be shaped, bent, twisted, and folded into limitless configurations. Ultimately, however, rigid PCBs and flexible PCBs serve, in the standard sense, the identical ultimate function, that is connecting various electrical and mechanical components together.
When to Use Rigid and When to Use Flexible – Rigid PCBs typically cost less than flex circuits. I only say “typically” because when contemplating the entire cost of ownership there are a few applications that, when using flexible PCBs, may be less expensive in comparison to using rigid PCBs. To get a true and accurate comprehension of the complete cost of ownership, you first need to appreciate the reality that flex pcb design may eliminate the need for components including connectors, wire harnesses, as well as other circuit boards. By removing these elements from the design, material cost, labor and assembly cost, and scrap cost are common reduced.
Many electronics (laptop and desktop computers, audio keyboards, solid-state drives (SSDs), flat-screen TVs and monitors, children’s toys, as well as other electronic gadgets) employ rigid PCBs instead of flexible PCBs. However, flex circuits could be seen in ultra-compact or high-performance devices, including GPS units, tablets, smart phones, cameras, and wearables. Greater sophistication is not really the only real reason to utilize flex circuits; low-tech applications (like under-the-counter LED lights, see figure below) may utilize flex circuit technology, in some cases since it makes installation much simpler.
Finally, a flex circuit and a rigid circuit may be used together-as a unified PCB-if the need arises. This method, perhaps, provides the best of both worlds. See Figure 2 below. Some Similarities and Differences Between Rigid PCBs and Flex Circuits. When making rigid PCBs, certain design rules has to be followed, including minimum hole sizes, minimum space and trace width, minimum distances to board edges, and copper and overall design thicknesses. Additionally, many manufacturing process steps are shared between koqcyp and versatile PCBs. Such process steps range from the drilling and plating of holes and vias, photo imaging and development, the etching of copper traces, pads, outlines, and planes, as well as the heating (baking) from the circuit boards for the purpose of removing moisture through the PCBs. At this point inside the manufacturing process, rigid PCBs visit the solder mask station while prototype pcb assembly visit the coverlay station.
Flex circuit overlay, or coverlay, as it’s also known, is really a lamination process used for encapsulating and protecting the external circuitry of the flex circuit. A flex circuit’s coverlay film is a lot like a rigid PCB’s solder mask, with one big difference…the coverlay film is flexible! In accordance with allflexinc.com, “The coverlay film is generally a polyimide film which is coated with a thermoset adhesive. Film thicknesses range from .0005” to .005” with .001” and .002” the most typical.”