Rigid Vs. Flex PCBs: Which Is Best For Your New Project

- Jun 02, 2019-

Learn about Rigid PCBs vs. Flex PCBs, when it's much better to make use of one kind rather than the various other, and discover some manufacturing actions associated with each of these PCB kinds.


A Printed Circuit Board Is Not Always a "Board".

When the term "PCB" is used, lots of people consider a rigid PCB (printed circuit board). However, the term PCB can describe either a rigid PCB or a flexible PCB. flex PCBs are much more frequently known as flex circuits, yet they are likewise recognized by various other names including flex boards, flexible circuit board, flexible printed motherboard as well as, a lot more officially, flexible electronics. Flex circuits have recently gained substantial popularity as a result of the truth that they can be shaped, bent, twisted, as well as folded into unlimited arrangements. Ultimately, however, rigid PCBs and also flex PCBs offer, in one of the most standard sense, the same best feature, which is linking numerous electrical and mechanical components with each other.


When to Use Rigid as well as When to Use Flexible.

Rigid PCBs commonly set you back much less than flex circuits. I say "typically" since when considering the overall expense of possession there are some applications that, when utilizing flexible PCBs, may be more economical compared to using rigid PCBs. To obtain a true as well as exact understanding of the overall cost of possession, you initially need to appreciate the fact that flex circuits might get rid of the demand for parts such as adapters, cable harnesses, and various other motherboard. By removing these parts from a design, material price, labor and also setting up cost, and also scrap price are all minimized.


Lots of electronic devices (laptop and desktop computers, audio keyboards, solid-state drives (SSDs), flat-screen TVs and monitors, kids's playthings, and numerous digital devices) use rigid PCBs rather than flexible PCBs. Nevertheless, flex circuits may be found in ultra-compact and/or high-performance gadgets, consisting of GPS units, tablets, smart phones, cameras, and also wearables.


Greater elegance is not the only factor to utilize flex circuits; low-tech applications (such as under-the-counter LED lights, see figure listed below) might utilize flex circuit innovation, sometimes due to the fact that it makes setup much easier.


Ultimately, a flex circuit and a rigid circuit can be utilized with each other-- as a merged PCB-- if the need develops. This strategy, perhaps, offers the most effective of both worlds. See Picture 1 listed below.

Figure 1. A PCB design containing both rigid as well as flexible PCBs. Picture courtesy of x-pcb.com.


Some Resemblances and also Distinctions Between Rigid PCBs and Flex Circuits.

When creating Rigid PCBs, specific layout policies should be followed, consisting of minimal opening dimensions, minimum area as well as trace size, minimum distances to board sides, as well as copper and also overall style thicknesses. In addition, many producing process actions are shared between rigid as well as flexible PCBs. Such procedure actions include the drilling as well as plating of openings as well as vias, image imaging and development, the etching of copper traces, pads, details,  and also the heating of the circuit boards for the purpose of getting rid of moisture from the PCBs. Now in the production process, rigid PCBs head to the solder mask station while flex circuits most likely to the coverlay terminal.


Flex Circuit Overlay.

Flex circuit overlay, or coverlay, as it's likewise known, is a lamination process used for encapsulating and securing the exterior wiring of a flex circuit. A flex circuit's coverlay film is similar to a rigid PCB's solder mask, with one large difference ... the coverlay film is flexible! According to XPCB, "The coverlay film is typically a polyimide movie that is coated with a thermal adhesive. 


The polyimide as well as adhesive coverlay is laminated making use of stress as well as warm, where the heat helps the sticky to easily move and complete any spaces in between traces and pads; this avoids the capturing of air between the layers. Again from allflexinc.com: "The adhesive flowing is necessary as it assists guarantee full surface area call and encapsulation. The adhesive will certainly have a tendency to exude out a little around the openings displayed in the diagram below. This oozing is commonly described as 'adhesive squeeze out' and is really a desired phenomenon.".


Once the coverlay lamination process is ended up, any component and/or feature openings are used boring, directing, or laser cutting. Etching can not be used.


IPC Requirements for Rigid and Flexible PCBs.

The listing of IPC criteria listed below puts on rigid PCBs and flex circuits. Keep in mind that this listing is not exhaustive, and also extra IPC criteria might require to be taken into consideration. You ought to get in touch with the ipc.org internet site for a full listing of available IPC standards.


  1. IPC-2221A, Common Criterion on Printed Board Style.

  2. IPC-2223, Sectional Design Requirement for Flexible Printed Boards.

  3. IPC-4101, Spec for Base Products for Stiff as well as Multilayer Printed Boards.

  4. IPC-4202, Adaptable Base Dielectrics for Usage in Flexible Printed Circuitry.

  5. IPC-4203, Adhesive Coated Dielectric Films for Use as Cover Sheets for Flexible Printed Wiring and Flexible Adhesive Bonding Movies.

  6. IPC-4204, Versatile Metal-Clad Dielectrics for Use in Manufacture of Flexible Printed Wiring.

  7. IPC-6013, Certification as well as Efficiency Spec for Flexible Printed Wiring.


To conclude.

Although both rigid and flexible printed motherboard fundamentally serve the very same function-- linking numerous electrical and also mechanical parts together-- both innovations have their area in life. While much of the exact same style regulations are used with both stiff as well as flexible PCBs, flexible PCBs need some extra rules due to their additional production process steps. As well as despite the fact that rigid PCBs might appear, at least at first, to cost much less, one must certainly take into consideration a design's overall expense of possession prior to declaring that flex circuits are too expensive.


Ultimately, it's important to note that not all board houses can making flexible PCBs. Prior to starting a flex circuit design, you ought to talk to multiple board houses and also talk about flex PCB construct options and also linked expenses.