Flexible VS Rigid PCB, Comparison of Two Common Circuit Boards

Overview: In the PCBA industry, we usually use PCB to refer to all types of printed circuit boards, including rigid PCB and flexible PCB. Though, in the USA, the term PWB (Printed Wiring Board) is frequently used instead of PCB. PCB is a circuit board are epoxy bonded fiber glass sheet used as wiring area for socketed and surface mounted components.   It is made by embedded metal surface called traces. Components are soldered to the board in a certain position with help of drilling holes, connected to the board circuitry.

Due to the particularity of the industry, we are very careful when choosing a suitable supplier and establish a long-term cooperative relationship after selecting a supplier. FS Technology believes that in addition to the selection of suppliers, it is also necessary to strictly screen the types of circuit boards, such as select rigid or flexible PCBA for different electronic projects. In this article, FS Technology will help you select an electronic circuit that is more suitable for your project by comparing these two types of PCBs.

Rigid vs Flex PCBA: Difference

For what kind of circuit board is suitable for your electronic project, I believe that all have unique answers and different theoretical basis. For example, when facing an application that requires extremely strong heat dissipation capability, an engineer may design an IMS PCBA with an insulated metal substrate. When faced with circuits that require higher signal transmission capabilities, designers are attracted to high-frequency PCBAs. Faced with the choice of flexible and rigid circuit boards, we should also consider from different aspects, such as price, function, properties, etc.

Rigid PCB vs Flexible PCB

Feature comparison:

In terms of characteristics, rigid PCB is a type of circuit board that cannot change its shape, which can provide higher reliability and stability for electronic products. The flexible PCB is just the opposite. The bending and shape changed the easy-to-twist properties of flex boards making them popular. Even though their underlying properties are reversed, rigid PCBs and flexible PCBs perform the same functions in the normal way, that is, to make connections among the numerous electrical and mechanical elements.

Price Comparison:

In terms of price, the price of the flexible circuit board is much more expensive than that of the rigid PCB under the same circumstances due to the more expensive material used to create it. Note that we’re talking about PCBs here and only PCB manufacturing costs. In some cases, the net price of the project may be high due to the use of rigid rather than flexible boards. The ultimate purpose of manufacturing circuit boards is to achieve electrical connections between components, so we have to assemble and process them. If you are a price-oriented customer and want to know the cost in detail, you need to analyze the cost of PCBA, here we will briefly take it. When comparing rigid and flexible PCBAs, you must consider the fact that flexible circuit boards can reduce the use of components such as connectors, wiring harnesses, and other parts of the board. When all these components are removed, the cost of materials, labor and PCB assembly will be reduced.

Overlays vs Soldermask Inks:

The printed circuit board is a relatively fragile electronic product, so a protective layer needs to be applied to its surface. The protective layer for flexible circuit boards is a cover film, and the protective layer for rigid circuit boards is solder resist ink. There is no essential difference between the two, the main difference is that the cover layer film is flexible.

The coverlay file is normally created with polyimide and coated with a thermoset adhesive. The ranges for film thickness from .0005” to .005” with .001” and .002” commonly used. Turnkey manufacturer use of heat and pressure to laminate the polyimide and adhesive coverlay here heats helps the adhesive to move without any hindrance and fills in the gaps existing between the traces and pads and it reduces the trapping of air among the layers. Adhesive movement is compulsory since it helps to make entire surface connections and encapsulation. The adhesive material will cause oozing about the holes. This oozing is known as adhesive squeeze out and it is a required process. After the completion of coverlay lamination process, any element and any holes in the components and/or features are made by drilling, milling or laser cutting. Etching will not be used.

App comparison:

The selection of rigid PCBA and flexible PCBA in different electronic device applications is based on different properties of electronic products. For example, desktop computers, mobile keyboards, TV toys, use rigid boards instead of flexible boards. While flexible boards are used in ultra-compact and highly maneuverable devices such as GPS, tablets, smartphones, etc. From these examples, you will find one thing in common: Rigid printed circuit boards are used in simple products, while flexible printed circuit boards are mostly used in advanced products. The reason for this phenomenon is that flexible PCBA can be applied to the design of three-dimensional space, which means that it can be used in more complex circuit structures. Of course, these are not absolute, flexible PCBA can also be used in low-end technology such as LED lights.

In today’s technologically advanced society, only one type of circuit board can no longer meet the needs of human beings for the functions of electronic products, Instead to use both together in one device, or a combination of the two is used – rigid-flex PCBA.

Rigid PCB and Flexible PCB: Similarities

Reasonable circuit board design is the key to ensuring its normal production operation. Turnkey PCBA manufacturers’ design requirements for PCBs include the following must-haves: the least hole size, space and trace width, minimum distance to board edges and copper, and overall board design thickness. With that, the PCB manufacturing process is the same for some production stages of rigid boards and flexible boards. These same manufacturing processes include: drilling and plating of holes and vias, imaging and creation of copper trace etching, pad plans and outlines, and baking of boards to remove moisture.

IPC Standards for Rigid and Flexible PCBAs

FS Technologies lists IPC standards for rigid and flexible boards here. Due to space reasons, we do not have a complete table listing. If you have a need for this, you can go to PCBA’s official website, and there are four non-profit PCB organization websites to check.

  • IPC-2221A, Generic Printed Circuit Board Design Standards
  • IPC-2223, FPC Sectional Design Standard
  • IPC-4101, Specification for Rigid and Multilayer PCB Substrate Materials
  • IPC-4202, Flexible Base Dielectrics for Use in FPC
  • IPC-4203, Adhesive-coated dielectric films used as overlays for FPC and flexible adhesive-bonded films
  • IPC-4204, Flexible Metal-Clad Dielectrics for Use in Fabrication of FPC
  • IPC-6013, Qualification and Performance Specification for Flexible Printed Wiring
Conclusion

As rigid and flexible PCBs are used for the same applications making connections between electrical and mechanical components, both work the same for electronics. But in numerous cases, similar design parameters are used for these two boards but flexible PCBA need additional rules since they need extra production phases. As rigid PCB is considered as expensive but you must consider design net cost before considering flex board expensive.

At last, it is important to note that all board creators have the ability to make flexible boards. Before starting a flex circuit design, you should talk to many boards creator to discuss flexible PCB manufacturing techniques and charges.

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