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 PCBflexible PCB and Rigid-flex 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.

The PCB industry typically mass-produces circuit boards for customers in the form of customization, so most customers are very cautious when choosing suppliers and establish long-term cooperative relationships with suitable suppliers. From the customer’s point of view, PCB manufacturing is a very simple matter, so they always spend all their time designing components and board configuration issues, circuit board shape and specification issues before the project starts. There is no doubt that these are correct and important things, but they underestimate another important point of PCB design-the strength level of the board.

There are many types of PCBs, and selecting the PCB type suitable for your electronic project will have a positive effect on your entire project. 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. In order to help customers better pick the circuit boards that are suitable for their projects, FS Technology will compare the two most common types of circuit boards in detail in this article-rigid PCB VS flexible PCB.

Rigid vs Flex PCBA: Difference

Rigid PCB vs Flexible PCB

For what kind of circuit board is suitable for your electronic project, I believe that all have unique answers and different theoretical basis. If you have difficulty in choosing the PCB softness and hardness, five important tips listed here will help you solve this problem:

  • Cost comparison
  • Feature comparison
  • Sophistication Comparison
  • Similarities

Price comparison of rigid circuit and flexible circuit

Cost is the key to determine the overall benefit of the project, so when customizing the project, the price of flexible PCB and rigid PCB has to be given priority. In the case of the same specifications, the price of flexible PCB is much higher than that of rigid PCB. The reason for this common phenomenon is simple, PCB manufacturers use more expensive raw materials when making flex circuits.

Common rigid PCB manufacturing materials: phenolic paper laminate, epoxy paper laminate, polyester glass felt laminate, epoxy glass cloth laminate.

Common flexible PCB manufacturing materials: polyester film, polyimide film, fluorinated ethylene propylene film.

Note that the content we mentioned earlier belongs to PCB bare board cost comparison rather than PCBA. While rigid circuits are better than flex circuits when it comes to bare board fabrication, it is undeniable that in some cases using an assembled flex PCBA can bring the overall profit of a project up a notch.

Whether your requirement is PCB manufacturing or PBC assembly, the ultimate goal is to get a finished PCBA to realize the electrical connection between components. 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.

After the above detailed analysis of the cost of the two, flexible circuits may be more economical in practical applications. If you have questions about this or have project requirements, please get the rigid and flexible PCB/PCBA price list through the contact email above.

Feature comparison of the flexible circuit boards and rigid circuit boards

Flexible Features vs Rigid Features

In this part, FS Technology will compare rigid PCB and flexible PCB from the perspective of characteristics to screen out the circuit board that is more suitable for your electronic project. 

Rigid PCB is a circuit board that cannot change shape, which can provide higher reliability and stability for electronic products, customizing this type of PCB will provide the following advantages for your project:

Features and advantages of rigid PCB

  • High density: With the development of integrated circuit, HDI, and SMT assembly technology, more components are mounted on the surface of the circuit board. Since rigid PCBA is stronger than flexible PCBA, it is easier to form HDI PCBA and endowed with more functions.
  • High reliability: Rigid PCB is a circuit type with a long history, and manufacturers have mastered this technology to the point of proficiency, so the probability of error is lower. In addition to the proficiency of production technology, a series of strict PCB tests are usually carried out after bare board manufacturing, these tests include: appearance inspection, burn-in test, flying probe test, etc.
  • Designability and productivity: Rigid PCB is a simple circuit structure. For various performance requirements of PCB (electrical, physical, chemical, mechanical, etc.), rigid circuit design can be achieved through design standardization. At the same time, with the development of automation process, manufacturers often quickly realize standardized and large-scale production through modern management technology, which makes its production much less difficult than flexible PCB.

Features and advantages of flexible PCB

  • Lightweight appearance: FPC has more appearance advantages than rigid PCB, and it can perform the same function with smaller size and lighter weight. Electronics manufacturers can use flex PCB to create electronic products that better meet the needs of miniaturization.
  • High flexibility: As the name suggests, flexible circuits have the characteristics of flexibility, which is incomparable to rigid PCBs. These flexible circuit structures can be easily bent, rolled up, twisted, folded and three-dimensionally wired, and can be easily handled in the face of more complex applications.
  • More effective assembly: Excellent electrical properties, high temperature resistance, and flame retardancy make it easy to cope with various harsh environments. At the same time, the flexible circuit simplifies the design requirements of the complex circuit structure, reduces the assembly workload and guarantees the circuit performance.

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. According to the characteristics of the two, try to choose the circuit structure suitable for your electronic project, whether it is rigid or flexible.

Flexible circuit design is more difficult than rigid circuit

PCB Design Complexity

When routing corners in a PCB design, must be considered the chances of EMI (electromagnetic interference) created for right angles. If you are using rigid PCB for your projects, then the design engineers of FS Technology recommend using a soft corner in place of the sharper forty-five degrees corners that are normally used in rigid boards.  For flexible PCB must consider the bend ratio. That is the ratio between the thickness of flexible boards with bend radius. If circuit faces the values less than the bend ratio must face mechanical failure. Whether you use a rigid PCB or a flexible PCB in your circuit, it is in your best interest to ensure that common layout errors do not occur, as long as your circuit board will function properly and as expected. 

Flexible PCB Overlays vs Rigid PCB Solder Mask

Overlays and Solder Masks

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.

Applications comparison of rigid PCBA and flexible PCBA

The selection of rigid PCBA and flexible PCBA in different electronic device applications is based on different properties of electronic products. When faced with the circuit design of simpler electronic products, electronic engineers usually use rigid PCBA instead of flexible PCBA in order to save costs, such as: TVs, electronic toys, mobile phones, computers, keyboards and mice etc. But for devices that require sophisticated design configuration or ultra-compact and high mobility, flexible boards are the right PCBA, such as: wearable medical devices, folding mobile phones, Bluetooth PCB, GPS, 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. Therefore, although the characteristics of flexible PCB and rigid PCB are opposite, they still contain many similarities, and some of their common points will be discussed here:

The same points in the manufacturing process of flexible PCB and rigid PCB

Rigid vs. Flex PCB Manufacturing

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 through-holes.
  • Imaging and creation of copper trace etching.
  • Pad plans and outlines.
  • Baking of boards to remove moisture.
  • Both boards come with the same connection configuration of components.
  • Thickness and hole size are normally the same for these boards.

Flex PCBAs perform the same tests as rigid PCBAs

PCB substrate functional evaluation is an important process, and after creating the board according to the project layout, you must consider performing PCBA testing. It is very simple to face the different errors in complicated PCB design which helps to make review the process thoroughly. Through PCBA production tests of your design, you can get the advantages of the latest automated verification. These same board tests include the following:

  • ICT
  • Flying Probe Test
  • Function Test
  • AOI Test
  • X-Ray Test
  • Laser Detection
  • Aging Test
  • Solderability Test
  • PCB Contamination Test
  • Microsection Analysis
  • Time Domain Reflectometer (TDR)
  • Peel Test
  • Float Test

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

Still have doubts about rigid PCB VS flexible PCB

So far, the content about “Flexible PCB VS Rigid PCB” has basically ended. We hope you have a good experience reading this article and can use the correct PCB substrate material at the exact position. Practice is the only criterion for testing truth, and we want you to bring these discussions into your thinking during the production phase of your project, before deciding which way to go instead of blindly working with suppliers and launching new product boards. Next let us make a summary of this article:

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 these PCBA 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 board’s creator to discuss PCB manufacturing techniques and charges.

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