Knowledge is power is one of those sayings that I used to scratch my head over as I struggled to understand how intellect could make you physically stronger. Fortunately, with age comes maturity and understanding. Now, it is quite clear that the right knowledge empowers you to develop solutions to overcome limitations and restrictions. An excellent example of this is how the knowledge of aerodynamics enables us to build airborne vehicles and travel through the skies even though our bodies are incapable of doing so on their own.
This concept can be applied to virtually anything, including PCB development where knowledge of the manufacturing process for flex boards allows us to build PCBs for applications requiring bendability. There are many reasons why a flex board design may be preferred; however, before deciding among one of several class types of flex boards, you should empower yourself with knowledge about the manufacturing process for flex boards.
Advantages of Flex Manufacturing Technology
Different flex board types vary to some degree, depending on their construction process. However, before highlighting these differences, we should mention the advantages of flex boards as compared to rigid boards. Advantages that can be gained from using flex PCBs, in general, include the following:
- Increased capability
Flex boards typically perform better in extreme temperature environments, can utilize more component and connector types and offer better resistance to radiation issues.
- Smaller size
Bendability provides a broader range of mounting possibilities, as well as the ability to condense the board area.
- Greater reliability
Usually, fewer interconnects and connectors are required, which contributes to less potential failure points, resulting in less maintenance or replacement.
Smaller drill holes and lower copper weights can also be leveraged when using flex boards.
The Manufacturing Process for Flex Boards
There are basically two types of flex PCB technology:
- Flex Technology - where the entire board is flexible.
- Flex-Rigid Technology - where the board is a combination of rigid and flex areas.
Much less implemented is what is referred to as Embedded Flex Technology, where a flex circuit or module is inserted within a rigid board layer prior to buildup.
Regardless of the type of flex technology you choose to implement, the manufacturing steps for the flex board portion is the same as for rigid boards with the important distinctions listed below.
The first and foremost manufacturing consideration for flex boards is the choice of material. There is no standard material for flex boards, such as FR-4 for rigid boards; however, polyimide and polyester films with copper clad laminate are commonly used. The lack of a preferred standard type provides you with various material options. A good selection method is to use the parameters below and base your decision on your board’s application.
- Dielectric strength
- Relative dielectric constant
- Loss angle tangent
- Volume resistance
- Limit tension
- Size change after etching
- Limit elongation
Additionally, you should ensure that your board meets the qualification and performance standards of IPC-6013D.
In certain situations, it is necessary to add stiffeners to support your board during the mounting of components. These include when large or heavy components need to be attached or any case that may degrade the structural integrity of the board. If stiffeners are needed, additional lamination cycles will be required that will impact fabrication time and costs.
Coverlay, more formally referred to as flex circuit coverlay, serves a similar purpose as does solder mask for rigid PCBs. Essentially, it is a lamination that protects the flex board from external contaminants, similar to solder masking. Of course, unlike solder mask, coverlay is flexible and particularly thin. Thicknesses of 0.005” are not uncommon.
Fixtures and Adhesives
In order to ensure the planarity of surface mount devices (SMD) during assembly, it may be necessary to use fixtures to maintain the board shape until the components are firmly attached. Another concern is that components may detach when the board undergoes stress from bending. Therefore, additional adhesion may be needed for affected components.
Flex PCB technology expands the potential applications for your electronic circuit design, especially into areas where smaller and bendable devices are desirable. Additionally, flex boards are typically more capable and reliable than rigid boards. Understanding the manufacturing process for flex boards empowers you to utilize these advantages fully.
|Tempo‘s Custom PCB Manufacturing Service
Tempo Automation is the industry leader in manufacturing PCBs quickly and precisely for prototyping and low volume production. We have the expertise and flex manufacturing capability to build your boards for whatever flex PCB technology you need.
And to help you get started on the best path, we furnish information for your DFM and enable you to easily view and download DRC files. If you’re an Altium user, you can simply add these files to your PCB design software.
If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on the manufacturing process for flex boards or how to design for flex board manufacturing, contact us.