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It doesn’t take to be an industry expert to figure out what flex-rigid PCBs are. These boards use both worlds, and they mix flexible and rigid material during the manufacturing process.

If you isolate the board’s rigid section, your PCB will look like any other ordinary board out there. It is a flexible part that makes this board unique.

You probably heard of flexible PCBs and their capability to bend and adjust the form to the application and space where you planned on fitting them. You also use these flexible materials in flex-rigid boards, and the only difference is that you mix them with “ordinary” materials. Thanks to that, you can get the best of both worlds, which should deliver the performance you were looking for in your application.

What are the advantages of flex-rigid PCB?

While ordinary PCBs can still be useful, the flexing capability revolutionized the market. Whether you choose a completely flexible board or start by trying a flex-rigid PCB, you can enjoy many benefits.

Here are some main advantages of utilizing flex-rigid technology:

  • Choose the board’s desired form–the benefit of flexibility gives you a lot of freedom when designing your PCB. You can take advantage of 3D space, which means there is no place where you can’t fir your board. That might lead to creative and unusual designs, but as long as you maintain optimal function and reliability, it is an approach you should consider.
  • Reduced size and weight – the material used enables decreasing the overall size of the board and reducing its weight. The result is a compact and lightweight PCB that keeps the application light and small, which can be important for your needs or customer expectations.
  • No solder joints – you don’t have to bother with additional connectors or solder joints because you put a flexible layer between rigid layers. That makes the manufacturing process easier and ensures improved reliability of the board.

Some other benefits include protection against chemical and UV exposure and using fewer materials, which should decrease the overall cost of your PCB.

How to choose materials for flex-rigid PCB?

The key factor to consider when it comes to PCB performance is the material. Substrate materials should be your primary concern, and flex-rigid boards tend to combine flexible dielectric and adhesive films.

The most common choice in the category of flex materials is polyimide. However, you can also go with polyester if you are looking for an affordable solution, or PTFE (fluoropolymer) if your application is complex and advanced.

When it comes to the difference between the popular materials, we should consider the dielectric constant. Polyimide has the highest one, and it also can handle extreme temperatures while ensuring optimal mechanical and electrical characteristics. The downside of this material is that it has a high moisture absorption level, which is something you need to keep in mind.

Polyester is similar in relative dielectric constant and volume resistance, but it has better moisture absorption. However, it also has a limited heat resistance and doesn’t handle temperatures over 150C well (unlike polyimide, which can handle the heat of up to 400C).

PTFE is a costly material with incredibly low moisture absorption and solid heat resistance (up to 260C). While you can consider it for your application, and it is popular in aircraft and military industries. But the price is the reason why not many people use it these days.

The most common materials feature a mixture of epoxy, acrylic acid, and polyester when it comes to flexible adhesive films. The last two perform well in adhesion; they can handle heat and chemicals well and offer admirable flexibility. Keep in mind that you should keep the internal thickness at a maximum 0.05mm because of high thermal expansion potential.

Epoxy doesn’t have great adhesive properties, but you can use it on internal and stick covering layers. Its main benefit is resistance to thermal shock, which can come in handy during the manufacturing process.

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