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About the technology of rigid and flex boards

Author:Luwis zeng Date:5/24/2018 3:52:34 AM
flexible and rigid boards have many benefits, many designers did not understand before, because their design does not have to use this technology. However, more and more designers are now facing the pressure to build more and more high-density electronic devices, and even more headaches for them are to continue to reduce manufacturing costs and reduce manufacturing time. In fact, this is really not a new technical problem. Many engineers and designers have already had headaches for a long time and the pressure they face is constantly increasing.

Soft and hard board is likely to become a novice on the road to new technology development. Therefore, it is wise to understand how to make flexible circuits and hard and soft boards. In this way, we can easily find the design mistakes and prevent them from happening. Now, let us know what basic materials are needed to make these boards.

Flexible circuit board materials

Substrate and protective film

First, let's consider ordinary rigid printed circuit boards. Their base materials are usually fiberglass and epoxy. In fact, these materials are a type of fiber. Although we call it "rigid", you can still feel its elasticity if you remove a single layer. Due to the cured epoxy resin, the board is harder. Because it is not flexible enough, it cannot be applied to some products. But for many electronic products that are simply assembled and the board does not move continuously, it is still appropriate.


In more applications, we need more flexible plastic films than epoxy resins. Our most common material is polyimide (PI), which is very soft and strong, and we cannot easily tear it or stretch it. And it also has incredible thermal stability, can easily withstand the temperature changes in the reflow process during processing, and in the temperature fluctuations, we can hardly find its stretching deformation.

Polyester (PET) is another commonly used flexible circuit material, and its heat resistance and temperature distortion are inferior to those of PI films as compared with polyimide (PI) only films. This material is usually used in low-cost electronic devices, printed lines wrapped in a soft film. Since PET cannot withstand high temperatures, let alone welding, a cold-pressed process is generally used to make such flexible circuit boards. I remember that the display part of the clock radio used this kind of flexible connection circuit, so this radio is often not working properly. The root cause is this poor quality connection. Therefore, we suggest that the soft-hard board should be selected PI film, and other materials are also used but not often used.

PI film, PET film, thin epoxy resin and glass fiber core are common materials for flexible circuits. In addition, the circuit also needs to use other protective film, usually PI or PET film, sometimes using mask solder mask ink. As in the case of a solder mask protection circuit on a hard board, the protective film can insulate the conductor from the outside and protect it against corrosion and damage. The thicknesses of PI and PET films range from 1⁄3 mil to 3 mil, with 1 mil or 2 mil thickness being more commonly used. Fiberglass and epoxy are thicker, typically from 2 mils to 4 mils.

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