What are the differences between the Poyester (PET) and Polymide(PI) material?

The flex pcb raw material and stack up will decide the flex circuit quality. According to the market demand, there are three types of base raw material used for Flexible circuit board. Poyester(PET), adhesive Polymide (PI) and adhesiveless Polymide (PI) . Do you know the difference between the PET and PI material? If not, let us learn about it together now.

The advantages and disadvantages of Polyester(PET) and Polymide(PI).

Attached is a form for your reference, hope it will be helpful you. And you can choose the right raw material according the below form.

Flexibility (2mm radius)BadGoodBest
Tear strength800g500g500g
Strip strength in the air1050N/M1750N/M1225N/M
Working temperature85~16585~165105~200

The advantages of PET material: Production process is less, price is cheaper, lead time is shorter.

The disadvantages of PET material: Polyester material can not pass through soldering flow. Then it can not be working in high temperature environment.

The advantages of polymide (PI): It’s easy to bend. Can work in high temperature.

The disadvantages of Polymide (PI): The price of raw material is much higher than Polymide.

Below picture is the single sided FFC, ENIG 3u’’, 10pin, 0.5mm pitch, and it is made of Poyester(PET) material


Below picture is a 1layer flex pcb, 4 mil PET material, print silver ink, carbon finishing mask, insulation( protective coating), carbon resistance less than 500 ohm.


Below picture is 1L FPC, it is made of adhesive polymide raw material. ENIG 1u’’, 1oz Cu, 1mil PI, 1mil coveraly, and the total thickness is 0.13mm+/-0.03mm.


It is a single sided FPC, ENIG 1u’’, 1/2ozCu, 1mil adhesiveless PI, 1/2mil coverlay.


If you have any questions or would like to learn more, warmly welcome you to contact us at sales@bestfpc.com

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What’s the difference between rigid-flex PCB and flex PCB with FR4 stiffener?

In the production of FPC, normally we need to add different stiffener to meet the total thickness or hardness, such as PI stiffener, FR4 stiffener and stainless steel stiffener. But the FR4 stiffener after laminated is very similar to the rigid-flex PCB, especially there are also have drilling holes in FR4 stiffener.

Do you know how to identify FR4 stiffener and rigid-flex PCB? Please refer to the below picture. On flex PCB, you can see there are many PTH holes, maybe these boards are need to insert connectors and connect it to other products. So they need the hardness in this area.

From the left sample, we added the FR4 materials on bottom side, there are also have vias on stiffener, but no copper in vias, so this is FR4 stiffener. It can only increase the hardness of flex. From the right sample, the green part are still FR4 materials, but we plated copper for all vias, so it’s a rigid-flex PCB.

FR4 stiffener VS Rigid-flex PCB

Rigid-flex board has many production processes, high production difficulty, low yield rate, so its price is relatively expensive and the production cycle is relatively long than flex PCB. If the FPC with FR4 stiffener can meet your requirements, then it would be a better choice for you.

If you have any other question about stiffener or rigid-flex PCB, please feel free to contact us at sales@bestfpc.com

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