What’s the difference between Adhesiveless and Adhesive Polyimide (PI)?

Today I’d like to share what’s the difference between Adhesive PI and Adhesiveless PI.

Item 1: Adhesiveless PI stack up

Adhesiveless PI stack up
Adhesiveless PI stack up

As you can see in above stack up, there is no adhesive connect the Copper layer and Polyimide.

There are four advantages of adhesiveless PI:

  1. Thinner Thickness

As you know, the thickness of adhesive is around 12.5um, 15um, 20um. If you have strict requirement for the whole board thickness, it will be a good choice to use adhesiveless PI.

2.Better Bending

Adhesiveless substrate is thinner than adhesive substrate, so it’s bending is better.

3.  Heat resistance

Due to the adhesive have poor performance in heat resistance, so without the adhesive, the adhesiveless base material have better heat resistance.

Under the same temperature, such as 200℃,the tearing strength of adhesiveless PI change a little. But the tearing strength of adhesive PI material rapidly decrease.

4.  Dimensional stability

The dimension of adhesiveless board change very small when the temperature increase. Even under the temperature of 300℃, it’s dimensional changing rate is no more than 0.1%.

Good dimensional stability will be great help for fine wiring process.

5.  Chemical Resistance

The adhesiveless substrate have good performance of chemical Resistance, it’s tearing strength have no obvious change with time increased.

The adhesive base material has poor chemical resistance, so it’s tear strength decreases greatly with the increase of time.

The only disadvantage for adhesiveless PI is it’s a little expensive than adhesive PI.

Item 2: Adhesive PI stack up

Adhesive PI stack up
Adhesive PI stack up

As you can see, the thickness of  2 layer adhesiveless FPC is 0.19+/-0.03mm.

The thickness of  2 layer adhesive FPC is 0.23+/-0.03mm.

If you need thicker thickness, the adhesive PI might can meet your requirement, the cost will be much lower than increase copper thickness or PI thickness.

There are two mainly advantages for adhesive PI:

  1. Thicker thickness.
  2. Cheaper price.

Anyway, if your project need thinner thickness or smaller line width and space (0.05mm), adhesiveless PI will be the best choice. Welcome to contact us at sales@bestfpc.com if you need to know more details.

What is the Dual access flexible circuit?

Have you ever been heard about the dual access flexible circuit? Why it named dual access flexible circuit? After you read my e-mail, you will find the answer.

Dual access flexible circuit board is similar to double side FPC, but it has different stack up to double side FPC. Why it named dual access FPC? Dual access can access to both side by copper, so it named the dual access flexible circuit. Dual access flex PCB only have 1 layer copper, and coverlayer on both side. They can connect both side by layout through coverlayer opening, and do not need to drill the holes like 2 layers flex PCB to connect both side.

Dual access flexible circuit samples picture:

Dual access flexible circuit sample
Dual access flexible circuit sample
Dual access flexible circuit sample
Dual access flexible circuit sample

Working principle: The coverlayer play the role as an insulator, the copper is a very good kind of conductor. One side is anode, and the other side is cathode. If they the current flow, they form a closed loop circuit.

Stack up of dual access flex circuit:

Stack up of dual access flex circuit
Stack up of dual access flex circuit

Dual access circuit advantages:

  1. It can be connected to both side through copper, and do not need to make a through hole. If it is 2 layers FPC. You have to make a through hole to connect both side.

2. The appearance will be more beautiful than 2 layers flex PCB. Because we can conduct by trace, it will be more beautiful than through holes to conduct.

Dual access circuit disadvantages:

  1. Complex production process: The production process is similar to 2 layers flex circuit, but it will be more difficult and complicate compared with 2 layers flex PCB. It is easy to scrap. And many factories can not make dual access circuit board due to production technique.
  2. Easy to wrinkle. Because the dual access is very thin. Only one copper and two coverlayers, it will be easy to tear up. When it comes to laminate process, is also very easy to laminate wrinkles and blister.

If you have any questions or would like to learn more details, please feel free to contact us.