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PCB Tech

How to improve the problem of broken holes and penetration during the use of rigid-flex PCB dry film
2021-09-08
View:33
Author:Belle

With the rapid development of the electronics industry, rigid-flex PCB wiring is becoming more and more complex. Most PCB manufacturers use dry film to complete the pattern transfer, and the use of dry film is becoming more and more popular. However, I still encountered many problems in the after-sales service. Customers have many misunderstandings when using dry film, here is a summary for your reference.

  1. The dry film mask has holes
    Many customers believe that after holes appear, the temperature and pressure of the film should be increased to enhance its bonding force. In fact, this view is incorrect, because the solvent of the photoresist layer will evaporate too much after the temperature and pressure are too high, resulting in drying. The film becomes brittle and thin, and holes are easily broken during development. We must maintain the toughness of the dry film at all times. Therefore, after the holes appear, we can make improvements from the following points:
    1). Reduce film temperature and pressure
    2). Improve drilling and perforation
    3). Increase exposure energy
    4). Reduce development pressure
    5). After the film is pasted, the parking time should not be too long, so as to avoid the semi-fluidized film at the corners from spreading and thinning under pressure
    6). Do not pull the dry film too tightly during the pasting process

2. When dry film electroplating
Leakage The cause of leakage is that the dry film is not firmly bonded to the copper clad laminate, which leads to the deepening of the plating solution and thickening of the "negative phase" part of the coating. The penetration of most rigid flexible PCB manufacturers is caused by the following reasons:


1). Exposure energy level


Under ultraviolet light irradiation, the photoinitiator that absorbs light energy is decomposed into free radicals, which initiates a photopolymerization reaction to form body-shaped molecules that are insoluble in dilute alkali solutions. When the exposure is insufficient, due to incomplete polymerization, the film swells and becomes soft during the development process, resulting in unclear lines and even the film layer falling off, resulting in poor bonding between the film and copper; if the exposure is overexposed, development will be difficult, and during the electroplating process The same is true in China. Warping and peeling occurred during processing, forming infiltration. Therefore, it is important to control the exposure energy.

rigid-flex PCB

2). Film temperature


If the film temperature is too low, the resist film cannot be sufficiently softened and cannot flow normally, resulting in poor adhesion between the dry film and the surface of the copper clad laminate; if the temperature is too high, the solvent and other volatile substances in the resist will quickly volatilize to produce bubbles and dry The film becomes brittle, causing electric shock warping and peeling during electroplating, leading to penetration.


3). Membrane pressure is too high or too low


If the film pressure is too low, it may cause uneven film surface or gaps between the dry film and the copper plate, which will not meet the requirements of bonding force; if the film pressure is too high, the solvent and volatile components of the resist layer will evaporate too much, resulting in dryness. The film becomes brittle and will lift and peel off after electroplating electric shock.


How to improve the problem of broken holes and penetration during the use of rigid-flex PCB dry film


With the rapid development of the electronics industry, rigid-flex PCB wiring is becoming more and more complex. Most PCB manufacturers use dry film to complete the pattern transfer, and the use of dry film is becoming more and more popular. However, I still encountered many problems in the after-sales service. Customers have many misunderstandings when using dry film, here is a summary for your reference.


  1. The dry film mask has holes
    Many customers believe that after holes appear, the temperature and pressure of the film should be increased to enhance its bonding force. In fact, this view is incorrect, because the solvent of the photoresist layer will evaporate too much after the temperature and pressure are too high, resulting in drying. The film becomes brittle and thin, and holes are easily broken during development. We must maintain the toughness of the dry film at all times. Therefore, after the holes appear, we can make improvements from the following points:
    1). Reduce film temperature and pressure
    2). Improve drilling and perforation
    3). Increase exposure energy
    4). Reduce development pressure
    5). After the film is pasted, the parking time should not be too long, so as to avoid the semi-fluidized film at the corners from spreading and thinning under pressure
    6). Do not pull the dry film too tightly during the pasting process

2. When dry film electroplating


Leakage The cause of leakage is that the dry film is not firmly bonded to the copper clad laminate, which leads to the deepening of the plating solution and thickening of the "negative phase" part of the coating. The penetration of most rigid flexible PCB manufacturers is caused by the following reasons:


1). Exposure energy level
Under ultraviolet light irradiation, the photoinitiator that absorbs light energy is decomposed into free radicals, which initiates a photopolymerization reaction to form body-shaped molecules that are insoluble in dilute alkali solutions. When the exposure is insufficient, due to incomplete polymerization, the film swells and becomes soft during the development process, resulting in unclear lines and even the film layer falling off, resulting in poor bonding between the film and copper; if the exposure is overexposed, development will be difficult, and during the electroplating process The same is true in China. Warping and peeling occurred during processing, forming infiltration. Therefore, it is important to control the exposure energy.

2). Film temperature
If the film temperature is too low, the resist film cannot be sufficiently softened and cannot flow normally, resulting in poor adhesion between the dry film and the surface of the copper clad laminate; if the temperature is too high, the solvent and other volatile substances in the resist will quickly volatilize to produce bubbles and dry The film becomes brittle, causing electric shock warping and peeling during electroplating, leading to penetration.


3). Membrane pressure is too high or too low
If the film pressure is too low, it may cause uneven film surface or gaps between the dry film and the copper plate, which will not meet the requirements of bonding force; if the film pressure is too high, the solvent and volatile components of the resist layer will evaporate too much, resulting in dryness. The film becomes brittle and will lift and peel off after electroplating electric shock.