PCB Technical - In the production of pcb circuit boards, the dry film is damaged or permeated. How should we continue to improve?

In the production of PCB circuit boards, the dry film is damaged or permeated. How should we continue to improve?

In many years of PCB production process, we have summarized a lot of actual production experience, especially for the production of some multilayer PCBs, especially for those boards with line width and line spacing of 3mil and 3.5mil. The requirements for circuit etching and pattern transfer are very high. High, not only for equipment, but also for human experience. The so-called "slow work produces meticulous work", high-quality goods take time to forge!

For multi-layer PCBs, its wiring is very precise, and many PCB manufacturers use dry film technology to transfer circuit patterns, but in the production process, many manufacturers have a lot of misunderstandings when using dry film. Our company now summarizes: Provide reference and learning for the majority of colleagues and friends, welcome to give suggestions and exchanges!

1. The dry film has broken holes when masking holes

Many customers mistakenly believe that after a hole occurs, the film temperature and pressure should be increased to enhance its bonding force. However, this idea is incorrect. After the temperature and pressure become higher, the corrosion resistance Excessive volatilization of the solvent of the layer makes the dry film more brittle and thinner. It is easy to be broken during development. The toughness of the dry film must be maintained during production. Therefore, after the production of broken holes, it is recommended that you make improvements in the following aspects :

1, reduce the film temperature and pressure
2, improve the roughness of the hole wall and the front
3, increase the energy of exposure
4, reduce the developing pressure
5, do not park for too long after the film is applied, so as not to cause the corners, the semi-fluid film to diffuse and thin
6, when sticking the film, the dry film we use should not be stretched too tightly

Second, seepage plating occurs during dry film electroplating

Occurrence of seepage, indicating that the dry film and the copper foil are not strong, so that the electroplating solution enters, and then the "negative phase" part of the coating becomes thicker. Most circuit board manufacturers have seepage, which is caused by the following bad reasons :

2, the film temperature is high or low

If the film temperature is too low, the resist film cannot be sufficiently softened and flowed properly, 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 volatility in the resist The rapid volatilization of the substance produces bubbles, and the dry film becomes brittle, causing warping and peeling during electroplating electric shock, resulting in infiltration.

1, the film temperature is too high or low

If the film temperature is too low, the resist film cannot be sufficiently softened and flowed properly, 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 volatility in the resist The rapid volatilization of the substance produces bubbles, and the dry film becomes brittle, causing warping and peeling during electroplating electric shock, resulting in infiltration.

2. The film pressure is too high or low

When the film pressure is too low, it may cause uneven film surface or gaps between the dry film and the copper plate and fail to meet the requirements of the bonding force; if the film pressure is too high, the solvent and volatile components of the resist layer will volatilize too much, causing The dry film becomes brittle and will be lifted and peeled after electroplating electric shock.

3, the exposure energy is too high or too low

Under ultraviolet light irradiation, the photoinitiator that has absorbed the light energy decomposes into free radicals to initiate a photopolymerization reaction to form a body-shaped molecule that is insoluble in a dilute alkali solution. When the exposure is insufficient, due to incomplete polymerization, the film swells and becomes soft during the development process, resulting in unclear lines or even the film layer falling off, resulting in poor bonding between the film and copper; if the exposure is overexposed, it will cause development difficulties and also during the electroplating process. Warping and peeling occurred during the process, forming penetration plating. Therefore, it is very important to control the exposure energy.

The above is the experience that our company has summed up in many years of production during production, for reference and learning by the majority of colleagues in the industry, welcome everyone to give advice and exchange!