How to Choose PCB Dry Film

Dry film is a kind of polymer compound, it can produce a kind of polymerization reaction (the reaction process of synthesizing polymer from monomer) after being irradiated by ultraviolet rays to form a stable substance attached to the surface of the board, so as to achieve The function of blocking plating and etching.

Generally divided into three layers, one layer is a PE protective film, the middle is a dry film layer, and the other is a PET protective layer. Both the PE layer and the PET layer are only protective and must be removed before lamination and development. What really works is the middle layer of dry film, which has a certain viscosity and good photo-sensitivity.

Dry film can be divided into four categories according to the thickness: (0.8mil, 1.2mil, 1.5mil, 2.0mil)

l                      0.8mil thick dry film is mainly used for FPC fine circuit production.

l                      1.2mil dry film is mainly used for inner layer board operations.

l                      1.5mil dry film is mainly used for outer layer operation. Of course, it can also be used for inner layer operation. However, because it is thicker, it is easy to cause side corrosion during the etching process and the cost is relatively high, so it is generally not used as the inner layer.

l                      2.0mil dry film is mainly used for some special requirements of the board, for example, when the larger secondary hole 1.5mil dry film cannot meet the requirements, it is only used.

Dry Film Main Features:

l                      Under certain temperature and pressure, it will stick firmly to the board surface;

l                      Under certain light energy irradiation, energy will be absorbed and cross-linking reaction will occur;

l                      The part that is not irradiated by light has no cross-linking reaction and can be dissolved by weak lye.

Dry Film Storage Environment:

Constant temperature, constant humidity, yellow light safety zone. Prevent storage with chemicals and radioactive materials.

In addition, common quality defects of dry film include developing residual glue, exposed foreign matter, poor vacuuming, unclean development, excessive development, open circuit, short circuit, line convexity, chipping, exposed copper, film drop etc.

Common Problems in the Dry Film Process

1. There is a residual film on the surface of the copper after development (the development is not clean)

2. Poor effect of masking method

3. The photo-resist layer in the thinner wire or unexposed area is not easy to be washed off during development (poor exposure)

4. The dry film is damaged during development or it is found that the dry film is warped or has irregular edges after development (over development)

5.When the wire is electroplated with tin and lead, the edge of the photoresist film will be warped, causing tin seepage (seepage).

6. Dry film wrinkles.

7. Air bubbles appear between the dry film and the copper surface of the board.