Analysis of the Causes of Foaming on the Surface of PCB Circuit Board

1. Gerber file pre-processing

The wiring and functional features on the FPC are designed by the customer, and the circuit board factory is only responsible for manufacturing it. The circuit board factory often finds that the design information sent by the customer does not meet the process capability of the board factory, such as line width and line. If the distance is too small, the aperture is too small, etc., then the engineer of the circuit board factory will communicate with you to confirm. Then, the data required for each process of FPC production, such as the layers, solder mask, silk screen layer, surface treatment, drilling, etc., are exported from the Gerber file, and then input to the production device corresponding to the process. in.

2. Board film output

In a strict temperature and humidity control environment, a laser negative film plotter is used to draw the negatives of the circuit board. These negatives are used as image exposure for each circuit layer in the subsequent circuit board manufacturing process, in the solder resist green oil process. You also need to use the film. In order to make the relative position of each layer of the line X-Y correct, each of the negative films is laser-punched for use as a positioning of subsequent different circuit layers.

3. Circuit board inner layer forming

The inner layer structure of the multilayer circuit board is usually made of a whole piece of copper foil substrate, and then the surface of the copper foil is cleaned by pickling at each step to ensure that no other dust or impurities are present, as long as there is any slight point. The foreign matter will affect the subsequent lines, and then mechanical grinding will be used to roughen the surface of the copper foil to enhance the adhesion of the dry film to the copper foil, followed by a dry film on the surface of the copper foil. An inner layer of the substrate film is attached to both sides of the copper foil substrate and mounted on the exposure machine. The film is precisely attached to the copper foil substrate by using the positioning hole and the vacuum, and the film is irradiated with ultraviolet light in the yellow light region to make the film. The unshielded dry film is chemically changed to cure on the copper foil substrate, and finally the unexposed dry film is removed by the developer.

4. Inner layer etching

Generally, a strong alkaline solution is used to dissolve the fire to etch away the exposed copper surface, that is, to remove the copper surface not covered by the dry film. When etching, pay attention to the formulation and time of the syrup. The thicker the copper foil, the longer it needs to be. The time and the wider the gap and the wider line are preserved, because the etching is in addition to corroding the exposed copper foil, and the copper surface at the edge of the dry film is also more or less corroded. Then, the cured dry film originally covered on the copper foil is removed by using a stripping solution, and only the copper foil of the line which is designed in the design is left on the copper foil substrate.

5. Image positioning target hole

In order to make the inner layer and the outer layer copper skin accurately aligned, the CCD positioning is used to find the target position that has been preset on the film beforehand and to drill the required positioning target hole. The action of the target hole must also be applied to all the inner and outer lines so that the copper foil lines of the inner and outer layers can be positioned on the same reference in subsequent processes.