Causes of Process Problems Caused by PCB Pretreatment

1. The problems that occur in the PCB manufacturing process are all kinds of strange, and the process engineer is often responsible for the forensic-autopsy (bad cause analysis and countermeasures). Therefore, the main purpose of launching this discussion topic is to discuss one by one in the equipment area, including people, machines, materials, materials, and conditions that may lead to problems, and everyone is welcomed to participate and express their opinions.

2. The process of using pre-treatment equipment, such as inner layer pre-treatment line, electroplating a copper pre-treatment line, D/F, solder mask (solder mask) etc.

3. Take the hard board PCB solder mask (solder mask) pretreatment line as an example (different manufacturers vary): brushing*2 groups->water washing->pickling->water washing->cold air knife->drying section ->sun plate closing plate->discharging closing plate.

4. Gold steel brushes with brush wheels of #600 and #800 are generally used, which will affect the roughness of the board surface and thus affect the adhesion of the ink and the copper surface. After the brush wheel has been used for a long time, if the product is not left or right When they are placed evenly, the phenomenon of “dog bones” is easy to occur, which will lead to uneven roughening of the board surface, even line deformation and different color difference between the copper surface and INK after printing, so the whole brushing operation is required. Brushmark test (in case of D/F, water break test is required), the width of brush marks is about 0.8~1.2mm, which varies depending on the product. After updating the brush, the level of the brush wheel needs to be adjusted. Make corrections, and need to add lubricating oil regularly. If the water is not boiled during brushing, or the spray pressure is too small to form a fan-shaped angle with each other, it is easy to produce copper powder, and a slight copper powder will lead to a micro-short circuit during the finished product test (Dense line area) or unqualified high voltage test.

Another problem that is easy to occur in pre-treatment is the problem of board surface oxidation, which will cause board surface bubbles or cavitation after H/A.

1. The position of the solid water retaining roller in the pretreatment is wrong, so the acid is brought into the washing section too much. If the number of washing tanks in the latter section is insufficient or the amount of water injected is insufficient, it will cause acid residue on the board surface.

2. The water quality of the washing section is poor, or when there are impurities, there will be foreign objects attached to the copper surface.

3. If the water-absorbing roller is dry or saturated with water, it will not be able to effectively take away the water on the product to be made, which will make the residual water on the board surface and the residual water in the holes too much, and the subsequent air knife will not be able to fully function. , the vacuoles caused at this time are mostly in the shape of tears at the edge of the via hole.

4. When the board temperature is still at the remaining temperature when the material is discharged, the board is stacked and closed, which will oxidize the copper surface in the board.

Generally speaking, a PH detector can be used to monitor the pH value of the water, and infrared rays are used to measure the residual temperature of the board surface. Wet conditions need to be specified. It is best to have two sets of suction wheels for alternate cleaning. The angle of the air knife needs to be confirmed before daily operation, and pay attention to whether the air duct in the drying section is detached or damaged.