PCB Technical - Cause analysis of NG in Multilayer PCB manufacturing process

1. There are many strange problems in the multi-layer PCB process, and the process engineer often takes the responsibility of forensic autopsy (analysis of adverse causes and solutions). Therefore, the main purpose of launching this discussion topic is to discuss one by one in the equipment area, including problems that may arise from people, machines, materials and conditions. I hope you can participate together and put forward your own opinions and opinions

2. The multi-layer PCB process will use the process of pretreatment equipment, such as inner layer pretreatment line, electroplating copper pretreatment line, D / F, anti welding (resistance welding) wait.

3. The multi-layer PCB manufacturing process takes the pre-treatment line for anti welding (resistance welding) of hard board multi-layer PCB as an example (different manufacturers of multi-layer PCB): brush and grind 2 groups - > water washing - > acid pickling - > water washing - > cold air knife - > drying section - > solar disc receiving - > discharging and receiving.

4. Steel brushes with brush wheels of #600 and #800 are generally used in the multi-layer PCB manufacturing process, which will affect the roughness of the board surface and then the adhesion between the ink and the copper surface. When the brush wheel is used for a long time, if the products are not placed evenly on the left and right, it is easy to produce dog bones, which will lead to uneven coarsening of the board surface, even line deformation and different color difference between the copper surface and ink after printing, so the whole brush operation is required. Brush mark test shall be conducted before brushing and grinding (water breaking test shall be added in case of D / F). The degree of brush mark shall be measured to be about 0.8 ~ 1.2mm, which varies according to different products. After updating the brush, the level of brush wheel shall be corrected and lubricating oil shall be added regularly. If water is not boiled during brushing and grinding, or the spray pressure is too small to form a fan-shaped angle, copper powder is easy to occur. Slight copper powder will lead to micro short circuit (dense line area) or unqualified high-voltage test during finished product test.

Another easy problem in the processing of Multilayer PCB is the oxidation of the board surface, which will lead to bubbles on the board surface or cavitation after H / A

1. The solid water retaining roller of multi-layer PCB pretreatment is in the wrong position, resulting in excessive acid brought into the water washing section. If the number of water washing tanks in the rear section is insufficient or the injected water is insufficient, acid residue on the board surface will be caused

2. Poor water quality or impurities in the water washing section in the multi-layer PCB manufacturing process will also cause the adhesion of foreign matters on the copper surface

3. If the water absorption roller is dry or saturated with water, it will not be able to effectively take away the water on the products to be prepared, which will cause too much residual water on the plate surface and in the hole, and the subsequent wind knife can not fully play its role. At this time, most of the resulting cavitation will be at the edge of the through hole in a tearful state

4. When multi-layer PCB is discharged and there is still residual temperature, it will be folded, which will oxidize the copper surface in the board

In the multi-layer PCB process, the pH value of water can be monitored by the pH detector, and the discharge residual temperature of the board surface can be measured by infrared ray. A solar disc retractor is installed between the discharge and stack plate retraction to cool the board. The wetting of the water absorption roller needs to be specified. It is best to have two groups of water absorption wheels to clean alternately. 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 falls off or is damaged.