1. Multilayer circuit board Giovanni bites copper

　　This problem must be traced back to the copper electroplating process. It is found that in the case of deep hole copper plating and blind hole copper plating with high aspect ratio, if we can provide a more uniform copper thickness distribution, it will reduce this kind of Giovanni bite. copper phenomenon. In addition, the stripping of metal resists (such as pure tin layer) and the etching of copper in the multi-layer circuit board process, once excessive etching occurs and there is side etching, fine seams may also be formed and electroplating liquid and micro-etching liquid may be hidden. .

　　In fact, the major source of Giovanni's problems is the green paint project, in which the side erosion and film relief caused by the green paint phenomenon are likely to cause fine seams. As long as the green paint phenomenon can appear positive residual foot rather than negative side erosion, and after the green paint is completely hardened, the lack of such Giovanni's bite copper will be excluded. As for the operation of electroplating copper, it is necessary to use strong stirring to make the copper electroplating in the deep hole more uniform. At this time, it is necessary to use the help of ultrasonic and Eductor to stir to improve the mass transfer and copper thickness of the bath. Distribution. As for the process of PCB immersion silver plating, the micro-etching copper bite rate in the front section needs to be strictly controlled, and the smooth copper surface can also reduce the existence of fine seams after green paint. After that, the silver tank itself should not have a strong copper bite reaction. The pH value should be neutral, and the plating rate should not be too fast. Fortunately, the thickness should be cut as thin as possible, and under the optimized silver crystal In order to do a good job of anti-discoloration function.

　　2. Improvement of discoloration of multi-layer circuit boards

　　The improvement method is to increase the density of the coating and reduce its porosity (Porosity). The packaging products must be made of sulfur-free paper and sealed to isolate the oxygen and sulfur in the air, thereby reducing the source of discoloration. In addition, the temperature in the storage area should not exceed 30°C, and the humidity should be lower than 40%RH. It is better to adopt the policy of first use to avoid problems caused by storage for too long.

　　3. Improvement of ion pollution on the PCB surface of multilayer circuit boards

　　If the ion concentration of the immersion silver plating bath can be reduced without impairing the quality of the plating layer, the ions carried out and attached to the plate surface will naturally be reduced. In the cleaning after immersion plating, it must be rinsed with pure water for more than 1 minute before drying to reduce the adhesion of ions. Moreover, the cleanliness of the finished board should also be checked regularly, so that the residual ions on the surface of the PCB must be reduced to a low level to meet the industry's standards. All tests that have been done should be kept in their records for emergencies.

　　4. Improvement of copper exposure on silver surface of multilayer circuit board

　　Various processes before immersion silver plating need to be carefully controlled, such as the detection of "water break" (WaterBreak refers to water repellency) and the observation of particularly bright copper spots after micro-etching the copper surface, all of which indicate that the copper surface may have some foreign body. The clean copper surface with good micro-etching must be kept upright for 40 seconds without water breaking. The connection equipment should also be regularly maintained to maintain the uniformity of its water quality, so that a more uniform silver plating layer can be obtained. During the operation, it is necessary to continuously conduct the DOE experimental plan test on the copper immersion time, liquid temperature, stirring, and pore size, etc., in order to obtain the best quality silver coating, and for thick plates with deep holes and HDI micro-blind hole plates. The immersion silver plating process can also be assisted by the external force of ultrasonic and strong current to improve the distribution of the silver layer. The extra strong agitation of these baths can indeed improve the wetting and exchange of water in deep and blind holes, which is of great help to the entire wet process.

　　5. Improvement of micro-holes in solder joints of multilayer circuit boards

　　Interface micro-holes are still a shortcoming that is difficult to improve in current immersion silver plating, because the real cause has not yet been revealed, but at least some related reasons have been identified. Therefore, while minimizing the occurrence of its related factors, of course, the occurrence of downstream welding micro-holes can also be reduced.

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The original document about the PADS design.Hybrid circuit board PCB