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Multilayer circuit board factory: various preventive methods of immersion silver plating process
The editor will introduce you to the following five common shortcomings of immersion silver plating on multi-layer circuit boards. We have found some prevention and improvement methods through yao water vendors, equipment vendors, and PCB circuit boards. The work of multi-layer circuit board factories to solve problems and improve yield is described below:
1. Multilayer circuit board Jiafanni bites copper
This problem has to be traced back to the copper electroplating process. It is found that all the objects are deep hole copper plating and blind hole copper plating with high aspect ratio. If the copper thickness distribution can be provided more uniformly, it will reduce this kind of Jiafanni biting. Copper phenomenon. Moreover, in the process of multilayer circuit board manufacturing, metal resists (such as pure tin layer) are stripped and copper is etched. Once over-etching and undercutting occurs, fine cracks may also occur and electroplating and micro-etching liquids may be hidden. .
In fact, the major source of Jaffani’s problems is the green paint project, in which the side erosion and film embossment caused by the green paint phenomenon are likely to cause fine seams. If the green paint phenomenon can cause positive residual foot instead of negative side erosion, and the green paint is completely hardened, then this lack of Gavani's copper bite will be eliminated. As for the operation of copper electroplating, it is necessary to make the copper electroplating in the deep hole more uniform during strong stirring. At this time, it is also necessary to stir with the help of ultrasonic and eductor to improve the mass transfer and copper thickness of the bath. Distribution. As for the PCB immersion silver plating process, it is necessary to strictly control the micro-etching copper bite rate in the front stage, and the smooth copper surface can also reduce the existence of fine seams behind the green paint. After that, the silver tank itself should not have too strong copper biting 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 silver crystal of Jiahua In order to do a good job of anti-tarnish function.
2. Improvement of discoloration of multilayer circuit boards
The improvement method is to increase the density of the coating and reduce its 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 of the storage area should not exceed 30°C, and the humidity must be below 40%RH, so that the first-use policy can be adopted to avoid problems caused by storage for too long.
3. Improvement of ion pollution on PCB circuit board surface of multilayer circuit board
If the ion concentration of the immersion silver plating bath can be reduced without hindering the quality of the plating layer, the amount of ions that are brought 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 attached ions. Moreover, the cleanliness of the finished board must be checked regularly, so that the residual ion content of the PCB circuit board surface must be reduced to a low level to meet the industry's specifications. The records of the tests that have been done should be kept in case of emergency.
4. Improvement of copper exposed on the silver side of multilayer circuit boards
The various processes before immersion silver plating need to be carefully controlled. For example, after micro-etching the copper surface, pay attention to the detection of "water break" (WaterBreak refers to water repellency) and the observation of particularly bright copper points. This means that there may be some on the copper surface. Foreign body. A clean copper surface with good micro-etching must be kept upright for 40 seconds without water breakage. The connection equipment should also be maintained regularly 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 test the DOE experiment plan for the immersion copper plating time, liquid temperature, stirring, and pore size, in order to obtain a good quality silver plating layer, and for thick plates with deep holes and HDI micro-blind holes. The immersion silver plating process can also be assisted by the external force of ultrasound and strong current device to improve the distribution of the silver layer. The extra strong agitation of these baths can indeed improve the wetting and exchange of yao water in deep holes 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 by immersion silver plating, because its real cause is still unclear, but at least some related reasons can be determined. Therefore, while minimizing the occurrence of related factors, of course, the occurrence of downstream welding microvoids can also be reduced.
Among the related factors, the thickness of the silver layer is the key factor, and the thickness of the silver layer must be reduced as much as possible. Secondly, the micro-etching of the pre-treatment should not make the copper surface too rough, and the uniformity of the silver thickness distribution is also an important point. As for the organic content in the silver layer, it may be reversed from the analysis of the purity of the silver layer by multi-point sampling, and the pure silver content should not be less than 90% atomic ratio.
As a professional PCB circuit board supplier, Co., Ltd. focuses on the production of high-precision double-sided/multi-layer circuit boards, HDI boards, thick copper boards, blind buried vias, high-frequency circuit boards, PCB proofing and small and medium batch boards.
