Five common silver plating defects of multilayer circuit boards have been solved by solution manufacturers, equipment manufacturers and PCB factories, and some prevention and improvement methods have been found, whICh can provide multilayer circuit boards factory work to solve the problem and improve the yield, as described below:
1, multilayer circuit board Javani bite copper
This problem must be traced back to the copper plating process. It is found that in the case of deep hole copper plating and blind hole copper plating, where the object is high thickness to diameter ratio, if the copper thickness distribution can be more uniform, this phenomenon of Giovanni copper biting can be reduced. And in the multilayer circuit board process of metal inhibitors (such as pure tin layer) stripping and etching copper, once there is excessive etching and side corrosion phenomenon, there may be thin cracks and electroplating solution and micro corrosion solution.
In fact, the big source of Giavani's problem is the green paint project, in which the side erosion caused by the green paint phenomenon and the relief of the skin film are easy to cause fine cracks. If the green paint phenomenon can be caused by positive stump rather than negative side erosion, and if the green paint is thoroughly hardened, then the absence of Gianni's copper bite can be eliminated. As for the operation of copper plating, it is necessary to make the copper plating in the deep hole more uniform in the strong agitation. At this time, it is also necessary to use the help of ultrasonic wave and Eductor to stir, in order to improve the mass transfer of the tank and the distribution of copper thickness. As for the process of PCB board immersion silver plating itself, it is necessary to strictly control the micro-etching rate of copper in the front section, and smooth copper surface can also reduce the existence of fine cracks after green paint. After the silver groove itself can not appear too strong bite copper reaction, the PH value is appropriate to neutral, and the plating rate is not too fast, but the thickness should be as thin as possible, and under the best silver crystallization can do a good job of anti-discoloration function.
2. Improvement of discoloration of multi-layer circuit board
The method of improvement is to increase the density of coatings and reduce the Porosity. Packaging products must be made of sulphur-free paper and seaLED to remove oxygen and sulphur from the air, thereby reducing the source of discoloration. Moreover, the ambient temperature of the storage area should not exceed 30℃ 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 surface of multi-layer PCB circuit board
If the ion concentration of the silver DIPping bath can be reduced without interfering with the coating quality, the ions brought out of the plate surface and attached can be reduced naturally. In the cleaning after dipping, it must be rinsed with pure water for more than 1 minute before drying to reduce the attachment of ions. And for the finished board, it is also necessary to periodically check its cleanliness, and make sure that the amount of residual ions on the multilayer circuit board surface is reduced to a low level to meet the industry specifications. Records of all tests performed should be kept in case of emergency.
4, the improvement of multilayer circuit board silver surface copper
Various processes before dipping and plating silver need to be carefully controlled. For example, pay attention to the detection of "WaterBreak" (water resistance) and observation of special bright copper spots after micro-etching copper surface, which indicates that there may be some foreign bodies in the copper surface. For clean copper surfaces with good micro-etching, the upright state shall be maintained without water breakage within 40 seconds. Wiring equipment should also be maintained regularly to maintain its water uniformity, so that a more uniform silver plating layer can be obtained. In the operation, it is necessary to carry out DOE experiment plan tests on copper dipping time, liquid temperature, stirring, and aperture size, etc., in order to obtain high-quality silver plating. In addition, for the dipping process of thick plate with deep hole and HDI micro-blind hole plate, the external assistance of ultrasonic wave and strong current can also be used to improve the distribution of silver layer. The extra force of mixing in these tanks does improve the ability of yao water to moisten and exchange in both deep and blind holes, helping the entire wet process.
5, multi-layer circuit board welding spot micro-hole improvement
Interface microholes are still difficult to improve the shortcomings of silver dipping, because their true causes are still unknown, but at least some related causes can be identified. Therefore, in minimizing the occurrence of its correlation factors, of course, it can also reduce the occurrence of welding microholes in the downstream.
The silver layer thickness is considered as the relevant factor. It is necessary to reduce the silver layer thickness as much as possible. Secondly, the pre-treated micro-etching can not make the copper surface too rough, and the uniformity of silver thickness distribution is also the key. As for the content of organic matter in the silver layer, it may be reversed from the purity analysis of multisampling silver layer, where the content of pure silver should not be less than 90% atomic ratio.