PCB Technical - Fix some common defects in the circuit board immersion silver plating process

Fix some common defects in the circuit board immersion silver plating process

Some problems may occur after the immersion silver plating of the PCB circuit board, so it is very important to prevent problems during the PCB manufacturing process. The editor will introduce some prevention methods.
The five common shortcomings of immersion silver plating have been studied on the spot by drug dealers and equipment vendors, as well as PCBs. Some prevention and improvement methods have been found, which can provide PCB manufacturers to solve the problems and improve the yield. Down:

Javanni bites the 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. In addition, in the PCB manufacturing process, metal resists (such as pure tin layer) are stripped and copper is etched. Once over-etching and side etching occurs, fine cracks may also occur and electroplating liquid and micro-etching liquid may be hidden.

In fact, the biggest source of Jaffani’s problems is the green paint project, in which the side corrosion and film embossment caused by the green paint phenomenon are the most 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 process of immersion silver plating, 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. Finally, the silver bath itself should not have too strong copper biting reaction. The pH value should be neutral, and the plating rate should not be too fast. It is best to cut the thickness as thin as possible for the optimized silver crystal. Only then can the function of anti-tarnishing be done well.

Improvement of discoloration
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 degree Celsius, and the humidity must be below 40%RH. It is best to adopt a first-in-first-use policy to avoid problems caused by storage for too long.

Improvement of silver-faced copper
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" (Water Break refers to water repellency) and the observation of particularly bright copper points, which all indicate that there may be something on the copper surface. Some foreign objects. A clean copper surface with good micro-etching must be kept upright for 40 seconds without water breakage. The connected 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 to obtain the best quality silver plating layer, and for thick plates with deep holes and HDI micro blind holes The immersion silver plating process of the plate can also be assisted by the external force of ultrasound 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 ability of the liquid medicine in the deep and blind holes, which is of great help to the entire wet process.

Improvement of ion pollution on board surface
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 on the board surface must be reduced to a minimum to meet the industry's specifications. The records of the tests that have been done should be kept in case of emergency.

Improvement of solder joint micro-holes
Interface micro-holes are still the most difficult shortcoming to be improved by immersion silver plating, because the true 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.
In addition, among many related factors, the thickness of the silver layer is the most important factor. It is necessary to reduce the thickness of the silver layer 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 one of the important points. As for the organic content in the silver layer, it is possible to reversely know from the multi-point sampling silver layer purity analysis, the amount of pure silver must not be less than 90%. ipcb is a high-precision, high-quality PCB manufacturer, such as: isola 370hr PCB, high-frequency PCB, high-speed PCB, ic substrate, ic test board, impedance PCB, HDI PCB, Rigid-Flex PCB, buried blind PCB, advanced PCB, microwave PCB, telfon PCB and other ipcb are good at PCB manufacturing.