With the rapid development of SMT technology, the future trend of printed circuit board will inevitably go to thin wire, small hole and multi layer high density packaging. However, such a high level of manufacturing a circuit board plating process will also face some technical bottlenecks, such as: how to make the central and edge panel uniform coating, how to improve the keyhole wall stress, how to improve the coating properties such as ductility and tensile strength are worth the effort of the subjects in the future.
The surface of circuit board, usually a board board size is about 24 "*18", if the central and edge uniform coating thickness is not easy, according to the Faraday law, the thickness of the coating and the applied current is proportional to the density of coating hypothesis is a certain value, the coating thickness distribution is the distribution of cathode current the influence of many factors including the current distribution in the solution resistance and electrode polarization, the plating of geometry, anode distance, applied current size, quality pass rate. According to the theory of electric field, plane potential and its stress is perpendicular to each other, while the electrode itself belongs to the equipotential plane, so the current flowing into or out of a plane and electrode will the point perpendicular to each other. The relation between equipotential plane and current direction distribution.
In the past five years, the large number of surface mount assemblies has made the circuit tend to be difficult for thin wire, small hole and multi layer. Therefore, the drilling, slag removal, copper plating and so on are facing unprecedented challenges.
Multilayer printed circuit board of high level is often regarded as a military purpose, through military specifications such as tin or drift of temperature cycle test, so the properties of coatings such as ductility, tensile strength can often determine the success or failure of the test, gloss and additives on improving coating properties play an important role in the basic reaction. A little body.
In electroplating is extended to decrease the roughness of the surface coating or increase the often need to add additives or gloss agent had proposed the reaction mechanism of surface formation of the convex part can absorb more luster, thus increasing the resistance, because the current always toward the lower resistance position, so that the current will flow smoothly in coating the part of rough reduction.
As far as the circuit board is concerned, the current distribution is mainly determined by the geometry of the plating bath, such as the distance between the anode and cathode, the arrangement, size, etc., and the gloss agent or additive has little influence on the current distribution. If the distribution of current is uneven, auxiliary devices such as shield or auxiliary cathode can be made.
The current distribution and the coating properties of the circuit board vias are mainly affected by the resistance of the solution, polarization of electrodes and mass transmission. To obtain good quality and uniform distribution of plating, it is necessary to emphasize the concept of design, for example, the use of special mixing method, pulse plating technology, etc..
Additives or gloss agents can change the physical properties of the coating, such as ductility, tensile strength, etc., but if the amount is too much, it may cause organic pollution to the quality of coating, in addition, it also increases the inconvenience of management. Therefore, it is worthwhile to study the method of pulse plating to improve the physical properties of coatings.