The main feature of the electroplating hole copper plating technology used by the manufacturer of multi-layer impedance circuit boards is the blind buried holes of the micro-through holes formed in the multi-layer
PCB circuit boards with "core boards". These micro-through holes have to be porized.And electroplating copper to achieve electrical interconnection between layers. The most important thing is the entry and replacement of the plating solution when the blind hole is used for metallization and electroplating. The manufacturing of multilayer PCB boards by
PCB manufacturers is coated or laminated on core boards.Quality layer (or coated with resin copper foil) and forming micro through hole. These micro-through holes formed by layering on the core plate are photoinduced, plasma, laser and sandblasting (mechanical methods, including non-introduced numerical control drilling methods)And so on. These micro-through holes in multilayer
PCB circuit boards are metallized through holes and electroplated with copper to achieve electrical interconnection between PCB layers. This section mainly introduces the characteristics and requirements of micro via holes in
PCB boards when they are orifice and electroplating.
For penetration, if it is vertical hole electroplating, through the PCB manufacturer in the plate fixture (or hanger) swing, vibration, plating solution stirring or jet flow and other methods to make the PCB between the two plates produced hydraulic difference, this liquidPressure difference will force the plating solution into the hole and drive the gas out of the hole and fill the hole. For the micro-hole with high thickness-diameter ratio (thickness-diameter ratio: the ratio of the thickness of the dielectric layer to the diameter of the micro-conductive aperture), the existence of this hydraulic difference is more important, and then the hole is porized.Or electroplating. In porous electroplating, some Cu2+ ions in the bath of the hole must be consumed. As a result, the concentration of Cu2+ in the bath of the hole becomes lower and lower, and the efficiency of porous or electroplating will become smaller and smaller. Add the effect of fluid flowing through the hole.The "laminar flow" phenomenon and the uneven distribution of current density (the electric current density in the hole is much lower than the current density on the plate), therefore, the coating thickness at the center of the hole is always lower than that at the plate surface. In order to reduce the difference of the thickness of the coating,The most fundamental method is to increase the flow rate of plating solution in the hole or the number of plating bath exchanges per unit time (assuming that the plating solution is replaced one time at a time, which is actually much more complex, but this assumption can explain the problem); and to increase the number of holes.It is obviously difficult or impractical to increase the current density of the plating solution in the hole, because increasing the current density of the plating solution in the hole is bound to increase the current density of the plate surface, which in turn results in the thickness of the plating layer in the center of the hole and the plating of the plate surface.Thirdly, the current density and the concentration of Cu2+ ions in the plating solution are reduced, and the flow rate of plating solution (or the exchange times of plating solution) in the pores are increased, so that the plating solution between the plate surface and the holes can be reduced.The difference in the concentration of Cu2+ ions (i.e. the difference in the concentration of Cu2+ caused by the partial consumption of Cu2+ and the change of bath) can be improved by means of this measure, but often at a sacrifice, between the thickness of the plating layer on the plate and the thickness of the plating layer (center) in the hole.PCB productivity (output) at the cost of this is undesirable; fourth, the use of pulse plating method, according to the different thickness-diameter ratio of micro-through hole, using the corresponding pulse current plating method {can significantly improve the surface of PCB platingThe difference between the thickness of the coating and the thickness of the hole can even reach the same thickness of the coating. Are these measures applicable to porous electroplating of micro-through holes in Multilayer PCB boards? As mentioned earlier, in multilayer PCBHole electroplating of micro through hole is carried out in blind hole. When the depth of blind hole is small or the ratio of thickness to diameter is small, the practice has shown that the above four electroplating measures can achieve good results. However, when the depth of blind hole is high or the ratio of thickness to diameter is large,What is the reliability of microvia electroplating? Or how can the depth or thickness-diameter ratio of blind holes in multilayer PCB be controlled? As for the microvia electroplating in multilayer PCB by horizontal holeelectroplatingDetailed reports have been reported, but one can imagine that reliable electrical interconnection can be achieved by horizontal hole plating when the thickness-diameter ratio of PCB board is not large. For the blind through-hole with larger aspect ratio, multilayer printed circuit board is required.Blind through holes on the lower surface are difficult to drive away the gas in the holes, and even the plating solution is difficult to enter the holes, let alone the exchange of plating solution in the holes, unless the plate surface is regularly. To sum up, according to the porosity of the above multi-layer PCB board,From the basic characteristics and principles of electroplating, it can be concluded that the horizontal hole electroplating is far inferior to the vertical hole electroplating in the processing of blind buried through holes in multilayer circuit boards (especially those with large thickness-diameter ratio, such as thickness-diameter ratio > 0.8).
