Study On Technique Of Copper Electroplating For Filling BVHs And THs At One Process

Printed circuit board(PCB) is an important electronic component, the support of electronic components and the carrier of electronic electrical connection. Printed circuit boards(PCBs) are found in almost all kinds of electronic products, such as cellular phones, computers, robots, as well as medical devices. High-density interconnected printed circuit boards(HDI PCBs) are designed consequently with the demand of modern electronic products for miniaturization and multi-functionalization. HDI board is a multi-layer, light-weight, stable and high density printed circuit boards, which could be achieved only with some advantage techniques, such as, microvias, fine lines technology and superimposing techniques. The microvias(through holes, blind vias, buried vias) are to achieve HDI board electrical interconnection between layers through hole metallization technology. The so-called hole metallization refers to the insulating hole walls of PCB plated with a conductive metal by chemical plating and electroplating method. Therefore, the merits of the hole metallization technology directly affect the conductivity, heat resistance and other quality of PCB. Conventional through-holes(THs) and blind microvias(BVHs) metallization process are as follows: First of all, make the hole wall of through-hole metallized, and then fill with resin or conductive adhesive. Secondly, fill blind microvias by copper electroplating. This method requires two electroplating lines and plating twice for filling BVHs and THs, and electroplating process is very complicated. Besides, a subsequent plug holes process easily leads to poor quality of electrical interconnection, which is difficult to meet the requirements for electrical interconnection reliability of HDI board. To solve these problems, an electroplating solution system for blind microvias filling in Bomin Electronics Company was chosen as tested system, the feasibility and effectiveness of copper electroplating for filling BVHs and THs at one process were studied systematically in this paper. The main contents and conclusions are given as follows:1. The effect factors for filling blind holes. With plating solution system for blind microvias filling as tested system, the single factor experimental program was adopted to examine the relationship between the main factors(copper sulfate, sulfuric acid, Cl-, organic additives, current density, plating time) on the filling performance of blind microvias to optimize the blind microvias electroplating filling process and electroplating formula. In addition, the interaction of additives and the effect of blind microvias' geometric size on filling performance were studied as well. The results showed that the concentration of copper sulfate, sulfuric acid, Cl- and organic additives, the current density and plating time are key factors which influenced the filling performance of blind microvias. The filling performance was improved significantly under optimized plating process and plating formula. In addition, there is mutually synergistic effect between the organic additives, and blind microvias' geometric size has a certain effect on filling performance too.2. Through-hole filling process with copper electroplating. To explore the feasibility and effectiveness of copper electroplating for filling THs with electroplating solution system for blind microvias filling in Bomin Electronics Company, orthogonal test was carried out to optimize the parameters of plating formula, and the results showed that the copper electroplating solution system could achieve though holes filling. For the THs of 100?m in diameter and 100?m deep(ratio 1:1), the optimal formula was: the concentration of accelerators, suppressor, levelers and H2SO4 were 0.5mL/L, 17mL/L, 20mL/L and 30g/L, respectively. The order of the effects of copper electroplating components on through-hole filling performance was suppressor > leveler >accelerator > sulfate. Under the optimized conditions, the filling performance was improved significantly and meets the IPC-A-600H-2010 quality requirements.3. The technology of copper electroplating for filling BVHs and THs at one process. On the basis of the above experiments, the feasibility and effectiveness of copper electroplating for filling THs and BVHs at one plating process with DC plating method were performed. The experimental data showed that it was feasible to fill BVHs and THs at one process under optimized condition. However, the agitating rate and holes location had certain influences on the filling performance. The experimental results indicated that the technology of copper electroplating for filling BVHs and THs at one process adopting DC plating method not only simplified the process and shorten the PCB production cycle, but also improved the conductivity, heat dissipation and mechanical strength significantly.4. The application of copper electroplating for filling BVHs and THs at one process. In order to demonstrate the practical value of the technology of copper electroplating for filling BVHs and THs at one process in practical production, a four-layer HDI boards(different geometry sizes of BVHs and THs) were chosen as experimental products, and a“Modified Pattern Plating” was put forward to decrease the thickness of copper deposition on board surface. The results showed that the copper electroplating solution system could achieve copper electroplating for filling BVHs and THs at one process, besides there was no copper deposition on board surface, which was very important for subsequent fine line patterns. Those results suggested that the technology of copper electroplating for filling BVHs and THs at one process could be applied to the production of HDI boards.