关键词: 积层法多层板, 酸性镀铜, 填孔, 整平剂, 竞争吸附, 电化学

Abstract:

Acid copper electroplating is one of the key technologies in buildup multilayer PCB (BUM-PCB) manufacture process and the most important technique to achieve electrical interconnection between any layer and high-density interconnection in a substrate. This article introduces the research focus of organic additives used in acid copper electroplating, and developing different kinds of micro-via filling copper electroplating technique applied in various scenarios, and some other technical problems from applications. First of all, according to the chronopotentiometric (CP) experiment results, the levelers with different polymeric molecular structures exhibited various responses of cupric deposition potential along with their increased concentrations, which is the critical information for studying the absorption and desorption behaviors of organic additives, and provides reasonable advices for additives formula design. Linear sweeping voltammetric (LSV) study is very helpful for studying the absorption behavior of organic additives under different potentials and quantitatively describing the degree of current change because of potential polarization that helps evaluate the stability of micro-via filling performance of particular additive formular. Secondly, with the use of gel permeation chromatography (GPC) we have widely studied polymer molecular structure in the aspect of molecular weight and polydispersity, which includes carrier and leveler. The precise information of polymeric molecular structure obtained from experiments can greatly enhance comprehension of the absorption mechanism of polymer additives. Corresponding electrochemical experiment results show that there is obvious correlation between molecular weight of carrier and its suppression effect. Examples of polymerization reaction of some levelers with novel molecular structure are presented, which aims at studying the influence of steric hindrance on electrochemical or electroplating performance by adjusting the length of carbon chain between two aminos and the number of heteroatom, like oxygen atom. Thirdly, different kinds of micro-via filling copper electroplating technique applied in various scenarios have been developed, which includes high-speed micro-via filling copper electroplating technique, ultrathin thickness controlled micro-via filling copper electroplating technique, highly uniform pattern line and micro-via filling copper electroplating technique, through hole and micro-via filling copper electroplating technique and through hole filling copper electroplating technique. Finally, technical problems from application of additives are simply introduced here. Copper plating equipment is the workplace for plating solution and its structure design and process parameters will profoundly affect the micro-via filling performance in the aspect of flow field and electric field. Large void is very easy to be formed inside micro-via under improper convection and deposition velocity. Virgin make-up solution (VMS) components also affect micro-via filling performance obviously in coordination with organic additives by changing overpotential of cupric reduction reaction. Precise determination of organic additives in aged plating solution is very challengeable because byproducts accumulated during manufacture have completely different absorption mechanisms compared to fresh plating solution.

Key words: build up multilayer printed circuit board, acid copper electroplating, via filling, leveler, competitive adsorption, electrochemistry