Investigation of Agitation Effects on Electroplated Copper in Multilayer Board Plated‐Through Holes in a Forced‐Flow Plating Cell

Abstract

The effect of electrolyte agitation in plated‐through holes (PTH's) of multilayer boards (MLB's) is investigated for high conductivity electrolytes with and without brightener additives. The experiments were carried out in an 80 liter forced‐flow plating system capable of agitation by air sparging also. PTH quality is assessed in terms of the PTH electrical resistance, the PTH deposit uniformity, and the deposit morphology. Correlations are made with plating current density, electrolyte velocity in the PTH's, and two dimensionless plating parameters, and . The results show that for additive‐free plating, the agitation requirements to prevent mass transport‐limited plating conditions increase rapidly with increasing current densities and decreasing cupric ion concentrations. At the current densities common in MLB production, the low levels of agitation produced by air sparging alone provide only for marginal plating conditions particularly at the board edges where the test coupons are located. The plating criteria for good PTH deposits, and are confirmed by the experimental results. Plating with Cubath®M additives is shown to be considerably less sensitive to variations in the plating parameters which are likely to occur in production. The criteria for good PTH quality can be extended to and , which allows for more latitude for plating current density variations.