Pattern copper through hole filling in VCP for IC substrate production

The only state-of-the-art through hole filling in panel plating providing inclusion-free performance is available for horizontal conveyorised systems with pulse plating since 2005 [1] and already used in full mass production. This process shows its benefits especially when it comes to achieving complete filling with minimum plated Cu, which is essential for low cost and efficient use of resources. For pattern through hole filling a new processes has been developed. This pattern through hole filling process presented hereafter has been designed for vertical continuous plating (VCP) equipment. For fine line structures with optimum filling pattern plating processes are required, dimple must be kept at a minimum as any dimple will accumulate in a stacked filled via structure. In order to meet the technological requirements for next generation packaging, parameters must be found to achieve pattern plating with excellent within-unit distribution. The new process is designed for use of DC current and therefore the technology applied in the above mentioned state-of-the-art inclusion-free process cannot be used. By that of course inclusionless filling performance is of utmost importance. This paper focusses on technological aspects and on difficulties to fill through holes of various dimensions and sizes that exist in the market. The challenge of the fluctuating drilling tolerances/ qualities (protruding glass fibres, laser drilling asymmetry) shown and ways are described how to minimise the inclusion rate. In detail the influence of electrolyte agitation, current density, inorganic and organic concentrations on the filling performance are described and discussed. The result of our investigations is a process with improved through hole filling capability at low void occurrence and excellent within-unit distribution. The new process has shown improved capability to fill through-holes in cores of up to 200 gm, while further investigation continues.