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High Aspect Ratio Package Core Production with Electrolytic Deposited Copper
Keywords: Core via filling with copper, High aspect ratio, Production cost reductions
A typical package core consists of copper clad dielectric which is drilled to produce the necessary through vias serving two functions either as electrical or as thermal conduits. The thermal vias are normally characterised by a low drill pitch and a localisation at the centre of the package core. The vias are plugged after metallisation with a resin material to give the core the required planar surface necessary to provide the basis for the subsequent build up layers. Use of electrolytic deposited copper has been introduced as a new method to fill such through vias, pure copper as a plugging material has obvious advantages due its higher thermal conductivity in comparison to any currently available plugging resins. Significant cost savings are also possible as a fully automated in line processing sequence is available for electrolytic copper deposition in comparison to the more labour intensive resin plugging methods. The package cores utilising this technology have however been restricted to a dielectric thickness in the range 60µm to 100µm and with through via diameter 75µm to 100µm due to limitations in the processing technology. With these dimensions a hole pitch of down to 250µm may be filled reliably and is currently in production, latest results from this technology are shown. Hole filling with higher aspect ratios and particularly with substrates thicker than 200µm has required improvements in processing to ensure uniform copper filling. This paper describes the optimised process for through hole filling and shows the results achieved with dielectric materials 200µm and up to 400µm thick. Current qualification results of substrate 400µm thick with through via 80µm diameter are shown together with the comparison of filling with via pitch variation between 1.0mm and 0.6mm.
Stephen Kenny, Global Product Manager
Atotech Germany
Berlin 10553,
Germany


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