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PCB-Jan2017

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46 The PCB Magazine • January 2017 by Ron Blake, Andy Oh, Carmichael Gugliotti, Bill DeCesare, Don DeSalvo, and Rich Bellemare MACDERMID ENTHONE ELECTRONICS SOLUTIONS Abstract This paper discusses a through-hole copper filling process for application in high-density interconnect constructions on thin IC and LED substrates where high reliability and thermal management are essential. The process consists of a two-step acid copper plating cycle. The first step utilizes periodic pulse reverse (PPR) elec- troplating to form a conductive copper bridge across the middle of a through-hole and is fol- lowed by direct current electroplating to fill the resultant vias formed in the bridge cycle. The ability of the process to fill a variety of through-hole sizes on substrates of varying thickness while minimizing the overall surface copper build-up are critical in applications re- quiring efficient thermal management as circuit miniaturization continues. The through-hole fill technology and fac- tors that affect its performance such as subs- trate thickness and through-hole diameter will be presented in this paper. Introduction Resin or paste plugging of through-holes in cores has been a part of build-up technology, es- pecially in IC substrate construction, for many years. Technological advances encompassing in- creased circuit density and stacked via construc- tion, coupled with higher power devices, have added an extra dimension of thermal manage- ment where a copper filled through-hole beco- mes advantageous (Figure 1). Advantages of copper filled through-holes include: • Reduction in CTE mismatch of resin/ paste plug • Stable platform for stacking microvias • Solid pillar structure within through-hole • Lower likelihood of adhesion failure on the plated-over filled via • High thermal conductivity of copper New technologies were developed to com- pletely fill through-holes and vias in build-up core layers in HDI and IC substrates with sol- id copper. Among the approaches for filling through-holes in a thin core board with copper was DC plating. FEATURE Electroplated Copper Filling of Through-holes: Influence on Hole Geometry

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