Authors: John Lauffer, David Bajkowski, Michael Gaige, Robert Edwards, Gordon Benninger and William Wilson Company: i3 Electronics, Inc. Date Published: 10/14/2018
Abstract: For the next generation of 3D-IC applications, glass offers many desirable properties that make it an ideal interposer. In order to realize these applications, it becomes necessary to be able to deposit a metalized layer on both surfaces and create a conductive via through the glass. In this paper we will present results on interposers that have fine line circuitry on both sides of the glass and have through glass vias (TGVs). One major challenge is how to create a TGV using either electrically conductive adhesives (ECAs) or Cu plating methods to achieve a high conductivity and reliable via connection. A major challenge in using ECA materials is how to effectively fill the vias. Our test vehicle has a TGV with dimensions of 50um diameter and a 300um thick glass substrate. A positive pressure screen printing process was used to fill the vias. These ECA materials exhibited a very high viscosity, due to the high Cu metal filler content, which make them very difficult to fill. In addition, a process to Cu plate a TGV has been developed for the same via dimensions as described above. Here a deposition process was used to produce a conductive seed layer in the via, followed by a Cu electroplating process to plate up a conformal Cu layer in the glass via. A unique Cu-plated via configuration has been developed to create a high performance and reliable TGV. In this work, we have plated both 100mm and 200mm wafers having variable via pitches down to less than 175um. The 200mm wafer has ~ 87,000 TGVs. From this work, a better understanding of different plating conditions on quality and uniformity of the conformal Cu plating through the thickness has been achieved. A discussion of the challenges associated in building glass interposers will be presented, which will include examples of recent builds of a double-sided Cu circuitry glass interposer having Cu plated TGVs.
Glass interposer, through glass via (TGV), semi-additive plating (SAP), electrically conductive adhesive (ECA).