ULTRA VIA SUBSTRATE FOR ADVANCED BGA APPLICATIONS
Author: Bill Chou Company: X-LAM Technologies Date Published: 1/25/2000
Pan Pacific Symposium
Abstract: Need for semiconductor devices have placed an increasing demand on the interconnect density and electrical performance of package substrates. For high pincount packaging the market is looking for flip chip assembly on organic packages, with a bump pitch of 180 µm in 1999 dropping to 130µm by 2003. Flip chip offers the highest I/O range and smallest form factor. Currently, vertically integrated companies that can benefit from the saving already favor flip chip. This major change from the wire bond solutions that are in production today pushes BGA substrate suppliers into new technologies to meet the density demands. Thin film build-up substrate provides for the next level of density needs for a wide range of packaging and interconnection technologies. In order to meet the future market requirements, a reliable, cost effective and high routing density substrate is needed. Thin film build-up substrates offer unique advantages compared to the tradition build-up substrates. By comparing X-LAM design to the 100 -250 um via pad required for traditional build-up, UltraViaTM can provide 2-3 times higher routing density than the state-of-the-art build-up substrate. This high routing capability results less signal routing layers needed for packaging design. The capability to control thickness ranges, and uniformity of the dielectric layer deposited from thin film process cannot be matched by the traditional lamination process.. This paper discusses the development of ultra-high density BGA substrate, UltraViaTM. Processes and materials to fabricate fine features are examined and demonstrated. A flip chip test structure was designed and built for BGA packages to illustrate the density capability. The first parts of electrical and mechanical test results are presented to show the selection of substrate material and processes. These structures have multiple thin film metal layers. The design rule calls for 32 um fine line pitch. The vias were on a 71µm pitch and had 30 um bottom diameter with landing pads of 54µm.
Key Words: HDI substrate, high density, thin film build-up