AC operation of high performance glass ceramic package interconnect and impact on manufacturing

Ceramic packages for high performance server processors have many wiring layers and via count due to the large number of input-output (I/Os) needed in high end computers to attain performance targets. Good AC operation of the interconnect is critical to attain since long traces and vias can be very lossy in these applications. The electrical impact of manufacturing changes implemented in these modules due to mechanical, thermal, or yield issues can be difficult to discern due to the large number of structures and parameter variation in the package. In addition, most of the signals in modern processors operate at a fundamental frequency well into the gigahertz range making traditional direct current (DC) electrical measurements less meaningful to designers and process development engineers. We quantify the AC electrical impact of package manufacturing changes using a high speed microwave vector network analyzer (VNA) on the module interconnects. We measure the effect of several of these changes on various ceramic multi-chip modules (MCM) as a function of frequency. We show how these measurements have lead to a modified cross section in high performance glass ceramic (HPGC) packages used for IBM large scale server processors.