High frequency modeling and characterization of pin and land grid array sockets

Abstract

A variety of CPU sockets are simulated and characterized for 2-port and &port S-parameters at high frequencies (45MhZ-15GHz) in single-ended and differential signaling configurations. Three-dimensional numerical simulations are performed with a commercially available FEM (f~te element method)-Based full-wave software: Ansoft HFSS. The simulation method, including three dimensional modeling, wave excitation and discretization, is rigorously validated with VNA (vector network analyzer) measurements. Using this developed simulation and measurement techniques, a PGA (pin grid array) socket with 478 pins and a LGA (land grid array) socket with 735 pins are analyzed and characterized to compare their performance for high-speed signaling applications. Both simulations and measurements are obtained with a test fmture consisting of motherboard transmission lines and socket adaptor vias, and their effects are removed using a de-embeddmg technique up to 15 GHz for 2-port as well as 4-port signaling. Validation results show very good correlation between numerical simulation and measurements for most critical electrical speciiications. The characterization results show that the LGA and PGA sockets have comparable performance to SGHz, but the PGA socket provides better frequency response from 8 to 15 GHz bandwidth for single ended and differential insertion and rem losses, referenced 50 ohms and 100 ohms respectively. Also, the differential frequency response (differential return and insertion losses) is better than that of single-ended signaling for these two sockets.