Probe card with probe pins grown by the vapor-liquid-solid (VLS) method

Abstract

Probe cards mounted with vapor-liquid-solid (VLS) grown silicon whiskers have been produced. In this development the mesa method, in which VLS whiskers are grown on silicon mesas topped with gold hats, has been successfully introduced which allows accurate positioning of the VLS whiskers. The VLS whisker grows vertically to over 2000 /spl mu/m in length and a diameter of 10-100 /spl mu/m has been obtained. The metal-plated whisker has enough compliance with the overdrive capability of up to 400 /spl mu/m to compensate for the prober error and the possible irregularity of the wafer surface which maintains reliable contact. Two fabrication methods to accomplish the wiring of the VLS whiskers onto the card assembly are proposed. One method is to transfer the VLS whiskers onto a patterned substrate after encapsulating in a transfer media, the other is to grow the VLS whiskers on a patterned silicon-on-insulator (SOI) wafer. The design concept of the whisker probe pins is also proposed. The card has the potential to be used as a narrow-pitch, high pad-count probe card which has more than 300 probe pins which are less than 50 /spl mu/m in pitch. The card obtained by the SOI process has potential application as a wafer level burn-in (WLBI) card with the same thermal expansion coefficient as a silicon wafer. Patterning on a SOI wafer enables a possible low-impedance transmission line in a high speed circuit.