The wafer level chip scale package (WLCSP) has emerged as one of the best device packaging solutions for the continuing trend towards smaller, thinner, lighter, and less power end products. Compared with face up wire bonding flip chip, WLCSPs provide the shortest possible leads, the lowest inductance, the highest frequencies, the best noise control, the highest density, and the greatest number of I/Os in the smallest device footprints with the lowest profile. This package/device performance should not be compromised by the interconnect between the sophisticated testing systems and the WLSCP device-under-test. WLCSP contactors and probe heads can have a direct impact on signal fidelity along with impacting testing costs, test system uptime, production yields, and the number of good units shipped per shift, per day, etc. The new generation of densely packaged, high-speed semiconductors in WLCSPs demand a high level of electrical interconnect performance to the test system while supporting multisite test for high levels of parallelism. The level of electrical performance required at test may not be attainable with traditional vertical probes and buckling beam probe technology. In test, WLCSP contactors and probe heads provide a vital link between the sophisticated high speed testing system and the increasingly complex WLCSP integrated circuits. As the vital link, contactors and probe heads must have the DC to GHz bandwidth for testing everything from digital computing devices to high frequency RF devices at ambient, cold and hot test temperatures.
In addition to electrical performance, mechanical reliability and ease of maintenance have always been regarded as the necessary attributes of a high performance contactor. These same reliability and attributes must be applied to WLCSP contactors for ensuring long probe life and long uninterrupted run times between cleanings and maintenance.
This paper will describe how high performance test spring probes are being designed and deployed to meet the electrical requirements of today's WLCSP testing environment, without sacrificing mechanical performance. In addition, the paper will provide information on WLCSP test sockets designed to standard size and footprint required for single and multisite contacting in automated test and manual/hand test. WLCSP spring probe contactors designs are reducing the cost to acquire and the cost to use while increasing WLCSP test throughput.