Electrical test strategies for a wafer-level packaging technology

A wafer-level packaging (WLP) technology is under development that provides compliant electrical leads with a density as high as 12,000 per cm². The leads are batch processed while the integrated circuits are still in wafer form through a series of relatively simple photolithographic steps. After electrical testing, the wafers are diced and the integrated circuits (ICs) are ready for direct assembly to an interconnect substrate. Sufficient lateral and vertical compliance is provided by the leads to accommodate the nonplanarity encountered during assembly and the thermal mismatch between the IC and substrate during normal operation. The high density of compliant leads presents both challenges and opportunities for electrical testing. This paper first summarizes the process technology used to fabricate these high-density electrical contacts. Several potential test strategies are then introduced that may take advantage of these contacts.