Elastic MEMS probe card based on the PDMS substrate

Abstract

A novel type of MEMS probe card that uses polydimethylsiloxane (PDMS) as an elastic substrate was designed and fabricated by MEMS technology. This proposed probe card structure has the advantages of good planarization, low resistance, higher probe density and a simplified fabrication process. To realize the probe card prototype, polyimide (PI) was employed as the interlayer to avoid micro cracks of the sputtered metal layer. Then oxygen plasma treatment was utilized to enhance the adhesion of chrome to PI. Also, silicon wet chemical etching was used to form the step adopted to compensate the height of the bonding wire. When the thickness of the PDMS and the PI layer was 150 µm and 50 µm respectively, the measured spring constant of the PI/PDMS substrate was 4582 N m−1, and that of the probe card structure was 7317 N m−1. The resistance from the probe tip to the end of the copper conductive line was as low as 1.4 Ω. In the RF range of 0–40 MHz, the characteristic impedance was above 20 kΩ, and the capacitance between the two adjacent probes was between 0.19 pF and 0.28 pF. It indicated that the designed probe card structure was suitable for testing of high-speed signal ICs.