An Experimental and Numerical Investigation Into Multilayer Probe Card Layout Design

This paper conducts experimental and numerical investigations into the microforce probing technique used to test the functionality of IC devices. The study commences by considering the case of a single tungsten needle probe and examines the relationship between the contact force and the scrub mark size on aluminum pads at various levels of overdrive and shooting angle. Subsequently, a three-dimensional computational model is developed to facilitate the design of an optimum multilayer needle card layout. The simulation results obtained for the profile and size of the scrub marks on the upper surface of the aluminum pads of an IC device are found to be in good agreement with the experimental observations. The validated model is then applied to analyze the effects of the tip length and beam length on the scrub mark profile and the stress distribution contours within the needle during a wafer level test. The results predicted by the finite-element model (FEM) for the scrub mark length under various beam lengths are used to specify a suitable design for a multilayer needle layout. Taking the case of DDR2 SDRAM of an aluminum pad of dimensions 70 mumtimes70 mum (length by width), the numerical results enable appropriate values to be assigned to the shooting angles, beam lengths, and tip lengths of the individual needles within a four-layer probe card