![]() Previous attempts to apply analytical solutions to the assembly had only limited success. Before investigating possible solutions, a finite element (FE) model of the unmodified probe card was developed. To reduce the deflection-induced variation in OT and force, the probe card structure needed to be stiffer. This small amount of unintended deflection is important, and the actual measured deflection is even larger. When theoretically considering the various effects that could alter the probe force from its design value, more than a 40% decrease resulted if only a 0.0005″ deflection were assumed together with the 0.00025″ planarity tolerance. The mean values of these measurements were 0.00072″, 0.00057″, and 0.00034″, respectively. ![]() The behavior of the corner and the behavior of the base of a shelf were similar, varying from 0.00045″ to 0.00065″. To improve the statistical confidence of the measurements, 100 sets were taken: a touchdown was performed, measurements were made, and the load was removed 100 times.Īs might be expected, the deflection at the cantilevered shelf tip was greatest, varying from 0.00060″ to 0.00095″ over the course of the 100 touchdown cycles. Measurements were taken at the tip of one of the ceramic shelves, at the shelf base, in the corner of a shelf, and on the top of the PCB. Allowing ï¿❐.00025″ for planarity tolerance and assuming 0.0005″ for probe card deflection, the maximum OT could be only 0.00175″ for some probes, resulting in 2.45g and, as a result, a high probe contact resistance.Ī digital dial indicator with low contact pressure was used to measure the deflection of the probe card under load. Taking into account the ï¿❒0% tolerance, the actual force could be as low as 1.4g per mil or 3.5g.ĭeflection of the probe card PCB reduces this value even further because it decreases the effective OT. This corresponds to a nominal 4.375g at the specified 1.75g ï¿❒0% per mil OT. Touchdown of a wafer on the dual-die shelf probe card is designed to produce 2.5-mil overtravel (OT). In Figure 2, the original design shows the through opening in the support PCB and the ceramic base glued into a rebate around the lower part of the opening.īecause stresses associated with the ceramic-shelf deflection could produce cracks and sudden mechanical failure, a detailed understanding of the mechanical system was undertaken. Only the probes are intended to bend, but the ceramic shelf and the thick FR4 PCB probe card also deflect under load. The technology used in multidie cards is similar to that found in smaller cantilever needle probe cards, but when the large number of probes touch down, high forces cause structural deflection. The shelf architecture provides the necessary mounting surfaces for the needle probes so the orthogonal groups of probe bodies do not mechanically interfere with each other. In the dual-die shelf probe card in Figure 1, a large number of connecting wires must be accommodated in a confined space. Because only a few different tip lengths are required, the behavior of all the groups of probes can be controlled within a tight tolerance. All the probes in a group have the same cantilever length and, with precise manufacturing, will exhibit nearly perfect planarity and uniform contact force. ![]() This construction provides uniform probe mounting. Groups of probes are attached to the ceramic base and the shelf to form a four-sided contact pattern. Shelf probes feature a ceramic base with strategically placed slots along three sides of a shelf. The key to repeatable high performance has been refining the so-called ceramic-shelf design.Īs in conventional epoxy-ring construction, one or more layers of cantilever needle probes are attached by epoxy to a ceramic base. Simple mechanical changes can significantly improve probe card performance.Įpoxy-ring probe cards with 2,000 or more probes are economical solutions to multi-DUT parallel test.
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