Influence of head-tip morphology on contact properties for microconnector of Ni–Co alloy

Abstract

To examine experimentally the influence of head-tip morphology on electrical and mechanical properties at the contact with a phosphor bronze, cantilever-type microconnectors of Ni–Co alloys were prepared by an electroplating technique. Here, the mol fraction y of Co in the Ni–Co alloy is 0.178, 0.204, 0.233 and 0.299. Among these alloys, the Vickers hardness is H _V = 510, 518, 525 and 478 for y = 0.178, 0.204, 0.233 and 0.299, respectively. Since the Vickers hardness is the maximum for y = 0.233, the Ni–0.233Co alloy may indicate the best wear-resistance. The loading and unloading manipulations were repeated to measure electrical resistance at the mechanical contact between the Ni–0.233Co microconnector and the phosphor bronze up to 10³ times. The repetitive measurement was conducted for microconnectors with thickness of 45 μm and head-tip curvature radii of r = 5, 25, 50 and 200 μm. Even at the initial repetition, the reliable electrical contact is actualized for r = 5 μm but not for r = 25–200 μm. The experimental result was quantitatively analyzed using a mechanical model. The analysis provides that the impression depth z of the head-tip into the phosphor bronze at the contact is mostly inversely proportional to r for r ≥ 5 μm. When r is measured in mm, the proportionality coefficient is 6 × 10⁻⁷ mm². As a consequence, the most reliable electrical contact of the Ni–Co microconnector with r = 5 μm is ascribable to the largest impression depth of the head-tip into the phosphor bronze.