Factors Influencing Thin Gold Performance for Separable Connectors

Abstract

Our recent publication provided an assessment of the performance of thin porous gold in an office environment. We concluded that thin gold (0.380-0.75 µm) on printed wiring board (PWB) fingers provided acceptable performance primarily because of the benign nature of the office environment. Examination of samples with field life up to nine years also revealed the absence of the classical failure mechanism of pore and/or edge creep corrosion on about 20 000 plated surfaces examined. Work since that last paper leads us to believe that nickel oxide formation is the predominant degradation mechanism. For this reason, we chose the thermal aging test at 125°C to model field performance. Data at exposures of about 1500 h appear to approximate a field life of about ten years for copiers. Using thermal aging, we assessed the factors affecting the contact performance of thin gold. The interactive effect of connector characteristics, wear, and gold thicknesses was evaluated in unlubricated system. Gold thickness on PWB contact fingers ranged from 0-1.0/µm over nickel underplating. For applications requiring 25 insert/ withdraw (I/W) cycles the factors affecting thin gold (0.380-0.750 µm) performance are 1) thickness determines the extent of wear, severity of underlayer exposure, and ultimately the extent of contact degradation, 2) wear on contact springs is more severe than on PWB fingers, 3) connector characteristics such as normal force, contact geometry, and gold thickness affect contact performance. A minimum of 0.380 µm of gold on PWB fingers is recommended. For applications with a lesser number of I/W requirements (<25), flash gold (0.10-0.25 µm) appears promising with two of the three connector types tested even though the finger surfaces appear eroded to the base underlayer. Gold dot (which is very thick) performed acceptably even up to 200 I/W. The advantage of lubrication on thin and flash gold is a logical extension of this study.