Abstract
Semiconductor parts are most often specified for use in the “commercial” 0 to 70°C and, to a lesser extent, in the “industrial” −40 to 85°C operating temperature range. These operating temperature ratings generally satisfy the demands of the dominant semiconductor customers in the computer, telecommunications, and consumer electronic industries. There is also a demand for parts rated beyond the “industrial” temperature range, primarily from the aerospace, military, oil and gas exploration, and automotive industries (−55 to +125C, and even higher). However, the demand has not been large enough to attract or retain the interest of major semiconductor part manufacturers to make these parts. In fact, wide temperature range parts are becoming obsolete and functionally equivalent parts are not replacing them.
Today, for some applications, it is difficult to procure parts that meet engineering, economic, logistical, and technical integration requirements of product manufacturers, and that are rated for an extended temperature range (typically beyond 0 to 70°C). In some applications, the product is available only in the “commercial” temperature range, with commercial packaging. If the product application environment is outside the commercial range, steps must be taken to address this apparent incompatibility. For example, oil exploration and drilling applications require small, advanced communication electronics to work underground at high temperatures where cooling is not possible. This is where uprating comes into play.
Despite the fact that a part can be uprated relative to functional performance at higher than specified temperatures, the original packaging and connectivity may not be reliable with long term exposure to greater than 150C due to Kirkendall voiding and general plastic degradation. However, if the original die with gold wire and aluminum pad bond is extracted from the original plastic commercial package and reassembled into a new ceramic package body, excellent reliability at temperatures exceeding 200C can be achieved. The original gold/aluminum bond interface can be removed and replaced with an electroless nickel, electroless palladium, immersion gold (ENEPIG) process, or a much more economical, automated process can be used. This process is discussed in the accompanying paper and utilizes additive manufacturing to place an aerosol jet silver deposition over the existing gold ball, interfacing with the remaining exposed aluminum. In this manner, a high-reliability connection system can be achieved which is immune to Kirkendall voiding for the temperature range of interest.
Additive manufacturing of an AlSi40 mirror coated with electroless nickel for cryogenic space applications