Electronic package sealing is a tricky process. It may seem straightforward: place components in a metal package and seal, generally using projection spot welding (aka cap welding). It is very important, however, to prevent moisture and oxygen ingress to the package during sealing, which, over time, will damage the sensitive electronic components housed within. This zero-moisture requirement is most commonly achieved by heating the package in an oven and then moving it into a glove box backfilled with nitrogen, removing both moisture and oxygen. With increasing frequency, however, manufacturers are starting to use xenon to backfill the packages. Why? Xenon is a large molecule with good thermal properties, and, because the outer valence shell contains eight electrons, producing a stable, minimum energy configuration in which the outer electrons are tightly bound, it is inert to most common chemical reactions, including combustion.
You may be wondering, “Well, if xenon is so superior, why would anyone continue to use the old oven and nitrogen method?” The answer is found in xenon’s expense – its one huge drawback. Just one liter can cost as much as $150! And many existing processes waste significant quantities of the costly gas during backfilling; any gas that is applied to the system but does not become sealed inside the packages is wasted.
A recent innovation in this arena is the use of a new projection welding technique that dramatically reduces the amount of xenon gas needed to backfill a package. This new cap welding technique (pictured) uses an innovative electrode vacuum and gas backfill system that enables packages to be evacuated, and then filled with gas before being hermetically sealed using projection welding. This process uses 10 to 50 times less gas reducing xenon consumption to as little as 5 cubic centimeters per part.
Low-Volume Xenon Resistance Welding
This technology has been successfully used to package high resolution infrared sensors and is expected to have numerous applications in photonics communications and others, where its efficient use of expensive gases will help reduce costs.