Advances in Hermetic Projection Weld Sealing

Abstract

In this article, we describe a novel process for hermetic projection weld sealing of semiconductor devices, considered by many to be an important legacy technology from decades gone bye, but not particularly relevant in today's arsenal of sealing technologies. We will demonstrate that with appropriate modifications to be described, this technology can used to seal various high power devices as well as high reliability semiconductors, crystals, hybrid packages, medical electronics, photonic devices, automotive electronics, etc. Its features primarily stem from the fact that it can be used to quickly and efficiently produce true hermetic seals in components. The welding is so rapid, that it is essentially a room temperature technology and the equipment is small enough that it can be housed in an atmosphere controlled chamber filled with any gas that is not explosive. Air, Nitrogen, Argon, Helium and their mixtures are the most commonly utilized gasses. The process is so adiabatic that it can be used to seal many liquids also. In some applications the technology competes against pulsed laser welding, but unlike laser welding the entire seal takes place in a few milliseconds because it is a single discharge, component-shaped spot/projection weld, which means that the entire seam is made in a single high speed discharge. So, in the same time that it takes a laser welding machine to make one of the many small overlapping spot welds required to make a seal, the projection welder has completed the entire operation. This process results in minimal stress and distortion, and maximum hermetic properties, strength and reliability, without requiring electroplating or preforms. Because the weld involves the localized high speed melting of metals, it among the highest energy density processes. A concern with the earlier resistance welding technologies has been the expulsion of particulates, both out of, and into the seal. This expulsion has been systemic and becomes progressively worse as the package size increases. In the course of this presentation we will demonstrate how this concern has been dealt with and corrected. Internal dew points can be held to −40 degrees, or lower if required. Other common applications for this technology include sealing and welding of nuts and studs for hermetic applications and sealing of devices for medical applications that must endure autoclave sterilization. In the course of this presentation, we will take you back to the roots of the original resistance welding process as taught by the early process developers so that you will understand how things have changed, and the reasons for the changes.