Apparatus and method for detecting leaks in packages

Abstract

This invention detects leaks in small, hermetically sealed packages, especially microchips or other packages of electronic circuits. The invention includes a procedure for detecting fine leaks, and a somewhat different procedure for finding gross leaks. To detect gross leaks, one places the package in a chamber, and varies the pressure in the chamber slightly. If the leak is not too big, one wall of the package, such as its lid, initially becomes deformed, but quickly returns to its original position, due to the leak. If the leak is very large, the wall of the package may not move at all. The position of the wall is monitored with an interferometer, preferably an electronic shearography apparatus. The movements of the wall show whether there is a gross leak. In the fine leak test, the package is placed in the chamber and the pressure is changed substantially, thus causing the walls of the package to deform. If there is a fine leak, a deformed wall gradually returns to its initial position. This gradual return can be measured by the interferometer, and the rate at which the wall returns to its starting position can be used to calculate the leak rate. The interferometer can be located inside the test chamber, or it can be located outside the chamber. At least one additional 'control' package is preferably placed inside the chamber, alongside the test package, to verify the accuracy of the test results.