Inspection of laser welded hermitically sealed packages using eddy current flaw detection method

This paper discuss a novel technique that employs eddy current test method to check for defects such as cracks, pin holes and sites of porous weld in laser welded, hermitically sealed aluminium alloy packages incorporating GaAs based bare Monolithic Microwave Integrated Circuits(MMICs). Two laser welded aluminium alloy packages whose designs were optimized for butt welding configuration are considered here and the application of eddy current test method to detect defects that can serve as potential leak channels is demonstrated. Traditionally, visual inspection followed by helium fine leak test in conjunction with the gross bubble test is employed to check the hermiticity of the packages. Visual inspection method suffers from inherent deficiencies as it cannot detect near surface and minute cracks that can serve as potential leak channels, thus causing the packages to fail in leak test. We have successfully demonstrated the application of eddy current test method to detect such defects thus giving an excellent idea about the quality of the seal. This will allow to attempt possible reworks before going for the leak test thus saving time and cost.