Pulsed Nd:YAG laser welding of Al-Si controlled expansion alloys and aluminum 4047

Aluminum Silicon alloys are lightweight, high thermal conductivity alloys that are increasingly being used for RF & microwave packages, electro-optical housing, power device base plates and other critical heat sinking applications. The manufacture of these packages requires the Al-Si body containing the electronics to be hermetic sealed using Aluminum 4047 lids. The heat sensitivity of the weld requires the use of a pulsed laser, however welding alloys with a silicon content over 27% becomes increasingly problematic due to cracking of the Al-Si alloy, when using near-standard aluminum laser welding conditions. This is due to the weakness of the Al-Si alloy under the solidification forces of the weld. The thermal performance advantage of the higher silicon content alloys has great potential for significantly improving power handling of the packages. Therefore, a welding process was developed using pulse shaping and a minimized average power approach that eliminated cracking in alloys with up to 40% silicon In addition a novel concept is introduced that enabled crack free welding of 70% silicon alloys.