| Abstract Scope |
Welding of sheet material requires very careful control as small fluctuations during the process can lead to periodic blow-through or lack of penetration defects. Welding of sheets of gold or copper, found in high reliability electronic applications, are even more difficult as absorbance in the infrared (IR) wavelength is approximately 2 and 5% respectively. Green laser welding, a previous technology, resulted in an increase of absorptivity, but there is large pulse to pulse variation, which can lead to pinhole weld defects. Blue laser welding, a relatively new technology, is more stable than green lasers and shows great promise for welding of these IR reflective metals. Under blue light, the absorbance for gold and copper increase to 67 and 70%. Foil welding does require advanced fixturing to ensure intimate contact between the copper sheets. To characterize blue laser welding, numerous welds were made on copper samples and characterized. Various parameter spaces were explored such as: pulse welds and continuous welds, welds under argon and air, welds with contamination, and welds with point defects. Temperature measurements were taken to characterize the heat distribution. The strength of the welds was measured and correlated to microstructural features that were characterized using µ-CT and SEM. From these results came a greater understanding of the copper welding process, identification of weld defects, and fixturing for sheet welding. This knowledge leads to a greater certainty for qualifying blue laser welding processes. |