Investigation of large area solder joints in temperature shock tests

Large ceramic-based substrates (Si3N4-AMB and Al2O3-DCB) up to the size of 48 cm² were mounted onto heatsinks by soldering using SnAg3Cu0.5 preforms of 300 µm thickness. The heatsinks were made of either an Al alloy, Cu or AlSiC, a composite material made of an Al matrix with SiC particles embedded. The samples were subjected to thermal shock cycles between-55°C and +125°C. The crack propagation due to solder fatigue was analyzed using ultrasonic and X-ray microscopy. The warpage was monitored, too. It shows that samples made of AMB substrates and AlSiC heatsinks markedly outperform those made using Al alloy and pure Cu heatsinks. By minimizing the CTE mismatch of the material stack, yet the largest bonding areas show no damage under the substrate even after 1500 thermal shock cycles.