Thermal reliability analysis of through-aluminium-nitride-via substrate for high-power LED applications

For the high-power LED applications, TAV (Through-aluminum-nitride-via) substrate with a high thermal conductivity provides better heat dissipation. However, the high thermal expansion coefficient mismatch between the AlN (Aluminum nitride) and copper film may cause the failure, and thus affect the reliability of TAV substrate. The objective of this study is to evaluate the reliability of TAV substrate by measuring its strength and the thermal stress of Cu/AlN bi-material plate during the thermal loading and then by comparing those experimental results with the finite element simulation. Two reliability tests are used in this study: one is TS (Thermal shock, -40°C/125°C), the other is PCT (Pressure cook test). Also, the strength of AlN material is measured by using three-point bending test and point load test. The reliability results show that TAV substrates have delamination and cracks after TS, but there are no failure being found after PCT. The determined strengths of AlN are 350 and 650 (MPa) from three-point bending test and point load test, respectively. The results of thermal deformation measurement show that the bi-material plate has thermal residual stress change after the solder reflow process, also indicating that a linear finite element model with the stress-free temperature at 80 °C and thermal load at ΔT= -110°C and 45 C can reasonably represent the stress state of the TS test from -40 C to 125 C without considering time-dependent effect. The further results of the finite element simulation associated with strength data of AlN successfully describe those of the reliability test.