Elimination of Thermo-Mechanically Driven Circumferential Crack Formation in Copper Through-Glass via Substrate

This work aims at understanding and eliminating thermo-mechanically induced circumferential cracks that form during cooling for a 400 °C annealed copper (Cu) through-glass via (TGV) with a mean outer diameter of 47.5μm , made in Corning HPFS fused silica glass. An exponential dependence was found between Cu metallization thickness and the likelihood for the formation of circumferential cracks. For the conditions used in this study, no cracks were formed in the HPFS fused silica substrate for Cu metallization thicknesses <12μm , however, for thicknesses ≥12μm , circumferential crack formation exponentially increased. From finite element analysis (FEA) studies, the corresponding threshold stresses for the initiation of circumferential stresses at 12μm was predicted to be 140 MPa. Therefore, for 400 °C annealed Cu TGV with a mean outer diameter of 47.5μm , made in HPFS fused silica substrate, circumferential stresses can be eliminated when Cu metallization thickness of less than 12μm is used.