Development of Glass Core Substrates for Long-Term Reliability Under Thermal Stress

In recent years, the characteristics required for mounting substrates for AI semiconductor manufacturing, which is developing rapidly, are large area, high rigidity, flatness, low thermal expansion coefficient, and low loss in the high frequency range. The solution that meets these requirements is a glass substrate and there are moves towards practical application of this around the world. To be adopted as a mounting substrate for semiconductors, it is essential to ensure long-term reliability. Especially stress relaxation when heat is applied is particularly important in designing the substrate. In this study, thermal stress simulation showed that inserting a resin layer between the glass core substrate and the copper wiring directly above it reduced the maximum stress applied to the glass substrate when 100°C heat was applied, from 120 to 90 MPa. Based on these results, we fabricated a glass core substrate with wiring and a resin layer and conducted a thermal cycle test (-55°C to 150°C, 1000 cycles, 20 TSVs in Daisy Chain). The results confirmed that the resistance change was within ± 1% for all 18 chips. We also used thermal stress simulation to calculate how stress changes in various glass substrate structures at an applied temperature of 260°C. The results showed that stress decreased as the via diameter increased and stress increased as the substrate thickness increased. It was also indicated that the X-shaped TGV was more effective at reducing stress than the straight TGV, and that the conformal type had less stress than the filled type in via filling. These results will help to move forward the practical application of TGV substrates, as it will be possible to choose from a variety of TGV structures.