Development of Glass core substrate with the stress analysis, transmission characteristics and reliability
Koji Fujimoto, Yashuhiro Okawa, Takahiro Tai, Satoru Kuramochi
Abstract
We have developed a glass core substrate with three types of TGV vias: fully, partially and conformally filled vias. Thermal stress simulation and thermal cycle tests were conducted to evaluate long-term reliability. In the thermal stress simulation, the heat characteristics and thermal stress for two types of via shapes, straight and X-shape, were analyzed, which indicated that straight vias were advantageous for suppressing heat generation, while X-shape was for mitigating thermal stress. In addition, in order to verify the long-term reliability of TGV core substrates, the three types of TGV via glass core substrates equipped with RDL (Re-Distribution Layer) have been used for thermal cycle tests. The results demonstrated that the resistance values of all via types remained stable after 1,000 cycles. In terms of the TGV glass core characteristics in the high frequency range, the s21 parameters have been measured for the three types of TGV vias (fully, partially and conformally filled vias) with coplanar waveguide structure of wiring. As a result, it was confirmed that the transmission loss (s21) of the TGV via section was extremely low at 30GHz, at 0.23dB for fully, 0.34dB for partially and 0.45dB for conformally filled vias.In conclusion, all the three types of TGV vias glass core substrates have been demonstrated to ensure long-term reliability and low loss characteristics in the high frequency range by thermal stress simulations and experiments, which enables us to select the optimal via structure depending on the application. This result will open the way for promoting the spread of TGV glass core substrates in the future.