For applications using Wide Band Gap (WBG) semiconductors, and for electronics for down-hole drilling, oil exploration, geothermal energy generation and power electronics, there is a growing need for capacitors that have robust reliability at temperatures of 125°C, 150°C or above. The development of more energy efficient power converters and inverters based on WBG semiconductors is driving the adoption of higher temperatures in a growing number of power electronics and automotive circuits since these operate at higher junction temperatures than traditional silicon. This has led to a growing need for high temperature capacitors with robust reliability. A Class-I C0G dielectric has been developed using Nickel electrodes for high temperature application up to 200°C and beyond. Since it is a paraelectric linear dielectric, these capacitors exhibit highly stable capacitance as a function of temperature and voltage, possess low loss (DF) and can conduct high RMS currents with a low temperature rise compared to other capacitor solutions. To maximize the capacitance density and achieve a high degree of mechanical robustness, stacks and leaded form factors are commonly needed. Materials for assembly of stacks are of interest due to the challenge of higher cost of attachment materials based on gold-solders or nano-silver pastes, as well as due to the presence of lead (Pb) in common high melting point (HMP) solders. This paper will report electrical properties and reliability test data on these Class-I C0G ceramic capacitors and stacks at high temperatures. It will also review thermal robustness and electrical characteristics of stacks assembled using Pb-free transient liquid phase sintering (TLPS) materials based on Sn-Cu and In-Ag.