Temperature Impact on Surface Roughness Modeling for On-Package High Speed Interconnects

The introduction of new dielectrics and adhesion promotion techniques for future interconnect technology generations is one of the key enablers for lower loss and higher bandwidth. However, temperature increase due to active die or environmental factors can cause variations in material properties and loss, which is required to be included in modeling assumptions to be able to set realistic specifications. High temperature can account for significant increase in dielectric loss and decrease in bulk conductivity. The former becomes less critical considering today's on-package high speed interconnect loss is largely dominated by conductors due to thinner substrate. The latter has a loss impact only at low frequencies due to skin effect, and high frequency conductor loss is considerably influenced by surface roughness. This paper presents a systematic methodology to show temperature impact on surface roughness modeling for on-package high speed interconnects. Correlation to high fidelity insertion loss measurements at different temperatures indicates the roughness correction factor extracted at one temperature does not fit all, necessitating an explicit temperature dependence for surface roughness models.