Determination of Package Die Temperature in a Set-Top Box Using JEDEC Thermal Metrics

This case study shows that neither the junction-to-ambient thermal resistance nor the junction-to-case thermal resistance will predict the die temperature of a package in a set top box application with reasonable accuracy. Instead junction-to-board thermal resistance, θ_JB, or junction-to-board thermal parameter, Ψ_JB, is proposed as the proper metric to be used to estimate die temperature under steady state conditions. Packages used in this work were 352 PBGA and 272 PBGA mounted on a 2-layer PCB which was designed to simulate a generic application. Nearby components with significant power dissipation were simulated using heater strips with specified power inputs. In the study, the die size varied from 7.1 mm × 7.1 mm to 11 mm × 11 mm. Measurements were taken in a generic set top box at various power inputs to the packages via thermal die and to the PCB via heaters.