The Thermal Resistance of Solder Joints in High Brightness Light Emitting Diode (HB LED) Packages

We present a framework to calculate the thermal resistance of Au–Sn eutectic solder joint $(R_{\rm th, Au\mathchar"707B Sn\,joint})$ in high brightness light emitting diode (HB LED) packages whose heat extraction capability controls the optical efficiency and reliability of HB LEDs. Using the transient thermal measurement combined with the structure function based analytical method and the finite element method, we find that the thermal conductivity $(k)$ of the thin solder joint becomes significantly smaller than the Au–Sn alloy after joining; hence, $R_{\rm th, Au\mathchar"707B Sn\,joint}$ constitutes a large portion of the total $R_{\rm th}$ of the package $\left(R_{\rm th}^{\rm PKG}\right)$.