Measurement of thermal resistance of first-level Cu substrate used in high-power multi-chips LED package

摘要

The thermal resistance of the first-level Cu dissipation substrate (R_(Cu)) with different Cu thickness is investigated in this work. Using the "constant-forward-voltage" method, the thermal resistances of the first-level Cu dissipation substrates (R_(Cu)) were measured against different Cu thickness. In the initial increase in the Cu thickness (up to 0.6 mm), R_(Cu) decreases with the Cu thickness. As the Cu thickness over 0.6 mm, R_(Cu) starts to slightly increase with the Cu thickness. The thermal resistance (R_(Cu)) of the Cu substrate is composed of the z-direction thermal resistance (R_2) and the two-dimensional horizontal spreading resistance (R_s). The initial decrease in R_(Cu) should attribute to the decrease in R_s with the Cu thickness. After the initial increase in R_(Cu). the R_(Cu) would increase and be dominated by the R_z increase with the Cu thickness. Intriguingly, a minimum R_(Cu) value occurs at the Cu thickness of about 0.6 mm. Also, in this paper, we discuss the possible inaccuracy factors of the "constant-forward-voltage" method.