Thermal and mechanical analysis of high-power GaAs flip-chips on CVD diamond substrates

Using numerical, analytical and experimental methods, we evaluate the struc tural and thermal performance of a large, 1 cm x 1 cm, GaAs die, flip-chip attached to 2.54 cm x 2.54 cm diamond substrates. In agreement with numeric al predictions, the GaAs dice's induced stress during the attachment proces s - 37Pb/63Sn solder reflow and high-temperature underfill cure - is below the fracture strength of GaAs. However, as numerically predicted, the stres s in the dice is higher for underfilled chips. This larger stress is measur ed indirectly through stylus profilometry where we experimentally determine the die deflection. The underfilled chips deflect more, which correlates w ith higher die stress. Both analytical and numerical results confirm this c onclusion. Experimental and numerical thermal studies demonstrate the impor tance of the case-to-ambient thermal resistance (theta(ca)). For our packag e, diamond offers tremendous thermal advantage only for theta(ca) values le ss than 1 degrees C W-1 and offers little to no advantage for theta(ca) val ues greater than 10 degrees C W-1. (C) 1999 Elsevier Science S.A. All right s reserved.