有关QFN72和CQFN72的热阻计算

摘要

In this paper, analyze of equivalentthermal circuit from junction to package for CQFN72 and QFN 72, as well as simplified calculation method of thermal resistanceθJC from junction to package are introduced. It is concluded that for normal design thermal resistance of CQFN72 is about 1.25 K·W-1, which is twice of QFN72. Main optimization approaches for CQFN thermal design are:to reduce ceramic substrate thickness adequately, add Wpost array into ceramic substrate, die thinning and use Au base solder for die attachment. Forthermal design, 4J29 or 4J42 pieces can't be applied in main heat sink area of CQFN, otherwise thermal resistance will be increased by 10%.%文章介绍了QFN72和CQFN72结到外壳的等效热路分析及结到外壳热阻θJC的简化计算方法，结果表明原设计下CQFN72的热阻约为1.25 K·W-1，几乎是QFN72的一倍。优化CQFN热设计的主要途径是适当减薄陶瓷基板厚度、在陶瓷基板中嵌入钨柱阵列、芯片减薄和采用金基焊料焊接等。从CQFN热设计考虑，不应在主散热区热沉下采用4J29或4J42焊接垫片，否则会使热阻θJC增大10%以上。