| 摘要 |
PURPOSE:To prevent a joining material from being broken by a temperature cycle test, by adapting a printed wiring board and a metallic stem such that an absolute value of difference between the maximum coefficient of widthwise thermal expansion of the printed wiring board and a coefficient of thermal expansion of the metallic stem is a specific value or less. CONSTITUTION:A plate-type metallic stem 1 is formed for example of iron having thermal expansion coefficient alphas of about 1.42X10<-5>. A heat dissipating member 2 is disposed at the center thereof and a semiconductor chip 3 is mounted on the top of the heat dissipating member 2. In this case, difference DELTAalphabetween the thermal expansion coefficient of a printed wiring board 5 alphap=1.8X10<-5> and the thermal expansion coefficient of the metallic stem 1alphas=1.42X10<-5> is 0.36X10<-5>. When the printed wiring board 5 and the metallic stem 1 overlap by a maximum width L=40mm and difference in thermal expansion coefficient in this case is represented by X, the following equations are obtained: 0.38X10<-5>X40=XXL, and X=1.52X10<-4>/L. Accordingly, if X is 1.52X10<-4>/L or less, a joining member 8 is not broken by stress in a temperature cycle test because no stress exceeding fatigue limit is generated. |
