Ball grid array (BGA) packages for MPU semiconductor device are considered as replacements of pin grid array packages. This is driven by the requirements for smaller size, thinner thickness, higher wiring density and higher performance. A thermal coefficient of expansion (TCE) mismatch between an A1203 ceramic BGA and a printed wiring board (PWB) causes a large stress in solder joints during a thermal fatigue test. Stress due to the TCE differences is also large in a leadless chip carrier (LCC) package, since this is the same surface mounting type package as BGA. By a finite element method (FEM) simulation, we found that a minimum stress value was obtained when the target TCE value was 9-14ppmrC. We developed a new ceramic material. The TCE and the Young's Modulus of this material are 11.5ppm/"C and 114GPa, respectively. By temperature cycling tests of BGA and LCC, we have confirmed that a relaxation of the thermal stress drastically increased solder joint reliabilities by using the high TCE new ceramic material.

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