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The thermal decomposition process of tetraethoxysilane (TEOS) in the gas phase has been studied using a gas-chromatograph mass spectrometer (GC-MS) connected to an electric furnace. TEOS decomposed over 500°C to give a TEOS dimer and trimer. It has been confirmed that formation of TEOS oligomers occurs in the gas phase. Ethylene, acetaldehyde and ethanol were also detected, which are low-molecular-weight products formed by thermal decomposition of TEOS. Ethylene was the principal product among the low-molecular-weight products. This indicates that triethoxysilanol is an intermediate in the formation of TEOS oligomers.

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The reliability of plastic ball grid array (PBGA) package is studied for different materials. The reliability of the PBGA packages using conventional Bismaleimide-Triazine type PWB and our original product PWB that is made of high Tg epoxy resin is evaluated. The PBGA package using our original PWB has a feature of lower warpage for the package, and has similar performance regarding the thermal cycling stability and the endurance during reflow soldering as compared with the PBGA using the conventional PWB. The endurance during reflow soldering for each PBGA is JEDEC STD Method A112 level 3. In order to improve the endurance during reflow soldering, not only PWB materials but also other factors are investigated. As a result, the molding compound with the property of low moisture absorption and the die attach material with the properties of high adhesion strength and fracture strength are effective to improve the endurance property during reflow soldering. The package crack mechanism during reflow soldering can be briefly described as follows. Moisture absorbed from outside the package gathers in a small crack inside the package. This moisture vaporizes at the crack and magnifies the crack. The delamination firstly occurs in gold plated area for wire bonding by thermomechanical stress. And the water vapor pressure accelerates the propagation of delamination or a crack. The delamination propagates in the inner and outer directions along the interfaces of week adhesion strength or through materials of low fracture strength. It becomes clear that the key properties of materials are moisture absorption, adhesion strength and fracture strength.