DBMI-added underfill can show excellent thermal reliability, due to the superior properties. of CTE, the elastic modulus, and water resistance. When the properties of a DBMI (2wt%)-added underfill were compared with those of a typical underfill (epoxy/anhydride system), the value of CTE was reduced to less than one-half at the solder reflow temperature (about 200 degreesC), the elastic modulus was reduced to less than one-half in the temperature region below Tg, and water resistance improved by 2 times.