The formation of decompression bubbles in polyimide adhesive tapes

The formation of decompression bubbles in three-layer polyimide adhesive tapes during die attach is discussed. Bubbles in the tape may be divided into three classes: moisture bubbles, trapped air bubbles and decompression bubbles. The formation of the latter is analyzed experimentally. A possible mechanism for the formation of decompression bubbles is presented. It is shown by a theoretical model, that pressure reservoirs in the die-side adhesive between lead fingers are built up during the bond process. After pressure release, these reservoirs push the base film under lead fingers up and create a tensile stress. Decompression bubbles might be generated by this mechanism.