Flip-chip bonding technique using indium bump for hybrid IRFPA(Infrared Focal Plane Array) is studied. The level of flatness of two chips that will be bonded is related to flip-chip bonding yield, and the mismatch in the coefficients of thermal expansion between HgCdTe and silicon is related to flip-chip bonding reliability. To improve flip-chip bonding yield and reliability, it is found that the indium bump should be high over 20um. The three methods of bump formation, lift-off, etch-back, and shadow mask method are studied and found not to be adequate to form high indium bumps. However, using the ICP $H_2$ plasma, indium bumps made by lift-off can be reflowed to hemispheres and the height of bump is increased from 10um to over 20um. In addition, the surface morphology of them is improved after the reflow. The structure of UBM(Under Base Metal) is studied. Indium bumps can be aligned precisely into base pad metal. The characteristics of reflowed bump is examined. It is shown that the reflowed bump is more stronger than the bump made by lift-off against shear strain. The proposed method of $H_2$ plasma reflow of indium bump is expected to enhance the flip-chip bonding yield and reliability of IRFPA's.
