Abstract
Two types of 0.5 mm thick UTSOP's (Ultra Thin Small Outline Packages) were developed, a conventional type with die pad, and a LOC(Lead on Chip) type. In both types, the die pad or the backside of the chip is exposed to the bottom of the package. In order to accomplish 0.5 mm thickness of the package, high strength alloy lead frames with 100 /spl mu/m thickness, and low-loop wire-bonding technology were used. The chip thicknesses in the conventional type, and the LOC type were 200 /spl mu/m and 300 /spl mu/m, respectively. Because, from the package structural point of view, the top half and the bottom half of the packages were unbalanced in terms of thermal expansion coefficients, the warpage of the packages was an expected problem. However, the warpage was reduced below 40 /spl mu/m by the material changes and the modification of lead frame design. Various molding compounds with different characteristics, and two kinds of lead frame materials were tried. Package reliability of the UTSOP's were evaluated.
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