Solder Pad Improvement
Original Publication Date: 1985-Nov-01
Included in the Prior Art Database: 2005-Feb-19
The solder joints of semiconductor devices joined to substrates by the "controlled collapse" reflow method are least sensitive to stresses when they are optimized in shape. Optimized shapes can be achieved by elongating the joints beyond their equilibrium molten shape. The elongation is most beneficial in those joints furthest from the stress neutral point (x) of the semiconductor device, where mismatches of the thermal expansion of the device 1 and substrate 2 are worst. Such elongation of joints furthest from the stress neutral point 3 is achieved by contouring the substrate in the chip pad region. The joints near the neutral point are shortened by the raised contour, while those furthest away are proportionally stretched during the molten stage of reflow.