In the infant mortality (IM) experiment and the final test (FT) of
IC reliability, the screening capability for the contaminated metal
particles is generally over than the size, W x L ~ 120 x 120 um2. For
the smaller size of these metal particles in ICs, the IM test is inferior.
Using an efficient test metrology combining the IM test and the soak
test to stress the sampled SRAM (Static random access memory) ICs,
the smaller contaminated metal size with scanning electron
microscope was measured, about W x L = 15 x 120 um2. The
composition of metal particle with energy-dispersive X-ray (EDX) in
material analysis exhibited two main peaks attributed to manganese
(Mn) and ferrum (Fe). In speculation, the humidity effect after the
soak test provided the electro-chemical reaction environment
between two neighboring IC pins, spacing 130 um, in the fine pitch
package. The IM test enhancing the electrical field accelerated this
electro-chemical reaction. Therefore, even though the smaller
contaminated metal particles exist, they with the double-combination
test still can be screened out. Due to this effort, the risk selling ICs to
customers is tremendously reduced. The assembly houses after
information feedback are able to trace the root causes in production
line and improve the package yield.