A method of predicting the effect of blob test in GSP sample testing is
disclosed. The method includes extracting failure density maps from sample
test results, where the density of any failed cell is expressed as the
number of adjacent failing sample cells; determining the existence of
local concentration of bad chips (blobs) as the occurrence of a detection
density value above a threshold which can be adjusted to control the
sensitivity of blob detection; determining the extent of such identified
blobs as the occurrence of adjacent cells with density values above an
inclusion threshold, which can be adjusted to control the sensitivity of
blob extent determination; calculating a residual sample yield Y.sub.NB
for the areas outside blob regions using the total sample cell count
N.sub.S, the passing cell count N.sub.G, and the count of cells in blobs
N.sub.B by equation:
##EQU1##
and re-evaluating the decision of whether 100% probe test is required or if
the cost savings can still be realized by performing only blob test.
