Acid Decapsulation of Epoxy Molded IC Packages With Copper Wire Bonds

Epoxy molded IC packages with copper wire bonds are decapsulated using mixtures of concentrated sulfuric acid (20%) and fuming nitric acid in an automatic decapping unit and, observed with minimal corrosion of copper wires (0.8-6 mil sizes) and bond interfaces. To attain maximum cross-linking of the molded epoxies, the post mold cured packages (175 degC for 4 h) were further, aged at high temperature of 150 degC for 1000 h. These packages are decapsulated using mixtures of higher ratio of concentrated sulfuric acid (40%) along with fuming nitric acid. The shear strength of copper wire bonds with 1 mil (25 mum) diameter of the decapsulated unit is higher than 5.5 gf/mil². The present study shows copper stitch bonds to Au, Cu, Pd, and Sn alloy plated surfaces are less affected on decapping, with a few grams of breaking load on stitch pull test, while stitch bonds on silver plated surfaces reveal lifting of wire bonds on decapping