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Acid Decapsulation of Epoxy Molded IC Packages With Copper Wire Bonds

 3 years ago
source link: https://ieeexplore.ieee.org/document/1707865
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Acid Decapsulation of Epoxy Molded IC Packages With Copper Wire Bonds
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Abstract:
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/mil 2 . 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
Page(s): 179 - 183
Date of Publication: 09 October 2006
ISSN Information:
INSPEC Accession Number: 9126515
Publisher: IEEE

I. Introduction

Ic packages are largely plastic molded with epoxy compounds, though some are hermetically sealed. Epoxy molding compounds (EMCs) contain epoxy resin (5–20 wt%), brominated epoxy resin (1–5 wt%), phenol-based hardener (5–10 wt%), tertiary amine-phosphorous ({<}1 wt%), silica/alumina/AlN filler (60–80 wt%), epoxy silane ({<}1 wt%), stearic acid ({<}1 wt%), wax (1 wt%), carbon black ({<}1 wt%), silicone or synthetic rubber ({<}1 wt%), etc. Even though EMCs instantaneously cure (cross-link) during molding, some fraction of epoxies remain uncured. Hence, post mold curing is practised at 175°C–200°C for 4–7 h to further polymerise and cross link. To estimate the reliability and understand possible failure modes, the molded and cured packages are to be decapsulated to examine for possible distortion of wire bond loops, short circuiting of the wires, wire debonds, etc., and considered for detailed study in this paper.

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