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METHOD OF SOLVING COPPER WIRE BOND HAST FAILURES FROM FOREIGN MATTER IN THE MOLD COMPOUND

IP.com Disclosure Number: IPCOM000230893D
Publication Date: 2013-Sep-17
Document File: 3 page(s) / 789K

Publishing Venue

The IP.com Prior Art Database

Abstract

The size of insoluble foreign particles in epoxy mold compounds must be less than the ball bond and wire bond gap to prevent stress at the ball bond that could displace the mold compound thermal-mechanical behavior at the localized region to allow shorter migration path of corrosive ions.

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Method of solving copper wire bond HAST failures from foreign matter in the mold compound

Abstract 

The size of insoluble foreign particles in epoxy mold compounds must be less than the ball bond and wire bond gap to prevent stress at the ball bond that could displace the mold compound thermal-mechanical behavior at the localized region to allow shorter migration path of corrosive ions.

Body

An electrical open failure was encountered after biased HAST 196 hours (130C/85% RH) on a C90FG device using EMC B compound in an LQFP type package.  The same failure mechanism also was observed on a C55 device using EMC A compound in an LQFP type package.  All of the failures were VSS opens, where on a single failed part / a single signal pin failed.  The product HAST reliability suggests this phenomenon is a low failure rate occurrence.  However it is still critical to C55 product, which is required to pass Biased HAST 192 hour.  Failure analysis found foreign material in the mold compounds A / B adjacent to the failing ball bond, where large foreign matter particle (~ 100 microns) was detected in the material.  For this case, the foreign matter particle was used as a catalyst in the mold compound for curing.  The large foreign particle at the Cu ball bond under extended biased HAST displaces the silica filler around the ball bond, which increases the stress at the bond, thereby weakening the bond interface to yield a crack allowing  the path for Cl ions to migrate under the ball  bond resulting in open Biase...