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Compliant Leads for Bonding TAB Surface Mount Components

IP.com Disclosure Number: IPCOM000108363D
Original Publication Date: 1992-May-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Anstrom, JR: AUTHOR

Abstract

TAB (Tape Automated Bonding) components are often soldered to circuit boards using pressure and heat applied by thermode blades. A typical application is shown in Fig. 1 where flat blades apply pressure and heat through the leads to reflow solder on the pads. Mechanical tolerances in tooling, leads, solder, and circuit board thickness combine to form gaps at some pads. Solder thickness is the only significantly compliant element in the system. If the gap size exceeds the solder thickness at a given pad, then little pressure or heat will be transferred. The result is a weak or open connection.

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Compliant Leads for Bonding TAB Surface Mount Components

       TAB (Tape Automated Bonding) components are often
soldered to circuit boards using pressure and heat applied by
thermode blades.  A typical application is shown in Fig. 1 where flat
blades apply pressure and heat through the leads to reflow solder on
the pads.  Mechanical tolerances in tooling, leads, solder, and
circuit board thickness combine to form gaps at some pads.  Solder
thickness is the only significantly compliant element in the system.
If the gap size exceeds the solder thickness at a given pad, then
little pressure or heat will be transferred.  The result is a weak or
open connection.

      This article describes a method of forming a compliant feature
into the TAB leads so that the total compliance at every pad exceeds
the largest vertical tolerance, thereby insuring pressure and heat
transfer.  The compliant feature is 2 to 3 times higher than the
maximum gap.  Fig. 2 shows the compliant leads before and after
bonding.  The leads are formed in an excise and form die
incorporating the compliant lead shape.  The pressure from the
thermode during bonding flattens out the form with forces sufficient
to exceed the yield strength of the lead material.  Every lead can
now transfer pressure and heat through the compacted lead form. Gaps
are eliminated.