Browse Prior Art Database

Controlled Gap TAB Bonding Process

IP.com Disclosure Number: IPCOM000109259D
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 2 page(s) / 80K

Publishing Venue

IBM

Related People

Anderson, S: AUTHOR [+3]

Abstract

Joining of silicon device chips to TAB Tape technology IS often done by a localized thermal process similar to the controlled collapse chip connection (C-4) process. However, the solder ball is, in general, not completely reflowed. The formation of a bond between the lead on the tape and the solder ball on the chip is accomplished before the solder ball collapses completely. Thus, a finite gap is left between the tape and the chip. Such packages are usually encapsulated using liquid encapsulants. If the gap is too small, the encapsulant cannot flow into the gap, thereby causing unreliable connections. The gap may also be uneven due to tilting of the chip.

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Controlled Gap TAB Bonding Process

       Joining of silicon device chips to TAB Tape technology IS
often done by a localized thermal process similar to the controlled
collapse chip connection (C-4) process.  However, the solder ball is,
in general, not completely reflowed.  The formation of a bond between
the lead on the tape and the solder ball on the chip is accomplished
before the solder ball collapses completely.  Thus, a finite gap is
left between the tape and the chip.  Such packages are usually
encapsulated using liquid encapsulants.  If the gap is too small, the
encapsulant cannot flow into the gap, thereby causing unreliable
connections.  The gap may also be uneven due to tilting of the chip.

      The disclosed idea is a controlled gap bonding process using
two cylindrical spacers during the bonding process to limit the size
of the gap.  Fig. 1 illustrates the concept.  The spacers are placed
in locations where they do not interfere with the C-4 pads.  The
spacers are usually available in fiber form.  They are laid in such a
way that there is just enough tension to keep them straight.

      The spacer material chosen is glass, quartz, polyimide, Teflon,
etc.  The material should be electrically insulating.  It should also
be able to withstand the bonding temperatures for a short time.
Bonding using the above process assures a known uniform gap.  The
package may then be encapsulated.

      A polymer fiber with a coefficient of ther...