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Browse Prior Art Database

Low Temperature C4 Chip Joining Technique

IP.com Disclosure Number: IPCOM000103346D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 1 page(s) / 48K

Publishing Venue

IBM

Related People

Ingraham, AP: AUTHOR [+2]

Abstract

Disclosed is a technique to be used with the low temperature chip joining process that eliminates chip tilt on C4 chip product with nonfunctional C4s and chip carrier pads (referred to as outriggers). It also provides height control between the chip and carrier by preventing the collapse of the C4 solder connections.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 79% of the total text.

Low Temperature C4 Chip Joining Technique

      Disclosed is a technique to be used with the low temperature
chip joining process that eliminates chip tilt on C4 chip product
with nonfunctional C4s and chip carrier pads (referred to as
outriggers).  It also provides height control between the chip and
carrier by preventing the collapse of the C4 solder connections.

      There are a number of chip products using the C4 technology
that have C4s strategically placed to prevent chip tilt during
assembly.  These C4s and their associated chip carrier pads are
electrically nonfunctional.  Thus, the C4s and pads have no
electrical wiring to functional areas of the chip or chip carrier
I/Os.  When a low melting temperature solder is electroplated onto
the carrier pads, the solder is only deposited on the functional
pads. Nonfunctional pads remain void of solder.  This application of
the low temperature melting solder to the C4 joining pads provides a
method of flip chip joining the C4 solder bumps at temperatures in
the range of 220oC.

      When a chip with C4s is joined to a plated chip carrier, the
low melting temperature solder melts and alloys with the C4 solder.
This melting and alloying causes the chip to collapse slightly, and
at times, this solder bump collapsing does not occur evenly across
the C4 footprint. With the absence of the low melting temperature
solder on the outrigger pads, there is no solder melting (or
alloying).  Therefore, the C4s at the...