Browse Prior Art Database

Controlled Collapse Thermal Joint Between Chip And Heat Sink

IP.com Disclosure Number: IPCOM000102972D
Original Publication Date: 1990-Apr-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 1 page(s) / 54K

Publishing Venue

IBM

Related People

Chu, RC: AUTHOR [+4]

Abstract

This disclosure describes a technique in which the magnitude and range of the thermal contact resistance between an electronic chip and a cooling device is reduced. This is accomplished by using Controlled Collapse Thermal Joints (CCTJ) at the interface of the mating parts. The CCTJs are made of reflowable solder and are deposited onto the back side of a chip, or alternatively, onto the cooling device. The deposition process is similar to the high density circuit I/O connections on the chip front side. The CCTJs are not deposited near the chip edge as there are no active circuits underneath, and a small distance is desired to assure the solder will not flow beyond the edge during the reflow process. The edge of the chip can be coated with a material (i.e., a polymer) in which the solder has poor wetting characteristics.

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Controlled Collapse Thermal Joint Between Chip And Heat Sink

      This disclosure describes a technique in which the magnitude
and range of the thermal contact resistance between an electronic
chip and a cooling device is reduced.  This is accomplished by using
Controlled Collapse Thermal Joints (CCTJ) at the interface of the
mating parts.  The CCTJs are made of reflowable solder and are
deposited onto the back side of a chip, or alternatively, onto the
cooling device. The deposition process is similar to the high density
circuit I/O connections on the chip front side.  The CCTJs are not
deposited near the chip edge as there are no active circuits
underneath, and a small distance is desired to assure the solder will
not flow beyond the edge during the reflow process.  The edge of the
chip can be coated with a material (i.e., a polymer) in which the
solder has poor wetting characteristics.  Once deposited, the cooling
hardware and substrate are assembled and then the entire module is
heated in a controlled manner.  The heating liquifies the solder and
a CCTJ is formed.  The cooling device is typically held against the
chip by a spring and its force determines the final spacing between
the parts. The high thermal conductivity of the solder coupled with
chip area coverage yields a low thermal resistance and a low spread
between best and worst cases.

      A high performance embodiment is achieved by using a staggered
CCTJ array at certain locations and a unifo...