Browse Prior Art Database

Localized Control of Thermal Expansion in Electronic Assembly

IP.com Disclosure Number: IPCOM000117448D
Original Publication Date: 1996-Feb-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Chang, CS: AUTHOR [+3]

Abstract

Disclosed is a method to control the Coefficient of Thermal Expansion (CTE) at specific locations of an assembly to certain describe values. This method allows flexibility in the choices of location as well as allowing the choice of CTE values to be set at the optimum range.

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This is the abbreviated version, containing approximately 96% of the total text.

Localized Control of Thermal Expansion in Electronic Assembly

      Disclosed is a method to control the Coefficient of Thermal
Expansion (CTE) at specific locations of an assembly to certain
describe values.  This method allows flexibility in the choices of
location as well as allowing the choice of CTE values to be set at
the optimum range.

      One example is an IC chip mounted on a chip carrier with wire
bonded connections between chip and carrier I/Os and an encapsulant
for environmental protection.  Since the CTE of the encapsulant is
usually higher than that of the chip, there will be significant
mechanical stress at the wire-to-wire chip joining points.  It is
disclosed that a thin slab of glass-ceramic, oxide coated silicon or
some other low CTE material that is electrically isolated, be placed
on top of the encapsulant.  In this assembly the encapsulant is
sandwiched between the chip and insulated slab.  If the top slab
material is chosen with a CTE value close to that of the chip, the
overall CTE of the assembly can be designed to significantly reduce
the mechanical stress of the wire-to-chip joint.

      One further application of this technique is to use the same
principle to reduce the mechanical stress found in solder joints of
components attached to carriers using Outer-Lead-Bonds (OLB).  By
selecting an insulated material having the correct CTE value and
cutting it into a shape similar to the area of the OLB line of solder
connection, a...