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Method for the addition of particulates and/or platelets to solder thermal interface material for enhanced electronic package performance

IP.com Disclosure Number: IPCOM000005052D
Publication Date: 2001-Aug-01
Document File: 4 page(s) / 40K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for the addition of particulates and/or platelets to solder thermal interface material for enhanced electronic package performance. Benefits include improved thermal performance and reliability, and improved assembly-line yield.

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Method for the addition of particulates and/or platelets to solder thermal interface material for enhanced electronic package performance

Disclosed is a method for the addition of particulates and/or platelets to solder thermal interface material for enhanced electronic package performance. Benefits include improved thermal performance and reliability, and improved assembly-line yield.

Description

The disclosed method concerns the addition of filler materials (such as particles and platelets) to solder thermal interface materials (TIM) for electronic packaging applications.

Chemical additions can be made to the either the filler or the solder to enhance adhesion of the phases if needed. The addition of the filler to the solder can be achieved by a number of methods, including (but not limited to):

Powder metallurgy

Liquid metal infiltration

Direct mixing into the melt

Placing particles directly on the solder prior to reflow

Reactive metallurgy

Particles and platelet materials could include:

Metals such as tungsten, molybdenum, nickel, copper, aluminum, silver, gold

Ceramics such as SiC

Diamond grit/powder

Graphite

Polymers

The filler size and type can be optimized to meet the packaging requirements. For example (see Figure 1), the addition of larger particles can control the solder TIM bondline thickness (BLT). For example, a solder containing tungsten particles can serve as a thermal interface material in an electronic package. Solders, in general, have relatively high CTEs and reasonable thermal conductivities. In contrast, tungsten has a low CTE of 4.4 PPM/C and a high thermal conductivity of 163 W/mC. In addition, the particles can act as spacers. If they are added in large enough quantity, they increase the thermal conductivity of the STIM and decrease the CTE.

Smaller particles can be used to increase creep resistance of the solder TIM and to lower the STIM coefficient of thermal expansion (see Figure 2). A multimodal distribution may be used when both effects or a higher packing density is required. The large particles help control the BLT.

A fine filler (see Figure 3) can increase thermal conductivity, increase creep resistance, and lower the STIM coefficient of thermal expansion. This filler could have any particle size distribution.

The disclosed method can, in principle, be applied to all solder TIMs including pure metals and alloys and all suitable particulates or platelets. Rare earth elements, or other reactive additions/modifications can be used improve bonding and wetability of the respective components as well as to oxides and nitrides.

Benefits

The disclosed method presents several advantages over conventional solutions. Control of BLT thickness though the filler results in a more reproducible package geometry, more reproducible thermal performance and more predictable performance in reliability testing.

This method of thickness control requires less stringent IHS dimensional positioning control during assembly and results in less expensive robots an...