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Method for nanoparticle-reinforced low temperature solder matrix composites for enhanced creep resistance

IP.com Disclosure Number: IPCOM000101581D
Publication Date: 2005-Mar-16
Document File: 3 page(s) / 40K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for nanoparticle-reinforced low temperature solder matrix composites for enhanced creep resistance. Benefits include improved functionality and improved reliability.

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Method for nanoparticle-reinforced low temperature solder matrix composites for enhanced creep resistance

Disclosed is a method for nanoparticle-reinforced low temperature solder matrix composites for enhanced creep resistance. Benefits include improved functionality and improved reliability.

Background

      Due to low melting points and high homologous temperatures, indium (In) and tin (Sn) based solders are highly susceptible to creep and fatigue at standard operating temperatures. As a result, solder joint reliability is greatly decreased during temperature cycling. Multiple reflows can further accelerate solder joint failure through microstructural coarsening. The conventional solution is to add underfill.

              Because of the high homologous temperature of the soft solder alloys (>0.5), grain growth is rapid at operating temperatures (~90-100ºC).

              A large difference in the coefficient of thermal expansion (CTE) occurs between the silicon die and the copper integrated heatsink (IHS). As a result, the assembled package warps when the chip is powered-on or thermally cycled. The warpage results in a tensile force at the solder to IHS interface. At elevated temperatures during temperature cycling, creep occurs due to the enhanced dislocation. To increase the creep resistance of an alloy, the dislocations must to be blocked (see Figure 1).

              The addition of precipitates strengthens matrix material. At low temperature, the precipitate is most effective in interfering with the motion of dislocations when the particle size is very small and the particles are widely distributed in large numbers throughout the lattice. However, at elevated temperatures, this technique is unstable because at elevated temperatures the precipitate either goes back into solution or is overaged.

General description

      The disclosed method is the addition of nanoparticles to solder capable of grain-boundary pinning or precipitation hardening. The method controls solder joint microstructure formation during reflow. The result is advantageous in many package applications that...