Non-eutectic Solder Alloys for TLPS Conductivity
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Solution Overview
Problem
Current transient liquid phase sintering (TLPS) compositions, particularly those using bismuth-tin alloys, face challenges with brittleness and poor electrical and thermal conductivity, which are exacerbated by mechanical stress and environmental factors, limiting their reliability and performance in electronic applications.
Innovation Solution
The development of TLPS compositions with a low-melting-temperature, non-eutectic alloy system where the proportion of facilitator element bismuth is minimized, utilizing a high percentage of reactive metallic element tin, which reacts with high-melting-point metals like copper to form intermetallics, enhancing conductivity and mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If eutectic bismuth-tin alloy is used in TLPS composition, then melting point is reduced for low temperature processing, but electrical conductivity and thermal conductivity deteriorate
Solution Approach 1:
The patent changes the alloy composition parameters by using non-eutectic ratios of bismuth to tin (specifically 4:1 or 8:1 ratios), which shifts the melting behavior while dramatically improving electrical conductivity. This parameter change resolves the contradiction by finding an optimal balance point that satisfies both low-temperature processing requirements and conductivity needs.
Solution Approach 2:
The patent creates a composite metallurgical structure where non-eutectic bismuth-tin alloy particles interact with copper particles to form intermetallic compounds. This composite approach allows the system to benefit from both the low melting point of the bismuth-tin alloy and the high electrical conductivity of copper-rich intermetallic phases.
2Temperature
If eutectic bismuth-tin alloy is used in TLPS composition, then processing temperature is reduced, but mechanical strength deteriorates under stress
Solution Approach 1:
The patent creates a composite metallurgical structure where non-eutectic bismuth-tin alloy particles interact with copper particles to form intermetallic compounds. This composite approach allows the system to benefit from both the low melting point of the bismuth-tin alloy and the high electrical conductivity of copper-rich intermetallic phases.
Solution Approach 2:
The patent changes the alloy composition parameters by using non-eutectic ratios of bismuth to tin (specifically 4:1 or 8:1 ratios), which shifts the melting behavior while dramatically improving electrical conductivity. This parameter change resolves the contradiction by finding an optimal balance point that satisfies both low-temperature processing requirements and conductivity needs.
3Temperature
If high proportion of bismuth is used in alloy, then melting point is lowered, but brittleness increases
Solution Approach 1:
The patent changes the alloy composition parameters by using non-eutectic ratios of bismuth to tin (specifically 4:1 or 8:1 ratios), which shifts the melting behavior while dramatically improving electrical conductivity. This parameter change resolves the contradiction by finding an optimal balance point that satisfies both low-temperature processing requirements and conductivity needs.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in TLPS compositions that are stronger, more electrically conductive, and better able to withstand mechanical stress, with improved reliability and homogeneity, even at processing temperatures below 250°C, by optimizing the proportion of reactive elements and minimizing detrimental characteristics like brittleness.
Implementation Method 1
In transient liquid phase sintering (TLPS) of powders, the liquid phase only exists for a short period of time as a result of the homogenization of the metals to form a mixture of solid alloy and/or intermetallic species
Implementation Method 2
The liquid phase has a very high solubility in the surrounding solid phase, thus diffusing rapidly into the solid, and eventually solidifying
Implementation Method 3
The reactive element(s) within the relatively low melting alloy then react with the receptive high melting point metal to form new alloy compositions and/or intermetallics
Implementation Method 4
During heating, the adhesive-flux polymer fluxes the metal powders, allowing TLPS to occur
Implementation Method 5
the adhesive-flux chemically binds the resultant metal oxides, rendering them harmless
Implementation Method 6
The formation of intermetallic species may be observed as an exothermic event using DSC
Data Source
AI summary
Transient liquid phase sintering compositions comprising one or more high melting point metals and one or more low melting temperature alloys are known in the art as useful compositions for creating electrically and/or thermally conductive pathways in electronic applications. The present invention provides transient liquid phase sintering compositions that employ non-eutectic low melting temperature alloys for improved sintering and metal matrix properties.