Spherical Filler Adhesive Paste for Thermal Stress Management
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Solution Overview
Problem
Existing thermally conductive adhesives for bonding high-density microcircuit components to substrates face challenges in balancing thermal conductivity with low elastic modulus to absorb shear stresses caused by thermal expansion mismatch, particularly for large area components and high expansion substrates, where prior technologies either had low thermal conductivity or were limited to small area applications.
Innovation Solution
The development of die attach pastes comprising 2-30 weight percent organic polymer resin, up to 30 weight percent fugitive liquid, and 5-98 weight percent inorganic filler, with at least 80% of the filler being spherical particles characterized by round edges, which enhances thermal conductivity and adhesion without inducing excessive stress, and allows for reworkability in multi-chip module technology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If higher modulus polymers are used to increase thermal conductivity, then thermal conductivity is improved, but elastic modulus increases making the adhesive unsuitable for large area components with CTE mismatch
Solution Approach 1:
The patent uses a composite adhesive system combining thermoplastic polymer particles (for flexibility and stress absorption) with thermoset polymer matrix (for structural integrity and thermal conductivity). This composite approach allows the adhesive to achieve both low effective modulus for stress absorption and high thermal conductivity, resolving the contradiction between these two properties in large area die attach applications
Solution Approach 2:
The patent modifies the polymer properties by controlling the glass transition temperature (Tg) of the thermoplastic polymer particles to be below the processing temperature but above service temperature. This parameter change allows the adhesive to be soft during processing for stress absorption, then become rigid at service temperature for structural support, effectively decoupling the modulus requirement during different stages
2Strength
If low modulus adhesives are used to absorb shear stresses in large area components, then stress absorption is improved, but thermal conductivity decreases
Solution Approach 1:
The dual-polymer composite system allows the thermoplastic polymer particles to provide low modulus for stress absorption while the thermoset matrix provides high thermal conductivity. The synergistic combination enables both functions to coexist, with each component contributing its superior property to the overall adhesive performance
Solution Approach 2:
The patent creates local quality differentiation within the adhesive by having thermoplastic polymer particles dispersed throughout the thermoset matrix. The thermoplastic regions locally absorb stress through deformation, while the thermoset regions maintain structural integrity and provide thermal conduction pathways, allowing different regions to perform different functions
3Temperature
If thermoset polymer powders are used for small area components with high thermal conductivity, then thermal conductivity is improved, but reworkability is lost
Solution Approach 1:
The patent introduces dynamic reversibility to the otherwise permanent thermoset system by incorporating thermoplastic polymer particles that can melt and solidify repeatedly. This dynamic property allows the adhesive to be reprocessed multiple times while maintaining the thermal conductivity benefits of the thermoset matrix, enabling reworkability without sacrificing thermal performance
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
The solution provides significantly higher thermal properties and electrical insulation with sufficient adhesion to meet industry standards, enabling the bonding of large area silicon dies to expandable substrates without excessive stress, while maintaining reworkability and compatibility with existing equipment and processes.
Implementation Method 1
The filler is selected to impart to the finished bonding layer desired conductive, resistive or dielectric properties
Implementation Method 2
Low modulus adhesives, described in U.S. Pat. Nos. 6,111,005 and 6,140,402, were lower in thermal conductivity, whereas the higher modulus adhesives described in U.S. Pat. No. 6,265,471 were higher in thermal conductivity. As higher function semiconductor devices grew in size and power, the need also grew for an adhesive with both high thermal conductivity and low modulus. Such adhesives were needed to absorb the bondline shear stresses caused by the thermal expansion mismatch
Implementation Method 3
The carrier maintains all the components in a fluid, uniform mixture, which allows the paste to be applied easily to the die-substrate interface. It also has suitable volatility to migrate from between the die and substrate following heat treatment of the assembly
Implementation Method 4
because the thermoplastic resins can be repeatedly melted and solidified, those constructions prepared using thermoplastic resins are reworkable
Data Source
AI summary
Adhesive paste of polymer resin, fugitive liquid and particulate filler with round edges provides improved performance characteristics.