Thermally Conductive Adhesive with Mixed Silver Fillers
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Solution Overview
Problem
Existing thermally conductive adhesives for bonding semiconductor devices to substrates in plastic packages face limitations in thermal conductivity, typically ranging from 3-4 W/mK, which restricts heat dissipation, and require high processing temperatures incompatible with plastic laminate packages.
Innovation Solution
A thermally conductive adhesive composition comprising 3-15% binder, 0-15% non-reactive solvent, and at least 85% thermally conductive filler, with a blend of silver powders having specific tap densities and surface area-to-mass ratios, along with optional additives, to achieve high thermal conductivity and low processing temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If organic binders are used for die attach in plastic packages, then low processing temperatures are achieved, but thermal conductivity is limited to about 3-4 W/mK
Solution Approach 1:
The patent uses a composite filler system combining silver particles with high thermal conductivity and low density, mixed with ceramic fillers, to achieve high thermal conductivity (greater than 60 W/mK) while maintaining compatibility with organic binders and low processing temperatures suitable for plastic packages
Solution Approach 2:
The patent changes the physical parameters of the filler materials by selecting specific particle size distributions, density ranges, and thermal conductivity values for the silver and ceramic fillers to optimize both thermal performance and processability at low temperatures
2Reliability
If inorganic binders are used for die attach, then high thermal conductivity is achieved (40-65 W/mK), but high processing temperatures are required (about 300°C)
Solution Approach 1:
The patent creates a composite adhesive system combining organic binder with hybrid filler (silver + ceramic) to achieve thermal conductivity comparable to inorganic systems while maintaining the low processing temperature advantage of organic systems
Solution Approach 2:
The patent uses silver filler which provides high thermal conductivity but is more expensive than traditional organic fillers, accepting the higher cost to achieve superior thermal performance without requiring high processing temperatures
3Reliability
If high filler loading is used to increase thermal conductivity, then thermal conductivity improves, but viscosity increases making dispensing difficult
Solution Approach 1:
The patent optimizes the particle size distribution and density parameters of the filler materials to achieve high filler loading (greater than 85% by weight) while controlling the viscosity of the adhesive paste to maintain dispensability
Solution Approach 2:
The patent uses a composite filler system combining low-density silver particles with ceramic fillers to achieve high thermal conductivity at high filler loading while the size distribution and material properties are selected to minimize viscosity increase
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 adhesive achieves thermal conductivity exceeding 60 W/mK and electrical resistivity below 10 μΩcm, with improved storage characteristics and reduced settling and shrinkage, enabling effective heat dissipation and strong bonding at low temperatures.
Implementation Method 1
The thermally conductive filler is a blend of two different powders including a second powder that has a tap density in the range of 3.2-6.9 g/cm3 and a surface area to mass ratio of between 0.59 and 2.19 m2/g and a first powder having a tap density between 4.7 and 8.2 g/cm3 and a surface area to mass ratio between 0.05 and 0.15 m2/g. The adhesive achieves thermal conductivity exceeding 60 W/mK
Implementation Method 2
The adhesive achieves thermal conductivity exceeding 60 W/mK and electrical resistivity below 10 μΩcm
Data Source
AI summary
A thermally conductive adhesive comprises a mixture of at least two types of silver particles including a second type having a surface area to mass ratio in the range of 0.59 m2/g to 2.19 m2/g and a tap density in the range of 3.2 to 6.9 g/cm3 and a first type having a surface area to mass ratio of 0.05 to 0.15 m2/g and a tap density in the range of about 4.7 to 8.2 g/cm3. According to certain embodiments of the invention the first type of silver particles includes oblong silver particles. The thermally conductive adhesive further comprises a binder, and optionally a solvent.