High-Metal Die Attach Paste for Void-Resistant Sintered Joints
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Solution Overview
Problem
Current semiconductor die attachment materials face limitations in thermal and electrical conductivity, mechanical reliability, and cost-effectiveness, particularly for high-power applications, with issues such as void formation, remelt during thermal excursions, and mismatch in coefficient of thermal expansion between semiconductor dies and packaging elements.
Innovation Solution
A new class of semiconductor assembly materials comprising two or more types of metal particles combined with a fluxing organic vehicle, which react irreversibly at a specific temperature to form a continuous metallurgically interconnected network, achieving a high volume fraction of interconnected metal (>60%) for stable and reliable electrical and thermal performance, while being cost-effective and compatible with existing infrastructure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal-particle-filled polymeric adhesives are used for semiconductor die attachment, then thermal and electrical conduction can be achieved at low power dissipation levels, but the electrical reliability performance is limited and conductivity has an upper limit due to practical limitations on filler amount
Solution Approach 1:
The patent utilizes the phase transition of metal particles from solid to liquid state during thermal processing. The metal particles melt and fuse together to form a monolithic joint, transforming from discrete particles to a continuous metallurgically interconnected network. This phase transition enables achieving high metal volume fractions (>60%) and superior electrical reliability that cannot be obtained with polymeric adhesives limited by filler content.
Solution Approach 2:
The invention creates a composite material system combining metal particles with a fluxing organic vehicle. The fluxing vehicle facilitates metallurgical bonding between metal particles during thermal processing, enabling the formation of a dense, interconnected metal network structure that provides both high conductivity and electrical reliability.
2Ease of manufacture
If lead-free tin-based solders are used for die attachment, then cost-effectiveness is improved compared to lead-based solders, but void formation occurs during thermal processing and the alloy does not exhibit elongation to mitigate CTE mismatch
Solution Approach 1:
The patent changes the processing parameters by controlling the thermal profile to melt the fluxing vehicle and facilitate metallurgical bonding before the metal particles solidify. This parameter control enables the formation of a dense joint with minimal voids and prevents remelting during subsequent thermal excursions, achieving both cost-effectiveness and mechanical reliability.
Solution Approach 2:
The invention utilizes phase transitions of both the fluxing organic vehicle (from liquid to vapor) and the metal particles (from solid to liquid and back to solid) to control the bonding process. The fluxing vehicle evaporates to create a vacuum that pulls metal particles together, while the metal particles melt and solidify to form a strong, void-free joint that resists subsequent thermal stress.
3Reliability
If silver sintering pastes are used for power semiconductor attachment, then thermal and electrical conductivity are improved, but the materials are expensive and do not bond well to many packaging element surfaces
Solution Approach 1:
The patent introduces a fluxing organic vehicle as an intermediary that facilitates bonding between metal particles and packaging element surfaces. The fluxing vehicle chemically interacts with both the metal particles and the substrate surface, creating a bonding bridge that enables adhesion to diverse packaging materials without requiring expensive silver sintering pastes.
Solution Approach 2:
The invention replaces expensive silver sintering pastes with a cost-effective formulation using base metal particles (such as copper or aluminum) combined with a fluxing organic vehicle. The fluxing vehicle serves its purpose during the bonding process and is consumed/evaporated, leaving behind a strong metal-to-metal bond that achieves the required thermal and electrical conductivity at lower cost.
4Reliability
If high metal filler content is used in conductive adhesives to improve conductivity, then thermal and electrical conduction efficiency increases, but the mechanical integrity of the adhesive is compromised
Solution Approach 1:
The patent exploits the phase transition of metal particles from solid to liquid during thermal processing. When metal particles melt, they naturally fuse together to form a continuous network structure that is inherently mechanically strong. This eliminates the need for polymer adhesive matrices that would compromise mechanical integrity when containing high filler loads, as the metallurgically bonded metal network provides both high conductivity and superior mechanical strength.
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 superior mechanical, electrical, and thermal interconnection performance with low void volume and high reliability, overcoming the limitations of prior art materials by forming a dense, interconnected metal network that maintains stability across multiple thermal excursions and standard industry reliability testing.
Implementation Method 1
two or more types of metal particles combined with a fluxing organic vehicle, which react irreversibly at a specific temperature to form a continuous metallurgically interconnected network
Implementation Method 2
The fluxing vehicle of the present invention serves to deliver the metal particles in a paste form, facilitates the reaction between the metal particles, and largely volatilizes during the thermal process
Data Source
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AI summary
A semiconductor die attach composition with greater than 60% metal volume after thermal reaction having: (a) 80-99 wt% of a mixture of metal particles comprising 30-70 wt% of a lead-free low melting point (LMP) particle composition comprising at least one LMP metal Y that melts below a temperature Tl, and 25-70 wt% of a high melting point (HMP) particle composition comprising at least one metallic element M that is reactive with the at least one LMP metal Y at a process temperature Tl, wherein the ratio of wt% of M to wt% of Y is at least 1.0; (b) 0-30 wt% of a metal powder additive A; and (c) a fluxing vehicle having a volatile portion, and not more than 50 wt% of a non-volatile portion.