Sintering Paste for Semiconductor Die Attach
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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 die 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, and are processed to minimize voids and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal-filled polymeric adhesives with high volume fraction of metal filler (approx. 30%) are used to achieve low electrical resistivity and high thermal conductivity, then electrical and thermal conduction performance is improved, but mechanical integrity of the adhesive is compromised and electrical reliability performance is limited
Solution Approach 1:
The invention changes the fundamental parameter of metal filler volume fraction from approximately 30% in conventional adhesives to greater than 60% in the sintering paste. This parameter change transforms the material from an adhesive-dependent composite to a metal-dominant sintered joint, fundamentally improving electrical reliability while maintaining mechanical integrity through the metallurgical bonding mechanism rather than polymer adhesion
Solution Approach 2:
The invention utilizes phase transition of the flux vehicle from liquid to vapor during thermal processing. The flux vehicle evaporates completely, leaving behind only the metal particles that sinter together. This phase transition removes the mechanical weakness of polymer adhesives while maintaining the conductive metal network, resolving the contradiction between mechanical integrity and electrical reliability
Solution Approach 3:
The invention creates a composite material system consisting of metal particles (greater than 60% volume fraction) and flux vehicle. The metal particles form the structural and conductive framework, while the flux vehicle provides temporary processing assistance. This composite structure enables high electrical reliability through the dominant metal phase while the sintering process ensures mechanical integrity through metallurgical bonding
2Reliability
If lead-free tin-based solders are used to replace lead-based solders for die attachment, then cost and environmental compliance are improved, but the alloys do not exhibit elongation characteristic and cannot effectively mitigate CTE mismatch, and void pockets form during thermal processing
Solution Approach 1:
The invention changes the processing temperature parameter to be below the melting point of the metal particles. This allows the metal particles to sinter together through diffusion and metallurgical bonding without melting and forming large void pockets. The resulting joint maintains ductility and elongation capability while effectively mitigating CTE mismatch, resolving the contradiction between reliability and power handling
Solution Approach 2:
The invention utilizes controlled phase transition of the flux vehicle from liquid to vapor, while the metal particles remain in solid phase throughout processing. This prevents the metal particles from melting and forming large centralized void pockets, maintaining a dense joint structure with high elongation capability and effective CTE mismatch mitigation
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 invention changes the composition parameters to use common, inexpensive metals such as tin, copper, and aluminum in various combinations. These metals provide adequate thermal and electrical conductivity for power semiconductor applications while being significantly more cost-effective than silver. The flux vehicle formulation is optimized to ensure good bonding to diverse packaging element surfaces, resolving the contradiction between reliability and ease of manufacture
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 cost-effectiveness, overcoming the limitations of existing materials by forming a robust, high-melting-point alloy network that maintains integrity through multiple thermal excursions.
Implementation Method 1
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
Implementation Method 2
processed to minimize voids and cost
Data Source
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 T1, 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 T1, 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.