Copper Paste Joining Without Pressurization
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Solution Overview
Problem
Existing methods for joining semiconductor elements without lead solder, such as those using sintered silver or copper, face challenges like increased material costs, production inefficiency, and reduced joining strength due to the need for thermal compression and pressurization, or insufficient densification without pressurization.
Innovation Solution
A copper paste comprising sub-micro and micro copper particles, where the sub-micro particles have a volume-average size of 0.12 µm to 0.8 µm and micro particles have a size of 2 µm to 50 µm, with a combined mass ratio of 80% or greater, allowing for sufficient joining strength without pressurization by suppressing volume shrinkage and maintaining sinterability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sintered silver is used for joining semiconductor elements, then connection reliability is improved, but material cost significantly increases
Solution Approach 1:
The patent replaces expensive silver particles with copper particles that have similar sintering properties. Copper is significantly cheaper than silver while maintaining the ability to form strong, reliable joints through sintering at low temperatures without requiring thermal compression pressurization.
Solution Approach 2:
The patent changes the particle size parameter of copper particles to sub-micro range (0.12 µm to 0.8 µm volume-average size). This specific particle size range enables the copper particles to achieve sufficient densification and joining strength without requiring pressurization, matching the performance advantages previously only available with expensive silver.
2Manufacturing precision
If thermal compression process with pressurization is used for sintering, then densification is improved, but production efficiency deteriorates
Solution Approach 1:
The patent replaces the mechanical pressurization system with a chemistry-based solution using sub-micro copper particles. The small particle size creates sufficient surface energy and contact area to achieve densification through thermal sintering alone, eliminating the need for complex pressurization equipment and improving production efficiency.
Solution Approach 2:
By changing the particle size parameter to sub-micro range (0.12 µm to 0.8 µm), the patent enables densification to occur through thermal energy alone without mechanical pressurization. The high surface area to volume ratio of these particles facilitates rapid sintering and densification at low temperatures, achieving both high densification and production efficiency.
3Ease of manufacture
If copper oxide particles are reduced into copper, then joining material is obtained, but volume shrinkage occurs
Solution Approach 1:
The patent performs preliminary action by using pre-formed sub-micro copper particles instead of starting with copper oxide that requires reduction. The copper particles are provided in their final metallic form, eliminating the reduction step and associated volume shrinkage while maintaining ease of manufacture through simple mixing and sintering processes.
4Productivity
If joining without pressurization is performed, then production efficiency is improved, but joining strength becomes insufficient
Solution Approach 1:
The patent changes the particle size parameter to sub-micro range (0.12 µm to 0.8 µm volume-average size), which provides sufficient surface area and contact points between particles to achieve strong joining through thermal sintering without pressurization. The small particle size enables dense packing and strong interparticle bonding that maintains joining strength while eliminating pressurization requirements.
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 copper paste achieves sufficient joining strength and reliability in semiconductor devices without the need for pressurization, reducing production costs and improving manufacturing stability, while maintaining high thermal conductivity and die shear strength.
Implementation Method 1
forming a sintered copper layer by sintering copper particles
Implementation Method 2
volume shrinkage when copper oxide is reduced into copper is avoided
Data Source
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AI summary
Provided is copper paste for joining including metal particles, and a dispersion medium. The metal particles include sub-micro copper particles having a volume-average particle size of 0.12 µm to 0.8 µm, and micro copper particles having a volume-average particle size of 2 µm to 50 µm, a sum of the amount of the sub-micro copper particles contained and the amount of the micro copper particles contained is 80% by mass or greater on the basis of a total mass of the metal particles, and the amount of the sub-micro copper particles contained is 30% by mass to 90% by mass on the basis of a sum of a mass of the sub-micro copper particles and a mass of the micro copper particles.