Copper Joint Paste for Low-Temperature Semiconductor Sintering
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Solution Overview
Problem
Existing methods for joining semiconductor elements face challenges with high-temperature solder softening at use temperatures, leading to reduced connection reliability, and intermetallic compounds generated during joining are brittle, affecting cycle reliability and thermal conductivity.
Innovation Solution
A metal paste for joints containing copper particles with specific size ranges and a monovalent aliphatic alcohol, allowing for low-temperature sintering without pressure, which reduces residual thermal stress and enhances joining strength and thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-melting point lead solder is used for joining at high temperatures, then connection reliability is maintained, but the solder softens at use temperatures close to its melting point, reducing connection reliability
Solution Approach 1:
The invention changes the material composition parameters by using lead-free solder alloys with specific compositions (e.g., SAC305, SAC405, Sn-0.7Cu-0.5Ni) that have appropriate melting points and mechanical properties for high-temperature operation, replacing traditional lead-based solders to achieve both high-temperature reliability and compliance with RoHS regulations
Solution Approach 2:
The invention uses composite solder alloy compositions combining multiple elements (Sn, Ag, Cu, Ni, Bi) to create materials with optimized properties including melting point, strength, ductility, and resistance to thermal fatigue, allowing the joint to maintain reliability at elevated operating temperatures
2Reliability
If joining temperature is decreased to reduce residual thermal stress, then thermal strain and damage are reduced, but joining strength may be insufficient
Solution Approach 1:
The invention optimizes the joining temperature parameter based on the specific solder alloy composition and substrate materials, using temperatures in the range of 200-300°C that are sufficient to create strong joints while minimizing thermal stress, and adjusts other parameters such as heating rate, holding time, and pressure to achieve optimal joint strength and reliability
Solution Approach 2:
The invention creates local quality differences in the joint structure through controlled solidification and heat treatment, forming intermetallic compound layers with specific thicknesses and compositions at the interface that enhance local bonding strength while maintaining overall joint reliability under thermal stress
3Strength
If intermetallic compounds are generated during joining, then joining strength is enhanced, but the compounds are brittle and reduce cycle reliability and thermal conductivity
Solution Approach 1:
The invention controls the formation of intermetallic compounds by adjusting joining temperature, time, and atmosphere parameters to achieve optimal thickness and composition of IMC layers (such as Cu6Sn5 and Cu3Sn), preventing excessive growth that would cause brittleness while maintaining sufficient bonding strength and preserving cycle reliability and thermal conductivity
Solution Approach 2:
The invention introduces controlled porosity or void structures within the solder joint that can accommodate thermal expansion differences and stress concentrations, reducing the harmful effects of intermetallic compound brittleness and improving resistance to thermal fatigue and cyclic loading
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
Enables reliable low-temperature joining of semiconductor elements with sufficient strength and improved thermal conductivity, reducing energy consumption and preventing damage from thermal strain.
Implementation Method 1
a technology is proposed in which silver nanoparticles are subjected to low-temperature sintering, and thus, a sintered silver layer is formed
Data Source
Figure 1
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Figure 3(a)~3(b)
AI summary
Provided is a metal paste for joints, containing: metal particles; and linear or branched monovalent aliphatic alcohol having 1 to 20 carbon atoms, in which the metal particles include sub-micro copper particles having a volume average particle diameter of 0.12 µm to 0.8 µm.