Cu-Co Particle Solder Preform for Heat-Resistant Bonding
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Solution Overview
Problem
Existing solder alloys used in bonding electronic components face issues with heat resistance, thermal conductivity, and reliability, particularly when used with high-temperature SiC semiconductors and in communication terminals, due to inadequate formation of intermetallic compounds and poor wetting properties of high-melting point metal particles.
Innovation Solution
A preformed solder composed of a lead-free alloy mainly containing Sn with Cu—Ni or Cu—Co alloy particles, where (Cu,Ni)6Sn5 is formed on the surface of the metal particles, enhancing thermal conductivity and reliability by facilitating rapid intermetallic compound formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If high-melting point metal particles (Ni or Cu) are dispersed in lead-free solder alloy, then thermal conductivity is improved, but intermetallic compound formation is insufficient and wetting properties are poor
Solution Approach 1:
The invention uses a composite metal particle structure consisting of a high-melting point metal core (Ni or Cu) coated with a low-melting point metal shell (Sn, In, or their alloys). This composite structure combines the thermal conductivity benefits of high-melting point metals with the excellent wetting and intermetallic compound formation capabilities of low-melting point metals, resolving the contradiction between heat resistance and reliability.
Solution Approach 2:
The invention changes the surface composition parameter of the metal particles by coating high-melting point metal cores with low-melting point metal shells. This parameter change allows the particles to maintain high thermal conductivity from the core while achieving good wetting properties and intermetallic compound formation through the shell, thus resolving the contradiction.
2Ease of manufacture
If solder paste or solder sheet is used for bonding electronic components, then bonding process is simple, but solder may be pushed out due to own weight resulting in decreased bonding strength
Solution Approach 1:
The invention applies preliminary action by pre-forming the solder into specific shapes (solder bumps, solder balls, or solder sheets with controlled thickness) that maintain their structural integrity during bonding. The low-melting point metal shell on the particle surfaces facilitates reliable bonding before the solder is pushed out, ensuring adequate bonding strength is achieved during the bonding process.
3Manufacturing precision
If solder bump is used to bond electronic part to wiring substrate, then bonding precision is improved, but bump height becomes irregular causing slanting bond and thermal stress
Solution Approach 1:
The composite metal particle structure with low-melting point metal shells ensures uniform melting behavior and consistent intermetallic compound formation across all particles. This leads to more uniform bump heights and reduces slanting bonds, resolving the contradiction between bonding precision and bump height uniformity.
4Temperature
If electronic part is exposed to high temperature during operation, then device functionality is maintained, but solder bonded portion becomes soft causing height irregularity and poor bonding
Solution Approach 1:
The invention changes the melting point parameter of the solder particles by coating high-melting point metal cores with low-melting point metal shells. The low-melting point shells provide reliable initial bonding and intermetallic compound formation, while the high-melting point cores maintain structural integrity and thermal conductivity at high operating temperatures, resolving the contradiction between operating temperature and bonded portion 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 solder bonded portion exhibits improved heat resistance, thermal conductivity, and reliability, suppressing void generation and maintaining structural integrity under high temperatures, suitable for bonding components like power modules and communication terminals.
Implementation Method 1
(Cu,Ni)6Sn5 is formed on the surface of the metal particles
Implementation Method 2
enhancing thermal conductivity and reliability by facilitating rapid intermetallic compound formation
Data Source
AI summary
Provided is a preformed solder including a lead-free solder mainly composed of Sn and a metal particle with a melting point higher than a melting point of the lead-free solder. The metal particle is formed of a Cu—Ni alloy having a Ni content of 0.1 to 90% by mass, or a Cu—Co alloy having a Co content of 0.1 to 90% by mass, and the lead-free solder may contain Ni when the metal particle is formed of the Cu—Ni alloy, or contains Ni when the metal particle is formed of the Cu—Co alloy, and (Cu,Ni)6Sn5 is formed on a surface of the metal particle. With this preformed solder, a bonded portion having heat resistance, thermal conductivity, and reliability higher than ever can be formed.