Dual-Alloy Solder Paste for Void Suppression and Low-Heat Reflow
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Solution Overview
Problem
Existing solder pastes face challenges in suppressing void generation and ensuring high reliability in solder joints, particularly due to the oxidation of Sb-containing powders leading to reduced wettability and increased reflow temperatures, which can damage electronic components.
Innovation Solution
A solder paste composition comprising Sn-based powder and SnSb-based alloy powder with Sb content of 10% or more, where the Sn-based powder has a lower liquidus temperature than the SnSb-based alloy powder, ensuring compatibility and wettability, and a mass ratio of 75:25 to 95:5 to facilitate void suppression and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SnSb-based alloy powder with 10% or more Sb is used to improve reliability, then solder joint reliability is enhanced, but reflow temperature increases by 5 to 10 °C causing thermal damage to electronic components
Solution Approach 1:
The solder paste is segmented into two distinct powder types: Sn-based powder (75-95 mass%) with lower melting point and SnSb-based alloy powder (5-25 mass%) with higher melting point. This segmentation allows the Sn-based powder to melt first at lower temperature, enabling reflow at temperatures that do not damage electronic components, while the SnSb-based powder provides reliability enhancement through controlled intermetallic compound formation.
Solution Approach 2:
The invention changes the compositional parameters by precisely controlling the Sb content in SnSb-based alloy powder to be 10% or more, and adjusting the mass ratio between Sn-based and SnSb-based powders to 75:25 to 95:5. This parameter optimization ensures that the liquidus temperature difference between the two powders is maintained at 5 to 10 °C, allowing the SnSb-based powder to melt into the Sn phase without requiring excessive reflow temperature.
2Strength
If SnSb-based alloy powder is used to improve reliability through solid solution deposition strengthening, then solder joint strength is enhanced, but oxidation of Sb-containing powder reduces wettability
Solution Approach 1:
The Sn-based powder with lower liquidus temperature acts as a preliminary melting phase that creates a molten Sn phase before the SnSb-based powder fully melts. This preliminary action ensures that the surface is already wetted by molten Sn when the SnSb-based powder begins to melt, preventing oxidation-related wettability issues and ensuring good interfacial bonding.
Solution Approach 2:
The invention creates a composite solder system combining Sn-based powder and SnSb-based alloy powder. The Sn-based powder provides excellent wettability and low-temperature melting, while the SnSb-based powder contributes strength through solid solution deposition strengthening. The composite structure allows both properties to coexist without mutual interference.
3Reliability
If SnSb-based alloy powder with high Sb content is used to suppress void generation, then void formation is reduced, but intermetallic compound formation may occur on powder surface
Solution Approach 1:
By controlling the Sb content to be 10% or more in SnSb-based alloy powder and maintaining the mass ratio of Sn-based to SnSb-based powder at 75:25 to 95:5, the invention optimizes the melting sequence and intermetallic compound formation. The Sn-based powder melts first and suppresses excessive intermetallic compound formation on the SnSb-based powder surface, while the SnSb-based powder still effectively suppresses void generation.
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 effectively suppresses void generation and enhances the reliability of solder joints by ensuring the SnSb-based alloy powder melts into the Sn phase, maintaining high wettability and preventing intermetallic compound formation, thus achieving excellent bonding performance.
Implementation Method 1
the SnSb-based alloy powder melts into the Sn phase
Implementation Method 2
Sb is an element which can improve the reliability of the solder alloy by solid solution deposition strengthening
Implementation Method 3
an intermetallic compound phase is formed on a surface of the second alloy powder by an alloying reaction between the first alloy powder and the second alloy powder
Implementation Method 4
deposition dispersion strengthening under forming fine SnSb-intermetallic compound
Implementation Method 5
the oxidation of Sb-containing powders leading to reduced wettability
Data Source
Figure 1(a)~1(c)
Figure 2(a)~2(c)
Figure 3
AI summary
The present invention provides a solder paste that suppresses generation of voids and has excellent reliability. A solder paste contains Sn-based powder, SnSb-based alloy powder with Sn and 10 mass% or more of Sb, and flux, wherein a liquidus temperature of the SnSb-based alloy powder is higher than a liquidus temperature of the Sn-based powder, and a content ratio of the Sn-based powder and the SnSb-based alloy powder is 75:25 to 95: 5. Preferably, the content ratio of the Sn-based powder to the SnSb-based alloy powder is 80:20 to 90:10.