Dual-Alloy Solder Paste for Low-Void Reliable Joints
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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 10% or more Sb, where the SnSb-based alloy powder has a higher liquidus temperature than the Sn-based powder, and a content ratio of 75:25 to 95:5, ensuring the SnSb-based alloy powder melts into the Sn-based phase during reflow, thereby improving wettability and reducing void formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Sb-containing alloy powder is used to improve solder joint reliability, then reliability is improved, but liquidus temperature increases requiring higher reflow temperature
Solution Approach 1:
The solder paste is divided into two distinct powder components: Sn-based powder (solidus 217°C, liquidus 220°C) and SnSb-based alloy powder (solidus 228°C, liquidus 256°C). This segmentation allows each component to contribute differently to the soldering process, with the Sn-based powder providing low-temperature melting and the SnSb-based powder providing high-temperature reliability enhancement.
Solution Approach 2:
The invention changes the compositional parameters by controlling Sb content at 10 mass% or more in the SnSb-based alloy powder, and setting the powder content ratio within 75:25 to 95:5 (Sn-based:SnSb-based). This parameter optimization ensures the liquidus temperature remains manageable while achieving the desired reliability improvement through solid solution strengthening and intermetallic compound formation.
2Reliability
If Sb content is increased to improve reliability, then reliability is improved, but wettability deteriorates due to oxidation
Solution Approach 1:
The Sn-based powder acts as an intermediary that protects the SnSb-based alloy powder from oxidation. The Sn-based powder has excellent wettability and reacts preferentially with oxygen, creating a protective environment that prevents Sb oxidation. This intermediary role allows high Sb content (10 mass% or more) to be maintained without the wettability deterioration that would normally occur.
Solution Approach 2:
The invention creates a composite solder paste system combining Sn-based powder and SnSb-based alloy powder in specific ratios (75:25 to 95:5). This composite structure leverages the complementary properties of each component: the Sn-based powder provides oxidation resistance and wettability, while the SnSb-based powder provides reliability enhancement through Sb content of 10 mass% or more.
3Reliability
If SnSb-based alloy powder with high Sb content is used, then reliability is improved, but void generation increases due to poor wettability and oxidation
Solution Approach 1:
The Sn-based powder serves as a protective intermediary that prevents oxidation of the SnSb-based alloy powder during storage and application. By maintaining the SnSb powder in a reduced state, the Sn-based powder ensures that the Sb remains available for beneficial intermetallic compound formation rather than forming harmful oxides that would cause voids.
Solution Approach 2:
The Sn-based powder performs preliminary oxidation during the soldering process, reacting with oxygen before the SnSb-based powder is exposed. This preliminary action protects the SnSb powder from oxidation and ensures proper wetting and void-free solder joint formation, while still allowing the SnSb powder to contribute its reliability-enhancing properties.
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 proposed solder paste effectively suppresses void generation and enhances the reliability of solder joints by maintaining high wettability and compatibility between the alloy powders, even at increased Sb content, ensuring excellent bonding performance without thermal damage to electronic components.
Implementation Method 1
the SnSb-based alloy powder melts into the Sn-based phase during reflow
Implementation Method 2
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
Data Source
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.