Solder Paste Composition for Thermal Cycling and Joint Crack Resistance
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Solution Overview
Problem
Existing solder pastes fail to simultaneously withstand severe temperature cycles and external forces, leading to cracking and malfunction in on-board electronic circuits, particularly in vehicles, due to inadequate viscosity control and composition of solder alloys.
Innovation Solution
A solder paste comprising a solder alloy with specific compositions of Sn, Ag, Cu, Bi, Sb, Ni, and As, which forms fine Sn-Sb intermetallic compounds and an As-concentrated layer, providing solid-solution and precipitation strengthening, while maintaining excellent wettability and viscosity stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional solder alloys are used in on-board electronic circuits, then the circuits can be manufactured with standard processes, but the solder joints develop cracks under severe temperature cycles between -40°C and +125°C
Solution Approach 1:
The patent modifies the chemical composition parameters of the solder alloy by precisely controlling the content ranges of Ag (2.8-4 mass%), Bi (1.5-6 mass%), Cu (0.8-1.2 mass%), and other elements (Ni, Fe, Co, As, Sb, In, Ga) to optimize the microstructure and thermal expansion characteristics, enabling the solder joint to withstand severe temperature cycling without cracking
Solution Approach 2:
The patent creates a composite solder alloy system that combines multiple elements with complementary functions: Ag and Bi for base properties, Cu for strength, Ni/Fe/Co for intermetallic compound control, As/Sb for surface and microstructure modification, and In/Ga for additional thermal stability, forming a multi-phase composite material that resists thermal fatigue
2Reliability
If the solder alloy composition is optimized for temperature cycle resistance, then cracking is inhibited, but the viscosity and wettability of the solder paste may deteriorate
Solution Approach 1:
The patent applies local quality by differentiating the functional roles of each element in the solder alloy: As and Sb specifically enhance surface properties and wettability, while Ag, Bi, and Cu provide bulk mechanical properties and thermal stability, allowing simultaneous optimization of both paste application characteristics and final joint reliability
Solution Approach 2:
The patent carefully balances the composition parameters to maintain appropriate paste rheology: limiting Cu to 0.8-1.2 mass% prevents excessive hardness that would affect wettability, while optimizing As (0.003-0.03 mass%) and Sb (0.003-0.03 mass%) ensures good surface activity and spreading characteristics without compromising crack resistance
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 paste effectively inhibits cracking and maintains reliability under 3,000 temperature cycles between -40°C and 125°C, and withstands external forces, ensuring the integrity and functionality of on-board electronic circuits.
Implementation Method 1
forms fine Sn-Sb intermetallic compounds and an As-concentrated layer, providing solid-solution and precipitation strengthening
Implementation Method 2
providing solid-solution and precipitation strengthening
Data Source
Figure 1
Figure 2~4
AI summary
A solder alloy is provided which can withstand the severe characteristics of a temperature cycle between a low temperature of -40°C and a high temperature of 125°C, withstand an external force applied due to, for example, riding on a curb or collision with a vehicle ahead for a long period of time, and can suppress change in viscosity of a solder paste over time. In addition, a solder paste, a solder ball, and a solder preform in which the solder alloy is used; a solder joint formed through the use thereof; and an on-board electronic circuit, an ECU electronic circuit, an on-board electronic circuit device, and an ECU electronic circuit device which include this solder joint are provided. The solder alloy contains, by mass%, 1% to 4% of Ag, 0.5% to 1.0% of Cu, 1.5% to 5.5% of Bi, 1.0% to 5.3% of Sb (or greater than 5.5% and less than or equal to 7.0% of Bi and 2.0% to 5.3% of Sb), 0.01% to 0.2% of Ni, 0.0040% to 0.0250% of As, and a balance of Sn.