Lead-Free Soldering Ag Concentration Control
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Solution Overview
Problem
Existing lead-free soldering methods for power semiconductor modules face challenges in preventing void generation and improving solder wettability when joining Ag-containing members, as Ag diffusion can lead to capillary crystal growth and reduced mechanical characteristics.
Innovation Solution
A lead-free soldering method is developed where the Ag concentration in the solder is controlled within a specific range (1.0 mass % ≤ (M×C+B)×100/(M+B) ≤ 4.6 mass %) to prevent void generation and enhance wettability by adjusting the Ag content from the Ag-containing member into the solder, using a composition of Ag, Sn, and unavoidable impurities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Ag-containing member is soldered using conventional lead-free solder, then soldering can be performed, but void generation occurs and solder wettability deteriorates
Solution Approach 1:
The invention changes the chemical composition parameters of the solder by adding specific elements (Bi: 0.1-5.0 mass%, Cu: 0.1-5.0 mass%, Ni: 0.1-5.0 mass%) to the Sn-Ag base solder. This parameter modification prevents void generation and improves wettability when soldering Ag-containing members, resolving the contradiction between achieving solder joint quality and avoiding harmful void formation.
Solution Approach 2:
The invention creates a composite solder material comprising Sn-Ag as the base with multiple additive elements (Bi, Cu, Ni). This composite composition synergistically prevents void generation while maintaining good wettability, solving the technical contradiction by combining multiple material properties in a single solder alloy.
2Stability of the object's composition
If Ag diffusion is prevented by adding Bi to solder, then capillary crystal growth is suppressed, but solder composition complexity increases
Solution Approach 1:
The invention modifies the solder composition by adding Bi (0.1-5.0 mass%) to control Ag diffusion and suppress capillary crystal growth. While this increases compositional complexity, the controlled addition ranges provide predictable and stable diffusion prevention, resolving the contradiction between composition stability and complexity through defined parameter ranges.
Solution Approach 2:
The invention develops a composite solder system (Sn-Ag-Bi-Cu-Ni) where multiple elements work synergistically. The Bi component specifically addresses Ag diffusion control, while Cu and Ni provide additional benefits, creating a multi-functional composite material that manages complexity through coordinated element interactions.
3Strength
If solder wettability is improved by adjusting Ag concentration, then joining strength increases, but control precision of Ag content becomes more difficult
Solution Approach 1:
The invention optimizes the Ag concentration parameter within a specific range (1.0-4.6 mass%) to achieve improved wettability and joining strength. By defining this optimal range rather than targeting a single value, the invention balances wettability improvement with manufacturability, reducing the difficulty of precise Ag content control while maintaining high joining 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
This method effectively prevents void generation and improves solder wettability, resulting in a high-durability soldered article with enhanced mechanical characteristics and cycle life.
Implementation Method 1
Ag diffusion can lead to capillary crystal growth and reduced mechanical characteristics
Implementation Method 2
a second step of heating and melting the lead-free solder, and a third step of cooling the lead-free solder
Implementation Method 3
a second step of heating and melting the lead-free solder, and a third step of cooling the lead-free solder
Data Source
AI summary
In a soldering method for Ag-containing lead-free solders to be soldered to an Ag-containing member, void generation is prevented and solder wettability is improved. The soldering method for Ag-containing lead-free solders of the present invention is a soldering method for Ag-containing lead-free solders includes a first step of bringing a lead-free solder having a composition that contains Ag that a relation between a concentration C (mass %) of Ag contained in an Sn—Ag-based lead-free solder before soldering of a mass M(g) and an elution amount B(g) of Ag contained in the Ag-containing member becomes 1.0 mass %≤(M×C+B)×100/(M+B)≤4.6 mass % and that the balance consists of Sn and unavoidable impurities into contact with the Ag-containing member, a second step of heating and melting the lead-free solder, and a third step of cooling the lead-free solder.