Low-Silver Lead-Free Solder Alloy for Thermal Cycling and Drop Shock
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Solution Overview
Problem
Existing lead-free solder alloys face challenges in achieving both good thermal cyclic reliability and drop/shock reliability, with high silver content improving thermal cyclic but compromising drop/shock performance, and low silver content vice versa, while also experiencing undercooling issues and aging effects that affect mechanical performance.
Innovation Solution
A low-silver lead-free solder alloy composition comprising specific weight percentages of silver, copper, bismuth, cobalt, antimony, and optionally nickel, which reduces undercooling temperature, process temperature, and improves mechanical strength and reliability by refining grain structure and enhancing solid solution strengthening, thus maintaining thermal cyclic performance while enhancing drop/shock reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional solder alloy composition is used, then desired materials properties are achieved, but undercooling and aging effects occur
Solution Approach 1:
The patent modifies alloy composition parameters by adding bismuth (0.1-5.0 wt% Bi) which suppresses undercooling during solidification, and optimizing copper content (0.5-3.0 wt% Cu) to control intermetallic compound formation, thereby reducing aging effects while maintaining mechanical strength
Solution Approach 2:
The composite alloy system incorporates bismuth as a key element that refines grain structure and suppresses undercooling, while copper forms controlled intermetallic compounds that strengthen the alloy without excessive aging sensitivity, achieving both strength and aging 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 alloy exhibits reduced undercooling, lower process temperature, improved thermal cycle and drop/shock impact reliability, and reduced aging effects, with superior mechanical properties and solder joint performance compared to prior art alloys like SAC305.
Implementation Method 1
improves mechanical strength and reliability by refining grain structure and enhancing solid solution strengthening
Data Source
AI summary
A lead-free solder alloy may comprise tin, silver, copper, bismuth, cobalt, and antimony. The alloy may further comprise nickel. The silver may be present in an amount from about 2.0% to 2.8% by weight of the solder. The copper may be present in an amount from about 0.2% to 1.2% by weight of the solder. The bismuth may be present in an amount from about 0.0% to about 5.0% by weight of the solder. In some embodiments, the bismuth may be present in an amount from about 1.5% to 3.2% by weight of the solder. The cobalt may be present in an amount from about 0.001% to about 0.2% by weight of the solder. The antimony may be present in an amount between about 0.0% to about 0.1% by weight of the solder. The balance of the solder is tin.