Lead-Free Solder Composition for High-Temperature Creep Resistance
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Solution Overview
Problem
Conventional lead-free solder alloys, such as the 96.5Sn3.0Ag0.5Cu alloy, do not perform well at high temperatures, making them unsuitable for applications requiring operation at 150°C or higher for extended periods, and existing alternatives fail to provide a favorable combination of high temperature reliability and mechanical properties.
Innovation Solution
A lead-free solder alloy comprising 2.5 to 5 wt.% silver, 0.01 to 5 wt.% bismuth, 1 to 7 wt.% antimony, 0.01 to 2 wt.% copper, and optional additions of indium, titanium, germanium, rare earths, cobalt, aluminum, silicon, and other elements, which modify the alloy microstructure for improved high temperature reliability and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder alloys are designed for higher liquidus temperature to improve high temperature performance, then high temperature reliability improves, but manufacturing complexity increases
Solution Approach 1:
The patent systematically optimizes composition parameters within specific ranges (Ag: 2.5-5 wt%, Bi: 0.01-5 wt%, Sb: 1-7 wt%, Cu: 0.01-2 wt%) to achieve the target liquidus temperature range (210-260°C). This parameter optimization approach balances high temperature reliability with manufacturability, avoiding excessive complexity while meeting performance requirements.
Solution Approach 2:
The patent incorporates optional elements (In, Ti, Ge, RE, Co, Al, Si) at controlled levels (typically up to 0.5-5 wt% each) to partially enhance specific properties such as creep resistance, wetting, or mechanical strength. This partial action approach allows manufacturers to selectively add elements based on specific application requirements, reducing unnecessary complexity while maintaining high temperature performance.
Data Source
AI summary
A lead-free solder alloy comprising: from 2.5 to 5 wt. % silver; from 0.01 to 5 wt. % bismuth; from 1 to 7 wt. % antimony; from 0.01 to 2 wt. % copper; one or more of: up to 6 wt. % indium, up to 0.5 wt. % titanium, up to 0.5 wt. % germanium, up to 0.5 wt. % rare earths, up to 0.5 wt. % cobalt, up to 5.0 wt. % aluminium, up to 5.0 wt. % silicon, up to 0.5 wt. % manganese, up to 0.5 wt. % chromium, up to 0.5 wt. % iron, up to 0.5 wt. % phosphorus, up to 0.5 wt. % gold, up to 1 wt. % gallium, up to 0.5 wt. % tellurium, up to 0.5 wt. % selenium, up to 0.5 wt. % calcium, up to 0.5 wt. % vanadium, up to 0.5 wt. % molybdenum, up to 0.5 wt. % platinum, and up 0 to 0.5 wt. % magnesium; optionally up to 0.5 wt. % nickel; and the balance tin together with any unavoidable impurities.