Lead-Free Solder Alloy Composition for Wave Soldering
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Solution Overview
Problem
Conventional lead-free solder alloys used in wave soldering, reflow soldering, hot air levelling, and ball grid arrays face issues such as high operating temperatures leading to webbing, bridging, excessive warping, and premature joint failure due to intermetallic compound growth and oxidation, which affect mechanical properties and stability.
Innovation Solution
A lead-free solder alloy composition comprising 0.08-3 wt% bismuth, 0.15-1.5 wt% copper, 0.1-1.5 wt% silver, and additional elements like nickel, cobalt, chromium, and zirconium, with the balance being tin, which enhances mechanical properties, reduces intermetallic compound growth, and improves wetting and oxidation resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high operating temperatures are used in wave soldering, then adequate soldering results are obtained without webbing and bridging, but dross formation increases and board warping occurs
Solution Approach 1:
The patent modifies the chemical composition parameters of the solder alloy by incorporating specific elements (Bi, Ni, Mn, Co, Cr, Zr) within defined weight percentage ranges. This compositional parameter change enables the alloy to achieve adequate soldering quality at reduced operating temperatures, thereby preventing dross formation and board warping that occur with conventional high-temperature processes
2Reliability
If conventional lead-free solder alloys are used, then environmental requirements are met, but intermetallic compound growth occurs leading to premature joint failure
Solution Approach 1:
The patent converts the potentially harmful rapid growth of intermetallic compounds into a beneficial controlled growth pattern by adding specific alloying elements (Ni, Mn, Co, Cr, Zr) that modify the intermetallic formation kinetics. These elements suppress excessive intermetallic layer thickening while maintaining lead-free composition, thereby extending joint service life and preventing premature failure
3Productivity
If solder alloy holds in tank for long periods, then production efficiency is maintained, but oxidation resistance becomes critical
Solution Approach 1:
The patent incorporates oxidation-resistant elements (Ni, Cr, Zr) into the solder alloy composition that actively protect the molten solder from oxidation during extended tank storage. These elements form protective oxide layers or react preferentially with oxygen, enabling the solder to maintain its properties during long-period holding in production tanks without requiring frequent replacement or special protective measures
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 achieves improved mechanical properties, reduced intermetallic growth, and enhanced oxidation resistance, leading to better solder joint reliability and reduced warping, bridging, and improved performance in electronic soldering applications.
Implementation Method 1
Solder alloys tend to dissolve the substrate and to form an intermetallic compound at the interface with the substrate. For example, tin in the solder alloy may react with the substrate at the interface to form an inter metallic compound layer.
Implementation Method 2
The alloy comprising from 0.08-3 wt. % bismuth, from 0.15-1.5 wt. % copper, from 0.1-1.5 wt. % silver, and additional elements like nickel, cobalt, chromium, and zirconium, with the balance being tin, which enhances mechanical properties
Implementation Method 3
the alloy must exhibit good wetting characteristics in relation to a variety of substrate materials such as copper, nickel, nickel phosphorus ('electroless nickel'). Good wetting also enhances the ability of the molten solder to flow into a capillary gap, and to climb up the walls of a through-plated hole
Implementation Method 4
oxidation resistance, which is important in solder spheres where deterioration during storage or during repeated reflows may cause the soldering performance to become less than ideal
Data Source
AI summary
An alloy suitable for use in a wave solder process, reflow soldering process, hot air levelling process or a ball grid array, the alloy comprising from 0.08-3 wt. % bismuth, from 0.15-1.5 wt. % copper, from 0.1-1.5 wt. % silver, from 0-0.1 wt. % phosphorus, from 0-0.1 wt. % germanium, from 0-0.1 wt. % gallium, from 0-0.3 wt. % one or more rare earth elements, from 0-0.3 wt. % indium, from 0-0.3 wt. % magnesium, from 0-0.3 wt. % calcium, from 0-0.3 wt. % silicon, from 0-0.3 wt. % aluminum, from 0-0.3 wt. % zinc, and at least one of the following elements from 0.02-0.3 wt % nickel, from 0.008-0.2 wt % manganese, from 0.01-0.3 wt % cobalt, from 0.01-0.3 wt % chromium, from 0.02-0.3 wt % iron, and from 0.008-0.1 wt % zirconium, and the balance tin, together with unavoidable impurities.