Low-Melting SnIn Solder Alloy Composition for Heat-Sensitive Reflow
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Solution Overview
Problem
Existing lead-free SAC solder alloys have high melting temperatures, which pose challenges in applications involving heat-sensitive components and require higher reflow temperatures, leading to thermal warpage and solder defects.
Innovation Solution
Development of low melting temperature SnBi and SnIn solder alloys with liquidus temperatures below 210°C, comprising specific weight percentages of Bi, In, and optional alloying elements such as Ag, Sb, Cu, Ni, and Zn, to achieve improved mechanical properties and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If SAC solder alloys are used to replace Pb-based solders, then Pb-free composition is achieved, but melting temperature increases above 215°C
Solution Approach 1:
The patent changes the compositional parameters of the solder alloy by incorporating Bi (2-54 wt%) and In (0-16 wt%) along with other alloying elements to modify the melting characteristics. This compositional parameter change enables the solder to maintain Pb-free status while achieving liquidus temperatures below 210°C, directly resolving the contradiction between Pb-free requirement and melting temperature control.
Solution Approach 2:
The patent creates a composite solder alloy system combining multiple elements (Sn, Bi, In, Ag, Cu, Sb, Ni, Zn, Co, Ge, P, Mn) with specific compositional ranges. This composite material approach allows synergistic effects where Bi and In lower the melting point while other elements maintain mechanical properties, thus achieving both Pb-free composition and reduced melting temperature simultaneously.
2Ease of manufacture
If high reflow temperatures are used for SAC solder alloys, then proper soldering is achieved, but thermal warpage of PCBs and components occurs
Solution Approach 1:
By changing the melting temperature parameter of the solder alloy through specific compositional design (Bi: 2-54 wt%, In: 0-16 wt%, and other elements), the required reflow temperature is reduced from above 215°C to below 210°C. This parameter change enables proper soldering at lower temperatures, thereby preventing thermal warpage while maintaining manufacturing feasibility.
3Productivity
If high reflow temperatures are used for SAC solder alloys, then soldering is completed, but solder defects such as head-in-pillow and non-wet open occur
Solution Approach 1:
The patent changes the liquidus temperature parameter to below 210°C through specific alloy composition (Sn with Bi: 2-54 wt%, In: 0-16 wt%, and controlled amounts of Ag, Cu, Sb, Ni, Zn, Co, Ge, P, Mn). This temperature parameter change allows soldering to be completed effectively at lower temperatures, preventing defects like head-in-pillow and non-wet open that occur with excessive heat, thus improving manufacturing precision while maintaining productivity.
Data Source
AI summary
Some implementations of the disclosure are directed to low melting temperature (e.g., liquidus temperature below 210° C.) SnIn solder alloys. A SnIn solder alloy may consist of: 8 to 20 wt % In; greater than 0 wt % to 4 wt % Ag; optionally, one or more of greater than 0 wt % to 5 wt % Sb, greater than 0 wt % to 3 wt % Cu, greater than 0 wt % to 2.5 wt % Zn, greater than 0 wt % to 1.5 wt % Ni, greater than 0 wt % to 1.5 wt % Co, greater than 0 wt % to 1.5 wt % Ge, greater than 0 wt % to 1.5 wt % P, and greater than 0 wt % to 1.5 wt % Mn; and a remainder of Sn.