Sb-Modified Sn-Ag-Cu Solder Paste for No-Clean PCBs
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Solution Overview
Problem
Lead-free solder pastes, particularly Sn-Ag-Cu based, exhibit high reactivity with flux components, leading to issues like increased viscosity and short pot life when using maleated rosin as the main flux resin, which results in tacky and dark flux residues, complicating the soldering process and inspection.
Innovation Solution
Adding 1-8 mass% of Sb to the Sn-Ag-Cu based solder powder suppresses the reaction with maleated rosin, maintaining a stable solder paste viscosity and extending its pot life, while ensuring a transparent and non-tacky flux residue.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If lead-free solder powder (Sn-Ag-Cu based) is used to eliminate Pb pollution, then environmental safety is improved, but reactivity with flux components increases causing viscosity increase and short pot life
Solution Approach 1:
Sb is introduced as an intermediary element that forms a protective interface layer between the Sn-Ag-Cu solder powder and the flux components (particularly maleated rosin). This Sb-containing layer acts as a mediator that reduces the direct reactive interaction between the solder powder and flux, thereby suppressing viscosity increase and extending pot life while maintaining the lead-free environmental benefit
Solution Approach 2:
The solder paste is formulated as a composite system containing Sn-Ag-Cu solder powder with added Sb element. This composite composition leverages the low reactivity of Sb with flux components to create a more stable paste system. The composite nature of the solder powder (multiple elements working together) provides both the lead-free advantage and the improved stability through synergistic interactions among Sn, Ag, Cu, and Sb
2Ease of manufacture
If maleated rosin is used as the main flux resin to achieve transparent and non-tacky residue, then residue quality is improved, but reactivity with solder powder increases causing short pot life
Solution Approach 1:
Sb serves as an intermediary substance that intervenes in the reaction between maleated rosin and Sn-Ag-Cu solder powder. The Sb forms a protective layer on the solder powder surface that prevents direct contact and excessive reaction with the maleated rosin, thereby extending pot life while allowing the maleated rosin to perform its function of producing transparent, non-tacky residue
Solution Approach 2:
The chemical composition parameters of the solder powder are modified by adding Sb element. This parameter change (compositional modification) alters the reactivity characteristics of the solder powder with maleated rosin, reducing the reaction rate and extending pot life while preserving the desirable residue properties that maleated rosin provides
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 addition of Sb to the Sn-Ag-Cu solder powder stabilizes the solder paste, preventing viscosity increase and maintaining a long pot life, along with achieving a transparent and non-tacky flux residue, enhancing the reliability and inspection quality of the soldering process.
Implementation Method 1
Adding 1-8 mass% of Sb to the Sn-Ag-Cu based solder powder suppresses the reaction with maleated rosin
Implementation Method 2
maintaining a stable solder paste viscosity and extending its pot life
Implementation Method 3
ensuring a transparent and non-tacky flux residue
Data Source
AI summary
As electronic equipment has become smaller in size, printed circuit boards which cannot be subjected to cleaning have been developed, and a no-clean lead-free solder paste is becoming necessary. In order for a solder paste not to require cleaning, it is necessary that the color of the residue be transparent and that the residue be non-tacky. A maleated rosin, which is a rosin suited for no-clean paste, has a high acid value so it is not suitable for a flux for lead-free solder. As a means of suppressing a reaction between a flux containing a maleated rosin and a Sn-Ag-Cu based solder alloy powder, a Sn-Ag-Cu-Sb based solder alloy powder is used which adds 1 - 8 mass % of Sb to a Sn-Ag-Cu based solder alloy. As a result, it is possible to provide a solder paste which has the excellent effect that the solder paste does not easily undergo changes over time and