1. Why Solder Flux Composition Analysis Was Needed
A manufacturer of automotive electronic PCBs was developing a halogen-free, water-soluble flux for lead-free wave soldering.
During mass production, two problems repeatedly occurred:
- uneven wetting with SAC305 solder
- white crystalline residue after water cleaning
The residue also contributed to poor surface insulation resistance (SIR), resulting in repeated rework. Adjusting the in-house formulation through trial and error did not solve the problem, and performance remained noticeably below that of an imported benchmark flux.
The customer therefore used solder flux composition analysis to understand the benchmark formulation and identify what was missing from its own product.
2. How the Water-Soluble Solder Flux Was Analyzed
Water-soluble fluxes can be difficult to analyze directly because high water content may mask signals from organic acids, resins and minor functional additives.
The sample was therefore separated and concentrated before instrumental analysis.
The analytical workflow included:
- GC-MS for co-solvents and volatile additives
- HPLC for organic acid activators
- FTIR for water-soluble resin and surfactant characterization
- TGA for total solids and non-volatile fractions
- LC-MS for minor corrosion inhibitors and antioxidants
- Ion Chromatography for halides and inorganic anions
- ICP-OES for trace metal impurities
The benchmark flux showed a total solids content of approximately 12.46%.
3. What the Solder Flux Composition Analysis Revealed
The analysis showed that the benchmark product was not relying on a single activator or solvent system. Its performance came from several formulation components working together.
Water-Based Carrier and Humectant System
The main formulation contained approximately:
- deionized water: 75.20%
- glycerol: 8.64%
- PEG600: 3.70%
The high-boiling humectant components helped control rapid water evaporation and supported better formulation compatibility and wetting behavior.
Multi-Organic-Acid Activator System
The benchmark used a combination of organic acids:
- citric acid: 4.25%
- DL-malic acid: 3.17%
- adipic acid: 1.70%
This provided activation across different temperature ranges during soldering rather than relying on a single acid component.
Water-Soluble Resin and Functional Additives
The formulation also contained approximately 2.35% water-soluble acrylic resin, together with lower-level surfactant, corrosion-inhibitor and antioxidant components.
The source analysis identified:
- alkyl polyglucoside surfactant: 0.61%
- MBT corrosion inhibitor: 0.28%
- antioxidant: 0.10%
No fluoride, chloride, bromide or iodide ions were detected in the benchmark sample according to the project data.
4. Why the Original Flux Caused White Residue and Poor Wetting
Comparison with the customer’s formulation showed three major gaps.
First, the in-house flux used mainly water without the glycerol and PEG600 humectant system. During wave soldering, rapid water loss contributed to precipitation of organic acids and white crystalline residue after cleaning.
Second, the activator system relied mainly on citric acid. Without the additional organic acids used in the benchmark product, activation at higher soldering temperatures was insufficient, contributing to uneven SAC305 wetting.
Third, the customer formulation lacked the same water-soluble film-forming and corrosion-inhibiting system, reducing protection of the soldering surface and overall formulation stability.
The failure was therefore not caused by one single ingredient. It resulted from differences across the solvent, activator, resin and functional additive systems.
5. Formulation Optimization After Solder Flux Analysis
Based on the analytical findings, the customer adjusted the formulation without changing the existing production equipment.
According to the project results:
- SAC305 solder spreading increased from 81.2% to 92.5%
- white crystalline residue was no longer observed after washing
- SIR stabilized above 1 × 10⁹ Ω
- storage stability improved and batch-related failures were reduced
This illustrates the practical value of solder flux chemical composition analysis service: the objective is not simply to generate an ingredient list, but to identify which formulation differences are responsible for performance problems.
6. Solder Flux Composition Analysis for Product Development and Troubleshooting
Xinbodi supports composition analysis and reverse engineering for solder flux products when manufacturers need to investigate:
- poor solder wetting
- white residue after cleaning
- SIR or insulation problems
- batch inconsistency
- competitor formulation differences
- halogen and ionic contamination
- raw material substitution
- formulation redevelopment
For complex water-soluble flux systems, combining sample separation with multiple analytical techniques can provide a clearer picture of the carrier, activator, resin and additive systems.
7. Solder Flux Composition Analysis at Xinbodi
Xinbodi Laboratories provides solder flux composition analysis for formulation comparison, reverse engineering, troubleshooting and product development.
For benchmarking projects, submitting both your own product and a reference or competitor sample can make it easier to identify meaningful formulation differences and determine which areas should be validated next.