Solder paste connects the alloy, flux and deposition process. A paste that performs well in one print and reflow environment may not be suitable in another. Buyers should confirm the powder size, flux chemistry, viscosity behavior, melting range and storage conditions before sampling.
1. Match the melting range to the assembly
Sn42Bi58 paste around 138°C is used where low-temperature processing is required. SAC305 and similar lead-free alloys generally reflow around 217°C or higher. Sn63Pb37 paste around 183°C may be considered where leaded material is permitted. The component temperature limit and downstream process sequence should drive the choice.
2. Select powder size by print requirement
Common paste powder sizes from the current range include Type 3 and Type 4 directions between approximately 20 and 45 μm. Smaller powder can support fine features but may change oxygen sensitivity, viscosity and storage behavior. Confirm the stencil aperture, pad geometry and component pitch with the paste supplier.
3. Review flux and cleaning requirements
No-clean, water-soluble and other flux chemistries behave differently in humidity and residue tolerance. Ask whether the assembly will be cleaned, what ionic contamination limit applies and whether the reflow profile has been approved for the selected paste.
4. Define storage and handling
Paste is a time- and temperature-sensitive material. Confirm refrigerated storage, warming procedure, mixing policy, stencil-life guidance and discard rules. Shipping method and transit time should be reviewed before arranging a sample.
| Buyer input | Why it matters |
|---|---|
| Melting limit | Protects components and downstream processes |
| Powder size | Supports the required stencil and pad geometry |
| Flux / cleaning | Controls residue and cleaning compatibility |
| Deposit method | Influences viscosity and stencil life expectations |
| Reflow profile | Determines whether the paste has an adequate process window |
Review the solder paste product range or compare lead-free and leaded alloys.
Evaluate paste with your actual print process.
Send the deposit method, powder target and reflow limits to arrange the next discussion.