Solder paste types are primarily defined by their metallic composition, particularly concerning the presence or absence of lead. This composition dictates their properties, application, and environmental impact.
Based on common industry standards and environmental regulations, two main types are often referenced:
Key Solder Paste Types
Leaded Solder Paste
This is the traditional form of solder paste.
- Composition: It consists of a metal alloy with lead and tin as its base constituents. Typical leaded solder compositions include Sn63/Pb37 (63% Tin, 37% Lead), which has a eutectic point (single melting temperature).
- Characteristics: Offers excellent wetting properties, lower melting points compared to many lead-free alternatives, and is generally more tolerant to variations in reflow profiling.
- Environmental Considerations: This solder is affected by environmental conditions and contains lead, a hazardous substance.
RoHS (Lead-Free) Solder Paste
Developed to meet environmental directives like RoHS (Restriction of Hazardous Substances), which restricts the use of lead.
- Composition: It is a composition of various elements such as copper, tin, silver, nickel, zinc, bismuth, and antimony. Common lead-free alloys include SAC alloys (Sn-Ag-Cu, e.g., SAC305: 96.5% Tin, 3% Silver, 0.5% Copper) and others containing bismuth or antimony to adjust melting points and properties.
- Characteristics: Typically have higher melting points than leaded solder and require more precise reflow profiles. They are essential for products sold in regions with lead restrictions.
- Environmental Considerations: RoHS is environment-friendly as it eliminates the toxic lead content.
Comparison Summary
Choosing the correct solder paste type is vital for successful electronics assembly, impacting process parameters, joint reliability, and regulatory compliance.
| Feature | Leaded Solder Paste | RoHS (Lead-Free) Solder Paste |
|---|---|---|
| Lead Content | Contains Lead | Lead-Free |
| Base Alloy | Tin, Lead | Tin, Silver, Copper, Bismuth, etc. (various combinations) |
| Melting Point | Generally Lower | Generally Higher |
| Environmental | Hazardous (Lead) | Environment-Friendly |
| Compliance | Not RoHS Compliant | RoHS Compliant |
Understanding the specific requirements of a project, including component compatibility, operating environment, and relevant regulations, guides the selection between these fundamental solder paste types.
