Gold-Based Solder Paste
Gold-tin solder paste is used in a variety of high-reliability applications, where its high melting point, non-creep, high-tensile stress, thermal and electrical conductivity, as well as proven usage life makes it a standard "known-good" material.
Advantages
- Highest tensile strength of any solder
- High melting point is compatible with subsequent reflow processes
- Pb-free
- Superior thermal conductivity
- Resistance to corrosion
- Superior thermal fatigue resistance
- Good joint strength
- Excellent wetting properties
- Resistance to oxidation
- AuSn is compatible with precious metals
- AuSn is RoHS complaint
Gold-tin Solder Paste
- 80Au/20Sn Powder
- Type 3 (25-45 microns)
- Type 4 (15-38 microns)
- Type 5 (15-25 microns)
- Type 6 (10-20 microns)
- No-clean flux
- NC-SMQ51SC (used in high-power LED and MEMS)
- NC-SMQ51A (for difficult to solder surfaces in die-attach)
- NC-SMQ75 (halogen-free and low-residue; requires <10ppm oxygen)
- Low-volume packaging
- Jars (10g per jar)
- Syringes (5cc syringes)
Alternative Methods of Using AuSn
| Characteristics | Solder Paste | Solder Preform | Evaporation | Alloy Plating | Plating by Layers |
|---|---|---|---|---|---|
| Minimum bondline thickness | 25.00μm | 12.00μm | 0.01μm | 0.25μm | 2.50μm |
| Cleanliness | Low cleanliness (flux surface contamination) | High cleanliness (when no flux used) | High cleanliness | Good cleanliness (trace of organic impurities only) | Good cleanliness (organic co-deposit impurities) |
| Deposition equipment | Stencil printer or dispenser | Manual or pick & place | Evaporation chamber | Plating line | Plating line |
| Device heat exposure | >280°C | >280°C | >Ambient | Ambient | Ambient + diffusion heating step |
| Strengths | Low-cost equipment; manual or automated assembly; rapid deposition rate | High purity; manual or automated assembly; preforms designed to match deposition footprint | Very high purity; rapid deposition; low-cost equipment; thin to thick layers | Good purity; deposition targeted to conducting surfaces | Good purity; deposition targeted to conducting surfaces |
| Weaknesses | Flux residue inclusion; thick deposits only; requires diffusion step; requires cleaning; refrigerated storage | Expensive automation equipment; thick depositions only; accurate manual placement difficult, may require flux or reducing atmosphere | Wide area deposition (material loss); may require diffusion step | Expensive equipment; difficult to control composition; low deposition rates | Expensive equipment; difficult to control composition; low deposition rates; requires diffusion step |
Factors to consider
- Higher yields and cost per unit make gold a viable option, even though the initial cost is higher than alternative solders
- A low oxygen atmosphere may be required if the application is flux free
- Some applications require pressure to promote good, void-free reflow on horizontal surfaces.
- In step soldering or processes that may require rework, soldering to gold plated surfaces results in an intermetallic that melts at a higher temperature than the original alloy. When using the AuSn alloy, this can be addressed by using high tin-containing alloys.
- Alternative methods, such as scrubbing, forming gas or formic acid, may be needed for oxide removal of the soldered surface.
Processing Options
- Vacuum soldering: flux-less and void-free soldering
- Die-attach: high process temperature
- Reflow: convection, infrared, and induction
- Laser soldering: targeted soldering
- Vapor phase reflow: uniform heating
- Manual Soldering: solder iron, hot plate, ultra sonic, and dipping
Gold-Based Solder Paste Technical Documents
Whitepapers
Application Notes
Material Safety Data Sheets
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