Gold-based solders have unique traits:
- Reliability
- Strength
- Corrosion-resistant
- Inert
Making them ideal for a variety of applications:
- Ultra high reliability joining and sealing
- Fluxless soldering processes
- Hermetic sealing
- Joining gold plated surfaces
Medical
Aerospace
Defense
Package sealing
Optics
Specialty MEMS
packaging
Additional advantages of gold-based solder:
- 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 Compared to Standard Solders | ||||
|---|---|---|---|---|
| Indalloy® Properties | 80Au/20Sn | 96.5Sn/3.5Ag | 63Sn/37Pb | 58Bi/42Sn |
| Solidus Temperature (°C) | 280 | 221 | 183 | 138 |
| Liquidus Temperature (°C) | 280 | 221 | 183 | 138 |
| Thermal Conductivity (W/mK) | 57 | 33 | 50 | 19 |
| Tensile Strength (PSI) | 40,000 | 5,800 | 7,500 | 8,000 |
| Shear Strength (PSI) | 40,000 | 2,700 | 6,200 | 500 |
| Thermal Expansion Coefficient @20°C (PPM/°C) | 16 | 30 | 25 | 15 |
Material Specs
- Casting process designed to produce a cleaner alloy and minimize impurities and oxides
- Lot traceability
- 99.9% and 99.99% purity
- Standard tolerance of ± 0.5% on gold content
- Certificate of analysis provided for each lot and maintained for seven years
| Gold Eutectic Alloys | |||
|---|---|---|---|
| Indalloy® Properties | Au20Sn | Au12Ge | Au3.2Si |
| Solidus Temperature (°C) | 280 | 356 | 363 |
| Liquidus Temperature (°C) | 280 | 356 | 363 |
| Thermal Conductivity (W/mK) | 57 | 44 | 27 |
| Tensile Strength (PSI) | 40,000 | 26,835 | 36,975 |
| Shear Strength (PSI) | 40,000 | 26,825 | 31,900 |
| Thermal Expansion Coefficient @20°C (PPM/°C) | 16 | 13 | 12 |
| 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 in using gold-based solders in your process
- Cost per unit and higher yields make it a viable option even though the initial cost will be 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.
Soldering Process Options
- Vacuum soldering
- Fluxless, void-free soldering
- Die-attach
- High process temperature
- Reflow
- Convection, infrared, induction
- Laser soldering
- Targeted soldering
- Vapor phase reflow
- Uniform heating
- Manual Soldering
- Solder iron, hot plate, ultra sonic, dipping
Gold Alloy Product Options:
PREFORMS
- Thickness from 0.0127mm (0.0005″) and greater
- Tight dimensional tolerances ensure repeatable solder volume
- Flatness measurement capabilities to 0.00254mm (0.0001″)
- Large die library with in-house tooling capabilities
- Eutectic alloys are best choices
- Tiny solid shapes from 0.152mm (0.006″)
WIRE
- Diameter starting at 0.025mm ± 0.0127mm (0.001″ ± 0.0005″)
- Tight dimensional tolerances
- Packaging designed to minimize breakage of wire in soldering process
- Maximum of 80% Au
PASTE
- Powder (80Au/20Sn only)
- 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)
SPHERES
- Sizes starting at 0.254mm (0.010″)
- Tight dimensional tolerances down to ± 5 microns
Gold-containing solders are an excellent choice with many superior attributes.
Cost considerations should be weighed against the high yield, high reliability attributes that make the total cost of ownership attractive.
For more information contact gold@indium.com.
