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 compliant

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)
- RMA-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)

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