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.
- Highest tensile strength of any solder
- High melting point is compatible with subsequent reflow processes
- 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)
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.
- 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
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Safety Data Sheets
Solder Paste Blog Posts
Today's Indium Mailbag question asks about the storage of indium-contained solder paste at a temperture well below the recommended temperature of -20.
What is the ideal time-above liquidus during solder reflow? Too long or too short can cause dewetting and charring, or not allow the intermetallic formation to wet.
The second stage of a reflow profile activates the flux in the solder paste and prepares the solder for reflow. This can be a critical stage to avoid defects such as tombstoning, voiding, graping, and non-wetting.
From One Engineer to Another®
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