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 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)
- 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
Phil Zarrow: Ron, we’ve discussed that performance of materials can affect productivity, and hence profitability. Can you give us an example?
Ron Lasky: Yeah. I was working with a certain customer that had a problem with their solder paste that we call poor response-to-pause. As you’re aware, probably several times a day, the assembly line has to be shut down to replenish components. And in that pause time, some solder pastes can stiffen up. And then we turn the line back on and you make a stencil print, that first print is bad. And you have to wipe that board and reprint it again. You lose probably about two minutes, maybe every two hours.
Phil Zarrow: And how can this affect the bottom line?
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