There are a wide variety of RoHS-compliant lead finish options available in the market including:
- Tin-bismuth (SnBi)
- Tin-copper (SnCu)
- Tin-silver (SnAg)
- Nickel-palladium-gold (NiPdAu)
- Matte-tin
Most IC manufacturers are choosing to use NiPdAu or matte-tin and
Catalyst has chosen to offer NiPdAu or matte-tin plating for our RoHS compliant devices. It is believed that the matte-tin approach adopted by Catalyst and many other semiconductor companies minimizes the risk of whisker growth. For more information on tin lead plating and whisker growth refer to the links at the bottom of this page.
Many RoHS-compliant parts are offered by Catalyst with NiPdAu (Nickel-Palladium-Gold) plating, we refer to these parts as "Green and Gold." There are no whisker growth issues associated with NiPdAu plating.
| Classification |
TS min (°C) |
TS max (°C) |
ts (sec) |
TL (°C) |
tL (sec) |
TP (°C) |
tp (sec) |
ramp up (°C/sec) |
ramp down (°C/sec) |
duration |
| Sn-Pb |
100 |
150 |
60-120 |
183 |
60-150 |
240+0/-5 |
10-30 |
3 (max.) |
6 (max.) |
6 min. (max) |
| Matte-tin & NiPdAu |
150 |
200 |
60-180 |
217 |
60-150 |
260+0/-5 |
20-40 |
3 (max.) |
6 (max.) |
8 min. (max) |
The key elements of the reflow profile are:
-
TP which is determined by the MSL (Moisture Sensitivity Level) of the package
- SnPb (non-RoHS-compliant) packages are rated to 240°C
- Matte-tin and NiPdAu are rated to 260°C
- TL which is determined by the melting point of the solder
- RoHS-compliant solders have a higher melting point than conventional SnPb solder
Backward Compatibility of "Green" devices
Matte Tin and NiPdAu packages are backward compatible with SnPb solder and may be manufactured with a reflow profile at peak temperature of 240 °C when used with SnPb solder. We strongly encourage thorough evaluation of solder reflow process so that optimum conditions can be defined before mass production.
We
do not recommend using SnPb packages with RoHS compliant solder due to the higher melting point of RoHS-compliant solders and the lower MSL rating of SnPb packages.
Moisture/Reflow Sensitivity Classification for Nonhermetic Solid State Surface Mount Devices (PDF)
Current Tin Whisker Theory and Mitigation Practices Guidelines (PDF)
Environmental Acceptance Requirements for Tin Whisker Susceptibility of Tin and Tin Alloy Surface Finishes (PDF)
Lead free assembly
Tin whisker activities
