Bluish Color of Sn-plating over Ni After 3X Reflow (Peak Temp @ 260degC) [Philippines] January 31, 2006Hi Guys,
We are plating pure Sn over Ni surface (originally it was pure Sn over Ni/ NiP surface).
The components (D2PAK transistors) undergo the ff process:
1. 168hrs soak @ Moisture Chamber (85degC / 85%RH).
2. Reflow 3 times in IR oven (total cycle time of reflow ~ 2mins); peak temp of 260degC.
Observations:
1. Components with Sn plating over Ni surface turned bluish after reflow
2. Components with Sn palting over Ni / NiP surface did not turn bluish
3. All Components that did not undergo Moisture soak did not turn bluish
Questions:
1. What's the mechanism/principle behind the bluish color?
2. Is it safe to say that the P content on the Ni/NiP surface prevents this bluish phenomenon?
Appreciate your help.
Jun Idjao
Semiconductors - Laguna, PhilippinesFebruary 13, 2006 The bluish color after reflow is Sn oxide. Presumably, the oxide thickness is up to 400-500A judging from the color.
On Ni underplate, Sn is forming IMC slowly with Ni, which gives it plenty of time staying in its molten state. Serious oxidation/reflow discoloration is observed.
On NiP underplate, Sn is forming better IMC with Ni and NiP. The IMC is forming faster and the crystalline IMC so formed between Sn and NiP is helping Sn to recrystallized faster. Therefore, oxidation is not as serious.
Danny Lau
- Hong KongFebruary 15, 2006 Just try running the freshly plated tin thru an alkaline cleaner and rinsing again before re-flowing.
Robert H Probert
Robert H Probert Technical Services - Garner, NC, USAApril 19, 2006 Dear Robert,
Do you notice that alkaline post-treatment, such as TSP, is not improving the Sn reflow discoloration problem? Instead, I think that acid post-treatment may be more effective in removing surface adsorbed organices (in a like-dissolve like manner?) which may contributed to reflow discoloration.
Danny Lau
- Hong Kong相关链接：
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