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Board with immersion Tin



Board with immersion Tin | 25 November, 2002


I made a board wich I plated with immersion Tin, I tought it should be the same result as we had with tin lead but we ran into a weird problem. WE use a 63/37 no clean paste and on the Board with Immersion Tin the solder just make a ball ON the pad...we ran the same profile with a board Tin-Lead and we get almost a perfect solder joint. Because it's immersion tin should we put our temperature higher?

We try to solder with a iron and the paste can hardly wet all the pad the fisrt time..if we do it a first time, cleand the pad and do it again it's more easy. If someone have work with it can give me some trick I would appreciate.

Thanks You

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Board with immersion Tin | 25 November, 2002

You might want to check the tin thickness. I believe you have a minimum of .65 microns in order to achieve a good solder joint through 3 thermal passes.

In an immersion tin process, the ability to solder is time and temperature dependant. As the intermetallic compounds reach the surface, they become oxidized and difficult to solder. Temperature accelerates the tin into copper diffusion rates, bringing the intermetallics to the surface.

First I would check your build specifications to see if a minimum Tin thickness is specified. I would then have the boards analized using Sequential Electrochemical Reduction Analysis ( used for pure Tin thickness ) or XRF Spectrometry ( used for total Tin from all layers ).

I think you should have .65 microns of pure Tin or 1.0 microns of overall Tin to achieve desired results.

That's just my opinion, I could be wrong!

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Board with immersion Tin | 25 November, 2002

Sorry, no tricks for you. The good news is: your reflow recipe should be similar for both imm tin and HASL.

Imm tin requires more attention to detail by both the fabricator and the assembler than HASL. There is a fair amount of discussion on imm tin in the fine SMTnet Archives on: * Minimum plating thickness that Jax mentioned. * Rate of corrosion of the tin when using activated fluxes. * Decrease in plating thickness with each succeeding thermal cycle. * Handling. * Storage.

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Board with immersion Tin | 25 November, 2002

there is a good article by AIM solder regarding tin. In a nut shell, if you do not apply flux or heat to tin finish you will never degrade it! I agree with the others that you need to check the thickness of the pure tin layer. We have forbidden tin in our factory due to the special processing that it requires. It actually cost us more many to process tin than any other finish due to difficult rework, inconsistencies from PCB suppliers etc...

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