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looking for HASL TIN thickness specification

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#56292

looking for HASL TIN thickness specification | 2 September, 2008

In order to check pcb quality by HASL TIN thickness plating repeatability, looking for any specification for the above.

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#56298

looking for HASL TIN thickness specification | 2 September, 2008

You should have a few microns of Sn on a board.

Vlad

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#56312

looking for HASL TIN thickness specification | 2 September, 2008

IPC-6012 Table 3-2. States "Fused tin-lead or solder coat - Coverage and Solderable". The lack of any specific dimension criteria doesn't make this any less a requirement. There must be complete coverage of solder on the land, and it must be wettable.

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#56315

looking for HASL TIN thickness specification | 3 September, 2008

That is why it has to be a few micron thick. Otherwise, it will form a layer of intermetallic which is extrremely difficult to solder to.

Vlad

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#56317

looking for HASL TIN thickness specification | 3 September, 2008

What do you mean by a "few micron thick"?

IMC thickness pre-cycling (NEMI Lead-free) * Cu3Sn: 3um [118 uin] * Cu6Sn5: 1um [40 uin]

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#56318

looking for HASL TIN thickness specification | 3 September, 2008

Do you mean "at least a few microns" or "no more than a few microns"?

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#56320

looking for HASL TIN thickness specification | 3 September, 2008

That sounds like a "Coupla microns thick" Dave.

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#56321

looking for HASL TIN thickness specification | 3 September, 2008

But Vlad was talking tin and Davef gave intermetalic thicknesses which Vlad said needs to be avoided by having a few microns of tin.

I'm not 100% sure but I suspect that DaveF is not convinced that Vlad knows what "intermetalic" means.

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#56324

looking for HASL TIN thickness specification | 3 September, 2008

I believe Vlad is a sales person for Sentec.

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#56329

looking for HASL TIN thickness specification | 3 September, 2008

At a former employer we required HASL thicknes to be a minimum of 0.75 micron (30 microinches), as measured at the thinnest point on any given pad. This would generally assure a minimum 1 year solderability shelf life. Usually when we saw a solderability problem, we found HASL thickness to be less than 0.25 microns, or the boards to be very old. Assuming the starting Copper pads were clean, the HASL process would produce an IMC layer with a starting thickness of typically about 2 microns. The IMC (Cu3Sn and Cu6Sn5) is readily solderable unless oxidized by exposure to the atmosphere. The HASL coating prevents this oxidation, but it is not completely impermeable to Oxygen. Thus, the limited shelf life, depending primarily on HASL thickness, time, and storage temperature.

Glenn

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#56333

looking for HASL TIN thickness specification | 3 September, 2008

Well, I'm not a sale person whatsoever. I'm a purely technical guy (even PhD :-)) who has been with the industry for quite a few years and I know very well what intermetallics means and how thck it should be for different board finishes and solders :-).

If HASL plating is too thin, then all Sn gets consumed to form Cu/Sn intermetallcs and then it's almost inpossible to solder it without using extremly aggessive flux.

I hope I have cleared the clouds, at least a little bit.:-)

Regards,

Vlad

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#56345

looking for HASL TIN thickness specification | 4 September, 2008

Not sure why you would... but here are a couple of links that may help if you are having manufacturing problems

http://www.smtinfo.net/docs/Electronic%20Production/9.htm

http://www.midwestpcb.com/capabilities/plating2.html

Granted I only have a Masters from Purdue, and been in this business for over 20 years.....

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