Analysis for pure tin coatings

[jedward]

Pure tine forms wiskers and is prohibited as a coating in aerospace applications.

Can x-ray fluoresence be used to determine tin concentration in thin coatings?
(thin being under about 0.0004 inch)

Are NIST traceable standards available for calibration of the equipment for this measurement?

 

[unclesyd]

Are you trying to quantify the Sn or just detect the presence of any amount?

I would check ASTM, though I think most of their tests are for plate or coated materials.

If NASA has a limit on the use or amount of tin in coatings they will reference a test, somewhere

The are numerous spot tests that that can detect very low levels of Sn around.

As a start I would give Koslow a call as they have a lot of spot tests available.

http://www.koslow.com/method.html

 

[jedward]

I am trying to screen surfaces of many materials and many small parts for tin concentrations that which exceed 97%.

X-ray fluoresence will measure the composition thru some small depth within the material, 0.5 mil or so.
(about 3% Pb, Ag or Sb is acceptable in hi temp solders)

Even pure tin at some small thickness will be reported as significantly less than 97 % due to the depth averaging. Without knowing the thickness, a wiskering problem could exist.

It is possible that fluoresence is not the way to go but also it is possible that very thin coating of pure tin do not result in wisker generation since their growth is related to stress in the tin.

Is there a minimum thickness for pure tin to grow wiskers?

 

[cloa]

Try reposting in the aerospace forum- they would more experience in such a particular conditon.