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Dull Solder



Dull Solder | 11 November, 1999

I experience dull solder at the reflow station runing some SMD LED. It is a reject for dull solder. Is there anything wrong in the setting of the oven temperature? Temerature too high or too low?

Pls advise. Thank You Rdgs.....

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Re: Dull Solder | 12 November, 1999

Hallo Edmund, what does dull mean in your case ? It�s nearly impossible to say something about it without more information. Dull or shiny isn�t a clear or better no indicator for good or bad. Some companies add other metalls to the solder to get rid of this shiny look(reflex) for better optical inspection. It�s influenced by contents of other metalls in your solder. In liquid state certain metalls or alloys of the pad and the lead are disolved and added to the solder and this new mixture determines the later appearance of your solderjoint. In your case it seems that especially from the LED-leads something dissolves into the solder that brings up that dull look. Could for example be goldplating what does no harm up to a certain amount, if it�s to much your joint will be what�s called "brittle" I think. Best thing would be, check your LED-leads for their metall finish(alloy), check the solderjoint for good wetting, good fillets and sufficient pull strength.

Second question: If your temperature is to low so that the paste deposit does not melt correctly it would look like a handfull of grapes covered with thin clear ice. Is it that what you see ?



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Re: Dull Solder | 12 November, 1999

Edmund, following-on from Wolfy:

Back in the old days, anyone who could spell "sodder" considered "bright and shiny connections" GOOD and "dull and grainy connections" BAD. Now, "dull and grainy" connections can be either GOOD or BAD, depending on the cause of the appearance. Two "dull and grainy" solder connection conditions are:

1) "Disturbed" solder joint: a solder joint that has an "angular, faceted" appearance that is caused by the solder joint being moved as it solidified. 2) "Grainy" solder joint: a solder joint that has a rough, gritty appearance that is caused by the solder microstructure giving the solder joint surface relief.

You probably don't have a "disturbed" situation, because we're only talking about "some SMD LEDs."

So probably, you have a "grainy" situation, which gives you options:

� Find a way to cool the solder joint faster. � Don't get the solder joint as hot, in the first place. This creates a finer solder joint microstructure. � Perform cross section analysis to prove that the "graininess" is not a reliability issue, only different, reflecting some process or design parameter influence.

Now taking a completely different tact, gold dissolved in tin/lead solder is often "dull / grainy." This can shows-up often on HASL boards with a few components with gold plated leads, amoung other components with fused leads.


Dave F

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