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.
My2�
Dave F
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