You've told us nothing about your situation, process, boards, or anything!!!
If you leave some boards with very fine solder connections on the shelf for a cuppla years, the grain will become coarse.
What do you mean when you say "grainy"? What is the grain size, measured after sectioning?
"Not shiney" is a process indicator. I am an advocate of NOT using visual appearance to define a good and bad solder joint. [The number of hours spent by the specification community trying to define what a "disturbed or grainy" solder joint is would/should make all of us disturbed!] Two dull 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 texture.
If you think you have a "disturbed" situation, look for equipment, handling, or fixture causes for the movement.
If you have a "grainy" situation, options are: * Try to find a way to cool the solder joint faster. * Don't get it so hot in the first place. This produces a finer solder joint microstructure without the fine solder joint surface texture. * Determine if materials added to solder are changing its appearance. For instance: Both gold and palladium in tin/lead solder can make connections look dull / grainy. * Consider that DI water can make solder connections look dull. * Remove crud [in barrels or on pads] that is floating to the top on the solder.
Use cross section analysis to prove that "graininess" is not a reliability issue. We did some extensive work in the 80's showing that a "grainy" solder joint is not a bad solder joint - only different, reflecting some process or design parameter influence.
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