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Crystallised Joints



Crystallised Joints | 23 April, 2004

Hi all

Does any one know problem with solder joint call crystallised joints. I have noticed that sometimes on our PCB when i look at the joints for example chips, LCCC, there are areas not smooth solder (very often in the center of the solder joint) but near solder pad and near components end solder is smooth and ok). Our process engineer said that it is crystallised joints but not effect the joint quality and it is cosmetic defect. Any comments ?


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Crystallised Joints | 23 April, 2004

Comments. Comments. Hell yeh, we got comments!!!

You are correct to question the appearance of this solder connection. Based on your description, it's defective. Well at best, it's VERY suspect.

That's the rule. If it's suspect, question it.

Here's your other rule for you to paste on your mirror to look at every morning: A good solder connection should be clean, free of pits and holes with a smooth, slightly concave, feathered fillet. [Don't sweat the "bright and shiny" stuff. They don't count any longer. That's granpa stuff.]

Now onto your "crystalized joint" ... using the term "crystalized joint" is pretty much meaningless, because all solder connections are "crystalized" to one degree or another. The grain of a solder connection increases with time and temperature.

Consider this: With our most innocuous, kindly assessment; your lumpy solder connection is a process indicator. A process indicator requires that you investigate and determine the cause of this anomoly, and then convince yourself that it's acceptable.

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Crystallised Joints | 26 April, 2004

We see this sometimes but I have found it to happen based on how fast the solder is cooled back into a solid. Pull strength test and thermocycling show no problem with solder joint integrity.

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