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Printed Circuit Board Assembly & PCB Design Forum

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Tombstone's

cbarnett

#22224

Tombstone's | 31 October, 2002

I have a production line that is running ceramic substrate's. The line begins having tombstone's when the outside temperature begins to drop. I have moved our nitrogen tanks to the inside of the building and this done nothing. Does anyone have any ideas on how to eliminate the tomsbstones?

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RDR

#22225

Tombstone's | 31 October, 2002

You may want to turn the nitrogen off altogether, in searching through the archives it has been stated and proven by many people that this could help a lot. I don't know why it appears to be outside temperature related. Could it be that the PPM levels in the oven are changing with the gas temp?

Russ

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Steven

#22231

Tombstone's | 31 October, 2002

If your processing with Nitrogen, tombstoning can be caused by your cooling rate. Go thru the solid/liquid phase of the solder slower..iN other words as you transition into or out of the liquidus pahse if 63/37 alloy 183C, ensure that your Delta are at a minimum. Keep in mind the more density difference you have due to ground planes, the more likely it is to experience these defects. Also the thicker the paste deposit, the more tombstones will be experience. And finally, make sure that the paste and components are deposited where they should be and not misregistered. Have fun.

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jason

#22280

Tombstone's | 6 November, 2002

You may want to check your stencil aperture design too. The base ball pad design worked fine to solve my tombstone problem.

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#22290

Tombstone's | 6 November, 2002

Is it possible that your HVAC system activity is having an effect on your product, as in drying out (or adding moisture to) your paste, or something like that?

Have you compared your profiles during wide swings on outside temperature? I'm still on this HVAC thing.....

Do you run FR-4 boards on the same line with no problems, or on a nearby line with no problems, or similar problems?

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