Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


0402's Tombstoning

Bryan

#8970

0402's Tombstoning | 14 October, 1999

We recently started designing boards using 0402's. The geometry was built using IPC specs but our contract manufacturer is having a yield problem. Approx. 20% of the 0402's are tombstoning. He claims the pads should be closer together; .4 mm between lands. Our own factory had no problem assembling 0402's. Has anyone else experienced this problem?

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Brian W.

#8971

Re: 0402's Tombstoning | 14 October, 1999

I would suggest comparing the profile your factory used and the one they are using. Run a profile on some of the 0402 parts. If the profile is not right, uneven heating will cause this to occur. It could also be the placement accuracy in combination with the profile.

Brian

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Brian W.

#8972

Re: 0402's Tombstoning | 14 October, 1999

I forgot to mention nitrogen usage. Check if the usage of notrogen is different in your ovens compared to theirs.

Brian

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JohnW

#8973

Re: 0402's Tombstoning | 14 October, 1999

Bryan,

0402's tombstonning isn't that uncommon and usually the 1st reaction is alway's the pad size aint right. If you've followed the IPC guidline's normally you should be fine but I'd double check the component supplier's spec's as well. brian's point about the profile is a good one, your unlikely to be using the same oven type as the sub contractor so your profile wont be exactly the same anyway since not 2 oven's ever are. You also as brian suggest's need to check on the N2 situation and find out what they are using plus what paste. the key's for the tombstonning are normally the ramp rates and the pad sizes which basically comes down to the wetting forces that your setting up, so maybe something else to consider is the end cap terminations and what the plating is vs the paste and the PCB finish, e.g. HASL / Silver palladium / gold etc. An old tric is to turn of the N2 and run it in air to slow down the wetting, you may also what to look at copper loading aorund the chip's and the direction's although with today's oven's this really shouldn't be a problem.

JohnW

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Dennis O'Donnell

#8974

Re: 0402's Tombstoning | 14 October, 1999

I once had similar problems. It went away when I switched to a different brand of solder paste. When I switched back to the previous brand of paste the problem came back. I don't know why but the solder paste brand made a difference.

go to: www.pcb-repair.com for other assembly solutions.

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