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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Nichol Rose

#14168

SMT | 20 September, 1998

Hello: I would like to know what causes tombstombing and how can it be prevented? Thx. Nichol

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Steve Gregory

#14169

Re: SMT | 21 September, 1998

| Hello: | I would like to know what causes tombstombing and how can it be prevented? | Thx. | Nichol Hi Nichol! A tombstone happens when solder doesn't wet equally on both terminations during reflow...now why that happens can be found by looking at 4 different areas (in no particular order): 1. Solderabilty of the part -Is the part is solderable on both terminations? 2. Reflow profile -Is the reflow profile what's recommended by the paste vendor? 3. Design of the footprint, overall layout -Does the footprint match the part? Is it within the IPC-782 guidelines? Is there any unusual copper planes or concentrated component densities in isolated areas of the board? Is one termination directly connected to a copper plane without using thermal reliefs? 4. Paste and placement -Is your solderpaste print registered correctly and complete in coverage, and component placement accurate? If you look at each of these areas to ensure that everything is yes (except for the copper planes and component density part, that should be no), you'll narrow things down why tombstoning happens every time you see it. Then you'll know what to do to prevent it in the future. Hope this helps ya! -Steve Gregory-

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