0.25mm tilt? That's pretty small depending on you BGA size. Is it failing? Or just your Q.E. being anal? What size BGA we talking about? What ball count? Just one board? Maybe cheaper to just repair.
Now assuming there is NO part under the BGA:
First check your board. Are all pads the same size? Most board houses will cheat on pad openings. If not check your Gerber to be sure you are asking for same size on all pads.
Next, check your part. Missing balls can cause tilt. Check your balls for coplanarity (on the BGA, not your pants).
Now check your stencil. All ball apertures the same? If so check for clogging. This is prolly the #1 reason for BGA defects (I know, I know, everyone blames the oven but the LAST process isn't always the PROBLEM process).
Check your print next. Getting a clean wipe? Is the print crisp? Got a way to measure it? If not check printer parameters.
Now check you placement. Is it placed on the pads or slightly off? Can you verify through x-ray (use a wet board)? Now if your placement machine is causing a tilt � you better check you board support or your nozzle. Something is seriously wrong if you can tilt-mount a BGA.
And now of course � the EVIL oven. It is possible to partially reflow a BGA. Kinda rare but is possible. Generally you either reflow or you don't. You can x-ray all you want, but unless you have a top of the line x-ray machine it is difficult to determine reflow from cold solder joints. If the BGA is in the middle of a largly populated area, you can just check everything around it. If everything else on the board reflow � then I'd suspect the BGA reflowed as well. Without knowing your board � hard to tell.
Fianally, is this board subject to multiple heat cycles? Two or more reflow solders, a selective solder, wave solder etc? If so it could be caused by a process you�d never suspect or are in charge of.
Now we patiently wait for the reply..........
Who posted to add weights? I gotta see that thread!
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