amazing save

We missed connecting two pins on a BGA, one of the LTM switchers.

Production found a way!

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Reply to
John Larkin
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Is that photo sfter reflow? I don't see wetting.

If not, will the extended ball survive refolw?

RL

Reply to
legg

These balls don't seem to collapse much, which means they are mostly soldered to the board. Seems to work. I took the pic with a cheap Amazon USB microscope. QC uses way better optics to inspect the soldering.

The fix was applied after the LTC part was already installed. They squished in a bit of paste between the balls and reheated the chip. Someone noted that we try really hard to not short balls, so doing it is easy.

Reply to
John Larkin

Lucky they were on the outer row!

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
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Reply to
Phil Hobbs

No foolin.

I had half of the LTM8078 dual switcher happily converting +24 to -7, but A Certain Party didn't want to waste the other half so reconfigured the schematic for dual/parallel mode. But in that mode, both FB pins need to be connected in parallel, and ACP missed that.

Reply to
John Larkin

I don't know what is required to make that happen, but I've seen techs do r epair work on a board where they add traces that are damaged. It would hav e been a simple matter to attach a short piece of copper between the pads b efore soldering.

I'm with legg, the solder balls don't seem to have wetted well, especially the one on the far left. I love it when a problem is pointed out and someo ne says, "It seems to work!"... It always gives me a laugh. That's right up there with, "Here, hold my beer!"

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Rick C. 

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Reply to
Rick C

If reworking those LTM parts, or even reflowing the whole board due to an unrelated component, it is very important to bake the board first if the board has sat around at all since it was last baked. I reflowed a board without baking it and about all of the LTM switchers failed, but nothing else.

Reply to
Chris Jones

Interesting. The LTMs seem to be reliable so far. We occasionally rerun a board through the oven if a BGA problem is suspected, usually on a big FPGA. The LTMs seem to survive.

The older LGA versions were awful. Lots of shorts.

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John Larkin      Highland Technology, Inc 

The best designs are necessarily accidental.
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Reply to
jlarkin

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