Can I ask when it is you want to inspect them? Is this part of a incoming
recieving inspection, or are you asking if there's any pick and place
equipment that will inspect them before placement?

I can tell you a little bit about the pick and place machine side of things
anyway. There's not too many machines out there that can do a good job
inspecting BGA balls. The problem is that it's difficult for most vision
systems to tell whether a ball is missing or not...because the pad for the BGA
ball is light colored too, and roughly the same size as the ball. So if a ball
is missing, many machines won't see it missing.

Even though I just left working for Zevatech (I'm back on the manufacturing
floor now...), I gotta say, Zevatech's new 760 just as good or better when
inspecting BGA balls as any other machine that I've seen. The key is
lighting...what they've done to overcome the problems with proper BGA
illumination, is to put a ring of LED's inside a plastic housing that sits
above the machines camera lense. Then, when the machine picks a BGA and goes
to the camera to look at it, it will turn the LED's on, then lower the BGA
down towards the LED's. This gives what's called "side-lighting" to the BGA
balls and the vision system can see if a ball is missing or not.

It really does work too! I had to test the latest version of vision software
before it was released, just before I left Zevatech. I took an exacto knife
and shaved one of the balls carefully from the BGA so that the pad was
definately the same diameter as the ball was, and it saw that the ball was
missing and dumped the part.

I've got a question though...I've not been involved in any high-volume
assembly using BGA's, I've built a few boards here and there with BGA's on
them...but not a whole lot. So my question is; do BGA's really come in once in
a while with balls missing? I've never seen a BGA that's been missing a ball
when it's come from a vendor. Do they ever come with missing balls?

I thought that was supposed to be the wonderful thing about BGA's...no more
coplanarity issues like with gull-wing leaded devices, and whatnot. If they
come in without missing balls, why do we make such a big deal about machine
vision being able to inspect them? I've always wondered that...

                                                                            -S
teve Gregory-

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