In a message dated 10/1/98 6:30:39 AM Pacific Daylight Time,
[log in to unmask] writes:
<< Technetter's
On a multi-layer board with parts on both sides, is it OK to use the
real-estate on the opposite side from a BGA to place resistors and caps? I
know this would affect BGA rework, but I'm running out of board space here.
:P
Advice, suggestions?
Thanks
Scott Holthasen>>
Mornin' Scott!
First, just let me say that if I could, I'd give you a big hand shake, and a
pat on the back! It's so refreshing to see someone actually think about how
their designs affect us worker bees on the production floor! B^)
Well, if I had my 'druthers, I 'druther there not be anything on the
bottomside, but we all know that's not being realistic with what we want these
boards to do nowdays. But if you're running out of room to the point that you
need to put things beneath a BGA, I'd try to put only resistors on the bottom,
that's coming from a perspective that they will stand up to the thermal
cycling of wave solder better than caps do. But it really doesn't make a
difference whether you put them beneath a QFP, PLCC, or a BGA, there's always
going to be the same risk that you'll also have to rework the chip components
beneath a large processor type device if that needs rework.
Have you utilized chip resistor networks in your design yet? I work at a
contract assembly company and I'm kinda' curious why I don't see them used
more often in board designs. They're widely available as far as I know, save
quite a bit of space, and really increase throughput during SMT placement.
Instead of placing one resistor per placement cycle, you're throwing down
four. I always see at least 2 or 3 resistor values on a board that are use
quite a few times in an assembly...(I think those values are called pull-up
and pull-down resistors aren't they?). They make capacitor arrays now as well,
I see them advertised in all the magazines, but I don't see many of them on
boards...how come?
-Steve Gregory-
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