FYI all, Bev Christian is a HE, not a SHE.

> -----Original Message-----
> From: [log in to unmask] [SMTP:[log in to unmask]]
> Sent: Wednesday, June 24, 1998 7:01 PM
> To:   [log in to unmask]
> Subject:      [TN] ASSY: BGA sanity check
>
> Regarding populating both sides of the board with BGAs, I think Bev
> Christian
> summed it up pretty well.  If you meet the parameters she mentioned, you
> should be fine with most PBGAs. The formula I use for calculating what
> will
> stay in place when re-reflowed is the sum of the lead (or collapsed
> sphere)
> surface area (all interconnects on the device) divided by the weight of
> the
> component in grams.  If it comes out to less than 30 grams/ sq in, the
> component will stay on as there is ample surface tension.  (Note, most
> ceramic
> BGAs or CGAs exceed this ratio).
>
> You sure don't need "differential heating" and you can do it on ANY reflow
> oven (not just an ETS whoopee-flow or whatever) that, as Bev mentioned,
> has a
> smooth running, edge conveyor
> HOWEVER........
> As Jerry Cupples wisely insinuates - beware when you do populate both
> sides
> with these.  Remember to allow room for removal and replacement (Design
> for
> Repairability 101) !  We don't live in a perfect world, you know.
>
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