Re: Recommendation for prototype CM (BGA reflow, mainly)


larwe wrote:
> > Just a steel plate with 25mm x 25mm square hole. I am thinking about
> > the same. Unfortunately, mime is 35mm x 35mm; otherwise, we could
> > share the stencil.
>
> You would use one of the self-adhesive BGA template things inside that
> hole?

Actually, no. I was thinking about the hole for existing mounted part.
For the current mounting, you do need a stencil for 300+ holes for you
and 475 for me.

>
> > > these chips are $30 each (the PCBs are $175 each). I really want them
> >
> > That's expensive, even if you have 10 layers. Are you counting setup
> > costs?
>
> 175 is for the protos, which are just going to be made in 4-off (3 to
> be stuffed, one to buzz out problems). It's an 8-layer board. In
> production it would be much cheaper of course but I have to assume at
> least one spin between proto and production.

It would not be much more to build additional boards, since the costs
are for the films and masks. You can always reuse the BGAs, but not
the PCBs. Especially, if you are using prototype qualities PCBs.

>
> > By the way, in productions, would you be mounting the BGA first, or
> > last? I am thinking about mount it last, but the stencils are more
> > tricky to make.
>
> This is the kind of detail I would expect a CM to solve; if I contract
> out assembly, they would make the stencil(s) and handle the details of
> that nature.

Then you would have to send out all the parts in advance.

We don't want to stock the BGAs and QFPs. So we are going to stuff
everything else at once, and mount the CPU (475 balls) and Flash (64
balls) last. We need cut-outs (square holes for the mounted parts) and
perhaps covers for them as well.

.