Recommendation for prototype CM (BGA reflow, mainly)

I am considering building a very small custom PowerPC-based (MPC8241)
SBC for something. I need a recommendation for a proto house that can,
at a reasonable price, reflow these BGA parts onto a PCB for me. I
don't want anything else stuffed, just this one part, since I need to
bring up the rest of the board piece by piece. I'd probably only want
three boards made this way. I don't plan to have a custom stencil made
for the first run PCB so it would need to be done with one of those
one-time disposable BGA stencils.

There would be a possibility of very limited production (<1k pieces)
but I'm more interested in the protos.

Any names people can point me to? I can find a million places in google
but have no way of judging them.

"larwe" <zwsdotcom@gmail.com> wrote in message 
news:1128086962.220984.244500@g14g2000cwa.googlegroups.com...
>I am considering building a very small custom PowerPC-based (MPC8241)
> SBC for something. I need a recommendation for a proto house that can,
> at a reasonable price, reflow these BGA parts onto a PCB for me. I
> don't want anything else stuffed, just this one part, since I need to
> bring up the rest of the board piece by piece. I'd probably only want
> three boards made this way. I don't plan to have a custom stencil made
> for the first run PCB so it would need to be done with one of those
> one-time disposable BGA stencils.

Tin-foil, a heat-gun and a sacrificial apprentice  :-p

> There would be a possibility of very limited production (<1k pieces)
> but I'm more interested in the protos.
>
> Any names people can point me to? I can find a million places in google
> but have no way of judging them.

I've used Invotech for low volume production runs and they were mostly OK 
with BGA and are a lot better now (I think we were used as guinea pigs.) If 
you talk about approx 1K volumes you might be able to wangle two or three 
development boards for free to prove their processes. 

> > at a reasonable price, reflow these BGA parts onto a PCB for me. I
> > don't want anything else stuffed, just this one part, since I need to
>
> Tin-foil, a heat-gun and a sacrificial apprentice  :-p

I don't even need the tinfoil for this, as there are no other parts on
the board - however my success rate with this method has been <50% and
these chips are $30 each (the PCBs are $175 each). I really want them
to be mounted by someone with a better yield :). Anything up to about
$100 per board is, statistically, good value!

> I've used Invotech for low volume production runs and they were mostly OK
> with BGA and are a lot better now (I think we were used as guinea pigs.) If
> you talk about approx 1K volumes you might be able to wangle two or three
> development boards for free to prove their processes.

I'll check them out, however I don't want to lie to anyone - the 1K is
very much a maybe.

larwe wrote:
> > > at a reasonable price, reflow these BGA parts onto a PCB for me. I
> > > don't want anything else stuffed, just this one part, since I need to
> >
> > Tin-foil, a heat-gun and a sacrificial apprentice  :-p

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.

>
> I don't even need the tinfoil for this, as there are no other parts on
> the board - however my success rate with this method has been <50% and
> 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?

> to be mounted by someone with a better yield :). Anything up to about
> $100 per board is, statistically, good value!
>
> > I've used Invotech for low volume production runs and they were mostly OK
> > with BGA and are a lot better now (I think we were used as guinea pigs.) If
> > you talk about approx 1K volumes you might be able to wangle two or three
> > development boards for free to prove their processes.
>
> I'll check them out, however I don't want to lie to anyone - the 1K is
> very much a maybe.

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.

> 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?

> > 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.

> 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.

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.

> > 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.

Hmm, I think I understand now. Different terminology. To me the
"stencil" is the device that exposes lands you wish to receive solder
paste. The plate you're talking about is what I would call a "screen".

> > 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

I don't have the equipment or technique to reball BGAs, though.

> > 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.

Right. Normally when I've worked with a CM, the CM has sent me a list
of the standard jellybeans they stock. I go down the list and see if
any of their standard parts can be used in certain spaces on my board
(for instance, if I have 0603 1/16W 10K pullups all over the place, I
don't care what the vendor is, probably - but if I have a 5nH inductor
in an RF circuit, it might be very important to have relay-wound or
ceramic, and substitutes might not be OK).

Anything I want that's special or otherwise not a standard part from
the CM, I buy and send to them along with gerbers and drill/route dwgs.

> We don't want to stock the BGAs and QFPs. So we are going to stuff

I don't want to stock them either - I want to have either nothing in my
hands, or complete boards. I don't want to have WIP boards; what are
you saving there, exactly? Not understanding your workflow :) Since you
have to buy the micro and flash to build the boards anyway, what good
are partial boards to you - why not just send everything to the CM at
once whenever you need a build?

larwe wrote:
> > > 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.
>
> Hmm, I think I understand now. Different terminology. To me the
> "stencil" is the device that exposes lands you wish to receive solder
> paste. The plate you're talking about is what I would call a "screen".
>

For me, they are different phases of stencils.  I need one to first
mount other SMDs except BGAs, then another one to mount the BGAs while
covering the rest.

> ...
> I don't have the equipment or technique to reball BGAs, though.

You can send out a batch of BGAs to reball them.

> ...
>
> I don't want to stock them either - I want to have either nothing in my
> hands, or complete boards. I don't want to have WIP boards; what are
> you saving there, exactly? Not understanding your workflow

We want to make 500 to 1000 boards with everything else but BGAs.  The
Processor ($40) and Flash ($20) are too expensive right now.  So, we
are only mounting 100 of them at a time.  Furthermore, we are still
waiting for the next generations of Processor and Flash, in the coming
months.

>:) Since you have to buy the micro and flash to build the boards anyway,

Not if they are not yet available and/or too expensive.

> what good
> are partial boards to you - why not just send everything to the CM at
> once whenever you need a build?

With properly made stencils, we might not have to send it out for the
BGAs.

> We want to make 500 to 1000 boards with everything else but BGAs.  The
> Processor ($40) and Flash ($20) are too expensive right now.  So, we
> are only mounting 100 of them at a time.  Furthermore, we are still
> waiting for the next generations of Processor and Flash, in the coming

Hmm, and you're absolutely certain that the new generations will be
100% pin  compatible, and you won't need to change any passives on the
board?

larwe wrote:
> > We want to make 500 to 1000 boards with everything else but BGAs.  The
> > Processor ($40) and Flash ($20) are too expensive right now.  So, we
> > are only mounting 100 of them at a time.  Furthermore, we are still
> > waiting for the next generations of Processor and Flash, in the coming
>
> Hmm, and you're absolutely certain that the new generations will be
> 100% pin  compatible, and you won't need to change any passives on the
> board?

I think so.  The client just want 1 of everything (probably over-speced
anyway).  Namely, 1G CPU, 1G SDRAM and 1G FLASH.  The current CPU is
66%, SDRAM is 50% and FLASH is 10%.  Next Gen CPU might be 70% to 80%.
We just need to add one more address trace for 1G SDRAM.  There is no
way to build with 1G NOR flash, so we are adding NAND flash to make it
up.  Anyway, these components cost more than the PCBs (approx $20 to
$30), so we want to defer buying them as much as possible.

Back to the original issue of mounting BGAs last.  I think the best way
is to make a heat shield for all other components except the BGAs.
Make an aluminium heating pad (and heating coil) below the BGA balls.
Apply solder paste with a stencil.  Pre-heat the board in the oven.
Put the BGAs in place and burn it with the aluminium heating pad for 10
seconds.

For our prototypes, we need to first mount some QFPs (they are actually
CPLDs temporary used for board testings) before the BGAs.  We can do
the same as in productions.  First of all, we need to design and custom
build some stencils and heaters.