What temp do you set your solder pot for with 63/37 leaded solder?  I just
started using one and I don't know what the ideal temp is yet.

Brian Kraut
Engineering Alternatives, Inc.
www.engalt.com

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu]On Behalf
Of Forrest Christian
Sent: Wednesday, March 14, 2007 5:45 PM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Small-Production PCB Manufacturer Experiences.


Vitaliy wrote:
> Yeah, these are relatively simple boards. Do you hand-solder them
in-house?
> Are they PTH?
>
We've been doing PTH in the past.   We're switching to SMD.

For PTH we've been doing solder-pot soldering, where you insert all of
the components through the board into anti-static foam.  Then you flux
the entire board, preheat/dry it a bit and then dip it into a solder pot
for 3 seconds.   Fast, quick, efficient.   Generally a board takes me no
more than 30 seconds to solder after everything is in place.

With the SMD, we're applying RoHS compliant solder flux using a manual
stencil process.   Small boards we're v-scoring so we're able to stencil
a few at a time.   After the stenciling, we manually place the
components (generally 1206 or larger so it's easy for a human to place),
and then bake.   The switch to SMD is because it's actually faster to
place SMD than PTH if you're good with the tweezers, and it's easier to
deal with RoHS that way.  PTH components (which we keep to a very low
minimum) get soldered by hand.  We generally try to keep the PTH pins
under 10 or so per board.   If it's more, we're leaving it in the Leaded
environment and the entire board as PTH.   Most of these devices are
RoHS exempt anyways.

>> Labor cost is roughly 0.003/second. ($10/hr,  16.666.../minute,
>> 0.003/second). Even if you figure 5 seconds a placement, the cost is
>> only about 1.5cents/placement.   Heck, even if we could only place one
>> every 30 seconds (even I can do this well), we'd still be in the same
>> ballpark.
>>
>
> Mmm... that doesn't really make sense to me. The relationship is linear,
> unless you have a huge fixed overhead.
>
The cost to manually place a component is mainly time.   Flux is dirt
cheap per board, and our volumes are small enough that we don't really
have to hire someone to do it.  However, we do have to consider at what
point is it cheaper to outsource.  What I'm saying is that at the going
rate of $0.10 per component at my quantities, I can hire lots of people
to do the placement for me.    If I could get assembly at
$0.01/placement I'd outsource in a minute.
> A lot depends on your market. If the potential market is big, and the
demand
> is elastic, it makes sense to produce larger quantities, but charge less
per
> unit so you can sell more. Keep in mind that your goal should be to
maximize
> your _total_ profit, so it doesn't matter how much profit you make on each
> unit (many people forget this).
>
My market is relatively cost insensitive.  My products are significantly
lower priced than the competition (like 1/10th of the competition), but
the market is extremely small.   500/year per product is my
expectation.  I also rev the products fairly quickly to respond to
customer needs so I generally will buy 1-200 boards, go through those,
make any design changes, and then proceed.

My niche is specifically figuring out how to do those very low volume
products which are simple to build (throw 40 components on the board,
and 8 hours of programming), and that noone wants to build because they
are interested in either selling 100 units at $5000 each or millions of
units at $19.95 each.

I'd rather sell 500 each of 20 different products at $150 each.

I expect to hit a nerve at some point on some product and find out that
500/year is a decade or two too low of a quantity for that product.  At
which point I'll pick up the SMD design

-forrest
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