Re: gEDA-user: Cheap 4 layer manufacturer?

[Randall Nortman <geda-lists@xxxxxxxxxxxxxxx>]

On Tue, Oct 11, 2005 at 12:00:45AM -0400, 9000 VAX wrote:
> On 10/10/05, Darrell Harmon <mail@xxxxxxxxxxxx> wrote:
> > On Mon, Oct 10, 2005 at 07:07:41PM +0200, Karel Kulhavy wrote:
> > > Are you going to mass produce them and sell?
> > >
> > > CL<
> >
> > I am considering doing that. I would not call it mass
> > production. I imagine something like putting a few
> > together every weekend. That way I would not have a huge
> > investment in parts.
> 
> Are you considering getting BGA and TQFP chips soldered by PCB board
> manufacturers? After working on the 0.5mm 144 pin EPM1270T144 with a
> solder iron and an absorbing copper braid (though successfully), I
> think it is not the kind of job that I can handle. I gave up the idea
> of toast oven before I even started, because I don't know how to
> control the temperature precisely.

I have soldered boards with 0.5mm pitch TQFP chips in a toaster oven,
placing them by hand but using a solder paste stencil from
www.stencilsunlimited.com.  I haven't actually tried applying solder
paste by hand from a syringe; it might work, but it would take longer
I would think.  Alignment is indeed tricky, but if you're close enough,
surface tension will do the job for you.  A steady hand is still
required.  The biggest problem I've had is bridging, which is easy
enough to clean up afterward.  I'm still refining my solder paste
technique, so I may be able to eliminate the bridging as well.

I don't even use a computer-controlled toaster oven, by the way,
though I do intend to rig that up when I have some time.  For now, I
do it by hand: preheat the oven to max temperature, put the board in
with the thermostat at 150F for about 30-60 seconds, then crank the
thermostat up all the way and watch carefully - have a small
flashlight on hand, and when you see the solder paste turn shiny, turn
the thing off and open the door to cool.  I've done boards with SMT
components on both sides this way (do one side first, then the other,
with some way to prop up the board on the second run).

I suppose it's risky, since I could overheat the components, but I
haven't had a problem so far.  The solder paste itself makes a very
good temperature indicator after all.  Also, I got a toaster oven with
a convection fan, which presumably helps keep he heat even.  (I was a
little concerned that it would blow small parts off the board, but the
airflow is gentle enough that it hasn't been a problem.  Then again,
the smallest I go is 0603; 0402 components might be another matter.)

The oven a 1500-watt Oster, and was $60 at Target.  It's got four
heating elements (two top, two bottom) and, as I mentioned, a
convection fan.

Randall