Richard wrote:
>
>
>
> Excellent and very powerful PCB CAD software already
> exists(KICAD,Eagle,etc.)for FREE! Do you really want to start your
> project with trying to first write your own routing software?? I don't
> think the "homebrewer" has on staff a seasoned team of code writers at
> their disposal : (
>
No, I don't want to reinvent and reimplement existing router apps. I am
thinking of using the scan to e.g correct component placement in the
input file of the Router, using maybe a router produced Gerber and
slightly shifting components, modifying/extending Kicad etc. etc. There
are many approaches thinkable and they don't seem insurmountable to me.
> Well, yes it does! The CAD software un-forgivenly demands this. It
> expects what you place in its "virtual design board" to be absolutely
> representative of the real world "outside physical placement" of the
> actual components location. When I have you print the component layout
> screen to the substrate, the CAD software later makes reference to
> this fine placement when you flip the module upside down and now needs
> to print micro thin conductive traces. Think about a 128 pin QFN IC
> with lets say 50 0404 SMDs. Your SMDs better be right on the money!
>
That problem is exactly what I tried to solve with my suggestion. Did
you ever try to manually place something onto something adhesive? When I
do, it's usually always a tiny little bit off. And then there is no
pushing around anymore and cursing won't help either, as soon as one
corner touches the adhesive surface, that's it. Well, I guess some
mechanical and optical (think parallax) help can be constructed. I'd
rather write some code, trying to take human failure out of the equation.
> In re of "probing" .... your wrong! All the SMDs remain
> 100%accessible, even the connections "inside" of the constructed
> "micro-hybrids". Yes, they are covered by the insulating mask, simply
> run your finished module through the printer again, this time printing
> the "inverted version" of the component screen. With a micro-sized
> drill or sharp needle point probe, slightly tag the surface to pass
> through to the conductive layer underneat
>
I like your idea of 'running your finished module through the printer
again, this time printing the "inverted version" of the component
screen'. Good thought. But I have difficulties to think of how that
would work in the real world. What is if there is a conductive layer in
between, e.g. a ground plane, which I can imagine you want considering
all this tight spacing and possibilities of capacitive coupling etc? Or,
if no layer, what if a trace crosses just there and you are poking your
needle through possibly more then one of them? It doesn't seem practical.
>
> That's very true! But think about it. Is the "homebrewer" equipped
> with special and very expensive "solder re-work stations" that allows
> changing out a 128 pin QFN or 0404 SMDs??? Your talking about ICs that
> cost on average $3 to $5 and descretes around 20 cents a piece.
> Have you ever tried to "solder wick" out a defective IC before?
> Chances are you'll lift every "pad" right of the board!
> My point is .... for the cost and time involved,if you have a
> defective module...PRINT OUT A NEW ONE!! In about 4 hours, your back
> up and running.
>
Yes, I hand solder surface mount components quite frequently. And yes, I
have tried and succeeded to "solder wick" out a defective IC before,
more then once. O.k. not a 128 pin QFN, but regular SOPs etc.. The
majority of SMT components ain't 128 pin QFN's anyway. Regular solder
station and a fine tip is all you need. I want to be able to do that
with my prototypes where an IC (your quote) 'cost on average $3 to $5'.
PRINT OUT A NEW ONE (your quote) and throwing away maybe 10 of the other
chips in the circuit worth $3 to $5 apiece does not sound like a great
option to me.
> Manufacturers today must commit their prototypes to the fabracation of
> "real" sized PCBs to even develop the circuitry through many ite
> ations of the "true sized" PCBs.
>
Very true. But that's not what you are doing with your technique. Your
'hybrid' is as far away from a a 'real' sized PCB as it gets.
The advantage of real prototype PCBs are also that I can put my finger
onto components or traces, introducing capacitance and changing circuit
behaviour, take a soldering iron and quickly add a cap, change an R etc
etc (with my cheap soldering iron), until i am ready for the next
iteration of the prototype pcb.That would possibly save substantially on
the number of iterations. Each iteration with your technique, even the
smallest, requires a complete redo. I can change an R in a minute while
you have a 4 hr turn around.
Derk