Hi Derk!
I'll address some of the points you make.
"...because software could be written to do the trace printing" -Derk
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 : (
".... but manual placement does not need to be as precise as you suggested" -Derk
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!
"What's about heat build up in the epoxy pot?" -Derk
This process is targeted to the ultra low powered new generation of microchips we all use today(MCU,RFID,GSP,ZigBee,GSM,etc.) Ultra low power equates to ultra low heat. Heat dissipation is not really even an issue here. The use of epoxy potting in my process was used for the complete elimination of fabricating an extremely complex multi-layer conventional PCB(FR4). The fact that the epoxy potting I'm using has great thermal conduction by the manufacturer's design was not even a considered attribute in my design, thou the relative bulk mass of the potted assembly does provide for an excellent "heat sink".
"prototyping, the fact that it's going to be very difficult to access
the circuit for probing (even many component pins might not be
accessible anymore) and replacing or adding components is absolute
impossible. For me, these are both things that are extremely important". - Derk
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 underneath.
"....Replace/Adding components is ... impossible.... " -Derk
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!
And this final thought:
I currently prototype with the expensive and NON-REUASABLE Scmart@ boards. Many of latest and greatest IC technologies today "complain" and are "unstable" in such a "rats nest" prototyping environment. Manufacturers today must commit their prototypes to the fabracation of "real" sized PCBs to even develop the circuitry through many iterations of the "true sized" PCBs.
Therefore; I respectfully do not hold with most of your observations or rationals. I do hope you continue to further asses this concept assembly and to share your thoughts into its development.
--- In Homebrew_PCBs@yahoogroups.com, Derk Steggewentz <derks@...> wrote:
>
> Richard wrote:
> >
> >
> > Hi Derk!
> >
> > ....mmmmmmmmmmmmm , well, first let me say that your thought process
> > is so powerful, I will have to assume that I fatally missed something
> > in your rational.
> >
>
> I guess so. Maybe because my unfortunate use of the term 'arbitrary'.
> Although with my suggestion you could position components arbitrarily
> because software could be written to do the trace printing (component
> locations are taken from the scan), it, of course, does most of the
> time makes no sense electrically/physically, as you pointed out (This is
> self explanatory and I implied it). So you should still do a well
> thought out component layout, but manual placement does not need to be
> as precise as you suggested (making a hardcopy of the layout, put the
> transparent adhesive foil on it, using a vacuum tool etc etc..). That
> should make it easier for quick prototyping in the home lab - wasn't
> that you initial idea?? It also would avoid mistakes in the component
> layout because the trace printing function gets its information from the
> actual physical scan of the components in place.
> Hope that makes my point a little clearer
>
> Now, talking about high speed components and capacitors - Besides trace
> resistance, the dielectric properties of the insulating ink and it's
> thickness, which I assume is rather thin (significantly thinner compared
> to multilayer pcb's), will sure have effects like coupling and unwanted
> filtering. Granted, this problem is known for PCBs as well, but it is
> understood to a degree.
>
> What's about heat build up in the epoxy pot?
>
> Another disadvantage, although it probably only plays a role for more
> complex circuits, is, considering you suggested this method for quick
> prototyping, the fact that it's going to be very difficult to access
> the circuit for probing (even many component pins might not be
> accessible anymore) and replacing or adding components is absolute
> impossible. For me, these are both things that are extremely important
> in prototyping. As a matter of fact, that's the whole idea of a
> prototype. Spice and breadboarding just don't give you the whole picture
> with increasing frequencies. Wouldn't matter so much for a final
> product, but with that I would go to some pcb manufacturer anyway.
>
> The last point actually would pretty much rule this method out for me,
> even if it would work. I just wouldn't see a place in my development cycle
> (design on paper, component selection, simulating w/ SPICE,
> breadboarding if necessary and/or possible, prototyping, probing and
> refining, finalizing).
>
> I still like the idea though, maybe just as a thought experiment - or
> maybe for some special cases I could see an application.
>
> Just some thoughts, Derk
>
>
>
>
>
>
>
>
> >
> > I'll respond briefly on this in hopes I'll get to better understand
> > the merits of your suggestions.
> >
> > In prima fasia, this would be a complete disaster. Placing the SMDs in
> > a "random" fashion, would seriously violate essential physical and
> > electronic associations that the components function provides.
> >
> > Example: With the very high speed microchips we use today, very heavy
> > use of decoupling and bypass capacitors must be used and must present
> > themselves IMMEDIATELY (asigned placement) on the IC pins they afford
> > their function to.
> >
> > "Random placement" of these components would folly at best.
> >
> > --- In Homebrew_PCBs@yahoogroups.com
> > <mailto:Homebrew_PCBs%40yahoogroups.com>, Derk Steggewentz <derks@>
> > wrote:
> > >
> > > Richard,
> > > I am following the thread. because I like the creative
> > > approach.Regarding accurate placement: Why don't you just place the
> > > components arbitrarily and after potting and peeling of the tape you
> > > scan the side with the exposed pins. With a piece of software (to be
> > > written) the user then can interactively identify the components on the
> > > image. With this information and the schematic the software has all the
> > > information to do the rest, including printing.
> > > Although I can see a few problems with the general approach I think
> > it's
> > > worth following.
> > > Derk
> > >
> > >
> > > Richard wrote:
> > > >
> >
>