idea for making fine-pitch SMD device trace widths possible

well, without unreasonably long build times, anyway.

Assuming that we have solder (or field's metal, whatever) trace deposit tool working, we'd not be able to do fine-pitch SMD devices b/c the reprap can't make the required "channels" that narrow. Nor can it make the walls between the pins narrow enough.

If we try, it gets exponentially slower as we decrease the extrusion width. Not only is the extrusion narrower, and shallower, but there's some hard resolution limits to stretching, so a finer hole is the only way, which is extruded at a slower linear rate as well, and the back pressure increases.

This really bothers me - many of the coolest chips (the atmel AVR with USB line, for instance) are only available as fine-pitch surface mount, or even BGA devices.

So I've been thinking about ways around it, and though of a really neat one that I though I'd share.

But first, the only other way I've though of for embeding fine pitch SMD devices is to first create (with a very fine and very slow plastic extruder head) an extended package device, which essentially changes it from a SMD to a funny-shapped DIP. Maybe radial, maybe with inside corners, maybe with "pins" sticking out the top.

So the neat idea I though of was:

Instead of channels that are created by the plastic depositing tool, you make a tool that carves channels and fills them with solder in one seamless step. Picture a heated pin being dragged through the plastic, with precisely-metered solder flowing down the backside.

Only one side of the pin would stay tinned, as the plastic would react and oxidize the front side, so it's a directional head. Since it's directonal anyway (and thus it can't do right angles), we may as well include a little heated "plow" to re-smooth the surface afterwards. That might allow multiple trace depths in one step. i.e. without switching back to the plastic extruder head. And we can make it wedge-shapped or half-round, so make sure there's a nice "vacuum" on the backside of the pin for the solder to be sucked down into. A truncated teardrop shape may be needed if the pin needs to be stronger and still leave a narrow solder trace.

If we assume the components are already placed, we also defeat the surface tension limitations. We can make a VERY small trace since we're pulling a string of solder with a fixed start point the solder won't "bead up" and not go all the way to the contact point. Backing the pin up to make the "end" contact might get a bit tricky, but it could go forward and scrape the top of the SMD devices' contact pad instead.

That would require that the contact pads be pre-tinned, but I don't see that as a big problem. Aren't some of them pre-tinned anyway?

I don't know if copper would conduct heat well enough. I've been thinking of a piece of fine-gauge nichrome bent into a loop like the hot knives that are often used for foam cutting. But since the pin is short (~.5mm), a bit of copper wire attached to a heated thermal mass above it may work fine.


Thanks, I needed to get that off of my chest. Now I can stop worrying at it. You can go ahead and tear it apart now. I'd love to hear a better idea. But even that this idea nor anything like it can't possibly work because I've overlooked X would work. But then I'd have to start worrying at it again.

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I'm building it with Baling Wire

Hi John,

AFAIK either solder nor Fields metall will form thin traces - both tend to form blobs when molten and placed on a plastic surface, so you will receive a sequenze of beads instead of a solid tray

For this problem i thought about printing covered cavities and fill them with a conducting fluid.

The simplest way will be feeding wires, but this is another path.

For inserting SMD`s it's much easier to fab or mill interface-modules, which rescale the pin-layout from fine-pitch to 1/20" or even coarser.

For this i'm experimenting with sheets of ceramic green and ceramic slurry for the body and metall-pastes for the pads, feeds and vias - so it should be possible to fine-fab (e.g. on my CNC-dispenser) the modules complete with the metall-trays, then heat/sinter them in the oven, populate with SMD and use as IC-modules in 'standard-pitch'-PCB's ...

Viktor

Not sure on how well it's going to work, but I have a sample of conductive plastic. I've been wondering about trying to enhance the conductivity with copper powder or very short copper fibers. one 1/8" pellet had a resistance of ~900 Ohms when I jabbed multimeter probes into it. We'll see how it is after I extrude a line of it over two copper wires.

I found this wandering the web related to this:
[www.dltechnology.com]
Thought it might be interesting to you chaps

DaveR

Hi David,

i'm in a weird situation - all around were companies and researchers trying to develop dispensers capable of dispensing small volumes and dots of high-viscous pastes - something smaller than 100 micrometers (or 4 mils).

We had some coopeartion with a group developing peristaltic microdispensers with this goal too.

Then i was in acute need of a process where i had to place droplets of 30 microns (or 1.2 mils) size of an extreme high viscouse glue (thicker than toothpaste).

As there were no fitting systems, i tried some ideas and developed on my own - here an image - an array of droplets 30 microns in diameter and 100 microns distance:


With the same method i was able to dispense droplets of 10 microns diameter or even submicrons - not very fast, but extremely precise in size.

We patented the idea and my boss tried to sell the idea and complete development to some big companies in the dispenser market.

It didn't work!

They found the idea great and very usefull, but as their customers actually are busy with systems in the range 0f 100 microns and evolving down to 50 microns, a system capable of ten times finer droplets would cause serious disturbances in the market, so we shouldn't interfere!!!

So i'm the only guy able of dispensing until sub-micron sizes with macroscopic methods (some AFM-systems are able of some nanometers with low-viscous fluids, but this is a complete different area), but no one is serioulsly interested ?!?

Viktor

"cause serious disturbances in the market, so we shouldn't interfere!!!"

This is Germany?

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Hell, there are no rules here - we're trying to accomplish something.

Opportunity is missed by most people because it is dressed in overalls and looks like work.

Thomas A. Edison

Hi Forrest,

... yes ... it's real life in Germany

My youngest sister lives now since 9 years in the USA (NewArk-region) and i was sometimes thinking about migrate somewhere else - but my wife didn't like the idea ...

Viktor

Dang Victor

"cause serious disturbances in the market" is the american dream! Build a better mouse trap and the world will beat a path to your door, is the saying over here.

Of course there is eventually some benifit to letting the wizzard mutter away in lab(grin).

Does the idea not scale up to larger sizes?

I just stumble across this:

[www.mitsuboshi.co.jp]

Victor, what is the patent number for this microdispenser.you developed and could not sell.

Hi DB,

it's DE102004007512A1 or look at the sketches here (pages 9-13): [depatisnet.dpma.de]

Viktor

Edited 1 time(s). Last edit at 03/15/2009 12:52PM by Viktor.