Automated Circuitry Making

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Revision as of 18:19, 14 April 2010 by DavidCary (talk | contribs) (How much precision does a automated circuitry making machine require?)
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Automated Circuitry Making

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This is the process of making electronics for the RepRap board. Primarily it is aimed at using a RepRap, combined with modified software to take an electronic representation of a circuit and create it as a physical object. There are varying levels of degrees here from copper only, to drilling, even component placement and soldering. A complete cycle electronics assembly machine would be an amazingly awesome and marvelous thing.

Obviously, all of these ideas require an actual RepRap machine as a prerequisite. (Ideas that do not require an actual RepRap are collected at alternative electronics).

PCB Creation

All of these processes start with a blank copper clad board and the desired end result of a circuit board with the traces required for the board. There are a variety of ways we are examining for this approach.

Milling Head Route

This method would use a router attached to the RepRap machine and would selectively mill away the copper to separate the copper tracks from each other. The things to be investigated are:


  • MillingDrillingHead -- how to make PCBs the next-most-common way, starting this copper-clad PCB and milling off the unwanted bits of copper.
  • how accurate can the milling be done
  • how small the area milled can be... at least between pins
  • if a reprap machine could withstand the stress (if not, can you re-inforce it / reprap new parts?)
  • Does the Replath software (Builders/ReplathHowto) handle milling a PCB correctly?

Apparently the Fabio board is already being made by a milling process, and one RepRap opto endstop circuit has been successfully milled (see example circuits below).

Etching / Resist Route

With this method you would be applying some sort of etch resist to the copper clad board by means of the extruder head. There are a couple ideas that we have been tossing around and are interested in pursuing. We basically only need one way to work. The etching itself is a simple process that is basically foolproof if one is using the correct precautions. Simple objects needed to do the lab work could even be printed with a RepRap machine (etch bath tray / bubbler / heater / beaker, stirring rods, etc.) This would make the etching process much simpler.

  • MakePCBInstructions -- how to make PCBs the traditional way, starting with copper-clad PCB and using an acid that can dissolve the unwanted bits of copper.
  • these would be fairly easy to do and pose the fewest questions of if it will work.
  • etching and semi-nasty chemicals are involved. not super fun.
  • Does the Replath software (Builders/ReplathHowto) handle placing thermoplast resist or ink resist correctly?

Thermoplast Resist

This is the ideal route. You are using something that already exists in the form of an extruder. You simply need to find the right combination of plastic, extrusion rate, etc. It would be a very elegant solution.

  • you already have an extruder, and practically no modifications required.
  • you could print a holder for the board to get perfectly lined up 2 sided boards.
  • the traces should be protected really well and thusly survive the etch process nicely.
  • afterwards, the plastic could also serve as an excellent insulator.
  • downside is that it may be tough to get the plastic off the board to solder.

ABS may end up being a material of choice in this process. It is temperature resistant (hot traces/soldering process), it has excellent insulation properties, and one of the most crucial: it dissolves in acetone. it remains to be determined just how easily this process occurs, however it is highly likely that the abs could be made thin enough for this to be simple. Also, if the ABS was left on prior to the drilling process, it might possibly serve as a nice guide for the bit before it hits PCB. It could also prevent/reduce burrs from forming during the drilling process. Afterwards, it could simply be cleaned off and the pads would be ready to solder.

Ink Resist

see DrawingPlottingHead

If plastic serves to be too difficult or expensive, then an ink resist process would probably work as an alternative. Instead of using an extruder print head, it would simply move a marker such as a Sharpie mounted in a holder that would draw the circuit onto the board. The holder itself could be printed out of RepRap parts and it would probably not even need its own controller... there would be no electronic parts.

  • Sharpie pens are cheap and universal.
  • you would also then have the makings of a drawing bot, useful for making art.
  • the ink resist might not be of highest quality with pitting being an issue.
  • it might be tough to find a pen of required tip size. testing needed.

Drilling the PCB

This is another task that is pretty mundane and repetitive. It also requires either extremely steady hands, or a drill press. Regardless, it is one that is well suited to automation. The holes locations and sizes are all known based on the circuit layout. The only thing needed to be done is to drill a hole at a certain coordinate. Drilling would be less stressful on a reprap machine. Especially if the hole being drilled was very small (1mm). This hurdle in the process should be fairly easy to clear. The problem it presents seems to be straightforward. However, perhaps Murphy will have something to say about that.

solder paste dispenser

Surface mounted parts are most easily attached by using solder paste. Fortunately for us, we theoretically have one, so before the SMT parts are placed, the syringe goes over each pad and deposits the required amount of solder paste on each contact.

Placing Components

This task appears to be a pretty daunting one to automate. It deals with components, except some of them have multiple contacts and a variety of form factors. Things could be simplified with moving to a reduced component part, and a technology more suited to automated production like SMT (surface mount technology)

SMT component placement Method

The pick/place head (Pick and Place ToolHead) deposits a component directly onto the solder paste which will ideally secure it in place until its ready to be soldered.


Through-hole Components placement

This is much more tricky, and it may be simpler to assemble by hand. However, through-hole ICs could be converted to surface mount by simply bending their pins outwards so they lie flat against the PCB surface. This would be easier than true SMT parts because less accuracy and fine detail would be required. However, the same technique would not be as easy to apply to other types of through-hole components, although it may be feasible


Soldering

After the surface mount parts have been placed on the solder paste, the board needs to be heated up. This can be accomplished with the help of a very common, simple household item: A toaster oven! This has actually been done before, and its a pretty elegant process. The solder will actually center the SMT parts, and will bead up nicely around each component leg. Here are more links on the topic from people who have actually done it:


alternatives to standard copper-clad FR4 PCBs

  • The first reprapped circuit was a RepRap opto endstop circuit (see examples below), a relatively solid chunk of plastic with some channels that were later filled with a special extruder that prints out molten solder.
  • "Copper Plating Wire Glue"
  • Simple PWM Output Design - Spoondriver ???
  • Instead of using copper-clad FR4 to connect components, somehow use copper wire placed by a SpoolHead and somehow stapled/glued/soldered to an appropriate substrate?


Fields Metal Deposition

This technique is definitely a departure from the norm of circuit manufacture, but its potential is still great nonetheless. The basic idea is that you use a heated extruder to melt and extrude Fields Metal, an alloy with an especially low melting point. Its lower than the plastic used to print with. Anyway, as you're constructing the part, you could lay down tracks of Fields Metal within the part itself, which leads to some very interesting options such as truly 3-dimensional circuits, parts with completely integrated circuitry, and a nicely integrated manufacturing process.

However, there are still some issues and unknowns involved. It is not known how well the circuits will stand up to regular usage (what if components heat up past the melting point of the metal) and it also doesn't lend itself well to automated pick and place processes. That being said, it is still promising and theres a good chance one of these techniques will pan out and become the dominant way of creating circuits with RepRap.

precision

How much precision does a automated circuitry making machine require?

through-hole PCB

Practically all through-hole components come with pins at 0.1" (2.54 mm) pitch. ... hole-to-trace alignment ... ... hole-to-hole alignment ...

surface-mount PCB

Many popular SMT microcontrollers have pins at 0.80 mm pitch (~32 pins/inch) -- such as the 32TQFP ATMega168 in the Fabio board or the 44TQFP ATmega644PA used in some other Arduino-compatible boards. Ideally the PCB has 0.4 mm trace/space (0.015 inch trace/space): the pins rest on 0.4 mm wide parallel metal traces, separated by 0.4 mm isolation gaps. If some places cut away a bit to much (0.2 mm trace / 0.6 mm space), or other places cut away a bit too little (0.6 mm trace / 0.2 mm space), it often will work just as well.

If your cutter or etch mask has enough resolution to "fan out" metal traces from those 32 (or 44) pins of the microcontroller to a wider pitch to the rest of the board, it has plenty of resolution for the traces and all other parts on the RepRap controller boards.

surface-mount pick-and-place

The pins of a 0.80 mm pitch part must be less than 0.40 mm from their corresponding pads, or it will "jump" during reflow -- any particular pin will look properly soldered to a pad, but they all will be off-by-one soldered to the *wrong* pad.

example circuits


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