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hacks:pcb

Objectives

To design a machine, method, or process to generate one-off printed circuit boards with the following conditions:

  1. Time from finished PCB layout to physical board must be less than 3 hours excluding setup.
  2. Traces for TSSOP packages must be possible (0.19-0.3mm traces, 0.65mm pitch).
  3. Two layers must be supported and properly aligned with minimal frustration.
  4. Board quality must be consistent and dependable.
  5. Minimal tool changes or chemicals.

Methods

Traditional

Toner Transfer

Works. Could be improved.

The traces are laser-printed in reverse onto some sort of glossy paper (e.g. magazine or photo paper), then transferred to a copper-clad board using a hot clothing iron or t-shirt press. The traces transfer to the board and act as an etch-resist. This guy has it dialed the best.

Issues:

  • A dedicated clothing iron is required
  • Inconsistent transfer (i.e. gaps in solid areas)
  • Multiple layers are difficult to align

UV Exposure

Works. Not well.

The traces are laser-printed onto clear acetate, then overlayed on a copper-clad board and exposed evenly to UV light. The board is then washed in developer solution that either washes away the exposed portions of UV-sensitive chemical, or wash away then unexposed portion, depending on chemical process used. The traces that remain on the board act as an etch-resist.

Issues:

  • UV chemicals are required to coat the board OR
  • Presensitized boards must be used, which are:
    • More expensive
    • Inconsistent from different manufacturers both in exposure time and development time
    • Require handling in a darkroom
    • Require rushing the process so as not to allow ambient light to ruin process.

Laser Cutter

Spray Paint

Has potential.

The board is evenly sprayed with a single coat of paint. After drying, the laser cutter vaporizes the paint along where the traces should go. Remaining paint is left as an etch resist.

Issues:

  • Laser power/speed must be fine-tuned to vaporize paint layer with excess copper heating (cut paths widen when copper acts as a heat-sink).
  • Paint layer is undesirably thick. May not be an issue?
  • Paint layer is difficult to apply evenly.
  • Vaporized paint leaves a residue that interferes with etching. Clean it with hydrogen peroxide or very very mild acetone bath?

Sharpie

Has potential.

Copper-clad is covered in Sharpie (permanent marker ink). Laser appears to “burn in” sharpie layer and make it resistant to acetone. After acetone bath, burnt in layer is left as etch-resist.

Issues:

  • Layer evenness is very difficult to achieve. Ink bath and rubber rollers will be attempted.
  • Acetone bath dilution must be tweaked.

Sugar

Laser printer toner is effectively sugar as a binding agent and carbon as a colourant. Because colour is unnecessary, sugar alone was attempted to be used as an etch mask.

Doesn't work.

  • Laser cutter has “air assist”, airstream designed to push slag through the workpiece as it is cutting. It blows the sugar off the copper instantly.
  • Using water to form a paste, still difficult to consistently achieve thin traces.

Toner

Doesn't work. Bad idea. Not dumb enough to try this.

Issues:

  • See above for air assist issues.
  • Nigh-impossible to work with cleanly.
  • Biohazard.

May be do-able on custom laser-diode CNC platform.

Acrylic Trench

Works. Not well.

Laser etch traces into acrylic medium. Fill etched area with conductive paint.

Issues:

  • Thick traces.
  • High trace resistance.
  • Can't be soldered onto.

Printers

Inkjet

Works. Not well.

Modify printer to print traces directly onto copper-clad. Use as etch resist.

Issues:

  • Typical inkjet ink is a dye as opposed to a pigment and is water-soluble. Ink cartridge must be filled with special MISPRO pigment:
    • Expensive.
    • Messy to refill.
    • Runny/blurry edges.
  • Double sided boards have alignment issues.

Laser

Works. Not well.

Laser printer can be modified to print directly onto copper-clad. Use as etch resist.

Issues:

  • Larger printed areas have inconsistent fill/gaps.
  • Alignment issues for 2-layer boards and multiple passes to fill in gaps.

Wax Inkjet

Works. Current status unknown.

Jeff Gough had some success with this. A piezo inkjet head (as opposed to a thermal inkjet head) used by Epson printers can be modified with a heated reservoir to print directly with wax.

Issues:

  • Print heads eventually had clogging issues.

Dye-Sublimation

Has potential.

Dye-sub is now available for the consumer market with Canon's Selphy line of printers. It works through a thermal print head sublimating wax or resin into a gas, then allowing to to solidify onto the print medium. It should work as an etch resist.

Potential issues:

  • Sublimation results in soft edges, may lead to improperly etched traces if print resolution is too low.
  • May rely on special coatings on print medium for ink to bind properly.
  • Water insolubility may rely on final clearcoat layer that is printed.

Thermal Transfer

Has potential.

Similar to dye-sub.

Issues:

  • Printers are expensive, niche, and difficult to find in appropriate sizes.

Thermal Wax Transfer

Has potential.

Similar to dye-sub. Replace ink transfer cartridges with wax paper or similar. Thermal print heads should transfer etch resist wax to copper-clad.

Issues:

  • Very likely.

Wax Printer

Has potential.

Some Xerox Phaser printers use a solid wax block as ink. Would work as an etch resist.

Issues:

  • Only available on business lines.
  • Expensive.
  • Huge.
  • May be difficult to modify to accept copper-clad.

3D Printer

Doesn't work.

Single layer of plastic laid down as etch resist. Laying down conductive material may soon be an option.

Issues:

  • Accuracy. Print heads tend to be at least 0.35mm.
  • Plastic shrinkage.
  • Will not stick to copper.

Mechanical

CNC Milling

Works. Needs a special setup.

Issues:

  • Messy.
  • Requires babysitting.
  • Limitations on trace sizes.
  • Endmill bits are expensive.

Vinyl Plotter

Works. Not well.

Issues:

  • Terrible accuracy.
  • Results in the strangest looking PCBs imaginable.

Electrical Discharge Machining

Has potential.

Electrical arc from brass wire to workpiece removes material in a very controlled and accurate manner to isolate traces. Reaction happens in a dielectric such as mineral oil or distilled water.

Issues:

  • Difficult to design machine for precision.
  • Expensive.
  • Terrifying.

Electro-Chemical Machining

Doesn't work.

Workpiece is set up as an anode while electrode is used as a cathode. Reaction takes place in a conductive electrolyte, such as salt water.

Issues:

hacks/pcb.txt · Last modified: 2014/03/21 03:43 by jarrett