Copper patterning

- Aug 13, 2018-

Copper patterning

The first step is to replicate the pattern in the fabricator's CAM system on a protective mask on the copper foil PCB layers. Subsequent etching removes the unwanted copper. (Alternatively, a conductive ink can be ink-jetted on a blank (non-conductive) board. This technique is also used in the manufacture of hybrid circuits.)

  1. Silk screen printing uses etch-resistant inks to create the protective mask.

  2. Photoengraving uses a photomask and developer to selectively remove a UV-sensitive photoresist coating and thus create a photoresist mask. Direct imaging techniques are sometimes used for high-resolution requirements. Experiments were made with thermal resist.

  3. PCB milling uses a two or three-axis mechanical milling system to mill away the copper foil from the substrate. A PCB milling machine (referred to as a 'PCB Prototyper') operates in a similar way to a plotter, receiving commands from the host software that control the position of the milling head in the x, y, and (if relevant) z axis.

  4. Laser resist ablation Spray black paint onto copper clad laminate, place into CNC laser plotter. The laser raster-scans the PCB and ablates (vaporizes) the paint where no resist is wanted. (Note: laser copper ablation is rarely used and is considered experimental.[clarification needed])

  5. Laser etching The copper may be removed directly by a CNC laser. Like PCB milling above this is used mainly for prototyping.

The method chosen depends on the number of boards to be produced and the required resolution.

Large volume

  • Silk screen printing – Used for PCBs with bigger features

  • Photoengraving – Used when finer features are required

Small volume

  • Print onto transparent film and use as photo mask along with photo-sensitized boards, then etch. (Alternatively, use a film photoplotter)

  • Laser resist ablation

  • PCB milling

  • Laser etching

Hobbyist

  • Laser-printed resist: Laser-print onto toner transfer paper, heat-transfer with an iron or modified laminator onto bare laminate, soak in water bath, touch up with a marker, then etch.

  • Vinyl film and resist, non-washable marker, some other methods. Labor-intensive, only suitable for single boards.