Drilling a laser-etched board

A board whose copper was etched on the fiber laser, and only needs its holes. Nothing on it was cut from the mill's origin, so its drill file cannot simply be run: SRM-CAM measures where three of its holes really are, fits the whole hole pattern onto the board, and writes a drill file for the board in front of you. Proven on a 90 × 72 mm board with 120 holes: worst pad 0.034 mm.

Novice or Pro?

This page is for Pro: Interface › Pro.

Export from KiCad→ Load, Mirror off→ Find three holes→ Write the drill file→ Drill in VPanel

1 · Export from KiCad

The board was etched on F.Cu, so the copper faces up on the bed. SRM-CAM's loader reads the bottom copper, so the F.Cu Gerber goes in under the B.Cu name:

  1. Plot the copperFile › Fabrication Outputs › Gerbers: F.Cu and Edge.Cuts, into one folder. Then rename the …-F_Cu.gbr file to …-B_Cu.gbr.
  2. Drill filesGenerate Drill Files…: Excellon, millimetres, PTH and NPTH in separate files, drill origin Absolute, into the same folder.

From the command line, the same: kicad-cli pcb export gerbers --layers "F.Cu,Edge.Cuts" (then the rename) and kicad-cli pcb export drill --excellon-separate-th --drill-origin absolute.

2 · Load it, and clamp the board

  1. Open the folderFile › Open Gerber folder… (Ctrl+O).
  2. Mirror offUntick Set up the job › Mirror for bottom-up milling. The picture then matches the laser preview: the copper the way it looks on the bed.
  3. Clamp it anywherePut the board on the bed and clamp it. Drag the picture on the stage to roughly where the board sits, so Go to it lands the bit near the first holes.
  4. Open the stepSelect Drill a board made elsewhere at the bottom of the left rail. It is there on single-sided jobs only.

3 · Find three holes

This is the same way the lab places a flipped double-sided board: SRM-CAM knows where the holes are in the Gerbers, and finds their exact centres on the real board by touch.

  1. Choose the holesSuggest three picks three holes far apart and well out of line, or tick Pick on the board and click your own. The spread makes the rotation accurate; the triangle catches a mirrored board.
  2. Go to itSelect a row and press Go to it: the bit jogs to where the picture has that hole. After two holes are measured it aims by the fit; on a measured hole it goes to the measured centre, so you can check it by eye.
  3. Find it for meWith the bit over the hole, about 2 mm above the copper, never at Z0 (its first move is sideways at the starting height), press Find it for me. It finds the centre through the Arduino's touch test, to about 50 µm. The fallback: lower the bit to just above the pad, centre it by eye and Capture, or type the position in.
  4. Read the fitAt three holes the fit is applied: the stage draws the board where it really is, and Worst pad says how far the holes disagree. Under 0.10 mm is good; 0.25 mm or more is too far out, and the app asks before writing anything under it.
What Find it for me needs here

A copper-free circle at the hole for the bit to find (a mounting hole in a copper pour works well), and the probe clip on the copper around it: a laser board's pads are isolated from each other, so the clip has to be on the copper that surrounds that circle. Where there is no copper the bit presses about 0.2 mm into bare laminate, which the drill removes anyway.

How it finds a centreA surface reference on the copper beside it, then short descents that touch copper or find none: march out, halve the gap to 50 µm, both ways in X, then Y. Click in the view to aim somewhere else.

Three, and by which pin

Three holes are required because two fit a mirrored board just as well as the right one. The third catches it, but only if each hole is found by which pin it is, never by where it sits in the picture. With the picture mirrored against the board, the three pins cannot be fitted by any turn and shift, and Worst pad comes out in millimetres: toggle Mirror for bottom-up milling and measure again.

Try itSuggest three, then Go to it and Find it for me for each. At three the holes move onto the real board. Then tick Picture mirrored against the board and do it again.

Let the fit stretch the board as well adds a uniform scale, for a laser whose output is a fraction of a percent off size. Leave it off unless the worst pad says you need it: it can hide a mis-measured hole as a fake stretch.

4 · Write the drill file, and drill

  1. Write the drill fileWrites <name>_drill_fitted.nc: every hole, moved onto the measured board. Nothing else is written.
  2. Don't touch XYDo not move the board, and do not reset X or Y, between measuring and drilling.
  3. Zero ZWith the drill bit, on the copper, with VPanel on G54; and with the bit on the copper, machine Z must stay above −50 mm (see Milling a board).
  4. Drill itIn VPanel: Cut, Add the one file, Output. There is no dry-run file for this job.

Then check every hole landed inside its pad ring, and leave the machine as you found it (see Leave it as you found it).

Previous← Double-sided boards