Tutorial Double Sided PCB

This tutorial makes the machine code for both sides of a double-sided board. First you sync the 2 sides with the 2-Sided plugin. Then you prepare all the jobs. You start the machine only after all the G-code is ready.

Read Tutorial Single-Sided PCB first. The steps for one side are the same.

This tutorial uses Beginner mode, the default level. See Beginner and Advanced mode.

The idea

A double-sided board has copper on both sides. When you mill the bottom side, the board is turned over. The bottom layer must be mirrored so that it lines up with the top layer after the turn. The alignment holes and the pins of the machine keep the board at the same position after the turn.

The order of the work is:

1. Sync the boards. Use the 2-Sided plugin. It aligns the bottom layer and the drills to the top layer, mirrors the bottom layer and makes the alignment holes.
2. Prepare all the jobs. Make the isolation, the copper clearing, the drill and the cutout jobs of both sides. Save all the G-code.
3. Cut the board. Drill the alignment holes. Engrave and clear the top side. Turn the board over on the pins. Engrave and clear the bottom side. Cut the board out last.

Do not make a job before you sync the boards. A job made from an object before the mirror does not follow the mirror. You must make it again.

Screenshot placeholder: images/Tutorial-Double-Sided-PCB-1.png — a diagram of the board turned over around the axis, with the alignment holes marked.

What you need

• Gerber copper files of the top and bottom layers.
• The Gerber outline (board edge).
• The Excellon drill file (the drills of both sides).
• The tool diameters of your tools. Include a tool for the alignment holes.
• A plan for how you turn the board: left to right or top to bottom, and how you fix the board on the pins.

Part 1: Sync the boards

Step 1: Load the files

1. Open the top copper with File > Open > Open Gerber (Ctrl+G).
2. Open the bottom copper with the same command.
3. Open the outline with the same command.
4. Open the drill file with File > Open > Open Excellon (Ctrl+E).

Screenshot placeholder: images/Tutorial-Double-Sided-PCB-2.png — the Project tab with the top, bottom, outline and Excellon objects.

Step 2: Mirror the bottom side and make the alignment holes

The 2-Sided plugin does the sync in 1 operation. These steps use the Beginner view.

1. Click Plugins > 2-Sided PCB (Alt+U). The panel opens in a new tab of the side panel. The tab shows the plugin name.
2. In Source Objects, select the top copper in Top.
3. Select the bottom copper in Bottom.
4. Select the drill object in Drills.
5. In Type, select the way you turn the board: L-R (left to right) or T-B (top to bottom).
6. In Alignment Drills, turn on Enable.
7. Set Drill Dia to the diameter of the alignment drill.
8. Set Offset, the distance of the alignment holes from the board.
9. Keep Failsafe and AutoAlign on.
10. Click Generate.

The plugin registers the bottom layer and the drills to the top layer. It mirrors the bottom layer in place. It puts the alignment holes in an Excellon object named Alignment Drills. The Top object and the drills are not mirrored. The full operation is 1 Undo step.

Screenshot placeholder: images/Tutorial-Double-Sided-PCB-3.png — the 2-Sided panel in the Beginner view with Top, Bottom, Drills, Type and the Alignment Drills section.

Note: For the mirror options of the Advanced view (axis, Point, Box, Snap reference, PCB Alignment), see Double-Sided.

Step 3: Check the sync

1. Show the top copper, the mirrored bottom copper and the drills on the canvas.
2. Check that the pads of the 2 layers and the drill holes are at the same positions.
3. Check that the text on the bottom copper reads backwards.
4. Check that the alignment holes are outside the copper.
5. If the result is wrong, undo with Ctrl+Z. Change Type or the options and click Generate again.

Screenshot placeholder: images/Tutorial-Double-Sided-PCB-4.png — the top copper and the mirrored bottom copper plotted together, with the holes at the same positions and the alignment holes outside the board.

Note: If AutoAlign stops because it finds too few matches, use Align Objects to move the layers to the correct position first.

Part 2: Prepare all the jobs

Make all the jobs now, from the synced objects. Give each job a clear name, for example board-top-iso and board-bot-iso.

Step 4: Prepare the top side

1. Make the isolation of the top copper with Plugins > Isolation (Alt+I). Click Generate Geometry. See Isolation Routing.
2. If you want to remove the copper between the traces, use Plugins > NCC (Alt+N). See Non-Copper Clearing.
3. Make the CNC jobs of these geometries with Plugins > Milling (Alt+M). Click Generate CNCJob object. See Milling.

Step 5: Prepare the bottom side

1. Select the mirrored bottom copper.
2. Make its isolation with Plugins > Isolation.
3. If you want, clear the copper with Plugins > NCC.
4. Make the CNC jobs with Plugins > Milling.

Step 6: Prepare the drill jobs

1. Make the drill job of the Alignment Drills object with Plugins > Drilling (Alt+D). See Drilling.
2. Make the drill job of the board drills with Plugins > Drilling.

The drills are not mirrored, so you drill them from the top side.

Step 7: Prepare the cutout

1. Make the cutout of the outline with Plugins > Cutout (Alt+X). See Cutout.
2. Make the CNC job of the cutout geometry with Plugins > Milling.

Screenshot placeholder: images/Tutorial-Double-Sided-PCB-5.png — the CNCJob objects of both sides, the drills and the cutout in the Project tab.

Step 8: Save the G-code

1. Select each CNCJob object.
2. In the Properties tab, click Save.
3. Save each job with a clear name. Put a number in the name for the order of the work, for example 1-align-drills.nc, 2-top-iso.nc, 3-drills.nc, 4-bot-iso.nc, 5-cutout.nc.
4. Save the project with File > Save > Save Project (Ctrl+S).

Part 3: Cut the board

Start the machine only after all the G-code is saved.

Step 9: Drill the alignment holes

1. Fix the blank board on the machine bed.
2. Set the zero of the machine. Do not change the zero until the board is finished.
3. Run the alignment drill job. Drill through the board and into the spoil board.
4. Put the pins in the holes.

Step 10: Cut the top side

1. Run the top isolation job. Then run the top copper clearing job, if you have one.
2. Run the drill job of the board drills.

Step 11: Turn the board and cut the bottom side

1. Remove the board. Turn it over in the Type direction that you used in the 2-Sided plugin.
2. Put the board back on the pins. With Failsafe on, the board fits the pins in 1 direction only.
3. Run the bottom isolation job. Then run the bottom copper clearing job, if you have one.
4. Run the cutout job last.

Screenshot placeholder: images/Tutorial-Double-Sided-PCB-6.png — the board on the machine, turned over, with the alignment pins through the alignment holes.

Check before you cut

• Check that Type matches the way you turn the board.
• Check that the bottom copper is mirrored. The text on the bottom copper must read backwards on the canvas.
• Check that all the jobs were made after the sync.
• Check the alignment holes on the canvas. They must be outside the copper.
• Use a test board first. Check the alignment after the first side.

See also

• Tutorial Single-Sided PCB
• Double-Sided
• Align Objects
• Isolation Routing
• Non-Copper Clearing
• Drilling
• Milling
• Cutout
• Glossary