4. Electronics Production¶
One relatively easy way to produce your own custom printed circuit boards is to use a milling machine which is this week’s topic.
PCB manufacturing with Roland/DGshape SRM-20¶
Generating toolpaths¶
Milling machine needs to know where to mill, and that is where toolpaths play a big role.
For Roland/DGshape general purpose milling machine a toolpath to cut out pcb can be created with mods.cba.mit.edu.
In mods, click right mouse button to open a menu, select programs, open server program, under machines - Roland - mill, select SRM-20, PCB svg to open a default program flow of generating toolpaths from svg files. Similar program flow is also available for png files.
Start editing workflow by deleting websocket, as our milling machine is not connected to network.
Replace deleted web socket by adding file saving module: click right mouse button, select modules, open server module, under file select save.
Connect new module’s input to toolpath module’s output (where deleted module was connected to) by clicking file at startpoint and endpoint. Resetting origin to 0, 0, 0 is also necessary.
Load .svg file, change dpi to something bigger, like 2400, remember that copper is white, so invert the png conversion. Check that size makes sense.
TODO, write out following points.
Set tool diameter, calculate and check that every cut is executed. Save output file
Load outline file, select mill outline, check that size matches Set tool diameter, cut depth and max depth
Same for linetest on 0.2 mm and 0.1 mm drill bits + outline.
Operating milling machine¶
Open VPanel and move bed to view position.
Use double-sided tape to attach pcb stock to milling bed. If milling fails, try masking bed and pcb stock with masking tape and glue them together.
Change tool to 0.2 mm v-shaped milling bit.
Set xy origin (front-left corner) and z-origin. In setting z-origin, move milling bit close to pcb surface, then open collet and lower milling bit so it touches surface and tighten collet.
In VPanel open trace .rml file (clear previous queue!) and hit run.
Check if milling machine is making good-looking progress by pressing pause and moving bed to view position, vacuuming might be necessary, if all is well, continue.
After milling traces is ready, DO NOT remove pcb or reset xy-origin, to proceed to milling outline. Vacuum machine and pcb.
Change milling bit, reset z-origin.
Run outline cut.
Vacuum machine, remove pcb, remove tapes from machine and pcb stock.
Inspect result.
PCB manufacturing with LPKF S62 circuit board plotter¶
Operating LPKF S62¶
Our FabLab got this one free & used after local polytechnic school had no future use for it. This model dates back to late 2005, so pretty old machine.
Turn LPKF machine on
Start Circuit Pro
Load default template
Start process planning wizard
Select PCB
Select single-sided top
FR4
Done
Click import data button
Select files
Check that files loaded ok, size matches, size is sensible etc.
Generate isolation and contour routing toolpath
Change isolation process to complete rubout
Change copper thickness to 35 um
Next tab, contour routing, change to horizontal gaps
Next tab, drills, no changes, next tab, fiducials, no changes, next tab, pockets, no changes, blind vias, no changes, start.
Start the board production wizard
Mount material to bed, leave smaller margin to front edge
Material settings, define usable area, don’t move design!
Placement, move design to desired position, change number of copies if necessary
Machine fetches tool and moves, asks for milling width test, select good placement for test line and select mill a line
Machine warms up for 3 minutes
Confirm focus height for camera
Move windows away from camera area
Measure line width, RMB, point-to-point or point-to-line
Adjust width if necessary 8 um per adjustment step. Adjust the black ring like a screw viewed from top. 0.20 - 0.25 um is recommended by AnttiM.
Accept width when ready, and machine starts working.
End mill 1 mm bit needs calibration too, machine mills a circle and human needs to check that circle area was milled completely. Accept width when ready.
After milling¶
I removed thin copper strips on outline of pcb with knife, filed off attachment points to pcb stock and added 6 layers of masking to bottom of pcb to act as a shim when inserting pcb to usb port.
Group work of the week - PCB milling process characterization¶
Our group today included me, Mona and Kenichi.
For this week’s group work we manufactured a linetest pcb with 0.2 mm and 0.1 mm drill bits. Outline was cut with 1.0 mm drill bit. Png image files were converted to traces with mods.
From the picture above we can see that with 0.2 mm v-bit we get minimum of 0.1-0.8 mm traces depending on pass count and 0.8 mm spacing. This 0.2 mm v-bit board was milled twice, first with really thin contact between the tool and the board resulting quite narrow spacings, second time with lower z-origin resulting wider spacing, but also a noticeable amount of burr.
With 0.1 mm v-bit we get consistent-looking 0.4 mm traces and 0.4 mm spacing.
Outline was milled with 1.0 mm contour router bit with 0.6 mm depth of cut per pass, total cut depth of 1.7 mm.
According to assessment guide, we need to list some characteristics of machine we used, so here they are:
Roland SRM-20 specifications
| Rule | Description | Value | Unit | Online sources |
|---|---|---|---|---|
| Feed | Speed which tool advances laterally | 0.1-30 | mm/s | 1 |
| Speed | Tangential linear velocity at the outer edge of the cutter | Depends on tool diameter | m/min | 2 |
| Plunge rate | Rate at which the cutter is moved vertically into the material or during ramping moves | Less than 50% of feed rate | mm/min | 3, 4 |
| Depth of cut (traces) | How much material is removed when cutting traces | Need to be calibrated per use | mm | |
| Depth of cut (outline) | How much material is removed when cutting outline | Less than tool diameter | mm | |
| Tooling (traces) | How small tool can be used to mill traces | 0.1 mm V-bit | mm | |
| Tooling (outline) | What tool size is used for milling the outline | 1 mm countour router bit | mm |