Week08: Electronics Production

Group Assignment

• characterize the design rules for your in-house PCB production process
• submit a PCB design to a board house

This group assignment document was written by Naoki Hayashi.

Workflow

A. CNC

The CNC machine we used was the Genmitsu PROVerXL 4030, located on the 5th floor of FabLab Kannai.

Power switch and emergency switch are located at the black power box.

Title	Spec
Working area	400 x 300 x 110mm
Accuracy	0.1mm

More info

B. Endmills

We have tested 2 types of endmills for traces, and 1 type of endmill for interior. We also tested ball-nose tapered endmill for both traces and interior. To efficiently mill fine traces and cut holes and outlines, changing endmills is required.

1. Install fine endmill to mill traces
   • 1/64 SE 2FL ALTIN End Mill: Standard option
   • V Bit End Mill 30 Degree 0.1mm Tip: Cheap
2. Change endmill to mill holes and outline
   • 0.7mm flat endmill

Because changing endmills is tedious, there are alternative ways such as auto tool changer and special endmills for both traces and outlines. We tested Ball-nose tapered endmill.

• R0.25-15-D1/8” -2F Carbide End Mill

How ro change endmills

1. Hold the chuck (upper) and loosen the chuck nut (lower) using 2 wrench
2. (Change collet depending on tool diameter: e.g., 1/8, 1/4)
3. Insert new endmill and tighten the chuck (Due to the lower limit of Z travel, endmills should stick out roughly 15mm from the chuck nut)

C. Generate G-code

We used the legendary mods.

1. Open mods
2. Right click on the white canvas
   Program > Open program > machines > G-code > mill 2D PCB
3. Select PNG file on the left
4. Select default presets: set PCB defaults
   • To only isolate trace: isolate traces (1/64)
   • To mill outline and holes: mill outline (1/32)
5. Generate toolpath at the middle: mill raster 2D
   • For holes and outline, we changed tool diameter to “0.7mm” since the endmill we used was 0.7mm diameter.
   • Generate toolpath: calculate
   • Preview: view (3D preview didn’t work without reloading the Mods)
6. Automatically download “.nc” file (G-code)

D. Attach workpiece

Attach material on the sucrificial MDF board using double-sided tape.

Check if double-sided tapes are not curled

in order to keep the top surface flat

E. Control CNC

We used gSender.

1. Conncet the CNC to PC via USB
2. Select port at the top left corner Conncect
3. Load G-code
4. Calibration
   • Move the tool to a starting position (on material) using the arrows X/Y
   • Zeroing X/Y using Zero X, Y
   • Put in a piece of paper on material
   • Carefully lower tool using Precise, which allows 0.1mm accuracy, until the paper doesn’t move
   • Lower further 0.1mm for a thickness of paper and Zero Z
5. Start job

Surfacing

In order to mill accurately, the top surface of the sacrificial MDF board to which the PCB attached must be flat.

1. Test if the MDF surface is flat by zeroing at a corner, and try lowering to Z0 at the other corners
2. If not flat, change endmill to a surfacing router (collet diameter needs to be changed to 1/4 as well)
3. Mill the top surface of the sucrificial MDF using Surfacing command which generate G-code for it
   • Larger area than the MDF
   • Small depth (e.g., 0.3mm)
   • Use vacuum to collect dust

Characterization

Below is a comparison of the results for three end mills: a 1/64 straight, a V-bit, and an R0.25 ballnose tapered end mill. Overall, the 1/64 performed well, with the V-bit being the best in terms of having the least burrs and maintaining the finest traces. Whereas, the R0.25 removed the finer traces more gradually and had the largest burrs.

1/64 Straight bit	V bit 30 degree	R0.25 Ball-nose tapered
Traces thicker than 0.12mm are retained	Traces thicker than 0.07mm are retained	0.10~0.16mm traces are gradually removed
A little burr occurred (may be due to wear)	Almost no burrs occurred	A large amount of burrs occurred though it was new
Good	Great 👍 (At least while new)	Not suit for PCB milling

Validation of the PCB design rules

As a result, we were able to validate the PCB design rules for the CNC machine:

• Copper clearance: 17 mil (0.4318mm)
• Copper width: 16 mil (0.4064mm)

Board house

We tried uploading the development board we designed to PCB Way, one of the board houses. Below is the process of exporting and uploading.

Gerber file is a standard file format used in PCB manufacturing. It contains the design data for each layer of the PCB, including copper traces, solder masks, silkscreen, and drill holes. Manufacturers use these files to produce the physical PCB.

1. MANUFACTURING > CAM Processor
   Check “Export as ZIP”
   
2. Local CAM Jobs > examples > example_2_layer.cam
   Included the logo layer
   
3. Go to PCB Way
4. Upload the ZIP file
5. “Get an instant PCB quote”

Week 08 Group Work Completed. And on to the Individual Assignment…

Each person’s URL is listed

• Shintaro Ito
• Naoki Hayashi
• Yuya Tokuyama