Week4- Electronics Production

Group Assignment for the week:

Characterize the design rules for your in-house PCB production process: document feeds, speeds, plunge rate, depth of cut (traces and outline) and tooling. Document the workflow for sending a PCB to a board house Document your work to the group work page and reflect on your individual page what you learned

Roland SRM-20

This is the Roland SRM-20 milling machine that we have in our lab.

We keep all the tools associated with the machine on top of the machine with the help of magnets especially the alen-key. The green button shown below is the power button.

Two end mills are used for this group assignment, 1/32” and 1/64” endmills shown below. We use the 1/64” for cutting out the traces and 1/32” for cutting out the borders.

Note: Never use 1/64” bit for cutting the boards through as it can break the bit.

MODS for SRM-20

First, download two of the linetest image files. This files will be used to see and test of our bits and machines accuracy to mill thin, 0.001 to 0.02 lines which will be very helpful in deciding the trace with of our circuit.

Interior file:

Traces:

We make use of Mods for convering our milling files from Png to rml files which is used by SRM-20

Navigating through Mods is quite tricky for the first timers. Here are the steps taken:

• When you land on Mods page right click on Program–> Click on open Program–> Scroll down to SRM-20 mill and select Mill 2D PCB

1. As shown below is for SRM-20. Here you can either use SVG or PNG file. We 1.selected a PNG file.

2. Next, 2.select 1/64 for milling the traces and 1/32 for milling the boarders. No need to make any changes other as the software does it for us.

3. Click calaculate and this generates a path for the milling. This might take times as per you design.

4. Make sure to turn on the Save file and tun off the object above it.

5. This will download the file for you. If the download doesn’t take place , Click on calculate again.

This is for Interior trace with 1/32” end mill.

Default G-code setting for 1/64 traces: -cut speed: 2.5mm/s, -plunge speed: 2.5mm/s, -job height: 2mm, -spindle: 11000RPM, engraving depth: 0.1524 mm.

Setting for 1/32 mill outline: cut depth: 0.024 in, max depth: 0.072, speed: 4mm/s, plunge speed: 2.5 mm/s, spindle: 11000RPM.

Preparing the Copper Board

Once the files have been dowloaded we go on to preparing the machine. Start by preparing your boards, we are using a single sided FR4 copper board. You can either use double sided tap or use an epoxy tape to stick your board to the bed of Roland. We prefer using epoxy tap for single sided board as it makes sure your entire board is fixed on the bed and it won’t matter if you are milling the exterior first which is not the case for double sided tape. If you are using double sided board then it will be hard to take of the epoxy board whne you want to mill the other side.

Place you copper board on the sticky side of the tape and make sure it is flat witout wrinkes in the middle.

Resizing, to the perfect shape.

Peel the paper and stick the bed on the bed very carefully. But before that remove the old boards

Milling

You tighten milling bit using an alen key, as shown below and make sure to keep it little shorter before preparing the Home for the machine.

Now, open the Vpanel for SRM-20 and by using the keys on the panel you can move the spindel to your desired location. (Always make sure to not waste your board by selecting the optimal position)

First, move the spindle to most corner side of the board by using the X and Y keys. The set that as your home by clicking on the X/Y under set orgin point.

Next, move the spindle to somewhere center on your intended milling space and slowly bring down the spindle using Z key on Vpanel. Change the cursor step to x100 or even X10 to slowly bring down the spindle and reduce the risk of hitting the end mill on the board which will break the end mill.

When the spindle is down enough, loosen the endmill and let it drop (gravity fall as Fran from beach lab calls it) on the board. Then tighten back the mill. This will you you Z so set that by clicking on the Z under set orgin point.

Roland SRM-20 is ready to mill your board, select the .rml files downloaded from mods by slecting Cut-> Add( Make sure delete all the other files) -> and open the file and -> select output.

On the Vpanel you can observe the speed the the movement of the spindle.

Line tests Result

This is the line test board that we successfully milled. 1/64 bit was able to mill the .001 line but it is too thin, as the milling size incresed the traces are more visible. This board help us guide and select the trace for our future circuit boards.

1/32 was perfectly able to cut though the board.

Conclusion: After the line test we found that a value of the line width around .001 mil are bit risky and not milling well, but the line width nearer to 0.015 and above are milled quite good and thus line width above 0.015 to 0.02 are best for traces milling.

Always make sure to clean the workstation after using the machine.

Fiber Laser

We refered the fiber laser for PCB tutorial on fabacademy website and used Tortech flex speedy 400. We followed the instructions on for design and converted the orginal png file into Vector file by using Trace bitmap. Also drew the broder in red on top of the black background, it was mentioned that the width does not matter for outline.

There is no copper materail on the job controller so we created PCB material in material database. Also gave the setting for red and black color as out PCB design has those colors. First and second trial with the setting given in the tutorial.

For Black(Engrave fiberlaser): Power-> 80 Speed->20 frequency->20000 and pass->9.

For Red(Cut CO2):Power-> 80 Speed->0.6 frequency->5000 and pass->2.

As seen in picture below, laser was not cutting through the PCB and then we adjusted the border on the engraved part of the PCV. It didn’t work either.

Tried increasing the frequency to 10000 for RED colore for cutting and tried again in 3rd image.

We were not sure if it was engraving properly, so we inverted the image in 4 and tried engraving the numbers and traces, and it was noticed that it was engraving properly for small surface area for the same setting. For the last try 5, We increased the frequency to 15000 for cutting and inceased the pass to 3 times. We were still unsuccessful at our task.

Finally, we decided to leave this for another time and start doing our assignment instead.