Category Archives: PCB
While in China I picked up a USB microscope for $25 USD. It’s an “2MP HD microscope with 600x magnification” according to the box and has 6 LEDs around the camera. I plugged it in and it was found right away by Linux as a video4linux device and works with VLC and Cheese. It’s been sitting next to my computer for about 2 weeks since I got back from China and I’ve been itching for some reason to use it. Tonight I made a small board on my CNC to test some new footprints and I thought it would be the perfect time to use the microscope to check out the cuts made by the bit. Using Cheese I was able to get some good shots of the PCB traces. The pictures are only 640×480, so I’m not too sure where the 2MP claim comes from.
I used my gcode_03 ULP script for Eagle (from my older site) to export the PCB to G-code. When I started working with the CNC for PCB routing I was using a 0.8mm end mill carbide bit, however I’ve noticed I get pretty clean cuts with a 30 degree “V” etching bit run at the max speed of my manually controlled spindle (Yes I know I need to find out the RPMs of that thing). The cuts made by the CNC are impressively clean and without burs. Each cut goes down 0.16 inches and the feed rate is 300mm/minute. The footprint is SOIC-8, the pads are 1.27mm x 0.635mm and the traces are 20mil. The cut is close to 0.5mm. The microscope did show what looks like copper particles in the track which was interesting to see. I’ve made a bunch of breakout boards and switch boards without shorting issues so I don’t know if these particles are big enough to cause a problem. Here are some pictures of the board using the microscope.
I’ve found myself in the situation a few times where I was trying to explain that PCBs can be routed using a low cost CNC, like the 3040 CNC I purchased on Ebay a while back. Since I have routed dozens of PCBs this sounds obvious to me, however it is not very obvious to some of the engineers I have explained it to, it seems as if they can’t visualize what can be accomplished. In those moments I wish I had an example PCB to show them. Not to mention a few times I was stuck without a quick way to measure small lengths, or I wanted to know the SMD footprint used for a resistor to see if I had one, or when I needed to compare the pin spacing of a cable to see if it is 0.1″. A few days ago I found a post about TinkerRule, a reference PCB that could be used to solve pretty much all the engineering scenarios I just mentioned. I really liked what they did and it inspired me to see if I could make a reference PCB on my CNC in the form factor of a business card to fit in a wallet, that way not only would I have a useful tool, but I would have a demo of the capabilities of my CNC PCB router too!
It turns out that my small 3040 CNC is quite capable of making a 2.125 x 3.25″ PCB business card with a number of useful features, including an inch ruler, centimeter ruler, some reference traces, reference vias, reference holes, and 0.1″ grid. The board also has 150 mil letters so it is easy to read. Plus, since the single sided copper board I used is only about 50 mils thick, it’s only 50% thicker than a credit card, so it isn’t a noticeable addition to my wallet. This was the first pass and there are 2 missed sections, this was due to my setting of the router bit a little too shallow…things to fix on Rev 2.
I already have identified some things I want to change on Rev 2, any ideas or suggestions?