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Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
Hi guys,
Making PCBs has been an extremely frustrating topic for me for a long time. I started doing toner transfers, and they worked every once in a while. I couldn't do much smaller than .1", so it was all DIP's with 40 mil traces. After that I jumped into UV, but I didn't have the time or capability to make a setup where I could keep all the variables minimized. That flunked. I got a nice board or two, so I knew it might work. Next I went and bought a CNC router and hoped to do it that way, and it did work well for a while, but I also used the machine for milling, so the table is now uneven enough that a PCB won't lay flat. When that happens, the bit will dig too deep making a very wide cut, or not cut at all being above the copper. You can minimize that by getting narrower engraving bits, but the smaller the angle, the easier it is to snap the tip right off. Now the machine is used exclusively for milling where tolerances are >1mm.
So now I'm back to UV again. Now I have the time to make a sturdy and functional setup, so I took a piece of wood, CAD'ed(how do people even say that) a top plate including an exposure window and control panel cutout. I found some nice 1 watt 385nm LEDs on ebay, so I drilled, tapped and bolted those LEDs down.
The paint dispensing machine at work broke the other day, so my boss gave me the broken power supply from when it was serviced(knows me so well ). It's overkill for 24v @ 650mA, but oh well, it fit the box well. All that was wrong with it was the "non-serviceable" through hole fuses. I had to reduce the feedback reference to have enough voltage to drop all the LEDs and the current regulator with a bit to spare.
The control is provided by an atmega328p micro-controller. It outputs to an LCD mounted on the panel, along with four buttons for changing the exposure times. The uC then switches a solid state relay providing mains power to the SMPS. A better option would be to control the 24v circuit via a mosfet because the power supply takes a couple seconds to fully power on. I chose the SSR because I didn't want to have to worry about leaving the box on with the SMPS idling. The delay could be easily compensated for in the code.
Now for some pictures:
Not really water! Don't drink it...
exposing, developing, etching
Not too bad considering I was just getting the ballpark exposure time. The sections were exposed 3, 4, and 5 mins. I actually overdeveloped the board, so i have a bit of pitting, but i used regular printer paper, so it's not as bad as with transparencies. I'm looking into getting a cheap printer with a higher dpi(1200), and using toner darkeners.
As you can see, in the smaller package(qfp), the printer seems to be the limitation. I assume that In my thin traces it's the same deal. If you look closely, my 6 mil trace looks very close to usable, the resist was a bit scratched in that area though. 8 mils should be a breeze. 10 and 12? awesome.
Here's what I mean with the printer:
With a bit more work, I could be making PCBs with 8mil trace, 8 mill clearance- with solder mask and rivet vias. It worked out much better than I expected!
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
I use Eagle Cad. In the past I've used Express PCB and Pad2Pad as well, but I've grown to like the extensive parts library in eagle, as well as the interface.
Registered Member #43257
Joined: Thu Feb 20 2014, 03:53PM
Location:
Posts: 33
hello, im going to throw in my 2cents here... i do screen printing, and the process of making a screen is very similar to this process for making PCB's...
my printer, prints very dark ink and very precisely, on transparencies. It is an epson 1100. I would be willing to print some stuff and ship it to you, if you like... I can print up to 13"x19" although i can't imagine you would want anything that big... I'll even ship for free as long as it is only a few bucks, and i don't have a million people wanting things printed. Consider it my contribution to the community :)
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UV exposure box and PCB fab
). It's overkill for 24v @ 650mA, but oh well, it fit the box well. All that was wrong with it was the "non-serviceable" through hole fuses. I had to reduce the feedback reference to have enough voltage to drop all the LEDs and the current regulator with a bit to spare.
