Soda Can Stencil

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DIY home-made SMT metal stencil - the definitive tutorial by Felix Rusu (LowPowerLab) (YouTube; Feb 11, 2013)
Thanks to Adafruit Industries.

"Dare to be naïve." - Buckminster Fuller

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Somehow, my "100%" acetone won't touch the red and white paint on the outside of a coke can.

 

277,232,917 -1 The largest known Mersenne Prime

Measure twice, cry, go back to the hardware store

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That obviously calls for some experimenting. Try a variety of soda and beer cans. Empty, of course. Thats part of the experiment!

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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I make PCBs using mechanical milling process ( both simple double sided structures and more complex multilayer structures.
Recently I made my first stencil from scrap 1.6mm and 0.2mm thick material.
The two sheets were laid on top of each other and tooling pin holes were drilled along one edge.
Board outline was machined into the 1.6mm stock and stencil apertures were machined into the thinner material using a60Degree V tool.
the two sheets were then pinned together such that the side of the stencil part having larger end of the apertures ( due to V tool) was against the frame.

Worked like a charm.

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ka7ehk wrote:
That obviously calls for some experimenting. Try a variety of soda and beer cans. Empty, of course. Thats part of the experiment!

Jim

Alas, I'm not old enough for "adult beverages" Nope! I got in this state totally without the aid of alcohol.

 

277,232,917 -1 The largest known Mersenne Prime

Measure twice, cry, go back to the hardware store

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Quote:
Somehow, my "100%" acetone won't touch the red and white paint on the outside of a coke can.

I can confirm - no way to remove paint with acetone. Neither internal nor external.
I have used an NaOH instead of HCl for etching.

No RSTDISBL, no fun!

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Maybe the paint comes off easier once you heat it. I thought I'd retain the epoxy inside to keep the back side from etching. Perhaps I'll try it later today. Soon off to the 4th of July parade.

 

277,232,917 -1 The largest known Mersenne Prime

Measure twice, cry, go back to the hardware store

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Quote:
I thought I'd retain the epoxy inside to keep the back side from etching.

It is very important to stop the process at the proper moment and not to over-etch. The best way I found was to mount stencil vertically and etch in a transparent container stopping the process when the light starts to come through. Still, stencils for QFN with 0.5mm pitch are hard to make that way because the clearance between pads is almost as wide as the thickness of the aluminum can (0.1mm). So I think a double-sided toner transfer could do the trick, improving resolution.

No RSTDISBL, no fun!

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ka7ehk wrote:
That obviously calls for some experimenting. Try a variety of soda and beer cans. Empty, of course. Thats part of the experiment!

Jim

Felix made an update to his blog entry for this on the variability of soda cans.
DIY SMD metal stencils – the definitive tutorial by Felix Rusu (LowPowerLab) (February 11, 2013) (search for UPDATE).

"Dare to be naïve." - Buckminster Fuller

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"Self adhesive shelving vinyl roll – $1 - dollar store"
Torby, have you tried that kind of vinyl with your PCB process?
TIA

"Dare to be naïve." - Buckminster Fuller

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Brutte wrote:
I can confirm - no way to remove paint with acetone.
For a kinda similar task, I inquired at an automotive paint refinishing supply retailer and the recommendation was a "Medium Reducer"; contents: butyl acetate, acetone, toluene, naptha, benzene, zylene, ethyl (whatever), cyclohexane.

"Dare to be naïve." - Buckminster Fuller

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No, I haven't tried the cheap vinyl shelf paper from Wal*Mart, which is one of the brands he says works well. I have a pretty good stock of purple stuff I got last fall.

 

277,232,917 -1 The largest known Mersenne Prime

Measure twice, cry, go back to the hardware store

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The paint came off easily with acetone and a "green scrubby."

Leaving the epoxy layer on to protect the back side didn't work, or else, I mistakenly put the transfer on the epoxy. Mark which side. The aluminum had dissolved away before I could see anything through the holes. Only took a minute or so.

Sharpie Marker did not work AT ALL to touch up the transfer. I made a bigger border around the design with sharpie and the acid took the ink off immediately.

I don't think you need HOOH to dissolve aluminum, except maybe to cut your 30% HCL. The aluminum (or aluminium, depending where you live) is VERY reactive to the HCL. Watch for the H2 fumes!

 

277,232,917 -1 The largest known Mersenne Prime

Measure twice, cry, go back to the hardware store

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That's great!! However, I have never successfully reflow soldered at home, though I have tried three times!!

You may only be one person in the world but, you may be the world to one person! "Life! Life, do you hear me? Give my creation LIFE!" Gene Wilder SKYPE Name: JonRobrt

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I haven't tried reflowing the lead free stuff yet.

For leaded solder paste, it's actually pretty easy. I use an electric skillet I modified just a hair so it gets a little hotter than designed. The part that plugs in with the temp dial comes apart with a screw or two, and inside is a simple thermostat. You'll see how it works. I bent it just a smidgen so it goes a little bit hotter than the 400f it was designed for. My thermometer doesn't go that hot, so I don't know what temp it reaches now.

To reflow, I set the board directly on the cold skillet and turn the knob all the way. It will take a couple minutes to reach the reflow temperature, and that's just what you want, a nice, smooth temperature rise. Watch closely, and suddenly, you'll see the dull gray paste turn bright silver. Keep watching, and it will magically suck itself into the joints. It's quite amazing to watch. This takes only a few seconds, like 10 or so, once it turns silver. Then turn the skillet off and leave it set till you can pick up the board with your fingers.

Large boards tend to reflow in zone like areas. Just leave it heat until all the areas "suck up" into the joint. If one zone is being slow, and is still gray while the rest is soldered, use something like a wood paint brush handle to press the PCB down in that area, and it will quickly catch up.

I think the toaster oven would be just as easy, except I worry about overheating tall parts like capacitors or enclosed headers. Since I heat from the bottom, these tall parts aren't poking up closer to the IR heaters of the toaster oven. Also, you can't see what's going on on the "back side" of the parts, while with the skillet, you can just turn the board around to inspect those pins. 30 mil PCB solders quicker than 60 mill. It was a little scary when I tried both sizes together as the thin stuff was all done and the thick hadn't turned silver yet. They came out ok, though.

I haven't successfully done ICs with no pins. I wonder if that's 'cause my boards aren't flat enough. I'm getting some from elecfreaks to try.

On home made boards with bare copper, the copper tarnishes during the slow cool down. The darker color copper solders easily, or you can polish it back to bright copper in a moment.

I have no way to put SMD parts on both sides of the board.

 

277,232,917 -1 The largest known Mersenne Prime

Measure twice, cry, go back to the hardware store

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I've done quite a number of boards in my $20 WalMart toaster oven. Mine has top and bottom heating elements, and haven't had any issues with tall-ish parts to date (although I haven't reflowed anything taller than a ~10mm high cap).

I've done down to 0.4mm QFN this way, with a 5 for 5 success rate, although those were done with purchased stainless steel stencils. They're nerve-wracking to stencil and place, though!

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Quote:

The aluminum (or aluminium, depending where you live)

Best thing I've read all day.

Avatar maliciously stolen from xkcd.com.

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Instead of putting this rather reactive metal into concentrated acid, I thought I'd try electrolysis and salt water. Much less frightful. I can switch off the frightening reaction and not have...

"So how come nothing's happening?" Oh, dummy RED to +, BLACK to -. I'd dissolved my cathode.

Two rather dismal failures so far, not counting reversed polarity; but I think I know what went askew.

 

277,232,917 -1 The largest known Mersenne Prime

Measure twice, cry, go back to the hardware store

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"Dare to be naïve." - Buckminster Fuller

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How cool.

 

I wondered, not having a laser printer, but with my son having a 3-D printer, if I might "Print" a stencil.

 

It is unfortunate that I can't retire yet, as there are so many great projects I'd love to work on!

 

JC

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DocJC wrote:
... but with my son having a 3-D printer, if I might "Print" a stencil.
A 3D printer may have adequate precision and accuracy with a possibility of a material similar to mylar (0.1mm (4mils) thick)

A good value single use stencil would be great for prototyping.

DocJC wrote:
It is unfortunate that I can't retire yet, as there are so many great projects I'd love to work on!
Could be able to do as an engineer would and purchase a service; might evaluate prototype PCBA fabs such that can get direct to testing.

Some retirees come back to engineering and design for their third career; it's impressive to see an elderly man still "working" part-time because he wants to.

Ideally there's less risk to create one's small business after one retires.

 

"Dare to be naïve." - Buckminster Fuller