I've always wanted to make my own soldering paste stencils. Some days ago I tried a method which should theoretically work, and it somehow did. I spreaded a coat of soldermasking ink (the only photosensitive, acid resistant thing that I have) to a piece of thick aluminium foil (the one that's used to make disposable food trays) and I insolated it. The soldermasking ink adhered very well to the aluminium. I covered the back of the aluminium piece with some plastic tape to protect it against the acid and I etched the stencil using diluted ferric chloride (it reacts veeery violently with aluminium). The result was pretty amazing for being the first time. However, aluminium is so soft that the stencil was useless as it was damaged while spreading the paste.
But well, it somehow worked, and if I could get the same results in a more usable material I could definitely produce usable stencils even for fine pitch components. So now I've ordered some 0.1mm copper foil to try again with a more proper metal. Copper should be much better for this as far as I know. It's not steel, but it's way more rigid than aluminium.
I'll keep you informed!
I would say pictures!!
I really love those homemade goodies and born from frustation things people come up with!
[quote author="Sjaak"]I would say pictures!!
I really love those homemade goodies and born from frustation things people come up with![/quote]
There will be pictures. The copper foil is ordered and should be here next week.
My goal is to solder fine pitched TQFP's or similar with those stencils. I mean, get pro stuff. The results I had with the aluminium were very very promising. I'll try different metals if that's neccesary. Anyone knows a not so nasty chemical that can etch stainless steel in a reasonable time?
Yes :) Pictures.
[quote author="erdabyz"]Anyone knows a not so nasty chemical that can etch stainless steel in a reasonable time?[/quote]
Part of the point of stainless it to make it etch resistant so it is a bad choice to etch. Get non-stainless steel if you want to etch steel.
For a good table of etching is to google "jmems etch rates" or refer to the list on the BYU cleanroom under wet etching (http://www.cleanroom.byu.edu/wet_etch.phtml (http://www.cleanroom.byu.edu/wet_etch.phtml)). The etch for stainless is not something that is safe to do at home. Do not use HF at home under any circumstances, a small amount of exposure can cause cardiac arrest.
I don't consider I2 : KI : H2O etch to be to nasty, but I wouldn't dump any of this down the drain.
If I were doing metal etching at home I would use Al or Copper. Both have not horrible etches. Be aware of the volatility of the acid or base, and also be aware of gas bi products. HCL for instance can make chlorine gas.
Personally you couldn't pay me enough to do metal etching at home. Stay safe.
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As for stencils at home. I thought of this also but I was going to go the plastic route. I got a cheap inkjet printer and took it apart. Then I mounted a fiber coupled laser to where the inkjet head was. The idea being that I could then print with the normal motor control with my laser. The class 4 NIR laser I acquired was not powerful enough to ash Kapton on a scale larger than a few um at a time. Tests with materials that produced smoke dirtied the fiber and eventually I killed the laser.
Typical laser cutters are CO2. I believe based on the absorption spectrum of Kapton a 405 nm laser would be more effective. Fiber coupled 405 is not cheaply available at this time though and I have been putting off getting back to this. Partially because the advance mechanism in the inkjet is not very precise. The idea remains reasonable however. One does not need a 30W CO2 to cut a Kapton film.
I already do copper etching at home in a regular basis. I do manufacture homemade PCB's, and I use ferric chloride as the etchant. I would use the same for the copper and it's not very nasty. Thanks for the etchants guide. I surely won't use HF... that's crazy stuff...
As for the laser approach, I also thought about it but I think it should be quite difficult to get working right. Turns out that lasers are my other hobby, and I already own protective eyewear and some quite powerful diode lasers built by me that could be used with some modifications. My most powerful 405nm laser should be less than 100mW. I also have a 445nm 1W one, but that has a multimode emmiter and the beam specs are crappy so it coudn't be properly focused for this task. I think that you could directly attach a laser diode module to the printhead, with its heatsink, optics and driver. It shouldn't be very difficult to get single mode 405nm emmiters capable of 600mW+ with decent enough beam specs if you know where to search (people harvests these diodes from blu-ray drives' sleds). That'd be cheaper than a fiber coulped laser and might give similar results with a proper lens. The problem would be the heatsink mass that would alter the printer's movements so it might need some hacking to make it slower.
I might try it someda, who knows. But for now, etching metal looks simpler.
I understand. I have a fair amount of experience with lasers as well. But my background is in semiconductors not lasers. I simply have used plenty of high power lasers in the lab. I saw some 10 W 980nm lasers on ebay (fiber coupled), but they were pricey. I don't think you would mount a free space laser to the head just a mirror. 100 mW I don't think would be enough 1W was iffy for a reasonable spot size as I recall for kapton in the deep blue.
If you're into CNC milling (I don't know that too many people here are, necessarily) then you could take a look here:
http://http://www.millpcbs.com/index.php?option=com_content&view=article&id=28&Itemid=49
There's also a video at the bottom of that page, if you're curious. I haven't tried this personally, but it looks like it might be a bit tricky to get decent resolution with it - also, the edges of the stencil might be a bit rough if there's much runout on the spindle (so you might be in trouble if you're using a dremel as your spindle).
Again, apologies for posting the CNC Milling reference to stencil making in the chemical etching thread!
I'm making a stencil right now. i don't have a proper camera on hand to picture the whole process, but I promise pics when it's done, and future tutorial if it works well enough. Stay tuned! results are due in 1 hour or so!
Oh yes! It has exceeded my expectations!
Pic of the result:
http://i51.tinypic.com/ww0sna.jpg (http://i51.tinypic.com/ww0sna.jpg)
Not bad huh?
The TQFP64 footprint has two sides badly etched, but it's a fault of my printer. The cartidges are almost empty and are months old, and it no longer prints as good as when the cartidges are new. The other two sides are perfect.
There are some holes with a bit of remaining copper, that's because I stopped the etching process a bit before it was completely done, because I was fearing over-etching. But those remanents are easily cleaned with some tweezers. Now i'd have to check its usefulness as a stencil, but I'm optimistic.
Can you tell me which board is this stencil for? Hint: it's a DP proyect.
looks promising - i'll be curious to hear how well the paste releases - looking forward to it.
[quote author="bearmos"]looks promising - i'll be curious to hear how well the paste releases - looking forward to it.[/quote]
I've tested it a bit with some paste and an old PCB, and depending on the angle of the squeegee during application, it either releases pretty well (the paste stays confined to the paste zone, without any spreading over the borders) or it releases terribly bad, leaving a paste mess over the board. But well, considering that with the proper angle it gives promising results, I'll just try to gather experience until I get it right. I guess it takes some practise.
I've also noticed that the paste layer gets a bit thick. Maybe too thick for some IC's. If this ends up working well, I'll try to get thinner copper.
[quote author="erdabyz"]
Can you tell me which board is this stencil for? Hint: it's a DP proyect.[/quote]
My best guess It is the picque~no board :D
Did I win did I? did I?
Yup, the diodes and resistor arrays give it away :)
[quote author="Sjaak"][quote author="erdabyz"]
Can you tell me which board is this stencil for? Hint: it's a DP proyect.[/quote]
My best guess It is the picque~no board :D
Did I win did I? did I?[/quote]
Yeah, but there's no prize... :D
pretty good. You should post the full how too when you have it perfected to your satisfaction.
I will try to solder the PICqueño with this stencil as soon as the FT232RL's arrive (I got them for china to save a couple of bucks, and more than 2 weeks later they're not here). If it works, i'll post a how-to.
@erdabyz,
In case you're looking for alternatives to applying the pattern, perhaps you could run your foil directly through a laser printer.
Interested in whether or not the toner would be applied correctly directly to metal, I once ran a piece of normal thin aluminum foil--taped to a piece of paper--through a laser printer. It worked great. I forgot whether or not I had removed the fuser first, but I'm pretty sure it was in.
So, theoretically, one could print a PCB or stencil directly with a laser printer.
Of course, the issue is whether or not the material can negotiate the feed mechanism. I figure that the most important step is to get the pattern on the metal. I can always fuse it myself--I think. Just need to avoid sneezing...
I own a laser printer but it's fairly new and I'm not like risking it for this xD. Surely it'd be epic if it worked but I haven't done any other stencil since that one, because for small proyects I don't really need them, and for big ones I found a place where they do professional stainless steel laser cut stencils for 50€ for a piece of 30x20, and other place who cuts a gigantic sheet of mylar for $25.
Doing homemade stencils this way is fairly complicated and tedious....