Getting into photo-lithography - Page 1
Forum section: electronics / beginners

author: cubemike99
author_rank: Contributor
timestamp: June 07, 2013, 02:52:40 am
content: Hello. I've made my own PCB's before using both toner transfer and routing. Maybe I'm doing something wrong, but I found toner transfer horribly unreliable. Routing is pretty nice, but the machine I have access to doesn't have very fine resolution, and I won't have access to it for much longer. Photo-lithography seems like a much better alternative; I mean, if it's good enough for nanometer scale silicon, it must be at least good enough for PCB's, right? The only downside I can see is that the pre-sensitized boards seem a bit expensive, especially since I have a bunch of standard copper clad board. So, has anyone had any experience with UV-sensitive solutions that are spread over normal copper board? Ebay is the only source of this I have been able to find, and am debating whether to take the plunge and risk it on thishttp://www.ebay.com/itm/Photoresist-for-Print-Circuit-Board-and-Developer-/300914919847?pt=LH_DefaultDomain_0&hash=item460fed49a7. Of course, I would still have to purchase transparencies and a UV bulb, which is not a negligible expense. Is the investment worth it?

author: Paul Price
author_rank: Super Contributor
timestamp: June 07, 2013, 03:28:22 am
content: Pre-sensitized boards seem expensive, but they save a lot of time and chemical exposure.

author: komet
author_rank: Unknown
timestamp: June 07, 2013, 09:19:31 am
content: You don't have to purchase a UV bulb. There is a free one in the sky.If you befriend an offset printer (the person, not the machine), they might make occasional films for you which are essentially the same quality as the films a real boardhouse would use. A fair price for an A4 film (which is huge in PCB terms, but on the small side for a printer) would be 1 to 2 beers.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 07, 2013, 09:31:10 am
content: I tried the spray photoresist a couple of times and the problems are getting a uniform thickness, and dust.Just not worth the time - leave it to the pros and use pre-coated boards.

author: Kostas
author_rank: Regular Contributor
timestamp: June 07, 2013, 10:03:04 am
content: Quote from: mikeselectricstuff on June 07, 2013, 09:31:10 amSounds reasonable, but have you tried any film photoresists? This should solve any uniformity and dust problems, but perhaps create new, lamination specific ones. Has anyone tried them?

author: cubemike99
author_rank: Contributor
timestamp: June 07, 2013, 12:49:52 pm
content: Quote from: mikeselectricstuff on June 07, 2013, 09:31:10 amWow, a reply from Mike himself! Thanks for your great channel.Just to be clear, what I'm thinking of purchasing is a liquid, not a spray, which seems like it would be easier to get an even coat with. Out of curiosity, what's the issue with a non-uniform thickness? Is it that certain parts become over-exposed?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 07, 2013, 01:23:38 pm
content: Quote from: cubemike99 on June 07, 2013, 12:49:52 pmdip coating is probably a better bet - still need to keep dust out. coating needs to be even so all the board has the same optimal develop time - if uneven, thin bits will strip before thick bits have developed.

author: AlfBaz
author_rank: Super Contributor
timestamp: June 07, 2013, 02:49:00 pm
content: Pre-coated boards are definitely the go and aren't that expensive. I have used thesehttp://kinsten.com.au/pcb/gd/with a purchased exposure box, this one herehttp://kinsten.com.au/eq/kvb30d/I also have purpose made etching tanks, heaters and a pump for bubbles in the etching solution for agitation, all bought from kinsten.I even have some powder that you mix with hot water. It deposits a "tinning layer on the etched boardFor the artwork I simply print onto a transparency (positive with the above mentioned boards). The problem with this is that the ink doesn't dry 100% opaque which can be problematic with small traces. The solution to this problem is simple, after printing sprinkle talcum powder over the film. The talc sticks to the ink making it completely opaque with the added bonus of preventing the film from sticking to the pre-coated board during exposure and lifting the chemical off the board, ruining it in the process. This technique gives me very well defined traces even as small as 4/4mil

author: cubemike99
author_rank: Contributor
timestamp: June 07, 2013, 03:33:21 pm
content: From just a minute or two on eBay, I found thesehttp://www.ebay.com/itm/16-pcs-4-x-6-FR-2-oz-Single-Sided-Copper-Clad-Circuit-Board-PCB-/310683211270?pt=LH_DefaultDomain_0&hash=item4856299606, which are literally a fifth of the price of precoated. The solution I linked is supposed to cover 1.5 m^2, which works out to a cost of 30 cents per 4x6 board. Add another 30 cents for a transparency, and you have $1.60 per DIY board vs $5.50 per precoated, and that's after I use my my existing copper stock. Unless home coating is so unreliable the cost benefit will be completely nullified, that alone makes me eager to try the solution.As to dust, I don't think it'd be too hard to set up a little tent from a clear garbage bag and coat inside that. And I don't think i'll have enough solution to dip, but I could certainly place some solution at one end of the board and let it flow down and drain onto a paper towel. Looks like I've already made up my mind.

author: AlfBaz
author_rank: Super Contributor
timestamp: June 07, 2013, 03:57:42 pm
content: Quote from: cubemike99 on June 07, 2013, 03:33:21 pm2oz copper! Your etchant will probably run out of steam halfway through the process. At least try and find some 1oz

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 07, 2013, 07:51:30 pm
content: Quote from: cubemike99 on June 07, 2013, 03:33:21 pm..but how much do you value your time...?

author: madires
author_rank: Super Contributor
timestamp: June 07, 2013, 08:52:42 pm
content: Quote from: cubemike99 on June 07, 2013, 03:33:21 pmI pay €1.80 for a single sided precoated FR4 Euro format (160mm by 100mm, 1oz/35µ) from a well known manufacturer at a local online store. Double sided is €2.15. And I can put those into the closet, forget about them and use them 5 years later without any problem.

author: sleemanj
author_rank: Super Contributor
timestamp: June 08, 2013, 12:38:35 am
content: I wouldn't bother with applying solutions, or expensive pre-sensitized boards.Dry film is cheap and readily available. You can apply it successfully with a clothes iron (for smaller boards, say 7x10cm max), or a laminator if you have one.If you were in New Zealand you could buy some from me, but since you're not you can eBay it instead.I'll save you a whole heaping of experimenting by giving you the attached document which I wrote

author: poorchava
author_rank: Super Contributor
timestamp: June 08, 2013, 06:31:27 am
content: I've been experimenting with preloaded material, but on the contrary to what we written a few posts above, the one which I used (Bungard brand) aged pretty badly and I couldn't set with one exposure time, as different batches needed different time.Spray paint isn't that bad and it makes it possible to first drill the board and then coat it and do the rest of the stuff.

author: Kostas
author_rank: Regular Contributor
timestamp: June 08, 2013, 07:12:47 am
content: Quote from: sleemanj on June 08, 2013, 12:38:35 amThank you!Quote from: madires on June 07, 2013, 08:52:42 pmPerhaps it's Bungard boards from Watterott? Their price is pretty good actually, even considering the postage, but then poorchava's experience is somewhat worrying.

author: poorchava
author_rank: Super Contributor
timestamp: June 08, 2013, 09:31:01 am
content: So maybe a bit more explanations: I was exposing them using 500W halogen floodlight. When I had fresh batch from TME (guaranteed to be fresh, I had to wait for transport because they had none on stock) it needed about 15 minutes of exposure. Other time when I had to have working circuit next day I bought it in retails store and I had to expose them for ~40minutes to get any effect. Maybe it's the fault of me using helogen light, and a proper UV tube would have still done the job, i don't know.And aside from that: positive 20 can be developed in NaOH. It's cheap as hell (I paid like 1.25€ for 1kg bag of 99.8% pure- a few years supply), not regulated in any way in EU. Bungard's stuff can be developed that way too, although the unexposed parts are quite vulnerable to the developer anyway. Bungard recommends using their chemical (duh...) which is hardly available and therefore expensive for hobby use. There are alternatives, but they are pain in the ass too.Dust is not that big of a problem. Just go to a room, spray the board, turn off the light and leave. After 10 minutes the coating is dry enough that dust won't stick to it."proffesional exposure box" is a total ripoff, no matter how much it costs and what it does. A cheap UV nail polish curing machine does the job same as well (that was actually compared against a proffesional one, because I had an opportunity to do so). And bored teenage girls sell that stuff used for next to nothing on auction sites (got mine for ~4€ or something like that).

author: madires
author_rank: Super Contributor
timestamp: June 08, 2013, 01:06:27 pm
content: Quote from: Kostas on June 08, 2013, 07:12:47 amReichelt, but Watterott should be fine too (I think I got the buspriate from Watterott). The oldest precoated board I used was 10 years old. I expected it to fail, but it worked pretty good. The only problem was the glue of the light protection film (black paper), it was quite sticky at the edges of the board. So I had to cut off about 2 cm of the border.

author: Kostas
author_rank: Regular Contributor
timestamp: June 08, 2013, 02:35:54 pm
content: 10 years? Awesome!Anyway, I was thinking about UV leds and specificallythese. 200 leds are probably nice for two largish boards, one upper, one lower for 2 sided pcbs. These straw hat leds have more evenly distributed light, so it should be easier to avoid any hot spots. Anyone have any experience - thoughts to share?

author: Arp
author_rank: Unknown
timestamp: June 08, 2013, 02:46:35 pm
content: I use flat 4k mcd, wide-angle leds. Approx.. 120-140 degree. Works pretty well, and can be pretty close to the board.

author: Kostas
author_rank: Regular Contributor
timestamp: June 08, 2013, 02:58:20 pm
content: Quote from: Arp on June 08, 2013, 02:46:35 pmInteresting, what's the exposure time you use?

author: Arp
author_rank: Unknown
timestamp: June 08, 2013, 03:08:42 pm
content: About 3 minutes with ~6mm Plexiglas and one layer of tracing paper in between.I used twice the amount of led than I originally intended to, but it was too late after having soldered 95% of the first board. Had to make another purchase. Box have worked really well thou, so besides some delay and hand cramps from all the soldering, no regrets

author: SeanB
author_rank: Super Contributor
timestamp: June 08, 2013, 03:24:18 pm
content: Replace the halogen with a blended mercury lamp ( 160W lamp) which has a lot more UV light output. Or use a old metal halide car lamp as a light source. Otherwise a 75 or 150W metal halide lamp fits in place of the linear halogen, and just needs the control gear fitted close to it to get a good light output.

author: AlfBaz
author_rank: Super Contributor
timestamp: June 08, 2013, 03:28:51 pm
content: What's wrong with a 2 foot UV fluro tube? Before I got that wiz bang exposure box (anything more than 60 seconds is over exposure) I used a twin 2 foot foru light fitting with 2 UV tubes, readily available at your local lighting shop

author: Arp
author_rank: Unknown
timestamp: June 08, 2013, 03:42:09 pm
content: I used leds due to space constraints and portability.

author: sleemanj
author_rank: Super Contributor
timestamp: June 08, 2013, 03:42:28 pm
content: I use standard narrow angle LEDs, because I didn't find any wide ones at the time, I built it into an old scanner ripped off a multifunction printer (I also used the power supply ripped out of the printer as it happens).Because of the very limited distance between glass and the bottom of the scanner and that they were 20 degree angle LEDs I had to really pack the LED's in very close to each other so as to not create dark spots (I worked it out as to how close they needed to be first). 100 LEDs didn't go far, a 5x6 is about the best I can manage with it. More than that at the moment and I wait for a nice sunny day :-)I've got another hundred or two to put in sometime but those wide angle ones look quite nice, would be able to spread them out much further, almost enough to make me want to start again.I've also seen (I think on hackaday, or maybe dangerousprototypes) somebody use a UV version of that self adhesive LED strip you can buy, easier than soldering a couple hundred LED's, but probably expensive.My box is only single sided, to do repeat exposures for double side or soldermask I use registration markers on the artwork in one corner (which appears in the same place on all the generated artwork, etch top/bottom, mask top/bottom..), I tape the artwork down to the glass, and then I have a corner cut from a transparent plastic set-square from the dollar shop that I tape down exactly over the registration marks, that way I can just butt the appropriate corner of the PCB into the "squared corner" and tape a presser on the opposite corner to hold it hard against it.I find this to be the best way to get a "mechanical" alignment, without actually pre-drilling alignment holes and some sort of pinning setup.

author: hlavac
author_rank: Frequent Contributor
timestamp: June 09, 2013, 03:16:46 pm
content: Quote from: mikeselectricstuff on June 07, 2013, 09:31:10 amSame here. Dust was the killer for me.

author: poorchava
author_rank: Super Contributor
timestamp: June 10, 2013, 09:39:14 am
content: The only thickess-related problem I have is, that the paint tends to gather around the edges of PCB and it's not very flat there. You can spin the PCB (using i.e. pc fan) to improve the lacquer distribution, but this is only good for on side and obviously rather messy.