PCB at home guide - Page 1
Forum section: electronics / projects

author: kurt
author_rank: Contributor
timestamp: February 18, 2015, 05:56:15 pm
content: Hi. I'm working on a guide outlining how I create PCB's at home. In the guide I create a double sided PCB with traces down to 6-mil (spacing down to 5). The guide is not fully done yet, but I figured I would plug it here early and maybe get some constructive feedback along the way. I make a small double sided PCB while taking a lot of pictures and writing descriptions as the work progress. It sure take a lot longer to make a PCB when documenting it at the same timeThe steps finished so far are creating UV masks, adding dry-film photoresist to copper clad, vacuum lamination of masks, UV exposure, photoresist development, etching, and photoresist stripping.The remaining steps are solder mask, tinning, drilling, vias, hole plating, and maybe a silk screen. I have had white UV ink and a plan for how to apply it for a long time, but have never bothered with it before. Maybe I make an attempt this time and add it to the guide if successful.Questions and comments are of course welcome.Here is the guide:http://kavionic.com/blog/Making_PCB.Enjoy!

author: void_error
author_rank: Frequent Contributor
timestamp: February 18, 2015, 07:01:24 pm
content: Nice guide, however, you don't necessarily need a vacuum pump, there's an easier way to make sure the photo mask stays as close to the board: surface tension. Add water between the mask and the board, press it so you remove excess water and it'll stay stuck for long enough to have the board exposed to UV. I've made several boards that way, some with 0.3mm traces and about 0.15mm spacing.Also tap water will do just fine for making the developer.

author: kurt
author_rank: Contributor
timestamp: February 18, 2015, 07:26:45 pm
content: How do you make your masks? My tracing paper masks certainly would not like being soaked in waterAre you able to print masks that have high enough contrast that you get by with a single layer? None of my printers achieve this. And how do you deal with registration when making double sided boards with the surface tension method? I would imagine the stress from the kind of pouches that I make would pop it loose rather quickly.The vacuum pump also play an important role in one of the next steps that I have not gotten to yet. Applying solder mask. There I use vacuum to spread the solder mask gel and to keep it smooth and level while exposing.And yes, tap water will normally work just fine. Only advantage is that you are guaranteed consistency. I don't know how much variation you will get from minerals in the water, but for a manual process like this it is unlikely to cause any issues. I will make sure to mention this in the guide.Thanks for the feedback!

author: george graves
author_rank: Super Contributor
timestamp: February 18, 2015, 07:41:39 pm
content: Hmmm. Tracing paper seems far from ideal, but you seem to have a system that works.That's one of the issues with all "PCB's at home" guides, any small change can mess things up. You really have to find a system that works for your tools and methods.I'll be interested to see the rest of the blog when your done.

author: kurt
author_rank: Contributor
timestamp: February 18, 2015, 07:55:25 pm
content: That is very true. There is a a few nice guides out there and most of them seems to work for the guy who made it. But copying their successes are often tricky. I'm sure mine risk having the same problem. It works fine for me thoughAnd yes. Tracing paper sure does not seems like the obvious choice. But it is by far what I have had most success with. It blocks a lot of UV even in the translucent areas though. With the UV box I use I can fully expose the dry film in <6 seconds when no mask is applied. With two layers of tracing paper the exposure time goes to 2 minutes. Indicating that only about 5% of the light actually gets trough. This might cause issues with less powerful UV sources, but with my setup the exposure time are still acceptable.

author: void_error
author_rank: Frequent Contributor
timestamp: February 18, 2015, 07:57:21 pm
content: Surface tension works for masks made out of overhead transparencies, I didn't notice you were using tracing paper. I've ditched overhead transparencies (don't work well with all printers) and went for something more reliable - regular paper + TRANSPARENT 21 spray - it makes the paper transparent to UV. For exposure I just slap a 2 mm thick rectangular piece of window glass to keep it nice and flat. Haven't tried making double sided PCBs yet so I don't have any ideas when it comes to aligning layers.

author: free_electron
author_rank: Super Contributor
timestamp: February 18, 2015, 08:58:26 pm
content: years ago i posted on usenet : The PCB Faq.it's got various techniques in it. go find it. including how to make your own bubble etcher and exposure unit.I also have a book on SMT technology that describes those things.

author: ttt
author_rank: Regular Contributor
timestamp: February 18, 2015, 09:17:52 pm
content: Nice guide. Personally I've had very bad luck with the photo method and have been going back to doing toner transfer. With a twist though: I don't use 'glossy' paper but vinyl sheets (http://www.amazon.com/gp/product/B00345V7CI). When going through the laminator the toner transfers cleanly without the use of water, no paper residue and expanding back nicely to its original size. I can do TTSOP20 no problem.The biggest issue with (color) laser printers is usually the yellow security dots which affect the transfer and cause shorts/bridges:http://www.seeingyellow.com/If you use a laser printer use a B/Wonlymodel. That's even the case if you do use the photo method as some yellow toner is opaque to UV light.

author: sleemanj
author_rank: Super Contributor
timestamp: February 18, 2015, 09:47:19 pm
content: Imho, going down to 6/5 is just crazy at home, your ability to inspect, let alone corect, any developing or etching issues goes out the window.I will do 8/8 only if ABSOLUTELY necessary and for the shortest segment I can, in normal cases I seldom go less than 14/12, which is enough to slip one trace through a pair of 2.54mm headers.I use simple physical clamping not vacuum, and uv leds (eight 1w leds currently) through diffusers onto single layer of heavy tracing paper mask for an exposure time 2m30s, developing in Sard oxy plus at 30g/L for about 3m (gently rubbing/wiping with fingers) then a maskless exposure of 6m to fully cure and if necessary a clean up development of 20s, allow to air dry until tack free, then inspect and touchup any issues before etching.

author: kurt
author_rank: Contributor
timestamp: February 19, 2015, 12:22:29 am
content: I have had the opposite experience ofttt. I used toner transfer for many years, and have successfully used 8-mil traces and QFN28 on a toner transfer board. But the results was way to inconsistent. I guess with the right printer and good transfer medium (the vinyl sheets sounds nice) it can work. But in my experience it has been a complete gamble each time. After switching to photolithography I have been getting very predictable and repeatable results. Just go to show that there is to much "magic" involved in doing this with makeshift tools I guess. To many factors we don't have 100% control over.And I agree withsleemanjthat 6-mil is stretching it. And I also write that in the guide. But nice to know that it can be done if you have to. 8-mil seems to be totally safe though. That said I normally start out with 10-mil and only go down in places that really needs it. No need to generate more pain than necessary. Unless you want to check if it is possible of course

author: sleemanj
author_rank: Super Contributor
timestamp: February 19, 2015, 02:39:02 am
content: FWIW, here is my current UV rig (umm, 4th one I've built I think) with some info...http://imgur.com/a/s8lbSSome additional details...Top is off a brother printer, the box is constructed from some ply and MDF found in one the various scrap wood bins on the side of the road in the local industrial areas.The power supply is also out of a brother printer at 30v ish feeding into a 2596 buck converter taking it down to 24v.The exposure LEDs are 1 watt UV leds spaced in a 3-2-3 pattern with 2 buck (MR16 style) drivers taking 24v input and driving 4 leds each.The white LEDs are two 12v piranha led boards (24 leds each) in series hanging off the 24v supply.Midway between the UV and the "platen" is a diffuser made from a piece of glass out of another printer with a translucent cutting mat cut down and affixed to each side. The glass platen also has cutting mat diffuser affixed to the underside (so 3 diffusers - it produces a very even light at the artwork, and really doesn't affect resolution enough to care).On top of the artwork and board I put a spongy layer made from two pieces of a cheap foam-type bathroom anti slip mat glued together.The lid closes flat on top of that, then a wooden bar goes across the lid. Each end of the bar has a hook-and-loop (velcro to you and me) strap which loops around handles on the sides and is used to pull the bar down tight compressing board tightly to the artwork.The controller is an ATMega, a rotary encoder and a few buttons, so you can turn the visible on and off, select/edit from preset exposure times, and start/pause/abort the exposure.

author: george graves
author_rank: Super Contributor
timestamp: February 19, 2015, 04:02:26 am
content: Quote from: sleemanj on February 18, 2015, 09:47:19 pmMe too. For home brewed PCB, make the thickest traces you can. And use a fake pour or fill if need be. It helps so much with the etching. Less copper, less time in the solution, less under cutting, and less pitting.Also, if your are doing a board at home, 95% of the time it's a single sided board - or at least you should start out that way. IMHO, you'll learn to layout much more effectively if you force yourself to only one side when starting out. And for home etching, make your life sooooo much easier.I see so many people use the smallest trace they can - even on production boards. Like driving a relay with a tiny trace - WHY!?!?!? What's the point? Even on short turn board. Why do an 8mill trace when you have enough room for a much larger trace? Other then being lazy and not wanting to up the trace size I guess? What if you miscalculated something, or the resistance of a tiny trace will drop voltage, or be exposed to some amps? Or your PCB get sent to the lowest bidder?

author: tautech
author_rank: Super Contributor
timestamp: February 19, 2015, 04:49:27 am
content: Quote from: george graves on February 19, 2015, 04:02:26 am+1

author: sleemanj
author_rank: Super Contributor
timestamp: February 19, 2015, 04:55:21 am
content: QuoteA few suggestions after reading it in no particular order.For the artwork generation, you might be interested in my gerb2etch script,http://github.com/sleemanj/gerb2etchHere's a quick screencast showing it's usage:Try using heavier tracing paper than 80 gs/m if you can get it, I use 110g (but that's with a laser). Using a laser printer, I don't bother with doubling up artwork, don't have any issue with bleeding through just one copy.After you develop the board, pop it under the UV without the mask for about twice as long as the original exposure, the traces will cure and harden considerably more, also any residue will left over will slightly "blue" too in the curing exposure which makes it much more visible, a dunk in the developer for a few seconds and rub with your finger will remove it.Applying the resist, for small boards, a clothes iron on a COOL setting (not as hot as you'd laminate, 55-70'C) can be just as easy, warm the board under the iron while you get the resist ready, then remove the inside layer and smooth it on with your fingers (or better, something sturdy and flexible as a squeegee, 3 of 4 credit type cards thickness), put a piece of paper over the whole lot, and reheat with the iron, applying light pressure and moving the iron around, pay attention to the edges. Once you've found the clothes iron temperature that is warm enough to get good adherence, and cool enough not to blister, mark that on your clothes iron dialIt's a good idea to allow the laminated board to cool for 10 minutes or so before exposing, but... we are all impatient.To strip the resist after etching, forget about NaOH, you don't need it. If you're in a hurry, just drop it in a bath of acetone for 20 to 30 seconds and it will curl up and lift off, if you're not in a hurry just leave it in the developer solution for 1/2 an hour and it will also float off.Looking at your board, you might be able to shorten your exposure a bit. You don't need it quite so dark first time through (but your resist might be different, or your camera) and a lighter exposure can mean for a quicker and easier develop. You might like to try some experiments using aPCB test pattern(well if it works for you then obviously not, but somebody new to the process would benefit from doing that).Ensure you rinse the board under running water after removing from developer (or stripping, or etching) solution, you don't really want a film of sodium carbonate drying on top of it, especially if you might not etch right away.After developing, allow it to air-dry a bit until it is totally tack-free, before you do any touch-up with a resist pen, otherwise the pen tends to get gummed up.

author: kurt
author_rank: Contributor
timestamp: February 19, 2015, 08:37:12 pm
content: Thanks for all the comments.Quote from: sleemanj on February 19, 2015, 04:55:21 amVery interesting. I looked high and low for a good free gerber rasterizer a few years ago, but could not find any. gerbv was one of the programs I looked at, but could not make it do exactly what I wanted. To long ago for me to remember the details. I see that you use gerbv to rasterize in your script though, so I might have to have a look at it again. I will probably keep my python scripts, but it would be nice to be able to produce the masks directly from gerber files.Quote from: sleemanj on February 19, 2015, 04:55:21 amI can get heavier paper. But what would that gain me? As for lasers, I have given up on mine. I have a 600 DPI HP1020 and a 1200 DPI Dell 1710. None of them give good enough contrast, and both of them make enough pinholes to make it close to useless for mask creation. And given that my inkjet give very good and repeatable results I have no big intensive to try to figure out why my lasers suckQuote from: sleemanj on February 19, 2015, 04:55:21 amI have never had an issue with the photoresist dissolving during etching even without post-baking. And I can easily see any residues after having the board out of the developer for a short amount of time when it dry up and turn grey. And at that point it is very quick to just brush over it a couple more times with the developer to get rid of it.I do however "UV-bake" the board after applying the solder mask to be sure it is fully hardened and as though as possible against wear and tear.Quote from: sleemanj on February 19, 2015, 04:55:21 amI prefer NaOH over acetone due to the lack of fumes. And it keeps my drains cleanAnd waiting half an hour for the developer to do the job is very rarely an optionQuote from: sleemanj on February 19, 2015, 04:55:21 amAs I describe in the article the exposure time was found by doing a calibration exposure. I just picked a random PCB layout rather than creating a dedicated test pattern to do the calibration. But the result are the same. I don't think I can alter it to much in either direction and maintain the ability to create 6-mil traces.Quote from: sleemanj on February 19, 2015, 04:55:21 amRinsing is mentioned in the guide. I rinse while scrubbing it with my fingers to make sure it is as clean as possible. I do not do touch-up's though. Most of my designs are to compact for that to make any sense. If I need to touch-up I consider it a failure and start over.I should probably mention that one of the main goals of mine is to create as high density PCBs as possible. That means tiny traces and double sided (or more). I have been reading many "How to get 100% success every time" guides with great interest right down to the page where I realize that they talk about PCBs with greater than 10, 15, or even 20 mil traces. And often single sided. With those toleranses just about anything will work. I totally agree that you should use as large traces as your requirements permit. But I like making electronics that goes into small RC helicopters and other things where size and weight is everything. And then single sided boards with 12-mil traces is not an option.So my goal has been to find a method and create the tools that makes it possible to create 8-mil or smaller traces with 6-mil or smaller spacing on a double sided board in the quickest way possible. And with a 100% success rate. Many would argue that with that kind of specs you would be better off just ordering the boards. And I do not disagree with that. But to me, part of what makes the hobby interesting is to be able to do this kind of things and make it look decent.

author: kurt
author_rank: Contributor
timestamp: February 23, 2015, 10:02:07 pm
content: Now the guide should be pretty much finished. I have added solder mask, tinning, drilling, vias, hole plating, and cutting (trimming the board and making non-circular cutouts).I also did some editing based on the feedback from this thread. And I added a link tosleemanj's gerber to PDF script (hope that is ok, let me know if not).Populating the board remains. I might add that to the guide as well. Or I might put that in a separate article. The guide turned out to be a lot longer than I had first anticipatedI did some experiments with silk screen to. But that didn't work out to well. It looks like the UV light reflects around internally in the white UV gel and turn thin clean lines into thick fluffy lines. So that was not included in the guide

author: george graves
author_rank: Super Contributor
timestamp: February 25, 2015, 09:15:12 am
content: Very nice wrap up to your guide. Your documentation of your through hole rivets was great. I've seen them before - but only as a "oh hey, I hear you can use these things" kind of way. Never seen them used in practice.Anyways, here ya go:http://hackaday.com/2015/02/25/diy-through-hole-plating-like-a-boss/Thanks for the great write up!

author: kurt
author_rank: Contributor
timestamp: February 25, 2015, 10:16:43 am
content: Thanks for the encouraging comment and hackaday article! That certainly gave the web server something to do

author: Fred27
author_rank: Unknown
timestamp: February 25, 2015, 10:34:57 am
content: Very nice article, Kurt. A welcome change from all the "Look at me, I can do toner transfer and use HCl/H2O2" rubbish people seem to like posting.I use very similar processes to you. I've got some copper rivets that I'm about to use for the first time (for vias), so that section was very helpful. The differences in my process, that you may find interesting are:I find metasilicate based developers (on presensitised boards) far more reliable that NaOH.I use Dynamask 5000 solder mask that is laminated on much like your etch resist. If you'd like some to try then PM me your address and I'll send you some. I've got more than I need.Ziplock vacuum food bags work much like your solution to hold the transparency downT-shirt mode on my Canon MG5250 lays down a nice thick layer of ink. No need to double-up.I tin before the solder mask. No idea which is better.

author: Fred27
author_rank: Unknown
timestamp: February 25, 2015, 04:07:40 pm
content: Looks like you made it toHackaday. Nice.

author: JBeale
author_rank: Frequent Contributor
timestamp: February 25, 2015, 06:33:12 pm
content: Very nice writeup on your web page, I enjoyed reading it. The finished board looks very clean and professional with the solder mask and tin plate.

author: kurt
author_rank: Contributor
timestamp: February 25, 2015, 10:00:28 pm
content: Thanks again for all the encouraging feedback.And thanks to youFred27for the offer on the solder mask. That is very generous of you. It sure seems like a simpler way of doing it. And probably give a better finish. I have been tempted to try it, but the liquid stuff give adequate results at about a tenth of the cost per cm2(not counting cutting loss for the film). So I have resisted the temptation so far. It is not that the absolute cost would be so high, it is more a principal thing I guessDo you know anything about the shelf life of that film?And as for NaOH. I only use that for stripping at the end. I guess your presensitized boards have a positive resist? I don't think NaOH would be very well suited to develop the negative resistBut it works for positive. I have heard elsewhere too that the metasilicate based developers are much easier to get right (much wider window for concentration, temperature, and time) than NaOH for positive resist though. For negative resist Na2CO3works very well and seems to have a wide enough window to make it reliable.My printer does not have a "T-shirt" mode. But now that I went looking for it I found a "HP Iron-on Transfer" mode that might be the same. Definitively something I will have to try out. I have experimented a lot with the printer settings, but somehow have never realized the potential benefits of that mode. Would sure be awesome if I where able to get away with a single layer.I don't think there would be any quality difference whether you tin before or after applying the solder mask. But I do it after to reduce the amount of chemical tin needed.

author: eliocor
author_rank: Unknown
timestamp: February 26, 2015, 01:21:12 am
content: Please can you give me some suggestions on what solder mask gel are you using? (seller/product number/...)

author: kurt
author_rank: Contributor
timestamp: February 26, 2015, 09:33:46 am
content: I buy it from whoever eBay vendor are the cheapest when I need it. So very little information available about the product. I have ordered twice from two different vendors, and they looked the same and worked fine. If I where to order now I would probably have bought this one ($9 for 5 10ml syringes) :eBay auction: #141392838028. I have also tried the 100g cans you find a lot on eBay and it seems to be the same stuff. I prefer the syringes though since it make it much easier to measure out the right amount to apply.

author: Fred27
author_rank: Unknown
timestamp: February 26, 2015, 03:02:39 pm
content: Quote from: kurt on February 25, 2015, 10:00:28 pmI'm not sure on the shelf life (either in theory or practice) but I suspect I won't use all I have before it expires. That's part of the reason why I'm happy to give some away!Iron on transfer mode sounds very similar to T-shirt mode - which also mirrored the image. It seemed to lay down a nice thick slightly textured layer of ink on the transparencies I'm using. Normal mode definitely dried looking a bit more like a coffee ring- clearer in the middle and more pigment around the outside. I'll try to take some decent close-up photos when I do my next board

author: Fred27
author_rank: Unknown
timestamp: March 04, 2015, 10:59:00 am
content: I haven't done any PCBs for a while and a screw up with my process left me a bit worried that my solder mask had expired. After some proper testing I can confirm that 1.5 years stored in a cardboard tube in a garage has had no impact on it at all - even though the light levels, temperature and humidity (tumble drier) vary greatly.2-3 minutes under a UV nail lamp worked as well as ever.I did try tinning after the solder mask and this damaged the mask. However, I hadn't bothered with the final post-developing cure step (a UV blast for 30 minutes and 150C for an hour). That was probably all it was.The offer of some to try out still stands if you want to compare the two.I was happy enough with my cheap nail lamp and thought that LEDs were unnecessarily complicated and expensive, but your exposure unit has inspired me. I've just ordered the same LED strip you used - although only one as I plan to make a smaller unit. I'll pop some white LEDs in there too so it can double up as a light box for aligning transparencies for double-sided boards.

author: kurt
author_rank: Contributor
timestamp: March 04, 2015, 09:47:39 pm
content: Quote from: Fred27 on March 04, 2015, 10:59:00 amThat is great news about shelf life. I'm very tempted to try out the film. Seems so much more convenient than the gel. Where did you buy the film? And what do you use to develop it?Quote from: Fred27 on March 04, 2015, 10:59:00 amAwesome to hear that you got inspired from itI built a dedicated light box for white light. If you are going to combine them I guess you have to halve the LED density in one direction. And you will get a less uniform distribution (unless you use the 60 LED/meter strip and get1/4of the density). And you will have to double the distance between the light panels and the PCB.I prefer two separate units since it give higher density which means more power, slimmer design, and more uniform lighting. And I used plexiglass on the UV box since it is more transparent to UV and easier to machine for the more complex mounting. For the white light box I used picture frame glass since it is much more scratch resistant and I do more handling of items on top of it than on the UV box. And the box is much simpler so I don't need to do any machining to mount it.The high density comes with a price though. None of the boxes are able to dissipate enough heat to stay on permanently without overheating. The UV box have the LEDs mounted on metal plates which help. I never need to run it more than 10 minutes at a time, and that seems to be fine. But the white light box have them mounted on the MDF back plate from the same picture frame I stole the glass from. And the LEDs get worryingly hot in a hurry. If I where to build it again I would use a metal plate instead. And I want to make it dimmable. For most things it is to bright and I usually put one of those milky white cutting boards that you use in the kitchen over it to dampen the light. Would be much better to dim the lights and reduce power dissipation than to run it at full power and block 70% of the light

author: Anks
author_rank: Frequent Contributor
timestamp: March 05, 2015, 12:05:34 am
content: Here is one I did using the film as solder mask. It looks all scratched in the picture but to the naked eye it looks fine.Ill try and get a better picture tomorrow when I don't have to use the flash or the light on my desk. I'm sure that is what's bringing the scratches from cleaning the copper out.

author: Fred27
author_rank: Unknown
timestamp: March 05, 2015, 04:32:28 pm
content: Quote from: kurt on March 04, 2015, 09:47:39 pmThanks for the extra info. I will play around with spacing and distance and see what I come up with. Your UV box seems lightning fast so something lower power would probably be fine. I will probably stick a diffuser layer in there, so maybe that would help. The usual 4 x fluorescent tube style commercial light boxes don't seem to have a problem with light distribution despite clearly having bright tubes with gaps between them, so maybe it won't be an issue.Quote from: kurt on March 04, 2015, 09:47:39 pmI got mine fromoctamex.de. I bought a load to make the shipping cost to the UK seem more reasonable. There's usually a few people selling smaller pieces on eBay. Sodium Carbonate is used to develop it. Nothing nasty or expensive.Quote from: kurt on March 04, 2015, 09:47:39 pmSurely a 555 and a potentiometer is about 10 minutes work?

author: kurt
author_rank: Contributor
timestamp: March 05, 2015, 05:08:44 pm
content: Quote from: Fred27 on March 05, 2015, 04:32:28 pmI opted out of using a diffuser for the UV box to reduce the amount of light that gets under the edges of blocked areas. Without one the max angle light can enter at with the LEDs I use is 30 degrees. And at that angle it will have very little intensity. And I believe the commercial fluorescent type light boxes have curved reflectors to make the light as unidirectional as possible. That being said, my old UV nail curing lamp didn't have any of that and it still worked pretty well. And yes, with 1188 LEDs the box emits a lot of light. Without any mask over the photoresist it is fully cured in 6 secondsQuote from: Fred27 on March 05, 2015, 04:32:28 pmThat was a bit more reasonable than the prices I have seen on eBay. Depends on how much it will cost to have it shipped to Norway though. Will have to check that out. Thanks for the link.Quote from: Fred27 on March 05, 2015, 04:32:28 pmIf only I could find someone that could make a PCB for it

author: Zepnat
author_rank: Regular Contributor
timestamp: March 06, 2015, 10:09:45 pm
content: Like your tutorial especially the part on making the solder mask. Using a vacuum to spread it is genius. That was the only part I had trouble with, getting a consistent finish with that uv ink all the same shade. I love the photo resist method it's so controllable and if you make a mistake it's easy to go back a step and carry on.Excellent well done best tutorial I've seen.

author: kurt
author_rank: Contributor
timestamp: March 06, 2015, 11:29:19 pm
content: Quote from: Zepnat on March 06, 2015, 10:09:45 pmThanks a lot for the very encouraging comments