aligning double sided boards - Page 1
Forum section: electronics / general

author: Rx7man
author_rank: Regular Contributor
timestamp: May 22, 2020, 09:18:49 pm
content: I got the PCB-fab-in-a-box kit, and I also got some chinesium toner transfer paper.. for the life of me I couldn't get the PCB fab TTP to work, but the chinesium stuff worked acceptably well, except for the fact it was shipped rolled up, and was a nightmare to get to feed into the printer.. it was a definite test of my patienceMy question though is how to accurately align both the top and bottom halves of the board.. I drew and edge around my PCB in Eagle (0.010") and used that on two edges of the board, but it's hard to double check it's right before etching and drilling.. Got tips?

author: RoGeorge
author_rank: Super Contributor
timestamp: May 22, 2020, 09:39:02 pm
content: Drill two or more holes before making the traces transfer, and use them for proper alignment.

author: KL27x
author_rank: Super Contributor
timestamp: May 22, 2020, 10:51:37 pm
content: If you forgot to do this and have already printed it out, you can either drill a locating hole in opposite corners of the dimension outline, if you printed that. Or you can select two thru holes or vias near opposing corners.I drill the corresponding holes right in my transfer paper. So after I heat/press the first side, the hole are visible in the paper. Drill through and leave the paper on there. Then place the second side on there, which also has the corresponding holes drilled, already. And line up with a backlight or use a couple pieces of wire. Heat/press the second side on there. Then remove the paper from both sides. Put a mark on the top edge of the board on the back of both papers, beforehand.The "secret sauce," when you make larger or more intricate board is to 1. pre-etch the board. Dunk it in the etchant for a few seconds, let it drip dry for 10 seconds back into the tank, then rinse it in tap water and dry it with a heat gun. 2. you can now use a lot higher temperatures without making the transfer bleed. When you can blast the board with as much heat as you want without smearing or fattening the traces, you can effectively eliminate the possibility of failed spots in the transfer. After you have experienced the time and care to lineup and transfer a double-sided board, then have had to redo that, because it failed, you will very quickly appreciate what 100% reliability does for you.This pre-etch + limitless temp method is only practical with a transfer paper that won't distort/melt under the heat or leave fibers stuck to the board. The label-backing paper you bought from China meets this description. The best stuff, IMO, is dextrin coated paper. I buy the stuff sold by Pulsar. It is thicker than regular printer paper - thin cardstock, really - and is very easy to use and to handle by hand and by your printer; I have an HP, and it does not degrade the print quality over time.

author: Rx7man
author_rank: Regular Contributor
timestamp: May 23, 2020, 03:33:26 am
content: I have that thicker dextrin coated paper and absolutely can't get it to work, I have an HP MFP25 Laserjet pro, prints just fine to it but I can't get the traces to come off, I've soaked the board and the paper fell off on it's own, still with some traces on it.. the green TRF foil does work well, but again, it's so thin it's really hard to get into the laminator without a wrinkleOne thing I've done that'll help with the "forgiveness" is made most of my pads offset ovals.. I'll try your tips on alignment, my traces are about .024" so they're turning out goodThanks for the help, I'll go try it again.. but I'll make some changes to the design first

author: james_s
author_rank: Super Contributor
timestamp: May 23, 2020, 04:02:29 am
content: When I was etching double side boards myself I used to align the two sheets over a light source and tape one edge, then slide the blank PCB into the already aligned sandwich.For successful toner transfer cleaning the copper before you begin is critical. I use a scotchbright pad to scrub it until it's bright and shiny then rinse it off with a bit of degreaser, when it's clean enough it will be bright and shiny and water should sheet off of it without forming droplets.Some printers work much better than others too, and I've head of problems with aftermarket toner, I've always used OEM cartridges in my printers since I can usually find them on ebay.

author: Rx7man
author_rank: Regular Contributor
timestamp: May 23, 2020, 04:22:04 pm
content: with the thick paper that's impossible.. I have been cleaning the copper very thoroughly, I have all sorts of degreasers available.. I've been using 320 grit sandpaper on the board lightly to get it bright and give a little bit of "bite" to the surface... On the last run I did I think I was running a bit too hot, going to turn the temp down a touch next timeIf you're using photo resist with transparencies, I think the sandwich system would work really wellI just got the top side printed, I'm going to put tape on the bottom side to mask it, then etch it, then drill my witness holes and try getting the bottom doneHere's the board, just because

author: james_s
author_rank: Super Contributor
timestamp: May 23, 2020, 07:24:16 pm
content: Try some Press n Peel blue film, I found that works much better than all the various magazine and photo papers I tried previously. If you're still having trouble see if you can find a different printer to try.320 grit sounds too aggressive, you don't want the board to be rough, it should look polished and smooth to the naked eye, those green scouring pads are perfect.

author: KL27x
author_rank: Super Contributor
timestamp: May 23, 2020, 08:52:04 pm
content: QuoteBut what does that mean? What adverse consequence occurs, when you "run too hot?" This is the crux of the high temp + pre-etch solution, and it requires the right paper.Using PnP, too hot means the plastic sheet melts. Using various normal printer paper or some photopapers, too hot means the paper gets stuck to the board and leaves a chia pet. Using label backing paper or Dextrin coated paper, too hot means the traces fatten and smear and create reduces clearances, artifacts, and shorts. Using laser printer backing or Dextrin AND doing a pre-etch, there's no such thing as too hot. There's only not-hot-enough-yet. Just get it hot enough.After one stick-it pass, I immediately put the hot board back in the laminator and slowly wave a 1200W heat gun on max power right over the board, a half inch off, right were it goes into the laminator. The only time I have to back off the heat is when doing a 0.007" thick copper clad. This super thin board, I can get the FR-4 to bubble. Using an IR temp gun, I am seeing a bump of an FR-4 board of 100 degrees higher, as it passes out the back of the laminator. Something like 360F vs 260F. As it goes into the front, being shot with the heat gun, that must be way higher.QuoteI would guess your process is barely hot enough to work with thinner papers, and the thickness/mass of the dextrin paper is too much? I used just a laminator, by itself, at first, too. It is hot enough to just barely work on smaller boards when everything goes right, but there are still failures. If you try what I suggested, there is no such thing as too hot. That's what the pre-etch does for you. It makes the board suck the melted toner up without distorting the image. Like blotter paper. I know it's hard to dunk a board into etchant and make it ugly, right after shining it all up. But you have to keep your goal in mind and maybe experiment. Take a leap of faith, here. The only downside of pre-etching is that you can't touch up the board with sharpie pen. It won't stick to the pre-etched surface. But you won't need to touch up the board when you figure it out. (When you figure out there's no such thing as too hot, now!)Personally, I had to egg out the holes that hold the rollers in my laminator, so that a 0.062" board would fit through there without jamming/stalling. But it still works fine with 0.007" board, now. Using the same laminator for maybe 10 years, now. Killed a couple heat guns in that time, though.QuotePersonally, I transfer both sides, first, then etch the entire board at once.I do 8 mil traces, 8 mil clearances, across the entire panel, 100% success, first try. AFAIK, this limit is set by resolution of my printer. Thinner lines won't print solidly, continuously. Who knows how much finer that could go with a higher rez printer? UV has very little advantage over toner transfer, regarding accuracy and work involved, when you learn the tricks. The pre-etch is one of those things that has been on the net since I started. The info was there. But a bunch of impatient people have nearly "unlearned" this info right off the internet, by not understanding what it does. In fact, now we have people who have "scientifically" debunked the pre-etch and have perfectly distilled what you actualiy need to do to get a good transfer:https://hackaday.com/2016/09/12/take-your-pcbs-from-good-to-great-toner-transfer/. THIS is what you are trying to do without a pre-etch. You're trying to reach the exact temp where the toner starts to melt but doesn't completely liquefy. This is about as reliable as heating your driveway just warm enough that the morning frost only partially melts. This is a fool's errand; it's the first rabbit hole that clicks in some folks heads, and they follow it down to the eventual conclusion; that they're morons who wasted their time and should just do UV for this much effort and problems and crappy resolution because they were wearing blinders the entire time, they didn't imagine other ways to reach the goal, and they didn't stumble over this better way because they found the one paradigm they are trying to perfect and never tried tweaking the other variables, independently. This hackaday author, for instance, he debunked the pre-etch AND high temp methods. Separately. He never tried them both, together, plus with the right transfer paper. If you wanna be all mythbusters, you might want to figure out what you're debunking before deciding what it's supposed to do. Everybody assumes it will help the toner to stick at the same borderline temps they have been consciously or unconsciously striving for. It doesn't. It allows you to not care about hitting this partial melt/plastic phase, at all. Using fiber-free transfer medium and a pre-etch, just torch the entire village and see what happens. Perfection. If you don't get perfection, use more heat. Until something melts or bubbles or catches on fire, you are not using too much heat. Ad once you find out the minimum temp where the transfer is 100% and the higher temp where the board delaminates itself, you will find a gigantic pacific ocean of a target rather than a little bitsy wishful thinking bullseye temp what you got to get the entire board to just exactly and not an ounce more. Just set your target correctly, and as long as you got your coordinates dialed in within the nearest 10,000 miles, you can whip it out start pissing, and you can't miss. This pre-etch "myth" isn't completely gone from the internet, because some small percent of people actually figure it out and occasionally pass it along.I also do not use the green foil. With this method and using a good etchant, I do not get but the rare pinhole in my planes. When you try to only partially melt the toner by just barely reaching the exact right temp, you get a resist that LOOKS good but might have incomplete adhesion and allow pinholes or even early separation of pieces of traces.It doesn't matter who you tell about this, though. Guy who posted a video on YT and has done this for an entire 2 weeks? He already has reasons his way is better and why your way is not practical for his specific needs. If they get 95% decent transfer, artifacts, defects, compete re-dos, they will just shrug it off as being out of practice or something and credit themselves with 100% success, so long as they pay attention to everything... nothing at all to do with a finicky process and practical statistical limits.I work with PCB manufacturers at least once a week. I order most boards. But I've been doing toner transfer for over 10 years, and I still find it practical to make my own boards on occasion, maybe a few times a year. They come out right on the first try every time. None of this "out of practice" bull shit. But keep lying to yourselves. At the rate most people make new boards, this phase will last at least a year or 2, and by then most people will discover JLCPCB. Then they will share their own experience of "the best way" (that they figured out) how to suffer through a toner transfer, in a pinch, foreverafter. And even though it's the same inferior crap plastered all over the internet, they feel like their limited experience is oh-so-important real world data. Sure, I'm a cranky bastard doing the same thing; only, I am actually an expert.

author: Rx7man
author_rank: Regular Contributor
timestamp: May 24, 2020, 02:55:02 am
content: I think I was running too hot because the paper was sticking to the board and wouldn't release.. I will try the pre-etch! I just get to fiddle with this a little bit in the evenings, progress is slow.

author: Psi
author_rank: Super Contributor
timestamp: May 24, 2020, 03:14:21 am
content: i used some 0.3mm drill bits to align a hole at each corner.Was a bit tricky but worked.

author: KL27x
author_rank: Super Contributor
timestamp: May 24, 2020, 04:57:08 am
content: QuoteJust an FYI, I have never had that happen with Pulsar paper. The coating dissolves after about 20 seconds in room temperature water. Even the thin boards I have on occasion bubbled in spots, at extreme higher-than-necessary temps, those worked fine, too. So maybe your paper went bad or is fake?When you go really, really hot, near the FR-4 bubbling temperature, the artwork starts to dissolve into both the board and the paper. So you can see an outline on both. The resist might look thin, but the paper still releases fine, and those boards etch and work fine, too.

author: Psi
author_rank: Super Contributor
timestamp: May 24, 2020, 06:18:28 am
content: If using some sort of glossy paper it's normal for the paper to stick to the PCB.You have to wet the whole thing and rub the paper off. It takes some effort.With PnP blue you just lift it up and the blue part effortlessly separates from the clear part. (toner has glued the blue down)

author: KL27x
author_rank: Super Contributor
timestamp: May 24, 2020, 07:14:28 pm
content: PNP removes the problem of fuzzies and smearing at higher temp. The plastic leaves a clean resist with no fibers. The textured surface sucks up liquid toner to prevent smearing. The only drawback is the pnp sheet, itself, will melt at barely higher temp than needed to ensure a transfer without missing sections. This is why I switched to Pulsar, which is a bit more expensive for me, but totally worth it. 100% success is worth a lot more than 95%.The blue plastic resist of Pnp has the other benefit of reducing pinholes. But the method I use nearly eliminates them, too. So the only difference to me is the slightly different cost. Pnp is also more pain to handle, curling/static.

author: Rx7man
author_rank: Regular Contributor
timestamp: May 26, 2020, 04:30:48 pm
content: still having alignment problems, I think my printer is distorting it somehow.. my two alignment points are right, and as I get further away I'm up to about .020" off or so.. For this project it was tolerable since I had my alignment points close to my smaller footprint parts

author: reboots
author_rank: Regular Contributor
timestamp: May 26, 2020, 08:03:31 pm
content: Quote from: Rx7man on May 22, 2020, 09:18:49 pmIt's been a long time since I fabbed boards myself, but I've made several double-sided boards using this method:1. Copy the board layout in software, and flip the copy so the bottom layer is now on the logical top with the artwork reversed. For Eagle I would make a working copy of just the .brd file, to break back-annotation; otherwise Eagle complains when you try to cut/paste layout. Perhaps there is a more civilized way.2. Align the top and flipped-bottom layouts. You could add alignment marks, but I just used the edges of ground pour for alignment. Print desired layers to the transfer paper.3. The paper I use isn't translucent, so I trim the outside edges to match alignment marks.4. Fold the paper so the cut edges meet.5. Put your PCB material in the crease, and iron as usual. I let the iron sit on top for a minute before ironing, so there's enough adhesion that movement doesn't drag and misalign the layers.I've become less and less careful with this process. Sometimes the design isn't exactly square on the PCB, but I've always gotten usable top-bottom alignment for vias and through-holes. Your mileage may vary.

author: SilverSolder
author_rank: Super Contributor
timestamp: May 26, 2020, 08:41:52 pm
content: Quote from: Rx7man on May 26, 2020, 04:30:48 pmI have seen this alignment issue too, i.e. where the printer is actually not outputting exactly the same size of print on each run... I could imagine slippage between the rubber rollers and the paper, as well as heat distortion perhaps working differently depending on which direction you feed the paper, the effect of humidity on that particular day, etc. etc. etc. can cause small differences in the print size.I find the repeatability is worse in the length direction than the width (assuming letter or A4 size paper) so perhaps the rubber roller slippage theory has something to it.Now we are down to the nitty gritty of the actual limitations of the toner transfer method. The larger the PCB, and the smaller the parts, the more these things matter.

author: KL27x
author_rank: Super Contributor
timestamp: May 26, 2020, 11:45:45 pm
content: It might be the paper, itself, moreso than expansion/constraction of the board and/or the laser printer? I notice some papers distort more than others. Is the paper distorting in the printing or the transferring? I don't know.Using pulsar, I have never had a noticeable distortion. If the holes are off, it seems to be consistent across the board, due to alignment rather than distortion. I haven't worked very hard to determine what works best for alignment, because I haven't had much issue, yet. But the last many I have done, I've drilled super tiny holes and use 30AWG bare wire to line up with the holes in the second side.

author: Rx7man
author_rank: Regular Contributor
timestamp: May 27, 2020, 05:00:35 am
content: Quote from: SilverSolder on May 26, 2020, 08:41:52 pmI did find a more civilized way of doing the printing in Eagle 7.6 at leastOn your board layout, select the layers you care about, Usually one of top or bottom, then Vias and also Pads... then print it, in the print options you have the option to mirror as well as select the position on the paper.I'll try printing it onto a transparency and laying them on top of each other to see if this is occurring during printing or if it's during the bonding... thinking about it, blaming the printer sounds like the easy way out, and my process is more likely suspect!Another thought that crossed my mind is the thermal expansion of copper, from room temp to bonding temp is 0.2%, or 2 thou over each inch.. on a 4" board that's 8 thou, not negligible when working with small parts!.. FR4 expands very slightly less

author: Rx7man
author_rank: Regular Contributor
timestamp: May 27, 2020, 05:02:29 am
content: Quote from: KL27x on May 26, 2020, 11:45:45 pmWhen I was trying to get that pulsar paper to work, I tried letting the board cool off completely before wetting the paper, that didn't work at all, the paper buckled when it got cold

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 27, 2020, 08:55:45 am
content: Quote from: Psi on May 24, 2020, 03:14:21 amwhat is your drill setup to drill with 0.3mm bit? i cant drill anything lower than 0.8mm (using my small diy CNC drill) without breaking the bit.

author: Psi
author_rank: Super Contributor
timestamp: May 27, 2020, 12:19:31 pm
content: If you want to drill 0.3mm get some normal HSS drill bits, don't be tempted to get the 0.3mm carbide bits.For drills that small carbide will only work if you have a rock solid (and i really mean solid) PCB drill press that can apply force perfectly to avoid snapping the bit.HSS wont last as long going into FR4, but they won't snap when you look at them funny.

author: KL27x
author_rank: Super Contributor
timestamp: May 27, 2020, 08:38:58 pm
content: Yeah, HSS is better if you're doing it by hand. And by hand, you can angle the bit to meet the other side, after you recognize an alignment issue. But if there are a lot of holes to drill, carbide in a drill press is way better, because steel will inevitably push the via/trace off the other side if your alignment is off. The carbide will punch through and leave the copper in place, so you don't deal with lifted pads.QuoteOne thing I have found is helpful, in general, is to not leave large empty spaces on a board. I always use ground pour where it otherwise doesn't matter. Don't leave thin traces with large space around them.* I don't know if it makes any difference, but after my hot pass, I immediately drop the board into a bucket of water. Well, for a single sided board. For a double-sided, I leave the paper on there (and dry!) until both sides are done, and the board cools down while drilling and aligning. So... I dunno if that's anything to concern yourself over.*I am convinced this makes the board etch more accurately. So I suspect it might help with UV as well.

author: SilverSolder
author_rank: Super Contributor
timestamp: May 28, 2020, 12:05:36 am
content: Quote from: KL27x on May 26, 2020, 11:45:45 pmI've seen distortion on the Pulsar paper, but only when attempting to make the largest PCB I've ever attempted with this method, a full letter sized PCB... 8" by 10.5" if I recall correctly.That was too much.The filled ground planes did not turn black enough, and distortion was an issue (double sided board, impossible to align top/bottom sheets due to distortion).I've never had a problem with getting the Pulsar paper off the board. Sure, there are remnants of paper on the board when it comes out of the water, but nothing that can't be carefully rubbed off using your fingers or a soft sponge.

author: twospoons
author_rank: Frequent Contributor
timestamp: May 28, 2020, 12:56:42 am
content: Being a PnP Blue user, I did alignment by adding a couple of moire patterns to opposite corners of the artwork. The moire was three concentric circles with equal line width and gap. Makes alignment very easy to see using a light box or just holding up to a window. The art was taped on two sides when aligned and the laminate slipped inside. You do need to leave a bigger margin to allow for the pcb thickness.The pre-etch idea is interesting. I guess I had something similar as I always used an abrasive rubber cleaner to clean the blank PCB.I seldom had issues with toner sticking or with pin holes. Dust could be a PITA though.Best result: 23/24 working circuits in double sided Kapton flex, using 5mil/5mil design rules. I was hoping to get just one and thought 5/5 was pushing it a bit hard, so I did a 24-up panel.

author: Rx7man
author_rank: Regular Contributor
timestamp: May 28, 2020, 07:14:02 am
content: with small holes, RPM IS KEY!.. I have no problems doing .5mm holes by hand, though of course my accuracy is going to be limited, I use a dremel with a flex shaft at max RPM.. 0.4 and 0.3 I think I could do, but it would be sketchy as heck and I know I'd be breaking bits.. I broke my .4mm when it fell to the floor.. GRRRAnyhow, I have my board assembled.. it ain't pretty, but it's functional.. I had a couple minor oversights.. I made a voltage divider and didn't realize I didn't have a necessary resistor value in stock.. it was just a 3:1 divider, and I was going to use a 10K/5K pairing.. thought about it a few minutes and just double stacked an extra 10K on there... Checked all my resistances and it seems to be fine.. Now I just have to solder the Arduino Mini to the header pins and it should be good to go.And just in case anyone is curious, It's a transmission overdrive/torque convertor lockup controller for an old dodge truck where the factory setup is pissing me off.. I added pin headers for a I2C OLED display, a bluetooth module, and a CAN bus module

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 28, 2020, 10:33:19 am
content: Quote from: Psi on May 27, 2020, 12:19:31 pmQuote from: Rx7man on May 28, 2020, 07:14:02 ami checked my stock i do have HSS bits (cheapo version) like this...https://www.ebay.com.my/itm/20-pieces-HSS-Twist-Drill-Set-Round-Shank-Drill-Bit-0-3mm-1-6mm-and-Base-Kit/333403235915?hash=item4da061a64b:g:Np8AAOSwA3dd0tmlbut currently i use china carbide one like this...https://www.ebay.com.my/itm/10pcs-0-3mm-to-1-2mm-PCB-Print-Circuit-Board-Carbide-Micro-Drill-Bits-Tool/141677858689?hash=item20fca88f81:g:8pEAAOSwNSxVAT0Gbecause they have same diameter (shank) to meet the drill motor's chuck. i manually balanced my cheapo motor+chuck for the diameter. with the HSS bits that doesnt have same mating shank diameter, my motor+chuck will be out of balance. the broken bits i guess are due to slight out of balance developed in time or difference shank diamter, or at higher speed, excessive runout made them broke. iirc i managed to break the HSS bits using out of balanced motor. so i think its something more on drill motor imbalance that made them break. higher quality drill motor and chuck will be needed imho.

author: Rx7man
author_rank: Regular Contributor
timestamp: May 28, 2020, 07:23:48 pm
content: yeah, I have the same carbide drill kit.. they're cheap enough at least!I'd like to find 1 to 2mm set, some of my larger headers I have to use the bit as a router since I dont' have the right size drillthe Dremel tool isn't bad, it's not perfectly balanced but it's pretty close, the weight of the flex shaft kinda gets in the way, I might try just holding the motor instead.. more weight but a flexier cable.. 6 of one, half a dozen of the other