DIY PCBs with 10mil/0.25mm trace width and hole clearance?

Discussion in 'General Electronics Chat' started by DaveH, Jul 27, 2009.

  1. DaveH

    Thread Starter Active Member

    Jan 1, 2009
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    There was recently an excellent discussion about PCB drilling and SMD soldering, where so many people contributed it really solved all the problems - at least in my head.

    I'd like to know if anyone has managed to 10 mil trace width PCBs with similar trace to pad clearance. 10 mil is 0.254mm. I guess this depends on what process you use.

    For me it's going to be print the gerber file copper pattern on an inkjet. Get that photocopied with settings to give high contrast and lots of toner, then iron that onto the copper clad and etch. This was suggested by someone else on the forum as I don't have a laser printer at home.

    I'm looking at a print out of the copper pattern and I'm thinking that's going to need a pretty sophisticated process to get it to etch cleanly. I'm thinking if I gave my gerber file to a PCB shop, they would be able to do it no problem, but for my process, I'm thinking I'm going to have to up the trace width to about 20mil or 0.5mm to stand a chance.

    What do you think?

    I think a bigger problem than 10mil trace width is having 10mil trace to pad clearance. That's surely only something a commercial PCB shop can do?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    I simply place my foil pattern on the resist coated PCB and expose for the correct time. After that, I get consistent results down to 4 mil lines. 10 mil lines and pad clearances should be no problem. If the toner is in contact with the coating so no light leaks under, the results are quite predictable.

    If this is the first time, you may need to experiment a bit to see how to achieve consistent results. There is no sophistication to etching - agitate the solution and it happens. Just use 1/2 or 1 oz foil to minimize undercutting.
     
  3. n9352527

    AAC Fanatic!

    Oct 14, 2005
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    I don't know about photocopying, but I print the gerber directly using a cheap Samsung laser printer (600dpi, the thickest and blackest settings) to a glossy paper and I get excellent result down to 10mils.
     
  4. DaveH

    Thread Starter Active Member

    Jan 1, 2009
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    Thanks guys, this is encouraging to know. Unfortunately I can't afford a laser printer or a UV exposure box, so I'm going to have to use my inkjet and get it photocopied - which is equivalent to printing on a laser.

    I was also wondering how to make my finished board look serious - I mean give it that green pro look? I've heard that's done using lacquer. I'm using single sided FR4, after the soldering is done do I just spray the board underneath? I remember when I used to make board, my soldering was ok but I used to get these crappy looking brown flux residues everywhere. Can that be removed with isopropyl? In fact I'm thinking of using seperate flux because I don't think these flux cored solders get the best joints. In audio circuits, one crap joint on signal path and the whole board is screwed.
     
  5. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    There are different types of flux. If you are using a mildly activated flux like Kester 44, isopropyl alcohol (>99%) should work. A little acetone will increase its strength, but then you have to worry about some clear plastics. IC chips and transistors are all fine. A little water cuts its ability to dissolve flux drastically. I use absolute ethanol + a little acetone. There are also water soluble fluxes, but I have very little experience with them. I tried one, but went back to my old Kester 44. As for whether to use cored solder, I assume your parts will be small as you need 10 mil traces. I cannot concur with you on the quality of joints using cored vs. non-cored small gauge solder.

    Good luck with TT. A laminator may be in your future. That is probably more expensive than a single 15W UV (BL) tube and fixture. In my experience, ink jet transparencies for the photo method are preferred over laser, as the ink spreads just enough to avoid the tiniest of pinholes.

    I would still recommend ferric chloride as the simplest, proven way to get the sharpest etching. There are plenty of independent data to support that vs. cupric chloride/peroxide methods.

    John
     
  6. John Luciani

    Active Member

    Apr 3, 2007
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    A friend of mine built a UV exposure box using UV LEDs he bought on EBay. He gets down to around 6mils or so.

    For the flux I would use water soluble flux and clean with hot water and an acid brush.
    Cleans up nicely.

    (* jcl *)
     
  7. DaveH

    Thread Starter Active Member

    Jan 1, 2009
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    Hi Jpan, well I'm not saying certain flux cored solder is no good, I'm just guessing thinking seperate flux is better. So you reckon it's possible to make a basic UV etch box quite cheaply? Please post only links on this. If I only need a light proof box, a bulb and just need to time the exposure, I guess I can do that. What do you mean TT?

    Hi John, I just looked at your sites. This looks really great. So do you make all these boards yourself or do you get them done by a PCB supplier and how about the assembly do you do all the soldering or is worth getting the supplier to make the finished assembled board? Looking at the pics of your products these look really professional - they've got that serious green look to them.
     
  8. John Luciani

    Active Member

    Apr 3, 2007
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    Thanks.

    I design all the boards myself but I have them fabricated at either PCB Express or
    Advanced Circuits. Both of these vendors have excellent quality and I choose either one based solely on price and delivery.

    To keep the prototyping costs low I panelize the designs. The panel I am doing this
    week will have a dozen designs (multiple copies of each). I will go with a 12" x 14" panel and cut the individual designs out of the panels. It will be around $500 for two panels.
    Roughly $40 per design to prototype.

    I assembly the boards myself. It would be extremely expensive to get prototype
    boards professionally assembled. You also need to produce a fair amount of documentation for the assembly process. With the proper tools it is not difficult
    to solder *leaded* SMD parts with an iron. The tools I use are at
    http://tinyurl.com/5foeou

    Unfortunately QFN and LGA and BGA parts require solder stencils
    and a hot plate (or oven) to solder. I hope to get setup for these packages
    in the near future.

    (* jcl *)
     
  9. DaveH

    Thread Starter Active Member

    Jan 1, 2009
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    Do you use PCB lacquer after soldering the components? I thought it kind of protects the exposed tracks from contamination. I don't really see the point of lacquer really because even if the surface of tracks oxidizes a lot over time or gets covered in dust and dirt it doesn't really affect circuit performance because it's only on the outer surface of the conductor that's getting dirty.

    The only thing I've heard about using lacquer is it gives the board a sealed look to it and makes it look green. I suppose it acts like an insulator. See this: http://www.maplin.co.uk/Module.aspx?ModuleNo=25345

    I saw somewhere else a Chinese lacquer manufacturer and they said you should apply it before you stuff and solder the boards and it acts like a kind of flux for all the tracks. That doesn't sound right to me, but what they were saying is that after the board is etched and you remove the etch resist to reveal the fresh shiny copper, the tracks start to oxidise within minutes, so you coat the board with this stuff immediately then you can stuff and solder the board whenever you want?
     
  10. John Luciani

    Active Member

    Apr 3, 2007
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    The boards I purchase have soldermask over bare copper so the traces do not oxidize.
    The pads surfaces come from the vendor with solder on them. There is no reason to use lacquer for normal operating conditions.

    If you make your own boards you can buy a tin plating solution to plate the copper.

    (* jcl *)
     
  11. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    My first "light box" was an 18" fluorescent light strip fixture (about $8 to $12) on each end of which I attached two pieces of board to hold it so the bottom of the tube was about 4" from the surface on which I set the boards. (see attachments). NOTE: The wrong type of UV tube was used in these pictures. I simply put something in place so you could see how it fits. The BL tube will have a white phosphor. Be sure to use the type of tube recommended by the manufacturer of your sensitized boards. The detail shows how I made the end pieces detachable for easy storage. The end piece was exactly 6" long. Here is a photo of the assembled box:

    [​IMG]

    Initially, I used a piece of aluminum foil balanced on the fluorescent tube as a reflector. It worked fine. Later I had a piece of polished aluminum sheet , so I used that. Exposure was 10 to 14 minutes using Injecterall. Different brands of sensitized board will vary. I recently inherited a nice 3-tube box, so no longer use this unit. Are you near Cleveland, OH?

    You will need two pieces of single pane window glass (4" X6") and 4 binder clips. My local mom and pop hardware store didn't even want to charge me for the glass. I gave him a couple of $ for donuts.

    TT = toner transfer, which is the method in which you iron on the toner from a laser printer.

    John
     
    Last edited: Jul 28, 2009
  12. DaveH

    Thread Starter Active Member

    Jan 1, 2009
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    Hi Jpan, unfortunately I'm in England. Thanks for this I get the picture and think I can improvise something. I'm going with 'TT' for now. I'm just doing some final optimisations with my copper pattern now. Tommorrow is the big day when I get it photocopied and iron on the photocopy to the copper clad and etch away.

    I must say my copper pattern looks great, it looks like a real pro job. If my circuit doesn't work, I've got a nice piece of modern art to sell on ebay.
     
    Last edited: Jul 28, 2009
  13. Wendy

    Moderator

    Mar 24, 2008
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    I've bought laser printers (hp) for as little as $10 at garage sales, but the toner cartridge was $40.

    You won't be able to get a photocopy to work for fine scales. There are distortions in the copying process that will make it impractical, been there, ruined that. Basically where a trace goes into a larger mass was pinched off. A laser printed copy, on the other hand, doesn't have this problem. Maybe you won't have the problem, good luck.
     
  14. DaveH

    Thread Starter Active Member

    Jan 1, 2009
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    Hi Bill, thanks for the warning. I think what I'm going to do is get the photocopy and at the same time give them a PDF of the Gerber file view and tell them to print it direct on a laser. At least that way when I get it home if the photocopy is no good I'll try the laser print out.

    In England we get ripped off for everything. To get a single A4 (letter size) sheet printout in a print shop will cost me about £5.50 ie. about $8 - nearly as much as you payed for your laser printer!

    I'm therefore looking around for a cheap laser.
     
  15. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    That cost is outrageous. Remember, with the photo method, you use your inkjet. You can get the sensitized boards for about $5 to $6 (3 X4.5") each. Double-sided is also quite easy.

    I suggest that you try the toner-transfer method to see whether you can get the resolution and quality you need before investing in a laser printer for it.

    John
     
  16. DaveH

    Thread Starter Active Member

    Jan 1, 2009
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    I can kinda report some success with toner transfer via photocopier. I took my inkjet printouts down to a cheapskate print shop that has a lazer photocopier. I told them to use glossy magazine paper I bought with me but they said the copier couldn't take it. They charge me 70 pence for 1 copy on a sheet of A4 special glossy art paper (I panelized up 3 boards onto 1 sheet - good idea guy who suggested that) I told the guy what I was doing this for and he seemed to understand. The copies came out looking good with precise traces and visible pile up of toner on the paper.

    Looking at the fused toner on the copper clad after ironing, the problem I've got is that in some areas the toner has fused well and in other areas there's no way that's gonna resist the ferric, the traces look too weak and broken up, some of the pads are a bit weak also. Luckily I looked in my old electronics drawer and found a dalo etch resist pen. I'm gonna go over all the bad areas with the pen and then etch. Also I'm having to go over the board with a needle to scratch away a bit more clearance where the adjacent toner traces look too close. I think what happens is that when you iron on in some parts of the layout the heat from the iron will spread out the toner a bit wider than the gerber file specifies.

    Another problem is I'm finding I can't get the paper off the board in between some of the traces. Surely the ferric will dissolve that and etch the copper underneath?

    Overall I think I've been a bit too ambitious with my 'process' - 10 mil traces and clearances of less than this is places is a bit over the top for a photopier method. I'm gonna have to check the netlist is right after etching with a continuity tester and needle probe.

    I think I can improve things a bit on another attempt. This time I'll leave the iron on for about 5 minutes instead of 2 minutes and keep it moving more. Also I'll let the board soak in water for 30 minutes to get the paper off.

    I've now got hold of a 0.8mm drill bit, but realise the Dremel needs a special micro chuck to hold it! Luckily I've got a big cordless heavy duty masonry power drill. That's going to be fun using that to drill pads by hand that will have rings of copper only about 0.25mm wide. :) I'm thinking of a home made IC with hammer and chisel next - but I see some guy has already done it.
     
    Last edited: Aug 5, 2009
  17. beenthere

    Retired Moderator

    Apr 20, 2004
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    You might want to look at this site - http://drillbitcity.com/

    The nice part about PCB carbide drills is that they all have 1/8" shafts. Just right for a Dremel.
     
  18. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    0.8 mm (1/32) is a standard Dremel collet, about $2.50 singularly and not much more for the set of 4, which includes 1/8, 3/32, 1/16, and 1/32 collets. For fine control, you might have better luck with the Dremel than with a much larger, hand-held drill. For precise, small-hole drilling, it is hard to beat a collet for holding the drill.

    John
     
  19. DaveH

    Thread Starter Active Member

    Jan 1, 2009
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    Well I would prefer to use the Dremel and didn't realise they have .8mm collet. The collet I have is about 2.5mm so won't hold it. Either that or I have to get the 4486 multi-chuck. I think I can get away with the big drill, the way I'll do it is hammer an indent into the copper first, that way the bit will seat properly when I pull the trigger on the drill. I see why some people prefer UV photoresist method now.
     
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