Tools for PCB cutting/drilling?

Discussion in 'General Electronics Chat' started by autorelease, Jul 21, 2009.

  1. autorelease

    Thread Starter Active Member

    Jan 26, 2009
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    I'm sure this question has been asked before; feel free to direct me appropriately if so.

    I'd like to start fabricating my own PCBs. I've had them professionally made before, but for one-offs, it takes too long and costs way too much.

    What kind of tools should a newbie buy to cut and drill PCBs? (I'm on a budget, so a CNC machine is out of the question :p)

    With regards to drilling, a Dremel and the work station look nice, but I've heard reports of shoddy construction. Any other recommendations?

    What about for cutting copper boards? Would a tile cutter with a tungsten carbide blade work? (I found one at Lowe's down the street for $18.)

    Other miscellaneous questions:
    - Is it difficult to make two-sided boards? Soldering seems like a challenge since the holes aren't plated through.
    - Can I use a spade bit to drill holes larger than 3/8" (for switches, etc.) in plastic enclosures, or will it destroy the plastic?

    Thanks,
    -matt
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    For drills and shaping (e.g., making cutouts), I find tungsten carbide is the only practical choice. HSS drills work for a few holes, but dull quickly. Many people, myself included, get resharpened carbide drills on e-bay. I got a lifetime supply of #66 (0.033) for a few pennies each. With carbide drills, you will need a drill press.

    Cutting the boards is a different matter and there are all sorts of ways to do it. Some people hack them to approximate size with a hacksaw and sand to final dimension. Tile-cutting saws (wet) are also reported to work. I use a thin-kerf carbide blade in a small table saw (like Dremel or MicroMark). I cut almost 1/2 way through from each side, then snap them. That requires very little clean up. Finally, Harbor Freight has a small shear that some people have had good luck with. The carbide tile cutter you found sounds like one of those things for scoring tile. It will probably not work. If it is a wet blade saw, you can't beat that price, so I would buy it even if I really didn't need it. Tell yourself, it is capital investment.

    Of all the steps in making a board, I dislike cutting the PCB to final size the most. Wear some sort of dust mask while you do it, unless you have a shear.

    John
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
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    Tungsten carbide is the only practical material for drills. You may break a couple until you learn the technique, but the extra expense is worth it. I have a dedicated PBC drill press. One of those Dremel rigs would probably do okay if the motion is rigid. Carbide is very brittle.

    I have bragged about a Harbor Freight 4" table saw, but no more. It still runs, but it is close to junk. The small egg motor pulls 900 ma, and gets hot enough that the leads melt off the brush holders. The bearings are sloppy, and come lubricated with what may be the secretions of a yak. But the diamond blade works great on FR4, and you don't worry about cutting off a finger.
     
  4. lightingman

    Senior Member

    Apr 19, 2007
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    Hello,

    This drill is just great for manual drilling of PCB's. It is fast accurate and if using carbide bits, produces perfect clean holes, even down to 0.5mm.
    I was lucky to have got this one on E-bay for 42 GBP + 15 GBP postage.

    Daniel.
     
  5. studiot

    AAC Fanatic!

    Nov 9, 2007
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    You can still get coordinate tables / lathe cross slides which allow coordinate drilling and even routing using a hand press.
     
  6. lightingman

    Senior Member

    Apr 19, 2007
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    Hi again,

    One other thing. I have recently acquired a large roland plotter. I have the idea of converting it into a CNC, PCB drilling machine.

    When I get round to it, I will try and post the details on the forum.

    Daniel.
     
  7. someonesdad

    Senior Member

    Jul 7, 2009
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    If you want to drill lots of holes, a drill press will save your sanity. If you're going to drill lots of little holes (say, on the order of a mm or two and smaller) you're going to want a smaller drill press with a fast spindle speed. The vast majority of cheap shop drill presses have spindles speeds that are way too slow by an order of magnitude or more. You can drill holes with slower speeds; it's just not optimum, especially if you're using carbide (and impatience leads to drill breakage). A good choice might be to mount a Dremel-style tool on something that can feed the drill. For small circuit boards (say, dimensions of a few inches on the side), I'd consider making a cam-operated table; the drill head stays fixed. There was an article on one in Home Shop Machinist or Projects in Metals a few decades ago.

    For drilling holes in plastic boxes, you can use a variety of types of drills. The problem is that most folks turn the drill in something powered. Unless things are held rigidly, things can grab or break. I sometimes drill things by hand; this keeps generated heat down and reduces breakage. More than 100 years ago, people drilled holes by hand, sometimes pretty large holes. If you're interested, look up "old man drill" on the web. I like to drill through thin plastic or metal with a small drill, then enlarge the hole with a tapered reamer. For thin stuff, step drills are also popular.

    Another effective "hold drilling" technique for plastic is to use a four flute end-cutting end mill spinning right properly along and have everything clamped tightly in a vise or to the mill's bed. Alas, most folks don't have a mill. However, this is a versatile technique and, with a boring head, you can make a close-fitting hole of any practical size. If you've got a lathe, you can also bore the hole.

    You can use spade bits, but ideally turn the bit by hand and clamp things down well. If you round off the profile of the bit, it will cut more smoothly (see the attached sketch).
     
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  8. autorelease

    Thread Starter Active Member

    Jan 26, 2009
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    Thanks everyone. My local electronics shop has lots of tungsten carbide bits, so I bought a set, along with a variable-speed Dremel (which I can use for other tasks as well) and a Craftsman drill press unit:

    http://www.sears.com/shc/s/p_10153_12605_00953169000P

    It feels pretty solid. I clamped it to my desk and tested it out on a small piece of 2-sided copper-clad board. I was able to drill holes with a #63 bit just fine, but it broke a #73 just as I was raising the plunger. This was probably because I wasn't holding the board down very well. The Dremel was set to its highest speed.

    What technique should I be using? Should I depress and lift the plunger slowly or quickly? What speed should I set the Dremel to? Should I clamp the board to the press so it doesn't move during drilling?
     
  9. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    You will break a bit occasionally. It may have just been the bit.

    As for clamping, I do not do that. I use Eagle for my layouts and finish by running drill-aid.ulp. That leaves a smaller hole that self centers on the bit. Default is 0.3 mm; I suggest something slightly larger, like 0.4 or 0.5 mm.

    If the drill is too fast, it will not center as well as when it is slightly slower. That is just a matter of feel. I use a magnifying visor with good lighting and bring the bit to almost touch and as centered as I can see it. Then with the touch, I release a little pressure on the board and it self-centers. At that point, I hold the board more rigidly and continue drilling. I usually do all of this against a piece of smooth hardwood as back-up for the drill. It actually goes pretty quickly, once you get into the rhythm.

    Small drills (e.g., #63 or #66) are very little problem. With larger drills, the piece may tend to climb up the drill, so be sure you have a good hold on it.

    If you break a bit in the board, be sure to remove all of the fragments. Sometimes, just a lip of the drill will snap off. A center punch from the reverse side or a pick will help remove the fragment. If you try drilling with the fragment still in place, the new drill will probably break too and you will bugger the hole.

    John
     
  10. DaveH

    Active Member

    Jan 1, 2009
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    This is a very interesting thread and I was about to ask similar questions so I guess I'll just join in the discussion here.

    I am doing a single sided board of about 10 square inches (irregularly shaped as opposed to rectangular/square). I'd say for a through hole board it's a pretty complex project. The gerber and drill files (if I was giving it to a pcb house to manufacture) have really tiny track widths and hole sizes of 0.7 mm

    I don't know if this is gonna work, but my tools are a dremel, a 1mm bit (not sure if it's carbide but it's all I could get hold of), ferric chloride pellets and protective goggles of course.

    As my bit size is wider than the 0.7mm hole sizes of my layout, I've tried to compensate by making my pad sizes a bit wider (typically around 2 mm) to give enough copper left around the hole.

    To cut the board I plan on using the cutting wheel attachment of the dremel.

    My worry is that my ferric chloride/laser printer/iron on process is not going to be high quality enough for the small track widths (like 0.5mm). Now that people have talked about using drill presses, I'm thinking may be I shouldn't attempt it by hand will a dremel, but I can't afford to buy anything else. I'm thinking it's a real shot it the dark. I think I'm gonna try and make my track widths a bit wider to make up for my not very sophisticated etching process.
     
  11. millwood

    Guest

    or you can avoid drilling by soldering through-hole parts the SMD way.
     
  12. DaveH

    Active Member

    Jan 1, 2009
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    That could be an option. It will give me practice at SMD techniques for my next project, where I attempt the feat of using an LQ64FP with dimensions of 12 x 12 mm, probably impossible to do a board for that at home, yet alone solder it.
     
  13. russ_hensel

    Well-Known Member

    Jan 11, 2009
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    I have used a hand drill on a drill press stand, not a very good setup. To hold the bit I have used a pin chuck, basically a chuck for very small drills, this is chucked in the larger drill chuck. Got it a edmund's scientific a long time ago. May not be useful esp. if the drill has a larger shank than tip.
     
  14. someonesdad

    Senior Member

    Jul 7, 2009
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    If you don't have a drill press, consider making a "horizontal drilling machine". Take a couple of hose clamps, screw them to a board, then hold the Dremel tool horizontally in these clamps. The work then sits on a wooden sled, guided by slots, rods, etc. (whatever you have that's appropriate). For a PC board, you can mount it to a home-made angle plate. Search the web, as it's a fairly common technique in both woodworking and metalworking. The advantage is that it's something you can build with stuff from the local home center.

    By the way, those Dremel tools are quite useful. I clamp one in a similar fashion in my lathe's toolpost and have used it for grinding, drilling, and milling in the lathe.
     
  15. millwood

    Guest

    I am experimenting with lqfp (48 - 64 pin in my case) now. I have tried a few chips (Luminary cortex m3 stuff) so far, and no good solutions yet, with either hand soldering and oven baking: the pitch is too fine.

    I am thinking about a combination of oven baking (one of ever other pins), and then hand soldering the rest.

    if you find a better solution, please let me know.
     
  16. DaveH

    Active Member

    Jan 1, 2009
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    I was talking to someone who said first flux all the pins on all 4 sides, then just cover all the pins with lots of solder blindly and don't worry about solder bridges forming everywhere, then take some solder braid and mop up the excess. Inspect everything with a magnifier and it will probably have no solder bridges left, with all the pins soldered to the pads.

    Now he made it sound easy, but may be he didn't realise that we are talking about very miniscule gaps between the pins. I did some searches on youtube and found some very good instructional videos that demonstrated this technique. I hope it works, otherwise I'm not sure how to prototype with such chips.

    I have an oven at home, but it's used to cook food. I wonder if it's possible to use that instead of a proper reflow oven? It's a pretty good fitted unit by a German company called NEFF - I last used it to make Wild Alaskan salmon, which tasted great.
     
  17. millwood

    Guest

    I did the copper braid approach: put on the paste, bake it and then use a solder to heat a f ine copper braid while wiping away the excess solder. it works except that sometimes you will get tiny bits of solder on the inside of the leads: ie in between the leads and the chip and then you have no way of getting it out.
     
  18. parawizard

    Member

    Jul 23, 2009
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    Have you tried making your own modified Toaster Reflow Oven? I just acquired a nice big toasty toaster oven for such uses of my own. :)
     
  19. DaveH

    Active Member

    Jan 1, 2009
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    A toaster sounds like a good idea. I guess it's best to position it horizontally and to take out the eject mechanism so the PCB doesn't fly out after the toasting cycle. What kind of toaster is it and have you had much success with it? I don't mind how crazy the idea is as long as it can do these fine pitch chips. I think I have a good chance at soldering the more normal SMD things by hand.

    Hi Millwood, about the braid approach. Now I haven't tried it myself, but if you have and you reckon the problem is that sometimes you get solder bridges between the pins that the braid won't suck up, what about using a sharp knife or razor blade to basically slice out the solder bridge? (as long as you aren't using a board with loads of layers where the adjacent layer might get damaged). With a magnifier you can check it if the bridge has been removed.

    Or I wonder if there are test leads with probes like needles so you can do continuity checks between adjacent pins to check there are no solder bridges. That could be a good idea I think.

    When you're on the verge of starvation, ideas come quickly. That Alaskan Salmon I made, wasn't done yesterday, it was about a week ago! I've got to find a solution for SMD stuff. There's got to be a way to do it at home.

    I understand that with SMD ICs the solder typical flows behind the lead (towards the body of the IC package), or at the end of the lead if there's space on the pad, have you guys ever had a problem where by a lead doesn't get bonded to the pad with solder. It seems most of the problems with home made SMT boards are with too much solder causing bridges and I've have heard of leads not getting bonded?
     
    Last edited: Jul 23, 2009
  20. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I have not done a LQ64FP, which I believe is 0.020 pitch. I have done 0.025 pitch parts using the flood and wick method, and it worked fine. There were no problems with non-bonding nor with bridges on the back of pins. I did not add flux to the pins, but did have a very thin layer on the board. Although you are "flooding" with solder, there is no need to over do it. You just need to be sure each pin has solder on it.

    John
     
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