At least one of my projects calls for 8 very tightly spaced holes for tiny buttons to protrude through, and even tinier (1MM) holes for fiber optic segments near each button hole, plus some other assorted holes for LEDs and controls, all on a small 2" x 2" panel. Well I don't know about you folks, but I've found drilling sequences of perfectly aligned and perfectly spaced holes in a plastic enclosure to be a difficult error prone task. One little slip and that enclosure is going to look unprofessional and sloppy. I've gotten better at it, but its still a time consuming process to get right.
Well I assume by now a lot of you know that PC boards, especially small ones, have finally become very inexpensive to prototype, thanks to direct from China fab houses like PCBWay.com. So a crazy thought came to me. What if I used my PCB software to lay out a board exactly the size of the control panel I need, placing all the holes exactly where I need them In the exact sizes I need them, and specifying no traces or through plating. Just order a minimum 1 sided board with all the holes where I need them, and a full copper pour on the side with copper. I could do it reversed so the side with the copper could face the inside and add shielding to my project. I could even tell the board house not to bother with the solder mask, plate through holes, or conformal coating. Meanwhile, I'd be assured that all the holes would be absolutely correctly drilled. I could even specify silkscreen to get all the control labels and product logos, as long as it was all one color, though I'd probably opt to just put my own labeling over the board.
So what do you think? has anyone done such a thing? If the costs were low, can you think of any reason why it wouldn't work? I know there are companies that do control panels for you, but I doubt anything would be a cheap as some of these China PCB houses.
Well I assume by now a lot of you know that PC boards, especially small ones, have finally become very inexpensive to prototype, thanks to direct from China fab houses like PCBWay.com. So a crazy thought came to me. What if I used my PCB software to lay out a board exactly the size of the control panel I need, placing all the holes exactly where I need them In the exact sizes I need them, and specifying no traces or through plating. Just order a minimum 1 sided board with all the holes where I need them, and a full copper pour on the side with copper. I could do it reversed so the side with the copper could face the inside and add shielding to my project. I could even tell the board house not to bother with the solder mask, plate through holes, or conformal coating. Meanwhile, I'd be assured that all the holes would be absolutely correctly drilled. I could even specify silkscreen to get all the control labels and product logos, as long as it was all one color, though I'd probably opt to just put my own labeling over the board.
So what do you think? has anyone done such a thing? If the costs were low, can you think of any reason why it wouldn't work? I know there are companies that do control panels for you, but I doubt anything would be a cheap as some of these China PCB houses.
I use pcb for mechanical if all possible. FR4 is very strong, if you do 2.4mm thick, it can be very strong. I even use pcb to hold components that take stress. It's all on the design. For added strength, I use copper pour on the surface and put vias onto the pour. This serve as anchors onto the board....just the the root of a tooth!!!
If you mount controls on the pcb, a copper pad area for the nuts and lock washers is good, as are plated through holes. It reinforces the fiberglass.
Well, yes... tbut in my case I'd be leaving holes for buttons to pass through, which need to allow some free movement, and other holes to let some 1MM light fibers pass, and those would be best to be a slightly snug fit. I know i have to expect some variation in hole sizes, and would have to ask the fab house what their nearest matches were. But I'd think trying to account for the thickness of the through plating would make it too much a game of chance.
When you specify a hole size to the pcb house, the finished board has that hole size, including the plating. It's figured into the process.
That has been the standard commercial practice for the last (at least) 15 years. The purchaser specifies a FINISHED (after plating) hole size, and the PWB fabricator figures out the drilled hole size before plating. (Assuming, of course, that he has adequate control over his process to achieve the desired result within the agreed tolerance.)
For reference . . . . the Seeed studio "Fusion PCB Specification" page at http://support.seeedstudio.com/knowl...-specification is a very complete reference to the tolerances and capabilities of a typical PWB fab house. The many graphical illustrations are especially helpful to understanding what the terms mean!
You may also find it useful to review the discussion of typical PWB drafting and fabrication practices in the thread "PCB layout design problem." at http://www.diyaudio.com/forums/software-tools/267239-pcb-layout-design-problem.html
Dale
Its interesting because for probably a dozen years I was using the same FAB house, and though it was rare this question would occasionally came up, usually because I had under estimated a hole size for a through hole part and wanted to avoid the same mistake. That board house told ME to allow a few mills for the plating, inferring it was on ME to guage that. I believed them because had the holes been what i specified, the parts would have fit.
But anyway, I'm fascinated by the idea of trying a control panel with a PCB, and for me I won't need any traces or plating. The two things I need to find out now is (1) how do I get BLACK PCBs (do I request that color for the solder mask layer? and (2) If I'm going to make a control panel PC board, it would be nice to include a small graphic. Is it possible to edit the silkscreen layer gerber file my PC Cad outputs to include a graphic, or are graphic bitmaps not possible in the gerber file format?
I'm just drilling plastic, but let me tell you... the first time I tried to drill 8 holes 1/4 inch apart in a perfect row, it came out so bad I'd be embarrassed to show you the result. I've gotten better at it, but its still something I'd avoid if this "PCB control panel" idea turns out to be a solution I could live with.
There is, of course, a tolerance associated with hole sizes (as well as the component leads that go into the holes) so don't try to design for line-on-line fits. Between automatic insertion equipment, and solder processes, a manufacturing engineer may spend an entire product's lifetime in an unsuccessful search for the optimum hole size.
I have seen several short-run PWB vendors advertise "colored" boards. It has never been clear to me whether the epoxy resin in the fiberglass board itself is colored, or if the color comes from a nearly opaque solder mask. I know that colored PWB material is available for production-volume orders but I don't know if the quick-turn, low-volume vendors are producing boards with it. See http://www.robotroom.com/Color-PCBs.html
I have never purchased any colored boards myself, though a previous employer used red soldermask on PWB's that were considered still in the development process, not yet unconditionally released for production.
http://imall.iteadstudio.com/open-pcb/pcb-prototyping/im120418004.html
http://www.seeedstudio.com/service/index.php?r=pcb
Company logos, and various other graphic symbols (e.g., the ESD icon) are commonplace on silkscreen layers as well as the copper itself, so Gerber must have provision for graphics.
Dale
Thats good to know, and now i don't feel so dumb! But its timely advise. I a current design my intention is to use 1MM fiber optic, to bring the light from some SMD mounted LEDs to the control panel. Its just to simulate a 1MM size LED really, and the panel is to thick for the LEDS with the tine 1MM bumps. But anyway, I had intended to have a thin strip of PCB with holes, whose only purpose was to align these short fiber pieces. In addition, since I'm not hoping to use black PCB for the front panel, there will be similar holes there. It would be NICE if the holes fit the fiber somewhat snugly, but not so tight that I have to re-drill. I figured 1.0MM was a pretty easy and standard size. But just to be safe I've specified my holes for these fibers to be 1.2MM. Easier to add a drop of glue than have to re-drill dozens of boards, right?
Thanks for all the good advice Dale. Having to do everything from the circuit design to the PC layout to the MCU coding to the enclosure and labels, my head is spinning. Such is the life of a would be entrepreneur i guess. But it sure is easier having this kind of expert advise!
Even if you achieve a snug fit, over time and with thermal cycling I suspect it would become loose. Starting with a slip-fit and adding glue is the way I'd start off. 1.2 mm might be a little sloppy for a 1 mm component.
The adhesive is an open question. There are at least half a dozen basic formulations of cyanoacrylate, each available from several suppliers. And epoxies - quick-set, standard cure, water-clear, thin body, etc, etc. And some recent kinds of glue I've never even tried. Be careful about your working processes - a glue smear can make a fine panel look really ugly!
Dale
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