OK, so this is probably a really stupid idea, but...
I'm getting antsy waiting for the first PCB I did to come back from OSH park and I want to do a couple of more prototypes. I don't want to spend a lot of time laying out stuff that won't work, so I was planing on waiting until I had the first board back before I did the next one so I could make sure I was doing things the right way and my library was working. But, I've got to get started on the next stage. So, I came up with this cracked idea to make a double sided layout, burn them on two boards and then glue them together. I figure I might be able to get them aligned if I drill a couple of the holes very carefully and use this as a way to keep them aligned while gluing and then drill the rest of the holes after it's together.
Anyone ever try this? Or, is it just too silly?
Getting it aligned is not the only problem.
The legs of many sockets may be too short for double whoppers.
Also some caps come with very short legs.
Quote from: RobA on July 18, 2013, 04:06:54 AM
... burn them on two boards ...
Why on two boards, when there are doublesided boards out there? It must be simpler to etch a doublesided board directly (though i have never tried).
I understand that you dont feel like doing an additional PCB layout for single etching. But how about this simple workaround: As I guess most of your traces are on one side (bottom) of the PCB, you can do "ugly jumpers" for the (fewer) top traces. it wont "look good" but will do the job and after all its prototyping.
Quote from: kothoma on July 18, 2013, 04:59:45 AM
Getting it aligned is not the only problem.
The legs of many sockets may be too short for double whoppers.
Also some caps come with very short legs.
I just happen to have some thinner than normal board -- not quite half as thin, but close. But, you are right, it could be a problem with some parts.
Quote from: Vallhagen on July 18, 2013, 07:17:54 AM
Quote from: RobA on July 18, 2013, 04:06:54 AM
... burn them on two boards ...
Why on two boards, when there are doublesided boards out there? It must be simpler to etch a doublesided board directly (though i have never tried).
Two reasons. The first is that I don't have any double sided board. I guess I could solve this issue. The second is that I have a hard enough time just getting transfer placed on the board so it would work. I don't think I have the spatial skills to pull this off. It would be worth trying though, if I end up doing this very much.
Quote from: Vallhagen on July 18, 2013, 07:17:54 AM
I understand that you dont feel like doing an additional PCB layout for single etching. But how about this simple workaround: As I guess most of your traces are on one side (bottom) of the PCB, you can do "ugly jumpers" for the (fewer) top traces. it wont "look good" but will do the job and after all its prototyping.
It's not so much that I don't want to a second layout. I actually started by trying a single sided layout and couldn't get it to work in a small enough space to be useful. The other thing is that this is a digital board and kinda needs a good ground plane...
But, you did prompt me to bring up the the layout again and realize why this is a bad idea. Metal bodied parts, like the crystal, are going to be a pain. The body crosses multiple traces and would short them. I'd also have to do a different version anyway with a larger standoff from the ground plane and the pads and it might not be a good test after that.
I think this idea goes on the junk heap.
I tried doing a double sided board. Near impossible to line up, d it was a complete and epic failure. 3 times I tried. Never again.
If you do go ahead with it, I wish you luck!
Sent from my thumbs using Tapatalk!
Quote from: stevie1556 on July 18, 2013, 10:39:24 AM
I tried doing a double sided board. Near impossible to line up, d it was a complete and epic failure. 3 times I tried. Never again.
...
That's pretty much what I figured would happen if I tried to line up things on a two sided board. I guess I'll just have to live with the time lag of getting them commercially produced.
I did a couple, but they were a horrendous nightmare, lining them up etc.. think it took a few attempts, but it worked.
Just get some boards made, it's so much easier and better!
George
Could you add two dummy pad in pre-defined spots on both sides of the layouts, drill a hole with one transfer as a guide, and line the other side of the etch up against those two holes?
I believe people create an aligned "sandwich" of the two pieces of art, tape one side of the snadwich together to form a hinge then slip the double sided board into the sandwich, secure the art to the board so if won't shift around, do the transfer. I would think some sort of laminator would be ideal for doing the transfer.
dave
Quote from: midwayfair on July 18, 2013, 01:20:56 PM
Could you add two dummy pad in pre-defined spots on both sides of the layouts, drill a hole with one transfer as a guide, and line the other side of the etch up against those two holes?
Yeah, this is pretty much what I was thinking of doing to try to align them. There are pads that'll be on both sides that are far enough apart on opposite corners of the board that I think I could just use them instead of making alignment guide holes though.
Quote from: davent on July 18, 2013, 02:11:30 PM
I believe people create an aligned "sandwich" of the two pieces of art, tape one side of the snadwich together to form a hinge then slip the double sided board into the sandwich, secure the art to the board so if won't shift around, do the transfer. I would think some sort of laminator would be ideal for doing the transfer.
dave
Interesting. I have to think about this idea. I don't have any sort of laminator. I'll look at what's available and the cost. I just use the iron on method now. It'd be a bit problematic doing a double sided though since the first touch of the iron tends to move the transfer a tiny bit as it sticks to the board. It would probably bit bit tough to keep the unfused side safe while doing the first side with the iron on method too.
After that, I'd still need to figure out an insulator to keep the front side metal parts from shorting the traces they cross and potentially having to solder the frontside pads under parts (yikes!).
Quote from: Vallhagen on July 18, 2013, 07:17:54 AM
But how about this simple workaround: As I guess most of your traces are on one side (bottom) of the PCB, you can do "ugly jumpers" for the (fewer) top traces. it wont "look good" but will do the job and after all its prototyping.
This is the best idea I've seen so far. Route mostly on the bottom and then manually wire up the top.
I did it the other day on dbl sided copper clad. the pcb came out great but my circuit didn't work in the end. i blew a day & a half on that and ended up frustrated. i have little hope of finding where the error is because some things are soldered in on the component side and obviously it is difficult to get any sort of a line of sight under the components, even though I left them partially raised. it is possible that wiring things up on the top could work better. that was the first idea I had but I decided to solder right on the pcb instead since there weren't too many connections there anyway. but i can tell you, even a few are a lot in terms of general PITA'ness. Plated through holes rule for double layer pcb's. If you could just figure out how to use those it'd be golden.
I would recommend making a version of your circuit that doesn't have a 9v pour on the component side. either that or increase the tolerance a lot as well as the size of your route traces, because the margin for error is just too great otherwise. of course if it is a complicated design I realize that could cause all manner of clearance problems....
Just what kind of circuits are people doing that they even need a double sided board? I've dozens and dozens of pcb layouts for everything from simple pedals to discrete component stereo amps and it's rare to even need a single jumper on the top side of the board.
dave
Quote from: Haberdasher on July 18, 2013, 03:51:55 PM
I did it the other day on dbl sided copper clad. the pcb came out great but my circuit didn't work in the end. i blew a day & a half on that and ended up frustrated. i have little hope of finding where the error is because some things are soldered in on the component side and obviously it is difficult to get any sort of a line of sight under the components, even though I left them partially raised. it is possible that wiring things up on the top could work better. that was the first idea I had but I decided to solder right on the pcb instead since there weren't too many connections there anyway. but i can tell you, even a few are a lot in terms of general PITA'ness. Plated through holes rule for double layer pcb's. If you could just figure out how to use those it'd be golden.
I would recommend making a version of your circuit that doesn't have a 9v pour on the component side. either that or increase the tolerance a lot as well as the size of your route traces, because the margin for error is just too great otherwise. of course if it is a complicated design I realize that could cause all manner of clearance problems....
Thanks very much for this info. It looks like everything I feared might happen would. And, given the fact that your etches are orders of magnitude better than mine, I'm pretty much doomed ;D. Oh well, I think I'll just have to live with the wait on this first board to see everything I need to fix on my layouts and then I'll have a bit more confidence to risk sending in multiples at a time.
Quote from: davent on July 18, 2013, 04:09:22 PM
Just what kind of circuits are people doing that they even need a double sided board? I've dozens and dozens of pcb layouts for everything from simple pedals to discrete component stereo amps and it's rare to even need a single jumper on the top side of the board.
dave
60 components, two of them 14 pin DIP's, one crystal, and a need for a large ground plane to connect the digital ground to. It all fits on to a 1.8" by 1.9" board. I suppose that it's possible to do single sided, but it's beyond my skills at this point.
Ah, makes sense now! Double sided it is.
Thanks
dave
Ive done double sided etches successfully, it helps to have a vertical etching tank so both sides etch evenly. You will also need some sort of registration system. I drilled four holes out of the pcb area, and then marked those on my pnp blue printouts so i ould line them up. Its hard to get perfect registration, dont use tiny traces. Remember sometimes you may need to solder both sides of a component.
To align the two layers with toner transfer, I transfer the first side, and then drill 4 (or more) of the .6mm holes towards the outside of the board. I then use sewing pins to push through the back of the transfer, through the holes and into some corrugated cardboard. Then apply the iron to side 2. YMMV
I've done several double sided boards successfully. There are a couple of tricks which help.
Use registration points on the four corners of each side of both top and bottom. These are 'crosshairs'. Transfer the bottom side first, then drill the four points carefully. Using a backlight, align the top transfer reg points to the bottom using the four holes as a guide and tape the transfer down.
Before printing, use an image editing program to remove all unconnected pads on the top transfer leaving only pads which have traces connected to them or vias.
Use small wires to connect vias from top to bottom.
Don't forget to reverse the top image before printing.
Quote from: madbean on July 23, 2013, 12:47:38 PMBefore printing, use an image editing program to remove all unconnected pads on the top transfer leaving only pads which have traces connected to them or vias.
Heck yeah, this is the part that would have helped me. I'm having one of those
now why didn't i think of that moments right now lol.
I may have to give this another shot....
Thanks for all the advice on getting this to work. I'll have to order a couple double sided boards to try it out on.
My order from OSH Park came in over the weekend. It got here quite a bit faster than I was expecting. So, I'm set with things for this round. Now that I know what I need to change in my library, I can feel a bit more confident just sending out a few prototypes at once. That should help with keeping my mind off double sided etching for awhile, but I'm sure it'll come up in my head again eventually.