First double sided DIY PCB, mega644

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finaly took the plunge and made a double side one, after a handfull of much smaller single sided "adapter boards".
I used the "magazine paper" to apply the resist, and the "sponge" method of eching.

The "hard bit" is actualy to made the vias. I used kynar wire but it's quite fiddly to "fill" them. I have a via under the 644 and that one I had to file down so the pins of the mega still touch the pcb :/

Anyone has a tip to "plate" holes ?

It's populated to about 80%. Still need to add the crystal, a tantalum, and replace the zero resistor with a ferrite bead.

And it all works! I can program the 644 from USB via the bitbang mode of the ftdi chip!

Just eched pcb:

Author of simavr - Follow me on twitter : @buserror

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sadly @home plating, especially thru-hole plating is not so easy. However it can be done. There is a site called Think & Tinker or something like that that sell a conductive ink that can be applied, in the through holes, and then the board plated, including holes. (this is done before etching)

Writing code is like having sex.... make one little mistake, and you're supporting it for life.

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Well I will have to try to solder the connectors so the connection is made, I assume a bit of solder on each side, and enough heat should do the trick of melting both ends on the pin...

Anyone know how to ensure via-to-polygons have thermals in eagle ? that would help the soldering a lot...

Author of simavr - Follow me on twitter : @buserror

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Quote:
Anyone know how to ensure via-to-polygons have thermals in eagle?

In Altium Designer you can select it in the design-rules (polygon-connection-style).

/Martin.

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I once worked with a system with little hollow rivets that go into the holes. Tedious and did not work too well either.

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I used an electro-plating machine called 'minicontac' from LPKF

The process was as follows:
1. drill thp holes
2. immerse in liquid carbon
3. electro plate
4. clean
5. drill nthp holes

Attachment(s): 

Last Edited: Fri. Aug 28, 2009 - 01:20 PM
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your pcb looks very good by the way
:wink:

do you use ferric chloride to etch it?

the trick to soldering under-smd vias is to use extremely thin wire (something like 35awg), then wick up the solder once you've soldered it. This maintains the connection, but lowers the 'bump'

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Nice work.

Maybe I'll try again.

The largest known prime number: 282589933-1

It's easy to stop breaking the 10th commandment! Break the 8th instead. 

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Timothy01 wrote:
your pcb looks very good by the way
:wink:

do you use ferric chloride to etch it?

Thanks! Yes, however instead of "bathing" the board I wipe it gently with a sponge dipped in the echant. This seems to cut down the etching by a good amount. This board (both sides) took about 3 or 4 minutes.

With "medium" magazine paper (not the cover, not the very thin pages) I rather easily get these results -- 12 mil traces, 0603 for most passives, and even 0.5mm pitch are quite easy.
For soldering I use solder paste, a toothpick to "blob" on the pads (you can make the paste a bit thinner by mixing a little liquid flux, like from a flux pen) and I heat using a gas "soldering iron" with a "hot air" attachment... that works beautifuly.

Quote:
the trick to soldering under-smd vias is to use extremely thin wire (something like 35awg), then wick up the solder once you've soldered it. This maintains the connection, but lowers the 'bump'

I tried that, with limited success. I probably need more practice :-)

Author of simavr - Follow me on twitter : @buserror

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Well only the "short" layer-connect via's should need the plating, really... The ones receiving component legs you simply solder on both sides, and for these ones you need to short, small gauge wire should do it, or enough solder to fill the via. It helps to make these via holes bigger than the rest, to help capilarity.

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UNiXWHoRe wrote:
The ones receiving component legs you simply solder on both sides

That greatly depends on the component. Consider how you would solder on both sides with a large radial capacitor, where the pins are short stakes, and not long wires. Also any number of multi-row connectors could be a problem.

Writing code is like having sex.... make one little mistake, and you're supporting it for life.

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In the case of a radial component like a cap or inductor, you COULD insert it, sit it on its side, solder on top, then flip the board, heat the leads and push the cap back in. Although obviously surface mount devices are more appropriate.

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If you can't solder on the top, you can solder a thin wire onto the pad on one side, then insert the component pin, then cut and solder the wire on the other side, thus creating a via with wire

All these methods are a bit tedious and on a complex board they are easy to forget or break or get desoldered by mistake

The best solution is to use thru hole plating especially for SMD boards where there are lots of vias

You can of course design the board differently by placing vias instead of trying to solder both sides of a difficult component like a radial cap or multi row connector. The vias are easier to solder than under a connector