making double sided PCB's at home

[rkovvur]

If you are about to prototype an electronic circuit, the PCB usually becomes a big hurdle. Either wire your components, breadboard them or send your design to fab house thats costs you a lot. I have been making PCB's at home for almost 10 years now. I have slowly progressed from using stadler lumocolor pens to using heat transfer method to finally using Eagle CAD and photosensitive board to develop and etch my boards. However one thing that has eluded me all these years is, making 2 sided PCB's. For most circuits, i try to get away by increasing board size and developing 1-sided PCB. Sometimes, 2-sided is inevitable. I am interested in knowing if some you experienced folk were able to overcome this hurdle and were able to make 2-sided PCB's (with or without PTH).

Thanks! :)

[Ron W3FJW]

I've been making 2 sided boards for years. I've found that using the bottom side for power distribution and ground plane and top side for signal paths is fairly easy. Registration isn't all that critical such as would be the case if using both sides for both signal and power distribution. Granted I don't make complex computer boards, but for Ham Rx, Tx, audio and test equipment projects with discrete components, it's entirely adequate. Haven't had the guts to try it for surface mounted components as my eyes aren't that great anymore.
All my layouts are done with .1" graph paper, One color for signal, one for power, and one for ground then tracing layouts onto a transparent film for each side. Developed using UV light and photo resist boards.
Downloaded Express PC Board a few years ago but haven't got around to trying it out yet as I still enjoy my pencil and paper (a hobby in itself).

[gedaso]

While I've made plenty of PCB's at home using laser toner transfer, press'n'peel etc (including one or two double-sided boards), these days I just get BatchPCB.com to make them for me. Takes a little while (a few weeks) but as a hobbyist with plenty of other things taking up my time, that is a delay I can afford. The price is nice too - $2.50/sq. inch for 2 layer boards plus $10 setup !

[Tomapowa]

Here's a few ideas I've used in the past (toner transfer and UV methods):

http://www.instructables.com/id/Two-sided-PCB-using-toner-method/
http://bygselvhifi.dk/pcbmanufacturing.htm

A search on google for "double sided PCB DIY" (http://www.google.com/search?hl=en&q=double+sided+PCB+DIY&btnG=Search&aq=f&oq=&aqi=) will turn up a few more ideas too...

As a challenge, all my prototype PCB I make are single sided (some easy, some not). I often find myself routing manually rather than allowing the autorouters to do their magic. I can often design a circuit to use a single-sided PCB where as most auto-routers can not... go figure (maybe if you gave it enough iterations, it would finally figure it out). Years ago as a graduate project/thesis I helped develop an auto-routing algorithm (originally developed for automating development of network topology drawings), but again this was only applicable for single-sided PCB designs... maybe that's why I like routing myself! :D

[Chippie]

I've been making 2 sided boards for years. I've found that using the bottom side for power distribution and ground plane and top side for signal paths is fairly easy. Registration isn't all that critical such as would be the case if using both sides for both signal and power distribution.

Ron, what an excellent idea...I'd never have thought of that!
I've always used Eagle, I lay out my pcb track layout manually with the shematic as a reference...Never bothered creating a schematic and then autorouting too much like hard work I guess..and it worked for me when I had to design a pcb for a 13.8v 15 amp smps based on a pc power supply!!

[Tomapowa]

Here's another good 2-layer PCB tutorial I forgot about:

http://www.robotroom.com/PCB2.html

And on the same site, I ran across this interesting "solar soldering" idea I had to pass on... LOL Talk about going "green" (well, except for the solder fumes) :rolleyes:
http://www.robotroom.com/Solar-Soldering.html

[orraman]

.
For proprietary Ultra Violet exposure units.
A ridged flat L shape in metal or plastic with a true 90 degree internal angle and about the same thickness as the PCB and slightly longer than the PCB sides is taped to the surface of the glass with double sided tape or single sided tape on the outside and ends of the L.

Oversized transparencies, one trimmed smaller than the other and taped on two adjacent sides when in alignment onto the other.
The opposite sides of the transparencies are trimmed to the board size with the required clearance from the image at a true 90 degrees.

Image up, the 90 degree of one transparency is placed into register with the internal angle of the L shape and taped to the glass outside the area of the PCB.
One side of the PCB is uncovered and the PCB is taped to the L shap and an exposure made.

Taking care to preserve proper orientation this side is covered with the original opaque covering and the process repeated on the other side.

An alternative to the L shape can be a ruler and a coin, with the transparencies and PCB slid along the ruler to abut against the coin.

For narrow home made UV boxes with two small UV tubes where the glass can be safely supported on only two sides. Transparencies as above.
Greater accuracy for DIY can be had by stacking and taping the transparencies on the PCB and drilling a small hole < 1 mm at either end and using sewing needles to wedge a transparency to the PCB. This requires that the needles overhang the glass and the pressure pad and one new hole has to be drilled for each new PCB.

Dave

[hugh m]

I've used Eagle and done 2 sided boards w/toner xfer and they have turned out quite nice.
Simply print the top side reversed and tape them together and slide the board in between and iron down. A little more finicky than it sounds but works well.

I think I also drilled a couple of alignment holes using one side then align to the other..

Hugh

[pldaniels]

I'm with Hugh,

I do my 2-sided prototypes (SMD mostly) using Eagle and toner-transfer. I also tend to make the second side mostly a ground plane with bare minimum component/trace count as possible. Once I'm content with the setup I send off to the PCB factory for a proper production run (sometimes if it's really simple I'll do 1-sided, join the links with wirewrap or similar and cross my fingers ;) ).

With toner-transfer, I suggest making all your vias quite a bit larger so that you have a reasonable amount of offset error margin. Even with two or three guide holes you inevitably get alignment mishaps.

I like to do the primary/complex side first, then do the simple side second as this gives the complex side a second heat bonding chance. As always, getting your board REALLY clean is the main issue. Additionally, make sure you use a separator between the iron and the paper with the toner, else you will end up with smudging/issues.

Paul.

[orraman]

.
In Post # 7 I used a lot of words and I am not sure that I conveyed a good understanding of the system so I have taken a photo.

This is a proprietary box made to use this system, here the L shape I spoke of is made of the glass holding plates. Unfortunately the illumination is not even into the corner and so the separate L shape adaption.

The system is successful and quite capable of good accuracy if care is taken in registering and taping the transparency to the glass and the PCB to the L shape.

Dave

[orraman]

.
Greater Accuracy

This picture shows a home made box with 2 X 8 watt UV tubes, transparencies with alignment pins in the holes, there are seven wire vias. The resultant SM Picaxe board is set up for control of servos with a potential divider for lipo cut-off.

In place of my lightbox I often use a length of acrylic plastic illuminated with a lamp placed on the floor to align and tape the small transparency to the larger and these to the PCB. With the PCB on top a small hole << 1mm is drilled through this sandwich and a scrap of PCB acting as a stripper plate to ensure clean holes in the transparency. One hole at either end so that pins can jam the transparency up from underneath against the PCB during exposure.

The full length glass is replaced with a short length so that with the pins can overhang the glass and the pressure pad.

Repeat alignment is excellent and the greatest deviations are due to distortion in the printer. I use strips of duplicate images even for a single board to aid alignment over a greater span and allow choice of the densest image.

Dave

[orraman]

.
Laser printers tend to leave the centre of the tracks lighter than the edges and it is common practice to stack two transparencies to gain denser images but this is much more troublesome for double sided boards.
For the toner transfer system http://www.pulsarprofx.com/ produce a Green TRF Foil and a laminator to seal the toner on the PCB.

It also does a fair job in increasing the image density on transparencies. :D :D

It creates a sharper edge on the toner making it easier to stay within the tracks when retouching those places that show up too light on the light box.
The TRF foil is floppy but laser overhead transparencies are available with an attached carrier sheet that allow observation of the foil on top of the 'working' transparency being fed into the laminator. Some tension is needed.

Note the two part foil on the left (did I say he was tight?) with it's working transparency on the slice of backed transparency used as a carrier, shown right, the green TRF foil compared to the metallic Red Reactive foil from the same supplier.
I had the idea that metallic red might be more effective in blocking the UV but no testing has been done.

Dave

[orraman]

.
On small boards wire Vias can be a pain, there is less room to bend the wire, so soldering the second side can melt the first and the wire is sucked out by cussedness. For single vias thin single wire doubled back on itself and drawn down small will hold position. 3 shown soldered and 4 not.
Lacing a single wire through multiple holes is quick and easy, shown all soldered but when working, the wire may be cut short after each soldering to reduce the heat conduction.

For those times when a 'through hole hole' is needed under a component I still have some of the discontinued (pity) Multicore strips of 'bails'.
http://www.megauk.com/through_hole_rivets.php offer Favorit hollow rivets from 0.4mm to 1.5mm and a tool to set them but they are said to be able to be set by hand. They also sell toner friendly, long lasting Laserstar transparency, at least since 97 7 (see above).

For interesting information, but it is pure pleasure to read the rest of his site.
http://www.electricstuff.co.uk/pcbs.html

Dave