DIY PCB

The most important tool is the temperature controlled soldering iron with fine tip. Also some magnification tool is highly recommended.

The general soldering technique is to have the iron on the part and gradually feed solder wire into the pool until the pool reaches desired shape/form/mass. Shape, aspect and coverage of the solder joint is standardized for some components and packages, but generally allows a very high grade of error. In most cases that should be the last stage of the soldering, but however, before that one needs to "tackle" the smd and position it and fix it in place. I generally resort to making a solder ball on the tip of the iron - this way i can use the other hand to hold part in place.

I did the EC22 board with a 2mm tip, but 1mm or even 0.4mm tips are much better. There is an important relation between the iron tip and the width of the solder. Basically the diameter of the solder has to be smaller than the tip. This allows the formation of a sphere of melted solder on the tip of the iron. If the solder diameter is higher than the tip, the solder will still be on the tip, but will not be a "sphere" and will not be exactly on top of the tip, but instead will be around it. As a sidenote, using the iron tip with the sphere of solder like that has 2 caveats: 1) the resin in the solder will be burned before touching the parts, which means flux is highly recommended (use only "no-clean" flux which means it doesnt need to be cleaned after); and 2) finer the tip => smaller the diameter of the solder (+more hand movement) => smaller the solder sphere on the tip (in few cases means more repetition).

For example of this "technique", a 0.4mm tip means using solder of 0.25mm, and with magnification it allows an impressive degree of miniaturization, but increases the hand movement alot and decreases the productivity, although also decreases the chances of solder bridges in some packages. Using a 1.0mm tip allows use of 0.5mm solder and speed increases a little. I would say 1.0mm tip and 0.5mm solder are closer to general use in Reprap electronics (the actual diameter is 0.5~0.54mm just different notations). The 0.4-0.5mm has more value in case of 0.5mm pitch packages, but none of those are present in current gen 3 electronics.

There are alot of good nice tutorials and explanations on the internet about soldering smd, youtube has plenty.

Get some background information of the process that you intend to do.

For people who havent done this yet, before anything, get a background of the process you intend to use. //www.Youtube.com is full witj a lot of videos on this topic, just try a search. Almost each video poster has a thing or two to say about it. Some tips are really good.

Paper

It all comes down to using the right type of paper, in combination with the proper etching chemicals.

A good recommendation would be to get a couple of different kinds of inkjet photo paper and test them out. Just make sure that the paper you buy for tests fits the printer specifications on paper: i bought 240 gsm photo paper once, but my printer jammed upon loading the paper, and there was no way i could get a print on it. My best combination seems to be an ordinary (no-name) inkjet photo paper and B327. However, different people will make different choices. Keep in mind that results seem to vary and a universal solution has not popped up yet.

Among many, one further link with comments about coated color copier paper is here: //aka47.adsl24.co.uk/serendipity/index.php?/pages/rightpaper.html

Some reported that some usual magazine paper can be used, check this here: //www.riccibitti.com/pcb/pcb.htm

Other paper types that can be tested:

- very thin "writing paper" - not the usual 70-80 gsm printer paper, but much thinner and looks like worst quality paper; these are extremely slim, sometimes printer takes 4-5 at a time; but the advantage is they are very "soluble" in water;

- label "background" paper, buy a set of A4 label paper, remove the actual labels, and use their "support" which has a very slick side; the toner comes entirely right off;

- transparencies: the ones that are for "laser", so they can deal with the high temperature; also there are sorts of specialized media (press-n_peel) for pcb in usual electronics store, but cost much more and they are just like the laser transparencies, and in my experience get better results, but maybe are worth a shot when everything else doesnt seem to work;

Aspects regarding the paper behaviour and ulterior removal:

For example (in my experience) HP photo paper, after peeling, will leave a thin residual layer that just can't be removed (some reported that feric chloride or other etch solution can disolve that through).

Some other photo paper peel just fine and the residual layer can be removed relatively easy. For me its a no-name inkjet paper.

Aspects regarding some inkjet photo papers shrinkage:

Normal paper doesnt change its dimensions, of course. However this is inkjet photo paper in a laser printer, and some types might just change shape. Not all of them. Or better said, they might do this more or less. The paper I am currently using, comes out bent in a C-shape, because of the heat affecting its layers differently. The front seems to shrink more at temperature than the back.

With a high light source in the background, compare with a normal A4 paper printed with same image to see the exact differences. I think it is important to notice this, as it only seems to affect the paper in its length. Sometimes, in case of long connectors, (more than 10 pins), this can become an issue as it may no longer fit the real part. Therefore, in case of critical long dimensions, make sure to choose the right orientation when printing, so this phenomena will have minimal impact on fitting the parts onto the board.

- orient the image on the sheet of paper in such a way that sensitive dimensions are horizontal to the way the paper enters into the printer's high temperature toner fixation unit.

- put the images of top and bottom layer one near the other (and not on top of one another: putting one image on top of page and one on bottom, may result in each image getting different shrinkage factors and thus not fitting anymore).

Just in case, double check this effect: 1) if the real parts fit on the paper, and 2) if the two images register properly with each other.

For very large boards, that need to be printed in separate A4 sheets: print a useless paper sheet before actually printing each layer. The reason is that laser printer laminator on standby is not heated, and in case of high shrinkage media papers, i suspect the temperature of the first sheet may be a few degrees different than the second (maybe the issue is printer specific, cant say). Just in my case if i print 2 sheets right one after another they dont fit perfectly. My workaround is to print one random paper before each layer print.

Refilling and cylinder

I think any generic laser printer should do just fine. However regarding cartridges, some of them are just reused and refilled over and over again. Usually the cylinder is part of the cartridge and wont get any newer. The toner can be refilled lots of times, but usually at some point the cylinder will degrade, e.g. it will print lighter and lighter shades of gray instead of dark black. I guess that means cylinder will grab and then deposit less and less actual toner on the paper. Bottom line, toner transfer works great with a fresh cylinder, but after 3rd - 4th refill, it gets harder and harder to get enough toner deposited to make a good pcb image. So there is a direct link between the quality of the cylinder inside the laser printer and the actual pcb quality made by this method.

Performance

I would say, self made pcbs in general can perform a little worse than the commercial boards in terms of noise, heat disipation, etc, but this can be considered as a potential issue only on step drivers - high frequency boards. Unless one chooses single sided boards to go with a special copper clad (aluminium substrate, 70um copper) that is generally used only on very high power circuits. Making 1.0-1.2mm alu one sided gnd (for microstripping top signals) and top side with 70um copper is quite imba, and this can get slightly even better than commercial variants. However the price of clad like that is much higher and its usage possibilities are rather limited. None of the boards below are done like that atm, but this is just an idea versus the performance opinions that people might have about DIY pcbs.

Optimizing a pcb layout This "optimization" process is rather reiterative, with incremental changes after each testing. However, after some tries and changes one should end up with a pcb that can be realized with toner transfer, double sided, in an acceptable manner.

The quality of a layout like this, will be determined by the patience of the one creating it: with enough reiterations of tests and small changes, one can achieve a good quality (if we can speak of quality in this context).

The point in our case is to get an image that should offer acceptable results - and for orthers aswell.

Optimizing a pcb layout in Eagle Of course, the usual pcb design will have design rules that wont be compatible with toner transfer. Basically traces being too thin and too close to each other. I dont know to manipulate design rules, in a way to make this part easier, so for me, all this part is basically manual Eagle editing: basically making increase all traces width as much as possible and spread things around.

General references:

- 12 mil only on very short distances like in headers, passing between other pins; ideally just 2-3 situations of those, and only like 3-4-5 mm in length each;

- 16 or 20 mil the finest traces only near the finest pitch tqfp pads, and on short distances;

- 24 mil or maybe 32 mil smallest medium length trace, and smallest via top-bottom connection;

- in rest, make all traces as big as you can;

- keep in mind that probably, any trace smaller than 24 mil will require constant checking in all stages;

- if the overall part density is too high to make these changes properly, consider increasing the pcb size and space out the components; commercial pcb manufacturing price is per square cm, thus designs are tight, but for toner transfer the marginal cost is much less significant and therefore the size increase is rather beneficial;

- components should be putted in an equally spaced manner, to make things clear, to have access to components, because of 2 things: 1) there is a good chance that debugging will be required at some point, and 2) you will be the one doing it.

As a sidenote, mendel printing its own pcb in the future would require similar approach to the layout(s).

Vias: its not rarelly that some pairs of two can be removed completelly by re-routing a trace only to one side. But dont exagerate with this or it can backfire, giving too much complications on that layer.

Try to get vias out from underneath the IC's, or any tight spaces. Put them in accessible spots instead.

Some vias can just remain under some parts, and these will need to be soldered first of all, then grinded down, so the part above it will fit properly. Lesser vias like that, the better.

Anticipate the way you will solder each via in relation to its surroundings. In tight spots, make at least a short thick trace that will hold the solder in place.

For further references on pcb design try the links at the bottom of this page.

Once the pcb layout is acceptable for home pcb making, it can be exported as black and white image, at 600 dpi. Afterwards can be imported in an image editor program for tweaks, mirroring, establishing best print orientation, and eventually printing more images inside a A4 page to make full use of the entire page.

Optimizing a pcb layout in the image editor of your choice Among other things, for example TQFP packages will have pads too close to each other for toner transfer to work, so this needs fixing.

One way to do it is to export the image and do further changes in an image editor program of your choice.

Basically for IC pads, insert white filled rectangles between the pads, or do any changes you may want.

This stage is probably faster like this, although there could be other ways to do it.

Also any time its needed, creating a "package fingerprint" for pad sizes after your heart and wish, in image editors is trivial once you have the datasheet info on that package.

Step by step instructions

1. Print image on your transfer paper, cut it in two separate pieces, for top and bottom layer.
- It is easier to register the top with bottom if these are separate pieces of paper.


2. "Register" the top and bottom:


- Prepare 3 pieces of scotch tape in adequate lengths on the corner of a table.

- With a good light source in the backround, carefully fit the top and bottom layer together.

- The combined image inside should be at least 1,5 cm away from the edges.

- Check those areas that will actually be drilled and do need to be aligned. Things cant go perfect and trying to register things like borders or corner holes is meaningless.

- Sometimes will give the impression that they just dont want to fit together. Make a spot fit, hold them by that, and give them a shock with index finger in another area, that should fix it.

- If you are happy with how the layers fit, put a piece of tape to each of the 3 sides, only leaving 4th one open (one of the smallest sides).

- At final inspection if you are not happy with the registration, you can always cut off the scotch tape and start over.

- When finished, put the "envelope" in the light once again and mark the corners of the image with a pencil or with any means. This will help later on to position the blank board inside, relative to the image on paper.

3. Clean a copper clad board and put it in the created "envelope"
- Clean the copper cald. This can be done with various methods: with sandpaper or with the grit part of a sponge and dishwashing substances, etc.

- The copper cald and the image should have at least 1.5 cm (or so) clearance to the edges. Because if the space is too tight, it can cause layers to shift when it is inserted.

4. Make the transfer. Laminator or household iron can be used. For household iron:
- Put a thick catalogue or book or magazine (sometihng useless that will be damaged by heat), on the corner of a table just to have one of the table's feets underneath to safelly apply pressure over it.

- Temperature setting of the iron should be close to max, or just max. Preferably try first by setting it to max then turn it back a little.

This also is the step where you need to decide the future of your love life:

- If you dont want a divorce right now, iron this scotch tape envelope between two other sheets of paper, to protect the iron.

- If you do want a divorce, this your opportunity to get it. Just go ahead and put the iron on top of the scotch tape, then ask your wife to iron one of your shirts, blaming her for the result. If this doesnt get a divorce right away, because by all chances, your wife has an enourmous patience, and does clean the iron, there is still hope. Watch her and exactly when she finishes, and ask her to make sure its clean enough because next week you need to do the rest of the boards. That should do it. Make sure to have running shoes on.

- Put some pressure on the iron and genltly iron both sides of the "envelope". Keep something between the iron and the scotch tape at all times. Or else have your lawyer number on speed dial.

- At the end of it, may use the tip of the iron and its edges to press all around the board's surface.

Notes:

1) toner not sticking, getting "gaps": board not clean enough, or pressure or temperature too low. Later on might need small corrections with etchant resist pen.

2) toner sticking too much and getting "cooked": probably iron temperature and pressure too high. Is better to get this instead of gaps. Later on acetone may not be enough to remove toner, so sandpaper may be required.

5. Remove the paper.
- After ironing, you can put the board in refrigerator for few mins, or directly in water. I personally prefer the fridge.

- After its cooled down put the paper envolope in water and scrub the most of paper with bare fingers, and the last layer with a toothbrush.

This is also the step where having a mother-in-law, can truly award, special, unexpected, huge amounts of hapiness (if done properly). All you have to do is use her toothbrush. You can also use an old discarded toothbrush, or just scrub the board with the fingers, but if you do so, you will get no special happiness later on. Like when you show the results to your mother-in-law and she asks how you made it.

- last bits of paper will not be visible to the eye when the board is wet - inspect when dry;

- last check before etching: if you are not happy with your imprinted copper clad so far, you can still clean everything up and start over again;

- if needed, some minor modifications can be made with the tip of a cutter or with an etch resistant marker:

- if some tracks are too thin, or have gaps, you can simply use a marker for any changes that require additional covering for some surfaces (many of the common markers are etch resistant);

- if some tracks are too close to each other, use the tip of a cutter or a sharp tool to remove some of the toner in between them;

6. Etch:
- Improvising an etching tank is not really complicated, and there are many ways to do it. Probably best would be a vertical thin enclosure with a bubble maker (aquarium) appliance on the bottom, and furthermore it can have an aquarium water heater on it (these heaters run only up to 32 celsius, but its good because etching shouldnt go over 50 degrees at any time). All ingredients can be found in the typical petshop / aquarium stores. Another easy alternative design would be horizontally with some movement involved, balancing or sliding (sliding is better). The net is full of examples for it. I made one from the carriage of a discarded ink printer with its head support, a gear and a dc motor and lots of hot glue - thats all that is needed (picture below in gallery).

- If you do not have an etching tank, you need to use gloves and make passes over the imprint with a sponge soaked in etching solution. You need increase the temp of the etching solution up to 50 degrees celsius to dramatically reduce the etching time, so the sponge method would be reasonable fast, with fewer passes. To increase the temperature, put the etching solution in a container, and in that container on its turn, in another container with 50-55 C degrees hot water. This way ensures that target temp will never be surpassed. With etching tank, increasing temperature is not a "must-have", but in sponge method is much more needed.

7. Clean the toner, cover in solder (tinning), apply component legend, drill:
7.1) with etching done, remove the toner with acetone (typical nails paint remover) and cotton pads (this is the only part where having a nice looking wife pays off); if the toner is too hard to remove it can be one of the following: too much toner deposited; iron temperature was too high; iron pressure was too high; as a result, sandpaper may be needed to clean the toner faster than with acetone;

7.2) if you want, you can cover traces with solder (there are more ways to do it). Cleaning and prior use of SK-10 (calofonia spray) on the pcb can help. Use of 0.25mm solder can offer good control on the amount of solder used.

a) with solder wick: put colofonia and some solder (preferably lead free just for this) onto an used solder wick and with a high temperature tool move it along the traces, and in the end use a clean wick to remove the excess solder. Although: if you do it right after removing the toner with acetone, the copper will not be oxidized yet so no need to sandpaper or clean it, and a bigger iron can be better in covering bigger areas faster and easier.

b) directly without solder wick: just with one of the big iron guns that resemble a pistol and use a thick wire as heated element: straighten the wire and brush it against a sand paper to flatten the bottom part of the wire tip, add only a little solder directly on it, and gently move it along the traces. Also can be done directly with soldering station and the biggest flat-tip available - i use a 4.0mm flat tip for this and i think it might be best method.

c) there are tinning chemicals around, specialized exactly for this job, but are expesive, need quite some time to deposit a thicker layer, and once the solution has been prepared has a limited life span so it needs to be prepared in small amounts as needed.

7.3) part's legend can be applied before drilling, basically as just another toner transfer; one may notice that especially with a bad drill bit and if drilling the holes from the bottom side, the holes on the exit will have an edge, which further on can impair toner transfer - therefore its better to put legend before drilling and not after;

- sometimes if the board is covered in solder, the legend paper wont stick for the first time; use another legend print the second time, and over cook it with extra pressure until the paper sticks to the board properly, then put it in water and after soaking scrub with the fingers.

- two things will cause extra dirt on the iron tip: toner wont resist the soldering iron heat, if it is near solder joints or over traces that will require "fattening"; also this time some paper will impregnate into solder that is on tracks; on conclusion if you dont like to do extra cleaning, you can choose either to leave copper as it is, or not to use legend;

7.4) after legend is applied drill all holes at needed diameters. Probably best is to use proper diameter drill bits, but 0.6 - 0.8 drill bits are brittle, so use these with extreme care and only where space is tight. For all rest that has enough space around, i just settled on using 1.0mm drill bit, mostly because its cheaper, stronger, and basically fit everything, so 1.0mm is the drill bit that i use the most. In rare cases some connectors might need 1.5mm holes. Best would be to use a drill press, but it can be done manually aswell.

8. Vias, making layer connections:

Soldering vias is not the only way, but is probably most used. There is a mechanical solution that uses rivets. There are some diy electroplating solutions also. All these are rather expensive and complicated and not worth for just a few boards. Hence the following is only about doing vias with the old fasioned solder iron.

Soldering vias is the actual hard part. This brings alot of happiness, but only in the small community of sado-masochistic electronists which are just tired of using flagellation, because this can get even better. Joking aside, this is time consuming and has to be done very carefully. You dont want to discover a bad connection via under an already soldered ic. Except of course, if you fit in the above mentioned category.

Soldering vias means putting a wire through hole and soldering it both sides, along the corresponding traces. Some electronics suppliers have a special argintated wire that seems to be very suitable, and in diameters down to 0.20-0.35mm - this is highly recommended (probably best choice, its so thin that in some cases wont need grinding if under ics). Remains of the through hole component's legs can be used too - save them once you cut them off- but these are very bulky. Virtually any wire can be used, just some are easier to work with.

The important part is how its done. Bend the wire along the corresponding traces top and bottom, as long as possilbe. The longer, the better. At least one of the layers should have a connection of 7-10 mm long, so it wont fall off later. My vias look like 20 amps current is passing through, but at least should be solid. You never know when you fall asleep with a hot air station in your hand over the pcb.

To be picky, consider doing vias with lead free solder (or why not, high temp solder), and doing ulterior components with normal lead solder. This way other heating sources will have minimal impact or will not affect them at all.

Many vias can be done in pairs at the same time: same wire going in, passing over on the other side, and coming back on the initial side.

Vias that are located under other parts may require extra attention. Do these carefully, with alot of flux and where possible the longest contact surface available. Depending on the wire diameter used, these may have to be leveled down with a dremel and a grinding bit, to a height that will allow the part to fit properly on top. Metering those vias resistance may be a good ideea before soldering the part on top of them. Also because after the ic is soldered there is no further access to that area, i prefer putting some extra solder on all traces there to have them thicker - "fattening" traces.

9. A few aspects, specific to soldering a DIY pcb:

- obviously any reflow must be done prior of soldering vias; subsequently the parts that have vias underneath would need hand soldering; however: you can iron solder entire boards top to bottom with same ease, reflow is kinda overrated for diy and single boards (matter of opinion, but reflow was made for high voume manufacture not diy, and i consider it to be good as such);

- soldered vias are bulky; they may affect other components placement, especially like a smd capacitor nearby, and in cases like that solder the component first and make the via on top side after;

- most of through hole components will need to act as vias aswell: make sure you elevate them and solder them both sides; especially idc headers and .100" pins are hard to reach on the top side, but a fine tip on the soldering iron will help;

- headers will need some mechanical resistance, consider soldering those both sides, regardless if they have further connections or not;

- make a strategy on how and in which order to solder each component and via; then anticipate any potential problem that may lay ahead; there is no general rule other than think it through, carefully;

10. A few mistakes, specific to DIY pcb:

- over etching can cause a range of problems, even traces dissapear (see top left side of the picture);

- one eternal issue for a man: holes. Commercial pcbs holes are plated through, so holes are electrically better than the trace itself, but that doesnt happen in diy world. In diy, generally the traces are farily small and drill bits are farily wide in relation. Its frequent that one drill hole in the middle of a trace can cut the trace off entirely, or at least to reduce its width considerably - its easier to anticipate and handle this issue in pcb trace optimization than in soldering stage, because in some cases with dense components, soldering iron may have easy access to only one side of that hole where the component will have to be placed.

- its fairly common to forget to solder on both sides for some parts or pins, or even to make vias in wrong spots, etc; it is good to have a reference image in front of the work, while doing it;

- meter connections and triple check everything versus the pcb design files before plugging in.

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