How to make etched circuit boards for surface-mount

I've received a lot of questions on how to build the surface mount component circuit boards found on this site. For example, if it is at all possible to make the boards at home, what exactly special equipment do you need, how complicated is it, where could I order finished boards, how on earth do I solder these small components, and more... So, I finally decided to try write up some of these things, in form of in-depth tips.

I'll assume you already have some knowledge and experience of DIY circuit board making using the phototransfer method, so this won't be an introduction nor a complete step by step guide (those you can find via google 'making printed circuit boards', for example the Printed Circuit Boards FAQ).

Note that for "large" tracks of > ~0.5mm width, on single-sided board projects, you can also try the other popular, professional-looking-PCB method. In this method you print out the mirrored PCB artwork with a laser printer onto paper or special plastic sheet, then use a heat gun or hot clothing iron to iron the laser toner from the paper/plastic directly onto the bare copper PCB. The board is then ready and can be thrown into the etching solution. Results are quite good, and the process is fast. However, IME this toner transfer method doesn't work well for double-sided boards (alignment?) and thin tracks (<0.5mm, gaps and peelings in toner transfer), and isn't suited for making many copies of the same board (unless you print out the thing again, that is). You can find a detailed description of one toner transfer process at http://esmonde-white.com/etching_pcb.html
The generally all-round 'best' method, yielding premium results with a bit of patience, still remains the phototransfer method. The tips related to SMD are presented here. Now, on to the questions:


Can I make these SMD PCBs at home?

Definitely yes. Though the copper track widths on many of the SMD PCBs may appear almost 'microscopic' (<0.2mm), it's not very hard to make boards that have the ultra-narrow traces still etched out very neatly and sharply. Contrary to what many believe, this doesn't even require any special equipment, expensive chemicals, nor any amazing talent.


Where can I order boards?

Unfortunately I don't really sell pre-made boards for these projects, mainly due to lack of time. It shouldn't be too complicated to make the boards yourself, though. But, there are PCB manufacturers like for example Olimex in Bulgaria who accept Eagle .PCB files, offer silk screen and solder mask, and ship out standard boards in 2 weeks + delivery time, worldwide, and have pretty good price and quality also for hobbyists. I haven't yet had any boards made by a PCB manufacturer, but Olimex should be quite good. It is however possible that the Eagle files on this site require some more info for Olimex to be able to manufacture the board. I haven't tested it. (candidates e.g. drill sizes info? silkscreen layers?)


What equipment do I need?

On the PC side:

For the PCB:

For photoresist exposure:

To develop the exposed photoresist:

Etching:


Do I need some special type of PCB board?

Nope. Any standard board will do just fine. For the best results you'll have to use the phototransfer method to make the SMD boards, which means the PCB has to be coated with a photoresist first. The easiest option is to use a pre-made photoresist board ("presensitized photo resist PCB"). But, it may be less expensive, and also more forgiving of accidental errors, if you coat the PCB boards yourself.

For home PCB coating, it's important to spray only a thin film of photoresist on the PCB copper side(s), in a dust-free environment. I've done all my SMD boards, single and double sided, using photopositive spray applied thinly to the board, and it has worked very well every time, even down to 0.20mm track widths. But if the coating is too thick the PCB takes longer to expose and tracks shrink to become smaller and blurrier.

To prepare the board, first scrub it clean from oxidized spots and fingerprints with a piece of steel wool, and wipe with some (met/et/prop-) alcohol. Then pick up the board in the hand using one sheet of household paper on the back side of the board. Hold the board tilted, start spraying from the uppermost board edge, spray pretty fast from left to right, and proceed downwards. When done spraying, keep the board still tilted for a while to let the photoresist flow down accross the board and spread out evenly (IMPORTANT!), and for excess resist to accumulate at the lowest board edge and soak out into the household paper. Finally, you can dry the board with a hair dryer or, from >0.5m (~2ft) distance, with a paint stripper / heat gun. Watch out that you don't blow any dust specks on the board. Generally it should be dry in 5..15 minutes. To coat the second side of the PCB, let the board first cool off before you spray on the photoresist. Also, be careful not to add any fingerprints or dust onto the copper in the meantime (or at least wipe them away with alcohol), otherwise the photoresist won't stick properly.

All in all, coating the boards yourself has the benefit that, should something during exposure or developing go wrong, you can always wipe the board clean (with isopropylene, methanol, ethanol, ...), re-coat it and try again.

Any dust, fingerprints, or oxidations on the copper MUST be removed before applying the photoresist, otherwise small gaps and open circuits will occur in the thin SMD copper tracks of the etched board.


Exposing the board

On the PC, print out the top and bottom layers onto an inkjet transparency sheet. Check that the settings are: black and white, paper type is inkjet transparency, quality is set to highest quality (or highest DPI).

In addition, the ink side of the sheet MUST later come in direct contact with the PCB, to get the sharpest results from the exposure. This means that you will probably have to print out the top layer mirrored/flipped, so that later the sheet can be flipped over such that the ink side is down on the PCB (and the artwork looks correct from above, e.g. mirrored+mirrored = end result 'un'mirrored)

If the board is double-sided i.e. you have printed out two layers, then the printed transparency sheets must be aligned before you proceed to the exposure stage. Combine the sheets so that the ink sides face each other and all drill holes etc align properly. Once the sheets are aligned, use scotch/whatever tape to firmly fix the sheets together, forming a 'pocket' or 'bag' into which you can slip the photoresist coated PCB. After you've placed the PCB inside this transparency sheet pocket, use a few bits of tape to fasten it so it doesn't move around while you move the bag/pocket or flip it around under the UV-A lamp.

For the UV-A exposure, it's best to slightly overexpose the board. For example, if 50 seconds worked well for standard boards, you should try maybe 1min 30s for exposing the SMD PCB artwork. This gives a clean, sharp exposure on the PCB. Before processing an entire PCB, it's naturally best to first test the exposure time setting with a small piece of scrap photoresist PCB, which you first expose and then develop with NaOH to check the result. Once it works well with the test piece(s), just use the same settings for the actual PCB board.

If the entire PCB doesn't fit under your lamp, either lift the lamp higher and use a longer exposure, or, better: first expose one half and then the other, with a small overlap region between the halves. You don't need to put any protective cover on the rest of the board while exposing one side/half. Neither is it necessary to work in a dark room - even working in daylight is perfectly fine, as long as you don't keep the PCB lying in the sun for many hours.


Developing

This and etching are the easiest part, and there's nothing special to the SMD develop+etch compared to the normal process. Anyways. To develop, use a moderately mild water solution of NaOH. Swish the PCB around in the solution, but be careful not to scratch the board. If nothing seems to happen in a minute or so, dissolve a bit more NaOH or chemical drain cleaner. It's better to use a mild solution that develops the board in 1-4 minutes, and you can control how sharply the track edges should come out. This is in contrast to some ultra strong solution that potentially wipes the entire PCB board clean (well... completely blank, really...) in just a fraction of a second.

Once all developed photoresist has been washed away, and the remaining photoresist artwork on the PCB looks nice and sharp, and the copper is clearly visible at all places where it should be, you can take the PCB out of the NaOH solution and rinse it with plenty of water.

If it looks like some tracks in the artwork are broken, you can still easily correct them: first tap the PCB dry with soft household paper, then wait a few minutes till it is really completely dry. Next, use a water-proof pen (for example those dedicated for drawing PCB artwork) to add the required corrections to the artwork. Let the PCB/ink dry for a few minutes before etching.


Etching

Well... just prepare some standard etch solution (ferric chloride, ammonium persulfate, natrium/sodium persulfate, or some nice dangerous DIY chemicals mixture), heat it up if required (FeCl3 works without heating), and let the board etch.

After the board has etched it's a good idea not to remove the remaining photoresist, if you want to store the board and solder it at some later time. Also, to remove the photoresist it should be fairly obvious NOT to use steel wool like often done with standard boards. Instead use household paper with alcohol to carefully remove the resist.


Soldering SMD parts

This is probably already covered very well on plenty of sites on the internet and in hobbyist magazines and book, but, in case you are completely new to soldering SMD parts here are a few quick tips:


(C) 2004 Jan Florian Wagner, OH2GHR
jwagner at cc hut fi