Reclaiming PCB manufacture

PCB manufacture is a basic part of our electronics design process. We have to test in prototypes before we reach production and testing in breadboards is not enough for many reasons, one of them being the fact that we want to test the PCB design itself before we produce thousands of them.

Reclaiming PCB manufacture as something we should be able to control easily is fundamental because it affects electronics design so hard it may be preventing some people from doing it.

Think about the price of PCB prototyping. It can be somewhat expensive, and every time you screw up the design you have to order a new batch with all the shipping costs (monetary costs and environmental costs) that arises.

Before we start to hack the system it’s a good idea to check some videos about how does PCB manufacture actually work.

Thanks to all that people that took the time and the effort to record the process. Here you have a starting point:

As I just did, the whole info of this post is mostly documented in youtube videos for various reasons:1) humans think youtube is the only way to put videos in the internet 2) I prefer to show you people actually doing what I talk about.

That said, let’s start with the very basics: make the layers.

Layers: copper, solder mask and drawings

There are multiple methods and all of them can be combined depending on the needs of the project.

UV masking

This is the preferred method, it’s very similar to what industry uses. It’s also elegant and clean (the film version is best).

This method is based on ultraviolet light, UV paint and some templates printed on acetate.

The templates are the base of the circuit, they are just the Gerber files printed in black on transparent film (or thin paper). The black part of the film is going to prevent the UV light from activating the UV paint in some areas preventing it from hardening in the UV oven so can be later removed with the developer agent.

The first step is to apply some mask on top of the copper (some PCB cores already have that applied). Sandwich the template correctly aligned and put the sandwich in under the UV light. Once is more or less cured, develop it to remove the uncured areas and cure it completely to let it sit. Now the copper is masked, you can etch it.

NOTE: For a perfect UV light application put the printed side of the template facing the PCB (ink touching the copper in this case, but the tip is valid for every step). This reduces the diffraction and contributes to a very sharp image transfer. Note that you may need to mirror the image before printing for this.

Once it’s etched remove the mask, and do a next step with UV solder mask. In this case you don’t need to etch, just apply UV light with the corresponding template and develop the result (cure it hard afterwards).

You can go an step further and make the drawings layer (AKA silkscreen) too. The process is the same but using UV paint of the color of your choice instead of UV solder mask.

As paint is hard to manage and you have to apply a very thin and uniform layer of each product. You can use film UV mask and dry film solder mask (Dynamask) to make this method much cleaner. Using a laminator or a clothes iron you can apply heat and pressure to the film so it’s stuck correctly in the PCB with no bubbles (laminator is best). The idea is the same but the results are cleaner and easier to reproduce.

There’s no way to add the silkscreen layer to the PCB with film so, if you need it, you’ll still need some UV paint for that.

NOTE: Fingernail UV paint can be used for silkscreen layer: there are many colors available and it’s easy to find. Also, the insulator (UV curing oven) can be a fingernail paint curing device. Minds exploding everywhere.

This process is not destructive. The templates only need to be printed once and they can be reused indefinitely.

Emulsion screen printing

This is probably not the best method in the world but it’s very interesting

Screen printing (AKA silkscreen) method is the craziest thing. It uses ancient techniques1 mixed with UV masking and the result can be pretty decent.

Apply several layers of UV paint emulsion in a framed silk mesh and let it dry.

Use printed transparent film templates (see method above) to mask the UV paint on the mesh and cure it in a UV oven (insulator).

Clean with pressure water to remove the uncured UV paint. Dry and cure it again.

You can make the three different layers this way: copper, solder mask and silkscreen layer.

Using the screen printing the classic way (put the silk mesh on top of the PCB and press the paint through it with a spatula) apply the three steps in a row:

  1. Mask the copper, then etch it and remove the mask.
  2. Apply the UV solder mask and cure it.
  3. Apply the silkscreen (UV paint) and cure it.

The difference this method has with others is the important part in this one is the screen creation. From that all the others steps are just using it to filter the parts of the PCB where the paint is going to be applied.

Transparent film templates and framed silk mesh can be reused for many PCBs, which is pretty cool.

The silk mesh is a good way to apply a uniform layer of emulsion, so you don’t really need to make the template on it. If you use a blank silk mesh you can just apply a thin layer of paint in the whole PCB and then put the template on top and cure it masked under UV light. The process is similar but instead of inserting the templates in the silk mesh itself, uses the silk mesh as a helpful tool to apply a uniform and thin paint layer. This is what they do in the first video I linked, up there in the intro.

Toner transfer

Horrible stuff, don’t do this. It’s neither clean nor elegant and involves home printers, which are the most effective torture device ever invented.

There are two basic ways to use toner transfer, both are equally disgusting.

The idea is to print with a classic laser printer in a paper that doesn’t hold the ink very well, like magazine paper or heat transfer paper and then transfer it to the PCB using heat from an iron or acetone.

The idea is the same than in the first method, but it’s messier and it makes you print once per PCB which is not desirable.

CNC

If you have a precision CNC machine you can avoid some mess.

Just remove the copper you don’t need with the CNC machine, apply solder mask to all of it and remove the solder mask from the pads with the CNC machine too.

It sounds easy but calibration and all that is going to be hard and you have to do it for each PCB you want to make because the PCBs are not perfectly plain.

The good thing is the CNC machine is very useful for the holes and the alignment. If your CNC is not good enough for a detailed machining it will probably work well enough for the drills anyway, so it’s a good tool to have.

Some CNC machines can be less precise than other so the solder mask removal might damage the copper. It’s not a big deal, you can do that step with one of the methods described previously.

The worst thing of this process is you need a CNC machine. Nothing else to say.

There are also some success stories using a pen plotter and etch resistant pens. You may want to try. You can also be a plotter yourself and paint with the pen in the PCB by hand if your pulse is steady enough2.

Laser engravers can be handy too. Laser is light so you can use it to activate a photosensitive film or paint in a hybrid method involving UV masking.

Recap - Layers

The first method’s principle is very similar to the actual principle of PCB manufacture. More than the method, the underlaying technique is: UV paint and painted acetate is the trick. Using a Laminator and UV film is a very decent way to apply UV paint in controlled way without all the mess.

The most critical part of this process is alignment. Working with two layer boards needs the alignment to be perfect. If you make that wrong the result is disastrous. Take care. The best way to keep everything aligned is to place holes in the templates and the PCB and align them with a metal rod or similar.

It’s funny to remember that the text and drawings layer on PCBs is often called silkscreen layer. That’s why it was printed using silkscreen method in the past. Nowadays they use a printer that can print directly on the PCB.

This means in the past both the first and the second method were used together in industry, so… Maybe you can combine them, too. I personally find the silk screen very handy to apply the paint uniformly but I don’t really like the silk screen as a masking method. Mixed approach ftw.

The toner transfer is just shit. You shouldn’t use it in any case.

Also… There’s something we didn’t solve yet… Guess what it is?

Vias: the lazy approach

The first most reasonable approach you can try with vias is to avoid them as much as you can. In many cases you probably can just solder them by hand using copper wire later or even use through hole rivets, a via press or whatever other hack you like.

But we (I) prefer to be fancier than that.

Vias: plating

Industrial grade PCB vias are plated in order to connect the top and bottom layers of the PCB. Plating has two steps:

  1. Activation
  2. Electroplating

First step prepares the holes to make the copper get stuck there in the second step. The second is just adding the copper using very cool method with high current and chemistry involved.

Activation

Cover with a solution that helps the electroplating process. There are some options: palladium, silver…

Easy way: to mix water waterproof acrylic ink with powder graphite and apply it on the holes.

Electroplating

Electroplating is a process that makes a metal cover another conductive material using black magic (chemistry + electricity).

The activation step is needed because the core of the PCB (some kind of fiberglass like FR4) is not conductive (that’s the whole point of it!). The activation layer covers the holes with conductive material to make electroplating work.

Preparation of the electrolyte:

There are many mixtures of electrolytes for plating. The easiest (not sure if it will work for PCBs but you get the concept):

Cooking note here: Vinegar is water + acetic acid (around a 4%, should be higher for our purposes but whatever). The idea here is it’s going to act as an acid

Cooking note 2: Vinegar is mostly water and pure water is a dielectric (you were thinking it isn’t huh?). Salts are what make water conductive (most of the water you’ll find in nature has salts, so it’s conductive as hell). When you put salt in the water, the ionic bonding on the salt is going to break, making water conductive. The more salt you add, more conductive water becomes (because there are more free ions out there).

Put copper cathode and copper anode and a kinda high current (between 1 to 10A, depends on the area and stuff) between them to prepare the electrolyte solution. Once it’s ready it looks blueish (around 2h).

You have to see some bubbles around cathode (the one connected to the V-).

Once you have the electrolyte you can store it forever.

Of course, the mixture can be better. You can buy premixed stuff or make powerful stuff yourself. Make some research3.

Electrolyte must be disposed with care, plan in advance how are you going to dispose it. Talk to your local government for correct disposal. You can kill animals and people if you do it wrong.
On the other hand, it can be stored for a long time and every time you use it the concentration will be higher so it’s better to store it.

Electroplating process

Vias that have the graphite applied can be electroplated using classic electroplating. The process is the same as the preparation of the electrolyte, but using the board in the negative voltage so it becomes the cathode, to make the electrons go from the copper anode to it.

Again you have to see some bubbles around the cathode (the PCB).

You have to add copper until the vias have some copper thickness on them. That process might be long if the concentration of copper in the electrolyte is very low.

Vias vs Etching

If you already etched the copper, some of the vias may not be connected to the voltage so it’s going to be impossible to electroplate them. This is a total failure. You need to make the vias first.

But then you may think:

“But in the etching process I’m going to etch the vias if I don’t do it correctly”

And that’s correct. There are some options for you:

Two-step masking with tin

PCB manufacture companies use a two-step masking method. First they mask the parts of the circuit they want to remove, so they leave the tracks, vias and pads uncovered.

They electroplate the PCBs with tin. The tin is going to cover everything including the vias but leave the masked parts.

Electroplating process is similar to what we already explained for the copper but the products you have to use are different.

Then they remove the mask and etch the board. The tin is going to act as a mask for the etching so what is left is the final copper fully covered with tin.

They finally remove the tin using tin stripper.

NOTE: The tin used for masking is not good enough for protection (because it suffers from the etching process) so it’s better to remove it and add the protection later (see below) using liquid tin solution.

One-step masking

You can also use any of the methods above (UV paint, UV film…) but very carefully, being sure that you masked the vias correctly.

Recap - Vias

There simple way for easy prototyping is to be lazy and the fancy way involves some chemistry that has to be treated with care.

Also, the etching is going to ruin the vias if you don’t mask them, so you need to solve that.

The good thing of the first method we proposed, using the tin, is the vias are easier to mask using the tin because the electrolyte is a really liquid product (water-like). The main problem is you need to electroplate with tin and that’s a long process that involves current, some chemicals and all that4. Industrial PCB manufacture uses this method.

The second method must be applied carefully but it works as well as the first.

Another interesting difference is that the tin is very good as a masking agent so the first method is more resilient to over-etching.

There’s the last bit to solve still, our circuits still have some raw copper that should be protected from aging.

Circuit protection: tin for the win

Copper is going to get old, get rusty and all that horrible stuff. You don’t want that. One of the possible solutions is to add covering layer of tin to the copper before you add the solder mask (or maybe after?).

There’s a simple method: Dip the PCB in liquid tin5, like a nacho in cheese. This will cover the copper with a very thin layer of tin that will protect it from corrosion.

The product is crystal clear so you can just watch until it’s done. Quite straightforward.

There are plenty of nastier methods out there that I don’t recommend:

Recap

So yeah. There’s some nasty stuff here and there but most of the process is mainly doable in a not-very-industrialized environment.

There are some great videos out there that achieve very good results:

We didn’t talk about PCBs with more than 2 layers. Normally a 2 layer PCB is enough for most prototyping applications. 4 layers are sometimes mandatory for complex circuits, which also require a design effort that is hard to achieve with a low budget anyway. The 4 layer process is more complex and alignment starts to become a real challenge but we may be able to do it at home anyway with some extra tools and cleverness6. It’s just a thicker sandwich.

Many companies don’t support buried vias, by the way, so don’t be so hard on yourselves. You may achieve the same level of mastery they have.

Thoughts

Being hackable is something every manufacturing process should try to achieve in my opinion. Of course, doing all this by hand is not fast enough, but we must reclaim the knowledge and the chance of making all by ourselves if we can. This is the real way to reach a technological sovereignty.

Putting all this methods together is also a valuable way to think again about the process we don’t really see. It’s simpler than it looks. Maybe tomorrow with some investment you can make your own prototype PCB production company that helps engineers in your area make technology for the people by the people without depending on third parties probably located far away from your location.

Not only that: all of this knowledge is interesting for many other areas. I always want you to get the concept, the root of the method.

This process can be easily summarized as:

“Render an extremely detailed image in a plain surface”

This is why the fingernail painting and screen printing are related with this. They are just methods to apply sharp images in plain surfaces.

Integrated circuits are an extreme example of this idea and they actually use similar UV light techniques (but obviously they don’t print the templates with an standard printer). Everything is connected (no pun intended).

But plain surfaces are not the only thing here! Plating and etching are also part of this process and they both are techniques that were invented way before the PCBs were a thing.

Plating is extremely interesting because it can help you protect metal tools or materials you have around (nuts, screws…), make some restoration works or do some jewelry.

Etching is also very interesting, you can use it to make stamps, engrave a label with your name for your mailbox and many other extremely useful and life-saving applications like the ones I just mentioned.

That said, if you are still thinking this process is too complex for PCB manufacture you may miss the point of the method. Just learn it and make it yours. Maybe in the future you’d need to make something, like…

Extra: Solder paste stencils

It’s funny to see how there are two parts of the same manufacturing process that hardly interact with each other when it comes to materializing them in a DIY way.

I’ve seen many tutorials for making simple solder paste stencils in the past.

Some of them use a thin plastic and engrave it with a laser plotter. It’s important to make the plastic melt instead of cutting through it, this way the cuts are cleaner and the solder paste doesn’t get stuck to the corners.

That’s an easy process you can do if you have a laser cutting machine, but I don’t have any so I have to dig further. Also, there are other methods that result in a higher quality and more durable solder stencils.

One of the most popular is using soda cans (easy way to get thin aluminum!) as the base for the stencil. You have to cut the can, make unroll it and remove the coating plastic, but once you have that you need to transfer the solder paste layer to it.

Most of the times I’ve seen this method, they use toner transfer method (I already said I hate it). Some people even use a laser engraver to cut blue kapton tape that is then put the aluminum as a mask.

Well… With the methods we visited here it’s much easier, isn’t it?

Maybe you don’t think making every PCB by yourself is a good idea, but investing some time in making one SMD solder paste stencil that you can use repeatedly for a long run might be a really good thing.

This also takes me to the next problem to solve: the reflow oven.

But that’s not going to be solved today.

  1. The first known use of silkscreen method dates year 3000bC in the Fiji islands. They used banana leaves for the screen. Awesome shit.↩︎

  2. Jokes aside, this is a valid reparation method when the mask cover was not applied correctly in some spot.↩︎

  3. Plating is done for other purposes that are not related with PCB manufacture. The most interesting research you can probably make is out of our specific topic. Have fun out there.↩︎

  4. Maybe you can use liquid tin here? IDK↩︎

  5. If you are an extreme hacker:
    Liquid tin is a mixture of tin chloride (SnCl2SnCl_{2}) and thiourea (can be obtained from silver polishers and other cleaning products).

    You can make the tin chloride mixing hydrocloric acid 30% + a piece of tin ~95%. It will make the following reaction, freeing the hydrogen to the air and leaving some extra residue in the bottom of the container due to the impurities of the tin:

    Sn+2HCl→SnCl2+H2Sn + 2HCl \rightarrow SnCl_2 + H_2

    Thiourea is what makes the tin get stuck to the copper. Buy a cleaner that has it as its main component and add it to the mixture.

    You can buy the whole thing pre-mixed so better don’t mess with all this stuff (I’m not adding here the proportions for a reason). Don’t come later saying it was all my fault.

    Youtube link on the subject↩︎

  6. The term engineering is derived from the Latin ingenium, meaning “cleverness” and ingeniare, meaning “to contrive, devise” - Wikipedia.↩︎