What/Where/Why/How?
What is etching and what is spray etching?
Etching is the process of eating away a pattern on a target material by using an etchant liquid that attacks the target material.
The most common target materials are copper and brass. The most common etchant liquids are ferric chloride, ammonium persulphate and cupric chloride
On a hobby scale it is common to submerge the target into a container filled with the etchant. This can be very slow and is often sped up by either mechanical agitation or using an aquarium / fish-tank bubbler. Even with the speed up from sloshing the container around this process can take 10-15 minutes for a PCB or over an hour for a thick brass plate.
The spray etching method uses the same etchant liquid as the submersion method, but instead sprays the liquid onto the target. This can speed up the process by an order of magnitude.
The advantages that spray etching has over the more mundane submersion method of etching is
- Faster
- Less manually intensive
- More uniform etch
- Produces sharper edges / better detail
Where are spray etchers used?
- Manufacturing PCB (Printed Circuit Boards)
- Etching plates for intaglio printmaking
- Etching brass nameplates / plaques
- Photochemical machining of mechanical parts (often used in model trains)
- Etching jewellery
- Etching stencils (if you can't afford a laser cutter hint hint)
- Automatically generating traffic by showing friendly site logos made from brass
Why a ROTARY spray etcher?
This rotary spray etcher can be built for between $50 and $100, depending on where you need to source your material. This is a lot less than the $300 plus that other spray etching machines would cost. It is also quicker and easier to build as long as someone else has made all the errors along the way FOR you.
How?
Well here is where I get to say "follow me on this remarkable journey of discovery"
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Background / Prior Art
Types of spray etchers
There are two main methods of building spray etch machines.
- A pressure pump and nozzles
- Rotary spray etchers that rely on centrifugal force
Pressure Pump Versions
This is the method that commercial PCB manufacturing equipment uses. In an industrial setting where reliability, throughput and lowest level of operator skill are valued over cost and size, it wins hands down.
This method is also fairly well represented in DIY projects on the web with at least three projects showing up with only a cursory search in google.
- Proto Trains design dates from 1996 but first appeared on the web in around 2002.
- Adam Seychell dates from June 2007. (Unfortunately missing in action at the moment and on the way-back machine without pictures.)
- Crreed on Instructables from Instructables dating from 2012
The commercial machines and the three DIY projects all approach the uniformity problem differently. Having some relative movement between the nozzle and target removes problems with high pressure spots. Having the target in a horizontal orientation reduces undercut.
|
|
Nozzle | Target |
Target Orientation |
| Industrial | Stationary | Moving | Horizontal |
| Proto Trains | Stationary | Moving (rotating) | Vertical |
| Adam Seychell | Moving | Stationary | Horizontal |
| Ccreed | Stationary | Stationary | Vertical |
Rotary Spray Nozzle Versions
Rotary spray etchers are a whole different kettle of fish when it comes to DIY projects. It seems that although newsgroups are littered with people starting a project to build one, only one DIY project seems to have been published on the web to look at. It is also not the easiest thing to find as it is in German and “spray etcher” will not turn it up in a google search.
Spruhatzanlage use google translate or BableFish to make a bit more sense of it
The German site although very professionally done and full of helpful pictures, does not address the pitfalls of building one yourself.
Pressure Pump Vs Rotary
Pressure Pump
Pros
- Can be scaled up
- Can be built with target in horizontal position (reduces undercut)
- Can achieve higher uniformity of etch if either target or nozzle are moving
Cons
- Expensive to build (relative to rotary)
- Difficult to find suitable pumps (Seychell recomends against Shurflo)
- Labour intensive to build (relative to rotary)
- Poor uniformity with static nozzle/target
- Risk of hoses coming loose and coating your workshop in etchant with some Spray Etcher designs
Rotary Spray
Pros
- Cheap to build
- Easy to build
- Excellent uniformity over a small area
- Lower risk of accidents spraying etchant around
Cons
- Can not be scaled up in size a great deal
- Target can only be vertical
- very difficult to get working well (until now)
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We have to fill in the rest of our days somehow.
There is a new instructable on the burner I want to try get done for the Zing competition. However it's pretty hard slog when all your parts from digikey have to come via kangaroo.
It no so exciting to watch the machine run in a video. I will try do a video of its use though. I will just cut/FF/timelapse the boring "spray" part.
Yes Yes Yes!
Stay tuned. About 10 people so far have told me they have built or are building The Etchinator and I have some feedback to improve the design.
I am also working on the write if for another few pieces of equipment at the moment.
Thanks so much,
Cat
I would suggest having a look at Adam Seychells spray etcher on the way back machine. The photos have gone AWOL, but the descriptions are all there.
Economics is not very kind to “scaling up” the design I show here.
With the spray tube etcher here there is one motor (the expensive part) per tube. If you scale up to 10 tubes you need 10 motors. In contrast pump/nozzle type spray etcher still only needs one pump.
Although the original motors I bought years ago where $5, recently the cheapest reliable source of motors I have found outside the US is $12. This means a 10 tube etcher would be $120 just in motors. Motors alone you are spending more in parts than a diaphragm pump.
Aside from the low cost of the small version, the etchinator comes out favourably because you don't need to construct a tank. The HDPE storage crate make a very convenient liquid tight container. If you are scaling up you are going to have to make your own PVC tank. The Etchinator style has lost both advantages now. It's no longer easier to build and it will be more expensive.
WRT you question about the impeller. I am looking at axial inflow radial outflow styles. Look at a car turbo charger photo off google to get an idea. There is still a small inlet hole but the impeller blades come down and face forward.
Also if you DO decide to scale up the spray tube etcher, you probably don't need the blinds. The angle issue I show in the digram on step.4 is not really about the angle of the impact causing undercutting. It is the angle of the impact having less force therefore a slower etch (poor uniformity). Any overlap from not having “blinds” will cause faster etching. If you just work out how far apart to have tubes to balance out the speed-up and the slow-down your should be right :)
But really I do recommend a pump version for anything much larger than what is shown. The pump version on a large scale will be
Cheaper
Easier to construct
Very marginally better results (Adams style, Creeds style will be MUCH worse)
Easier to automate
The pump Creed used is apparently not etchant safe and will die a horrible death without modification. (See the link in Step.1 to Adams experience with the same pump). In that link Adam recommends FloJet instead (which is the brand proto-trains used).
Hoses running outside of a containment vessel are not a great idea. Read the section “Etching tank No.4” in the proto-trains link in Step.1. Watch Creeds video and pause at 3:21. Now imagine that pressure relief hose on the OUTSIDE of the tank. That is the volume of corrosive fluid being splashed around the shop when the hoses let go.
A second PVC containment vessel that contains ALL hoses and the pumps is probably a good plan. PVC is cheap and making the outer tank will only be expensive in time. Weigh that up against time cleaning up after a spill WHEN it happens.
Finally these days if you look at that festering pit flea-bay and search for “PCB Ceramic Spray Nozzle” you actually find something. I have never bought or used these so I don't know what the quality is, but they are not too expensive to give a try.
Regards,
Daniel
It seems there is a fair bit of interest happening. I am going to try find someone local with a 3D printer to come up with a printable design for it.
It should make easier one of the more fiddly parts of the build.
I have also had feedback from a few people to make the etcher easier to keep clean.
Did you etch the Hackaday logo from a solid sheet? How come it doesn't get massive undercuts?
The Hack-a-Day logo was made from the same 0.7mm (1/64") as the Instructable Robot. The lack of undercut is the "extra way big" advantage of spray etching. The droplets hitting the target at speed and close to perpendicular help etch directionality.
If you tried to do the same etch depth (0.35mm) sloshing around in a container full of liquid, you would get about 0.2mm undercut. Sloshing gives a wanted to unwanted direction of etch ratio of about 3:1 on fresh etchant down to 2:1 on spent etchant.
The Etchinator gives more like 10:1 down to 5:1. If you want better than that you are going to have to build something like Adam Seychell did.
Making a note that the offset is vertical to better cover the item being etched would be a good idea.
An easier way to ensure the motor couplers align with the tubes would be to turn a step on them. Use a ratcheting PVC pipe cutter (a good one) and you'll have perfectly straight pipe to coupler connections.
Good old Reverse Garbage eh? They are not as good as they used to be but I have scored some nice material from them over the years. I miss them now I have moved to the country.
With respect to posting your other projects - well just call me Colonel Mustard ;-)
Well done!
I'm Australian as well, I have not found other's alike that have attempted home etching with the quality we are after ( repetitive small production i guess ) and I', glad to see another is out there somewhere! I'll 'follow' you on instructables so we can discuss further pcb, and material finding in Australia as I know this is hard sometimes
The stripes you are referring to are in an appendix of what can go wrong if you don't build it accurately.
If you follow the plans there will be no stripes.
Are all etching solutions compatible with this box and its materials / glue agents? Will they survive the chemicals or can they errode. I use a 50/50 peroxide and hydrochloric acid mix for my etching, and I have used ferric chloride as well.
Can I use more than one chemical in this system by simply 'flushing' it after each use with water, or some solution that will not effect the next chemical that will go into it. If so, not only etching can be done, but also a chemical cleaning solution before and after the etching all in one container.
I hope these questions are useful for any one else interested
You can clean out the tank and reuse different chemistries.
I would be careful with the cleaning if you are going to try use it for other applications. I know that some of the cleaning and electroless steps in through hole plating are very sensitive to contamination. I can only suggest reading and following the guidelines for the other applications chemicals.