Author Topic: How do you do your PCBs?  (Read 8036 times)

Offline PekkaNF

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How do you do your PCBs?
« on: January 18, 2016, 02:54:52 PM »
I'm not too reat on PCB making.

And I'm now into this kind of stuff:
https://www.elektormagazine.com/magazine/elektor-201409/27026

PCB # 130297-1
https://www.elektormagazine.fr/magazine/elektor-201406/26534

SMDs and stuf....two sided, way too small tracks...

Pekka

 

 

Offline CrazyModder

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Re: How do you do your PCBs?
« Reply #1 on: January 18, 2016, 03:29:05 PM »
I have this process for 1- or 2-sided PCBs with SMDs:

1. Make board in Eagle
2. Print on overhead projector transparent sheets with a cheap laser printer
3. Expose PCB with some old (huge) sunlamp
4. Develop with NaOH
5. Etch with FeCl3
6. Drill holes
7. Rub high spots from drilling with scotch brite
8. Tin it by smearing with plumbers tin "stuff" and shooting it with a hot air gun
9. Try hard to ignore the (visual) mess this last step leaves behind with half burned PCBs and swear never to do it again :)
10. Spray it with some transparent stuff which is supposed to make it even easier to solder, and protect the copper from oxidizing
11. Solder

There you go! Looks like it's a big effort, but all steps are actually quite easy and clean. I regularly find myself doing it even though I only have a few connections to make, I just dig the look of even very small PCBs compared to individual cables on an experimental board.

Offline PekkaNF

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Re: How do you do your PCBs?
« Reply #2 on: January 19, 2016, 04:04:57 AM »
You use photosensitive boards or do you spray on positive 20 or other UV-sensitive resist?

I have tried to buy some, much of them have gone old before I got them. Is there any other method to check, except to exposure, develop and etch and then try to figure out which step went wrong?

Has anybody tried toner transfer/laminator method?

Pekka

Offline sparky961

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Re: How do you do your PCBs?
« Reply #3 on: January 19, 2016, 06:15:02 AM »
I've used something called "Press n Peel" quite a lot. It works pretty well if you're careful. Better for boards with some room between traces though. I found it worked much better than direct toner transfer. If you're willing to pay the shipping I'd hapilly send you a few sheets to try out.

Offline RussellT

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Re: How do you do your PCBs?
« Reply #4 on: January 19, 2016, 06:19:18 AM »
I've done toner transfer with toner transfer paper.  It works OK but I always find the ironing on step fiddly.  It is difficult to keep the film still while you're getting it fixed to the copper and difficult to be sure it's all stuck down properly - especially if the tracks are narrow.

I've tried some of the suggestions on the internet for using glossy paper - they don't work nearly as well as the proper stuff.

I've never tried a double sided board but I think that it would be  difficult to register the second side.  If I had to do a double sided one I might do two boards and put them back to back.

I also try and keep my tracks and pads as fat as possible - easier to drill and solder.

Here's a picture of one I did last month - which gives some idea of how clear the edges are.

Russell


Offline philf

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Re: How do you do your PCBs?
« Reply #5 on: January 19, 2016, 07:21:28 AM »
Or, if you have a CNC router or mill, try machining them. No messy chemicals, no UV lamp, cheap copper clad board.



Phil.
« Last Edit: July 13, 2017, 01:12:12 PM by philf »
Phil Fern
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Offline jiihoo

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Re: How do you do your PCBs?
« Reply #6 on: January 19, 2016, 07:34:23 AM »
Hi Pekka,

I've used "Thermal transfer paper for PCB" (check ebay.co.uk with this search term, I don't want to link to any individual seller). Works on PCBs of "normal" complexity (i.e. try to avoid traces that are overly thin). All of mine have been fairly simple and the last were done a "few" years ago.

To make a simple double-sided board, iron the transfer on one side first and then drill a couple of locating holes to position the other side correctly. Fold the edges of the 2nd transfer paper to keep it positioned correctly. Try to make 4 extra "locating holes" on your PCB design if you can; if you used some of the normal holes for this then consider plugging them before etching as the edges of the holes you just drilled are not protected and will etch somewhat. Anyway don't make your boards 2-sided if you don't have to and when you do, try to keep the other side simpler to make the locating less critical.

My stack of 20 sheets of thermal transfer paper is from 2014 and none of them have been used  :( (but I am sure that I'll find a good use for them real soon now...).

You are welcome to a couple of sheets if you want to try them without waiting for long delivery from far away... Just PM me.

The Positiv 20 UV resist is usually good for a long time after the expiration date.


Jari

Offline PekkaNF

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Re: How do you do your PCBs?
« Reply #7 on: January 19, 2016, 07:53:11 AM »
Thanks.

I have really been thinking of building a small CNC router just to do euro card size PCBs max. Just so hard to get started. I have seen some professional ones and hobby models or DIY types just feel so hopeless.

Direct toner method sounds nice, if it works. Specially if you can print also component outlines, markings and solder mask. I wonder if 3D printer could be used to dispence any of that stuff?

There were some nice stuff on lab when I was studying. Two sided was no problem: taped two repro films together on two sides (easy to index), then slip sensitized and oven dried PCB in between and tape tags on corners to immobilize the PCB and "pouch". But now I have only household stuff.

I'll have to take your offer JH, PM will follow....I have greatest faith on UV resist method, but I really like the direct toner transfer idea.

Pekka

Offline Joules

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Re: How do you do your PCBs?
« Reply #8 on: January 19, 2016, 09:09:11 AM »
With a small cnc like my old Roland MDX3, you have the option of coating you PCB, then scratch the resist for normal etching.  It means even a small cnc machine can produce boards.  I made this tool to go in the 6mm collet of my little MDX3.
Just get doing and make swarf, you can decide what its going to be later.   :thumbup:

Offline CrazyModder

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Re: How do you do your PCBs?
« Reply #9 on: January 19, 2016, 02:35:44 PM »
You use photosensitive boards or do you spray on positive 20 or other UV-sensitive resist?

I use pre-made boards from Bungard.

Quote
I have tried to buy some, much of them have gone old before I got them. Is there any other method to check, except to exposure, develop and etch and then try to figure out which step went wrong?

The story, as far as I can tell, is that they are forced to print a shelf date on the boards by regulations. In fact, they seem to hold for many years with no problems. Mine did, I'm sure; I have not tracked how old my boards are, but I have certainly used ones of 5 years or older with no noticeable difference.

Has anybody tried toner transfer/laminator method?

I've tried it and found it as hit-and-miss as the other people here.

Really, the NaOH/FeCl3 method is not messy at all. If you are able to pour a liquid from one container into another without making big splashes everywhere, then you'll be fine. Sure, those are chemicals, but only mildly dangerous to humans. You won't get blind from fumes or destroy your lungs or something like that. You can store them indefinitely in plastic containers with no risk of them breaking (check the data sheet for which kind of plastic; I got my containers in a local apothecary when buying 2 liters of aqua dest there, for free ;) ). The dangers appear when you simply pour the used stuff in the toilet (especially the FeCl3 - I have heard that the utilities can track that and you'll get really punished, and the ground water will go to hell ;) ). You can use and re-use the FeCl3 a very long time though, it is very benign. The other danger is of course to clothes, and the FeCl3 will - duh - etch metal, so don't use it in the kitchen in the good stainless steel sink or the wife will put you in pain. :) All should be pretty obvious. Eye protection and simple gloves should be standard, no questions asked.

There *are* other chemicals that can be used for PCBs which *are* indeed very dangerous indeed. That's why I use NaOH/FeCl3. The FeCl3 step takes a long time (can be like 30-45 minutes) at room temperature, but that's fine with me.

All of those parts are easy to source and cheap (like 1-10€ cheap). The printer is kind of important though; I assume not every printer will give good results on transparents. A slight cloudiness does not hurt, but if there are holes in the print,  you will get holes in your copper. Mine cost < €100. And you can use it for standard printing as well, so I don't count it as investment at all.

Offline John Rudd

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Re: How do you do your PCBs?
« Reply #10 on: January 19, 2016, 03:07:41 PM »
Guys,
In order to speed up the etching process, I warm my ferric chloride in the microwave oven....depending on the wattage of yours( 'er indoors I should say)...for 10 secs a time...and agitate the board in your etching bath....
It does make a difference.....

John.....pcb etching dept.
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Location:  Backworth Newcastle

Skype: chippiejnr

Offline awemawson

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Re: How do you do your PCBs?
« Reply #11 on: January 19, 2016, 03:32:03 PM »
Mine not only warms the Ferric Chloride, but agitates it by pumping air bubbles from below'

Made by Mega, it has a developer tank, etch tank and tin plating tank, with water rinsing slots in between making it all very convenient - has a handy sink built in as well.

Amazing what you can pick up on eBay.  :lol:

 This is the second one I've owned. The first one got sold when I moved to reduce volume of the move itself, but this is an improvement as the last one didn't have the sink.  :thumbup:
Andrew Mawson
East Sussex

Offline CrazyModder

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Re: How do you do your PCBs?
« Reply #12 on: January 19, 2016, 04:34:53 PM »
Yes, if I am in a hurry (and the wife is not around), I simply put my etching container into a hot water bath in the kitchen. Careful not to over-etch, then.

I've made myself a bubbling device as well, but *that* was messy indeed and I just don't need that step to go fast.

But as the OP is hesistant about the method, I'd just like to point out that both of these things are completely optional and just speed things up.

Offline John Rudd

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Re: How do you do your PCBs?
« Reply #13 on: January 19, 2016, 05:08:53 PM »
I ought to point out that overheating the ferric chloride is not good....
It will turn to ferrous chloride....


John....pcb etching lab services..
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Offline philf

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Re: How do you do your PCBs?
« Reply #14 on: January 19, 2016, 06:00:38 PM »
One method I don't think has already been mentioned is pcb transfers. Similar to Letraset you have pads, tracks etc which you rub down onto bare copper. The transfer is etch resistant. I have some of these in a drawer that I must have had for 40 years so I guess mine won't work now. Electronics magazines often used to include rub-down transfers of a whole pcb for their projects. They were printed by a local guy in Stockport.

I wouldn't like to do a very complex circuit with this method. I used it for doing pcb artworks on drawing film. We had a setup like Andrew's at work so etching was no problem.



Phil.
« Last Edit: July 13, 2017, 01:11:47 PM by philf »
Phil Fern
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Offline sparky961

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Re: How do you do your PCBs?
« Reply #15 on: January 19, 2016, 09:43:04 PM »
Further to my previous reply, I definitely prefer UV presensitized boards but if you mess up its more costly 'cause you can't just remove the resist and try again. The benefit is very fine traces and crisp edges.

Last time I wanted a board I just ordered it online. Can't beat the quality, delivery was quick, no mess or chemicals to deal with. Price is still up there but only if you consider your time free.

Offline PekkaNF

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Re: How do you do your PCBs?
« Reply #16 on: January 19, 2016, 11:59:01 PM »
Thank you

I'll try Bungard pre sensitized boards and normal laser printer transparencies.

I may try thermal tranfer paper method too, just to have something to compare and that looks like a cheap method.

I do have few UV-tubes, really should build the exposure box. I even bought the acryllic and specially asked the non UV filtering type and got the UV filtering type. Surpricingly I found out too that much of the windlow class has UV filtering...Probably should buy the cheapest picture frames there are to get few correct size glass panels, I'm sure they have no UV protection!

Pekka

Offline efrench

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Re: How do you do your PCBs?
« Reply #17 on: January 20, 2016, 01:28:36 AM »
I'm in the process of designing my first PCB.  This is the process I'll probably use to create the board:
http://quinndunki.com/blondihacks/?p=835

The board itself will be about 2"x2" with 150 odd holes.

Offline CrazyModder

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Re: How do you do your PCBs?
« Reply #18 on: January 20, 2016, 01:41:40 AM »
I may try thermal tranfer paper method too, just to have something to compare and that looks like a cheap method.

Sure. In Germany people  traditionally use pages out of the printed catalogue of one of the big electronics shops, for whatever reason that seems to work best (or it is simply because people who do things like this have this kind of catalogue lying around :) ).

Quote
I do have few UV-tubes, really should build the exposure box.

I have one of those old sunlights (I think it is a "Philips HB 171/A" or similar to it) and just prop it up on something when I need it, I didn't feel the need for a proper box yet.

Quote
I even bought the acryllic and specially asked the non UV filtering type and got the UV filtering type. Surpricingly I found out too that much of the windlow class has UV filtering...Probably should buy the cheapest picture frames there are to get few correct size glass panels, I'm sure they have no UV protection!

 :D

Offline awemawson

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Re: How do you do your PCBs?
« Reply #19 on: January 20, 2016, 02:55:06 AM »
I worked in an electronics lab at Mullards Southampton back in the late 1960's where we had a thing like an Etch-O-Sketch, manually operated you put a clear but coated  film on the bed and shaved the waxy coating off leaving clear track that was then reproduced photographically. The waxy coating was red. When you made a mistake there was a bottle of correcting fluid to cover your mistakes.

Somewhere I too have transfers like Phil's, also a 'tape pen' that lays down tracks from a reel onto your art work.

Then of course there was the 'Dalo Etch Resistant Pen' that you drew your tracks directly onto the copper.

Then 'someone' (me!) found that a thick layer of layout blue was a good etch resist, and was flogging it as such in adverts in the back of Practical Wireless and Wireless World in little bottles. That was in the early 1970's
« Last Edit: January 20, 2016, 05:53:04 AM by awemawson »
Andrew Mawson
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Offline PekkaNF

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Re: How do you do your PCBs?
« Reply #20 on: January 20, 2016, 02:56:20 AM »
Sure. In Germany people  traditionally use pages out of the printed catalogue of one of the big electronics shops, for whatever reason that seems to work best (or it is simply because people who do things like this have this kind of catalogue lying around :) ).
Incidentally I think I have the right catalog to the job, starts with little blue "r"?

Do people soak it long or use other deucedly clever method?

Quote
I have one of those old sunlights (I think it is a "Philips HB 171/A" or similar to it) and just prop it up on something when I need it, I didn't feel the need for a proper box yet.

I have bunch of T5 small tubes, 20 cm long or so... Really would like to build a small enclosure a) To keep it safe between uses b) to make it as small as possible. I have way too much trash, treasures, thrashures.

Pekka

Offline awemawson

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Re: How do you do your PCBs?
« Reply #21 on: January 20, 2016, 03:03:17 AM »
When we were kids just after the war, Sunray lamp treatment was all the rage for pale under nourished children. We had a lethal lamp with a Mercury discharge tube shaped like a horse shoe, little red button on the back to press to start the discharge.

It stayed in a cupboard for years until I needed a uv source for exposing PCB art work. Only took seconds !

Now I have a proper Mega exposure unit with built in timer.
Andrew Mawson
East Sussex

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Re: How do you do your PCBs?
« Reply #22 on: January 20, 2016, 05:34:23 AM »
Unless it's a really simple, single sided design, I send the gerbers off to somewhere like Seeed and get them made.
Simple designs I route out on the CNC.

Offline tom osselton

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Re: How do you do your PCBs?
« Reply #23 on: January 20, 2016, 12:45:09 PM »
I have a flip top plate maker for printing presses it has a carbon arc with timer and vacum do you think this would work on the photopolymer paper?

Offline PK

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Re: How do you do your PCBs?
« Reply #24 on: January 21, 2016, 01:58:38 AM »
Made by Mega, it has a developer tank, etch tank and tin plating tank, with water rinsing slots in between making it all very convenient - has a handy sink built in as well.
We had one of those units for many years. We used Ferric Chloride etchant and ours didn't look much like that picture when we finally sold it. Before that we had one we made from glass. Before that we used one we built from PVC Sheet. Before that we had a little hobby one.....You get the idea..buy decent tanks ..

Our process was:
Inkjet print onto transparency (inkjets have better resolution)
Lay the top and bottom transparencies on piece of paper and align them, hold in place with tape.
Put double sided Kinsten board in and expose both sides in our DIY exposure box.
Etch,
CNC drill.

A word of caution. Making a double sided exposure box is a good idea. Making one with short wavelength tubes is VERY DUMB!  The lighting supplier sold me UV tubes used to sterilise water. Hand on my heart those lights were on for less than 5 seconds and I spent the nigh in emergency with sunburned corneas. I never knew my eyeballs could hurt that much!

The advent of the US$1 per board prototyping services out of china mean that we no longer do in house boards... It's just not worth it...

PK

Offline CrazyModder

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Re: How do you do your PCBs?
« Reply #25 on: January 21, 2016, 01:54:51 PM »
Yeah, looks like you used that tank commercially?

The methods outlined up there are certainly primarily for hobby purposes. If I find a timeslot somewhere between family and work, usually on late Saturday or Sunday, I want to make a smallish PCB right now and not wait for a delivery, no matter how fast or cheap it is. Also, often I notice something wrong with the layout only after the fact, and then it's no biggy to just go ahead and fix it right there and then, and do another run. ;)

Sure, if it's a bigger project with many ICs, vias etc., then a service will probably be the better choice.

Offline grg12

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Re: How do you do your PCBs?
« Reply #26 on: January 21, 2016, 02:55:23 PM »
LEDs emitting UV light with wavelength between 340nm 420nm work great with POSITIV-20 photoresist. I built a small (free version of Eagle sized :) ) lightbox using 168 of them and cheapest picture frame i could find (expensive ones have UV filter to preserve picture colors from fading). Laser-print on tracing paper (transparency foil tends to shrink during printing), then the print goes for a few minutes in jar filled with lacquer thinner vapours (cottonball with a drop of thinner) - this causes laser toner particles to expand a bit - the print has more "opacity" afterwards.

Offline awemawson

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Re: How do you do your PCBs?
« Reply #27 on: January 21, 2016, 03:13:42 PM »
This thread has encouraged me to plan to complete the 'air plumbing' to my CNC mill so not only can I then use my high speed air spindle to route PCBS, but also power the lock on my 4th Axis as well  :ddb:

Spindle is a simple jet of air impinging on a gear wheel and it spins at an enormous speed with the lubricated air emerging though the bearings to cool them, as they spin far faster than their upper design speed  :clap:

Involves a bit of swinging in the rafters so one for when I'm off light duties  :lol:
Andrew Mawson
East Sussex

Offline CrazyModder

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Re: How do you do your PCBs?
« Reply #28 on: January 21, 2016, 04:06:07 PM »
spin far faster than their upper design speed  :clap:

That's what we're here for, on MadModder!    :drool:

Offline PK

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Re: How do you do your PCBs?
« Reply #29 on: January 21, 2016, 06:16:27 PM »
Yeah, looks like you used that tank commercially?
I've mentioned it in other threads, its true we do commercial work. As such some of what I put up may not be relevant to the hobby user. We did however start out as, and continue to be, hobbyists. All those pictures were from my shed at home. At work we still apply the 'DIY or die' approach to building new machines and capability. We're very much of the same mind set.

In any case, feel free to ignore everything I say, just tell my wife you're doing it, she'll appreciate the company..

Specifically here, all of those tanks are appropriate for one off boards at home...

Quote
The methods outlined up there are certainly primarily for hobby purposes. If I find a timeslot somewhere between family and work, usually on late Saturday or Sunday, I want to make a smallish PCB right now and not wait for a delivery, no matter how fast or cheap it is. Also, often I notice something wrong with the layout only after the fact, and then it's no biggy to just go ahead and fix it right there and then, and do another run. ;)

Yes, I need it now! comes up every now and then. The problem with the etching is that the photo emulsions and chemicals have a limited shelf life (especially in the heat). If you are doing two boards a year then it can be difficult to get a good result.

When I get the 60KRPM spindle running at home I'm going to have a go at isolation routing.

Mostly though, because SMD is pretty much unavoidable now, the fact that commercial boards come with solder masks makes them pretty much the only choice..


Offline CrazyModder

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Re: How do you do your PCBs?
« Reply #30 on: January 22, 2016, 03:20:33 AM »
Nah, I don't want to ignore you, I just want your tanks!  :drool:

Wasn't intending to downtalk your solution - non-native speaker and all such.

Offline PekkaNF

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Re: How do you do your PCBs?
« Reply #31 on: January 22, 2016, 03:31:16 AM »
Thank you all very much. This has been most useful.

Hobby means very different things for most of us. And it all depends what we are doing :wave:

For me Traub and other machinery awemawson has looks pretty involved, but fits still into "hobby" category.

I also understand if a "hack" is enough for some.

I'm often somewhat in between, my background is electrical engineering, but never designed any of that for living. Still I have much respect to volts and amps. :zap:

I like much of the stuff that is professional/semiprofessional, even if I can't get the stuff. Often it is very nice to know alternative methods.

My motivation to PCB making is that I only make those assemblies I can't buy or does not exsist or needs combining some simple "stages" to get the end result. And I usually want it now. Therefore I like DIY PCBs even when they are crappy. I ahve manged to gobble something up, but SMD is a new challenge. There is a big danger that I will learn something.

I have made in past two sided PCBs, but only to solder trough components and no real vias. Plenty of jumpers. I have reached my limit and trying to take the next step.

I think I have seen writeups about the laminated solder masks same way than etch resists. Never tried one.

Is chemical tinning any alternative or addition to solder mask? Some fluxes seem to work differently even on kit boards.

Pekka

Offline awemawson

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Re: How do you do your PCBs?
« Reply #32 on: January 22, 2016, 04:16:17 AM »
Pekka, I use 'electroless tinning' - it really is very easy - the cleaned etched copper clad board is immersed in a warm solution:

https://www.megauk.com/tin-plating.php


As an aside my personal take on the professional /amateur discussion is this: If some one joins and pushes their commercial products and services solely for their own benefit then they are spammers and should be removed - that's not what the forum is about. However if someone active in any of the spheres we discuss and enjoy here chips in and offers advice, or points to one of their products that would solve a problem someone has, or a process that they use then surely we can only benefit  :scratch:

I'm sure that John Stevenson won't mind me quoting him as an example: he runs a commercial jobbing shop, is very knowledgeable regarding machining and CNC, and is involved with ArcEurotrade - one of our suppliers. His contributions to this and many other 'hobby' forums has been legion. I don't think that anyone here would want him to 'cease and desist'

Personally I've never made my living using any branch of mechanical engineering or CNC - it was always a hobby totally different from the industrial process control computers I earned my living looking after. Even before I retired I always would refuse to take payment for all those little jobs people bring you - no problem trading favours, but not actual payment, firstly as I didn't (and don't) want any local authority being able to claim I am 'commercial', and secondly I don't want the commercial and moral pressures of deadlines and specifications - after all, I do it 'cos I want to do it.


....... just my personal take, not necessarily Forum Policy - that's for Eric to set out.
Andrew Mawson
East Sussex

Offline CrazyModder

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Re: How do you do your PCBs?
« Reply #33 on: January 22, 2016, 04:39:13 AM »
I did not at all mean it in a derogative or "cease and desist" way. My comment with the unlucky word "commercial" in it should have read like this:

"You seem to have used these tanks in a professional way, they look much better than my randomly hacked diy tools."

Just to clear that up!

Offline PK

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Re: How do you do your PCBs?
« Reply #34 on: January 22, 2016, 04:59:33 AM »
:-) Looks like the missus is drinking alone tonight then.

The last board I etched was done in glass tray over a gas hob using ammonium persulphate.  I basically boil the solution with the board in it. I've used microwave ovens and her tupperware too.

Offline PekkaNF

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Re: How do you do your PCBs?
« Reply #35 on: January 24, 2016, 12:33:48 PM »
One more distraction: How does the vacuum system works on two sided UV PCB exposure unit?

I only have used method were PCB is slipped in a artwork and put between two glass plates.

I'm wondering how much stress vacuum creates on glass plates and is cheap 2 mm or 3 mm glass plaet enough for euro card size?

I have small quiet compressor that has vacuum inlet. Might consider vacuum. There must be some stuff I'm not aware of.

Would it be possibe to use exact same thickness (probably easiest to use even same PCB material) as a "frame" that has eurocard (100*160 mm) or such cutout for the PCB under construction. Maybe neoprene seal on perimeter to seal the artwork - or glass plate?

Pekka


Offline PK

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Re: How do you do your PCBs?
« Reply #36 on: January 24, 2016, 05:33:58 PM »
 :doh:
One more distraction: How does the vacuum system works on two sided UV PCB exposure unit?

I only have used method were PCB is slipped in a artwork and put between two glass plates.

I'm wondering how much stress vacuum creates on glass plates and is cheap 2 mm or 3 mm glass plaet enough for euro card size?

I have small quiet compressor that has vacuum inlet. Might consider vacuum. There must be some stuff I'm not aware of.
Vacuum is easily substituted with mass for the DIY case. You just need to hold the transparency onto the PCB. Holding it stupid hard doesn't (in my experience) make any difference.
The lid on my exposure box weighed maybe 6-7Kg. I used 5mm toughened glass, about 450mmx250mm. I recall supporting it at the ends with two bits of round bar and standing in the middle. Unbelievably strong stuff!
PK

Offline PekkaNF

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Re: How do you do your PCBs?
« Reply #37 on: January 25, 2016, 04:21:19 AM »
:doh:
One more distraction: How does the vacuum system works on two sided UV PCB exposure unit?

I only have used method were PCB is slipped in a artwork and put between two glass plates.

I'm wondering how much stress vacuum creates on glass plates and is cheap 2 mm or 3 mm glass plaet enough for euro card size?

I have small quiet compressor that has vacuum inlet. Might consider vacuum. There must be some stuff I'm not aware of.
Vacuum is easily substituted with mass for the DIY case. You just need to hold the transparency onto the PCB. Holding it stupid hard doesn't (in my experience) make any difference.
The lid on my exposure box weighed maybe 6-7Kg. I used 5mm toughened glass, about 450mmx250mm. I recall supporting it at the ends with two bits of round bar and standing in the middle. Unbelievably strong stuff!
PK

Jep. I just wonder:
* Previously I had trouble finding material that will not absorb UV (surpricingly many glass and PMMA sheets does..) and like to keep it thin. Found 2 mm picture frame glass, this does not take much load.
* Taking care to put "ink" side next to photoresis, hmmm. not extremely flat if loaded only on edges...
* Would like to expose it two sided - one go - putting books or weight lifters on top of it is not viable
* Plastic C-profile seems to clamp it good enough, might go for that.

Usually KISS is best, sometimes it just takes few tries to get there and boil it down to minimum. :lol:

Pekka

Offline PK

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Re: How do you do your PCBs?
« Reply #38 on: January 25, 2016, 05:15:51 AM »
Honestly?
You're overthinking it.
I ran 5mm glass and my exposure times were bang on for the wavelength (ie around 90 seconds) .
The plastic film and the copper layer crushes more than good glass bends.
That box that I showed a picture of (which had slotted mounts for the hinges BTW so the top plate of glass could always be parallel with the bottom) made hundreds and hundreds of boards with 10 mil tracks.
By all means, go buy special glass, vacuum pumps and dilthium crystals, it's fun to make these things as flash as you can (I'm serious, I really get it..).... but getting your dev/rinse/etch chemistry under control, or a temperature controlled storage box for chemicals and emulsion coated boards will have orders of magnitude more effect on the finished board than a few microns of gap between a film and a board.

Offline PekkaNF

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Re: How do you do your PCBs?
« Reply #39 on: January 25, 2016, 06:03:02 AM »
Ok. Thank you. My suspicion has a reason: Few years ago I bough 1 metre long 5 mm thick PMMA (acrylic) that was supposed to transparent to UV. It Blocked most of it. When I asked them to double check it with BIG LETTERS, I got the type an sure enough it had a filter added....they refused to deliver small amount "stadard" PMMA that would not filter UV, noobody-wants-it!. Then I bough some "good glass" and you may guess it. IT HAD UV FILTER TOO. Fool me once - well - fool me six times?

I put presensitized PCB and different "transparent" material on both sides and nothing in 10 mm space between the glass and PMMA. That way I figured that while 30 s exposure showed up almost good eneough without any "filter" 120 s was marginal on that first UV-transparent acrylic sheet I got and the "glass" need nearly same. I had cut the acrylic to size and I was in process of finishing the light box.

I'll build slap together 2 sided unit that assumes sandwich of max. 2-classes (2-3 mm), two transparencies and PCB of 0,6 - 1,5 mm + plastic C-profile to keep them clamped. If that doesn't work I'll take up on knitting.

Pekka

Offline PK

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Re: How do you do your PCBs?
« Reply #40 on: January 25, 2016, 08:42:42 AM »
If that doesn't work I'll take up on knitting.
Don't sell yourself short... there's always gardening!


I would never have thought that UV filters on glass would be a thing in your part of the world.... Actually, I've never heard of them applied to glass or perspex anywhere. Wow... Must remember that.

Back on topic. I'm sure you can get to a place that sells the right tubes.  Just in case the UV tubes also have UV filters on them, the tubes in 'bug zappers' work pretty well for smaller boxes..
PK

Offline PekkaNF

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Re: How do you do your PCBs?
« Reply #41 on: January 25, 2016, 09:55:16 AM »
If that doesn't work I'll take up on knitting.
Don't sell yourself short... there's always gardening!

Incidently, I like gardening, but it is under 20-35 cm of snow now. Garage is too cold for my complexion, therefore I'm confined indoors :lol:

I would never have thought that UV filters on glass would be a thing in your part of the world.... Actually, I've never heard of them applied to glass or perspex anywhere. Wow... Must remember that.

Back on topic. I'm sure you can get to a place that sells the right tubes.  Just in case the UV tubes also have UV filters on them, the tubes in 'bug zappers' work pretty well for smaller boxes..
PK
I know. Most of the winter I only see sun from outside...maybe the seller tried to be nice and sell me "the good stuff"?

I have some tubes: UVA lamppu 8W T5, philips Actinic BL
http://www.reichelt.de/Etching-Machines-Exposure-Equipment/UV-LAMPE-1/3/index.html?&ACTION=3&LA=2&ARTICLE=936&GROUPID=3376&artnr=UV-LAMPE+1

The acrylic turned out to be: PLEXIGLAS® XT 0A000 (20070)Standard solid sheet grade; largely UV-absorbing....Hmm. maybe I should make a light table out of that to filter rest of the residual UV that is left on yellow lamp :lol:

Pekka