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Old 25th Feb 2021, 10:27 am   #22
David G4EBT
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Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 4,475
Default Re: Dalo Pen replacement

Originally Posted by MrBungle View Post
Meant to update this seeing as I last posted in here in August, far too long ago. I've disposed of my etching stuff and chemicals now. I'm usually only building one-offs so it is way too much work to take on with limited time and messy to boot. Since the last post I've done two dead bug boards on FR4 and one in Kicad which was shipped off to JLCPCB. Feet up on the desk and read a book for a couple of weeks!
I'm with Mr Bungle on that and I think KiCad, Sprint etc is worth a thread in its own right.

Recently, two forum chums have got to grips with those programs and have each gifted me one of their first 'JLCPCB' PCBs based on PCBs I had an involvement in designing, but which needed converting to Gerber files (which I can't create) to have them made commercially. The PCBs cost just a pound or so and are works of art. Plated through holes, screen printed. I can attain a good standard of homebrew PCBs but they fall far short of JLCPCB ones and ironically probably cost me about a fiver for a 75mm square PCB and hours of work.

All for the sake of getting to grips with Sprint or KiCad.

JLCPCB aren't some little outfit down a back street. 800,000 customers in 170 countries and they turn out 20,000 PCBs a day. Quite why they want to bother with the likes of us is a mystery, but it's very much to our benefit that they do, at rock bottom prices and no minimum order value. Worth taking a tour of the factory:

As many will know if they've followed and of my 'Homebrew' threads over the years, I've been an avid homebrew PCB maker (for more than 50 years in fact). In the early days, when Dalo pens came along, I gave them a go, but had little success with them. Try as I might, the coating always proved too thin and though the tracks came out electrically sound, they were pockmarked with holes as though they'd been got at by woodworm. If I tried to apply a second coat, all if did was to dissolve the first layer, so I resorted to using Humbrol modelling paint instead.

Then back when magazines were full of constructional articles, and Practical Wireless was both 'practical' and about 'wireless' and had an eclectic range of other electronic projects (before it morphed into a Ham Radio mag which is neither practical nor about wireless), Veroboard came into vogue in the mid 60s. I was never very keen on it, but made countless projects with it, some quite complex.

Then magazines started to featured projects using PCBs, for which they provided the artwork, and a PCB service. Initially, I used to get a photocopy of the PCB, tape it over a piece of laminate, drill through all the holes, remove the paper and 'join the dots' with Alfac dry-print rub-down transfers, which have ceased production in recent years.

One technique I've often used, including in recent years, is to design or convert PCB layouts so they can be created by using a layer of sticky-backed plastic ('Fablon'). I stick it onto the laminate, glue a copy of the artwork onto the Fablon with a Pritt stick, then cut around the lines with a scalpel and rule, peeling away the waste. It has the merit of leaving lots of copper on the PCB which speeds up etching time, obviates 'undercutting' of tracks and pads, makes it easier to drill the holes and looks neat.

I've attached some examples showing the original artwork, and my conversion to the scalpel process to show what I mean.

In the late '70s there was an article in PE on how to make a UV light box, which I built. Initially I used pre-sensitised UV laminate with limited success. Hard to get the exposure right and the developer concentration. Either under exposed, or over exposed in which case the lacquer was washed clean off the board. Also, I was left with little useless offcuts of laminate. I then resorted to self-spray UV lacquer which I used with a good success rate, and if it failed, I could just clean the lacquer off the laminate and re-spray. Then along came negative resist UV dry film, which I've embraced with a vengeance.

In the early days, like many I guess, for the UV mask I used photocopied acetates from copy shops (Pronta Print et al - do they still exists?). Nowadays I use microporous film. Every stage of homebrew PCBs has to be spot on or failure ensues, and the surest way to fail is to use CAD software which isn't meant for DIY use (Thin tracks, small pads etc). I've ironed out all the wrinkles at each stage but it's a tortuous process, often taking longer to make a PCB than it takes to build the finished project.

The bottom line is that if I'd spent a fraction of the time I've spent doing this, getting to grips with Sprint or KiCad instead, I'd have save countless hours, and not a little expense. I need to re-direct my efforts - how hard can it be?

Examples of PCBs using the 'Fablon' technique:

Pic 1: Small regulated PCB - original layout converted to 'Fablon'.
Pic 2: Signal generator PCB.
Pic 3: An example of a section of a (poorly designed) PCB layout converted.
Pic 4: Two amplified loop antenna PCB layouts from Gary Tempest designed 'Manhattan' layouts.
Pic 5: A 'Cirkit' HF amateur radio 15 Watt HF transmitting linear amplifier.

Apologies for broadening the thread out from Dalo pen replacements, but it outlines all the alternatives I've used due to my lack of success using Dalo pens.

I hope it's of interest.
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