PCB etching, photoresist method questions - Page 1
Forum section: electronics / projects

author: Aryl
author_rank: Newbie
timestamp: January 18, 2015, 04:21:13 am
content: Made my first two attempts at using the photo method today, using a UV salon nail paint curing box as the light source.The first one turned out looking pretty good but unusable because some 16mil traces got eaten. I used two layers of transparency sheets as a mask, the sheets were printed out by a local print shop as dark as their machines would go.The second one I used three layers of transparency sheets, the board is usable but has some extreme pinholes compared to the first. No broken traces.I'm having some confusion as to why the second one had so much more pinholes.The first had two sheets, was exposed in 5 evenly spaced increments of 30 seconds each (It was supposed to be a test to figure out a good exposure time). When placed in the developer it was almost immediately developed, I only kept it in there for ten seconds or so.The second one I exposed for 20 seconds (The entire board) and took several minutes in the developer.The only explanation I can think of is that because I exposed it for less time and had to keep it in the developer for much longer the pinholes had time to completely develop with the rest of the board.Same transparencies used, same alignment on the first two, I just added a third.Pictures should be attached.I've been scouring the internet for helpful information, I thought it would be worth asking how successful people on here have been and if anyone has any tips on avoiding all this pinholing, I can't find any better laser printers to use.

author: sleemanj
author_rank: Super Contributor
timestamp: January 18, 2015, 07:36:40 am
content: Pre-sensitised, dry film, spray on, paint on, positive, negative... ie, what type of resist?What type of developer?

author: Aryl
author_rank: Newbie
timestamp: January 18, 2015, 07:58:01 am
content: Presensitized positive MG Chemicals boards, MG chemicals 418 positive developer. According to the MSDS it's just sodium hydroxide.I'm thinking this is just over etching as the board looked flawless after developing, but I only kept it in the etchant (Ferric Chloride) until the copper on the inside of the circle was dissolved. It was agitated the entire time, I was constantly brushing it with a plastic bristled paintbrush while it was submerged.

author: sleemanj
author_rank: Super Contributor
timestamp: January 18, 2015, 08:23:59 am
content: Quote from: Aryl on January 18, 2015, 07:58:01 amThis thread may help:https://www.eevblog.com/forum/beginners/my-first-try-at-making-a-pcb/

author: wraper
author_rank: Unknown
timestamp: January 18, 2015, 03:13:49 pm
content: Quote from: Aryl on January 18, 2015, 07:58:01 amVery typical result. To develop with NaCl you need photomask with very dense blacks and precise exposure time. If blacks are not very dense, right exposure time becomes very tricky. Also you needVERYtight developer concentration and temperature control. Better use Negative photoresist or use silicate based developer for positive photoresist.Read developing part here:http://www.electricstuff.co.uk/pcbs.html

author: homebrew
author_rank: Frequent Contributor
timestamp: January 18, 2015, 06:48:00 pm
content: Just my 2 cents as a hobbyist ...I did a lot of boards myself and for some time I had access to a professional UV exposure unit. I always ended up with results like yours, because I couldn't produce "films" that were "black" enough in the UV spectrum.What I ended up with was a 500W Halogen Flood lamp, mounted 40cm above the PCB. And I used two transparencies on top of each other, both ink-side down and a thin glass on top of it to hold everything down ...Yeah, this setup is very unprofessional in every aspect: Wrong peak wavelength, a (crazy) lot of heat, quite long exposure times (8-10min) etc. etc. but it always gave me near perfect results ...I used standard Bungard FR4 material and NaOH as a developing agent.But anyway, I completely stopped etching my own boards because of the hazards (got a small splash Fe3Cl in one eye - luckily just painful but without injury), the problematic heavy metal waste and all the obstacles of doing proper two-layer layouts with alignment, drilling and vias, solder-mask ...You can now get a professionally made PCB (100x160) for around 50 EUR (or even cheaper) ... but yes, it takes a week or two ...Happy etching!

author: Aryl
author_rank: Newbie
timestamp: January 19, 2015, 03:44:12 am
content: Thanks for the advice everyone, found my problem, it was over etching due to not agitating the board enough. It was just eating through the resist.This time I bought some foam brushes, scrubbed at the area to be removed for the entire time it took to etch, focusing on the area around the traces first. I also heated up the etchant with boiling water and changed the exposure time to one minute.It's as perfect as I could have ever hoped for. A handful of pinholes in the ground plane, but that doesn't matter. The traces are perfect, the logo I designed came out better than expected...this is really cool. It's a huge leap from messes of wires on a breadboard.

author: Unknown
author_rank: Unknown
timestamp: January 19, 2015, 05:09:40 am
content: Quote from: Aryl on January 19, 2015, 03:44:12 amThat's not normal, particularly with MG Chemicals board. In my experience it's damn near impossible to overexpose or over-develop (though I think that's exactly what's happened), and I've never seen the resist etched through. I might believe it if it were something like Kinsten, which (again, IME) is softer and easier to overexpose/over-develop.Your first couple of results look like what you get from using inkjet-printed transparencies or a laser that really needs its drum replaced, coupled with overexposure. And while scrubbing certainly speeds up etching, I've never needed to do it with MG Chemicals board; gently rocking the tray is enough.I think you've stumbled on a way of balancing out the problems, rather than something reliable. My guess is the real problems are (a) poor quality mask, and (b) gross overexposure from way too high light intensity at the board surface.Does your UV curer use lamps or LEDs? What sort of printer was used for the transparencies? Did you use glass or something to sandwich the transparency printed side down to the board?I'd try (a) getting a decent laser print on good tracing paper, and (b) increasing the distance between light source and board - a good 2"-3" inches at least.FWIW, I use a single layer of laser printed transparency paper (Brother HL-2270, Sihl 'Utoplex' tracing paper). 12-16 thou is easy with MG board, and 8-10 thou is reliably possible with a bit of care.

author: kolbep
author_rank: Frequent Contributor
timestamp: January 19, 2015, 05:21:19 am
content: Well done.Now, the question we all really want to know,What is it?

author: Aryl
author_rank: Newbie
timestamp: January 19, 2015, 06:43:05 am
content: I'll try moving the lightsource further away, it's about an inch or so away, less along the edges. The bulbs are fluorescent, two at the top and two angled on the sides, I'm using this, it has 4 9-watt bulbs:http://www.amazon.com/Salon-Edge-Acrylic-Shellac-Curing/dp/B006QO4BRMthe board is sandwiched to the transparencies with glass, I'm using a 5 x 7 picture frame with a spring loaded cardboard back so it keeps them sandwiched pretty well. The transparencies are pretty good, with three stacked I can only see one small speck of light on the ground plane when held up to a bright light source. They were printed by a local printshop on laser printers.The board looks perfect after developing, it's only near the end of etching that the pinhoels/pitting happens.Quote from: kolbep on January 19, 2015, 05:21:19 amHah, get ready for a bit of a read.I designed and am trying to make a new instrument cluster for my car (1986 Saab 900), making all the gauges and everything myself so it fits in the stock housing.This board is the front of the tachometer, the outer ring holds 24 WS2812B RGB LEDs (Adafruit Neopixels), the inner has 16 for either a clock or boost/vac gauge, have not decided yet. The other pads near the leds are for 0805 decoupling capacitors.Each gauge was designed to have a small AVR powering it so I can change their function whenever I wish, all the gauges communicate via i2c to a "master" atmega328 hooked to a 20x4 LCD screen so I can have exact readings from sensors.Each gauge is made of a "stack" that plugs into eachother, so it's somewhat modular and if I want to change something I don't have to redesign the whole thing, just one of the three plates. First plate is the display portion, second is the AVR, oscillator, ISP header and the third is the input.For the tachometer the input plate consists of an R/C filter, optocoupler, schmitt trigger and a few other components to convert the 12v NOISY square wave into a clean 5v signal to trigger an interrupt on the AVR.I figured it would be a good first real project. Not dead simple, but complicated enough that it's still a challenge. I've had to learn quite a bit to get it all to work, totally worth it.

author: Fred27
author_rank: Unknown
timestamp: January 19, 2015, 10:25:29 am
content: I'd definitely recommend a silicate based developer. I also use the same sort of nail lamp. I removed the two side bulbs to reduce the risk of light getting under the transparency and it still work well.I get great result using a Canon MG5250 inkjet printer for the transparencies in T-shirt printing mode. It gives really thick coverage and also automatically mirrors it.Another recommendation - Ziplock vacuum food bags to hold the transparency down tight against the PCB.http://0xfred.wordpress.com/2014/02/28/further-pcb-improvements/

author: kolbep
author_rank: Frequent Contributor
timestamp: January 19, 2015, 12:43:20 pm
content: Thanks for the info.It sounds like a great project

author: poorchava
author_rank: Super Contributor
timestamp: January 20, 2015, 06:59:45 am
content: Dry film is also nice, but can be a bitch to apply so that there are no air bubbles trapped underneath.You can enchance your laserjetted exposure masks by putting a teaspoon of acetone or a nitro thinner into a jar, hanging the mask on a string, closing the lid and heating the jar A LITTLE BIT (so that it feels warm to the touch). Solvent vapors will be absorbed by plastic particles in the toner making them sticky, but also swell a little which causes the black to become almost completly opaque.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 20, 2015, 11:06:41 am
content: +1 for silicate developerUse thick tracing paper, not transparency film.

author: poorchava
author_rank: Super Contributor
timestamp: January 20, 2015, 11:15:47 am
content: Yep, transparency likes to shrink a little bit form the heat when fusing the toner. That amount of shrinkage is not a problem for slideshows and such, but can be a killer when doing PCBs, especially if you're using finer pitch stuff (like 0.5mm QFPs and SOPs)

author: ElektroQuark
author_rank: Unknown
timestamp: January 20, 2015, 11:16:34 am
content: CAS number for the silicate developer?Maybe I will try it.

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: January 20, 2015, 12:05:12 pm
content: Using direct laser print transfer is much easier than using UV light boxes, I've made several boards in recent months using shiny paper (eBay item 261640812271) which costs less than 12 GB pounds for 100 A4 sheets delivered, and an ordinary clothes iron to transfer the toner. My laser printer is a Samsung M2020, which was one of the cheapest I could find. Laser toner is very resistant to warm ferric chloride, acetone removes it afterwards. Don't forget to print your tracks as a mirror image and to print on the shiny side of the paper...For a quick try, you can print onto glossy inkjet photo paper with a laser printer. You will find it needs soaking off in water then quite a bit of rubbing with a finger under a running tap to remove all the paper residue. With the special paper, it just peels off and needs no washing. However, I have used glossy photo paper with perfect results on SMD boards down to 0805 sized parts.Double sided boards with tracks on both sides are possible, although for the most part I use SMD boards which are single sided or double with just an earth plane and a handful of wire links through for ground connections.

author: madires
author_rank: Super Contributor
timestamp: January 20, 2015, 12:23:59 pm
content: Quote from: homebrew on January 18, 2015, 06:48:00 pmTake tracing paper (90-95 g/m²), print layout with a laser printer (disable toner save mode) and use something like CRC Solvent 50 (less expensive than special toner sprays) to get a nice solid black.

author: Aryl
author_rank: Newbie
timestamp: January 21, 2015, 12:50:13 am
content: I'll try some tracing paper for the next board. Surface mount soldering sure is a lot easier than I thought it would be, probably helps I ditched my old firestarter iron for a new hakko 591. This has got to be the nicest tool I've ever owned.First try, and it all works

author: Unknown
author_rank: Unknown
timestamp: January 21, 2015, 12:52:43 am
content: Quote from: Solder_Junkie on January 20, 2015, 12:05:12 pmEach to their own, but I'd disagree. I use both, but with UV & presensitised board it's (usually) easier to get the process right initially (& it's more consistent when you do), no need to retouch tracks when the toner fails to stick, no scrubbing to clean the board beforehand or remove the resist afterwards, and I can go from hitting "Print" to having a ready-to-solder board in my hand in 10 minutes.The biggest downside is cost - decent +ve resist board costs ~50% more than blank PCB.

author: ElektroQuark
author_rank: Unknown
timestamp: January 26, 2015, 09:28:26 pm
content: Quote from: EdoNork on January 20, 2015, 11:16:34 amAnyone?

author: akis
author_rank: Frequent Contributor
timestamp: January 26, 2015, 09:56:12 pm
content: I use tracing paper, over 100gsm, like thishttp://www.amazon.co.uk/gp/product/B009LHXTX8?psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00It does not crease too much in the laser printer, and most of the times the toner sticks to it fine.Large areas of black are a problem. I have tried placing two transparencies on the UV box, but aligning them is very hard.You must experiment with your UV box and the proper exposure time for the type of transparency, the type of the board, the UV box etc. Mine is like 7 mins.A very important factor is the UV box temperature. As it warms up it gets stronger so for example when I say "7 mins" I mean with pre-warmed up UV box (2-3 mins at least and immediately before exposure).Doing two sided is the same issue - if you get one side different to the other, it's probably the UV box being warmer on the second side!Development is extremely temperature sensitive, I use a warm water bath to keep the developer at a constant 24C-25C and depending on its strength it takes about 45-90 seconds with vigorous agitation throughout.I etch using ammonium persulphate, so I can splash it everywhere (not intentionally) without worries. It will not eat through the resist. It is quite slow though, and must be kept at 55C (so I use a hot water bath for it). But it is safe and etches really well.

author: Michal_S
author_rank: Contributor
timestamp: January 26, 2015, 10:44:56 pm
content: I use SENO 4007 developer (don't know it contents, but it doesn't contain NaOH). Used NaOH earlier, and it was extremely difficult to get it right, even using laboratory scale, for example it often was to strong and ruined the board immediately. With SENO 4007 I get consistent results with no worries.

author: george graves
author_rank: Super Contributor
timestamp: January 26, 2015, 11:16:52 pm
content: Quote from: poorchava on January 20, 2015, 11:15:47 amI get a small amount of shrinkage with the toner transfer method. Not sure at what point it's happening at. But a 10 pin header will be ever so slightly too small. Someday I'll figure it out and compensate for it.

author: tautech
author_rank: Super Contributor
timestamp: January 26, 2015, 11:42:53 pm
content: Quote from: george graves on January 26, 2015, 11:16:52 pmYour paper is shrinking when passing through your printer.Print to plain paper first, then stick your cut to size tranfer paper over the image and print again.That should fix or reduce the problem for all but big PCB's.

author: george graves
author_rank: Super Contributor
timestamp: January 27, 2015, 05:54:02 am
content: I think I'm just going to print to a PDF. Import that into illustrator, and scale it there once I measure the fudge factor.

author: ElektroQuark
author_rank: Unknown
timestamp: January 27, 2015, 07:53:38 am
content: Quote from: Michal_S onTodayat 10:44:56 AMThank you.It's sodium metasilicate. CAS number 6834-92-0.I have searched for SENO 4007 material safety datasheets and some of then has the wrong CAS number.The manufacturer info shows the composition, sodium metasilicate.

author: Siwastaja
author_rank: Super Contributor
timestamp: January 27, 2015, 08:48:37 pm
content: Negative dry film photoresist (Dupont Riston, sold on Ebay, for example). This is the stuff used in PCB industry. Can be laminated using a standard office laminator. With a good printer, point UV source, 18µm (½oz) copper clad and heavily bubbled etching bath, I have no problem whatsoever dealing with 8mil/8mil tracks/clearances on a regular basis (went succesfully down to 4/4 for testing). But the main point is the robustness and high yield. I don't want to spend hours redoing stuff and fixing broken traces. YMMV however, and I have seen people enjoying all kind of other processes which they claim usable but then spend time fixing things and generally accepting lower quality.This stuff has quite a bit of tolerance for differences in exposure. It's still important, but not overly critical. Most importantly, the process is quite robust; once you nail it down, your yield is near to 100%. This is because the photoresist film is extremely uniform, and because you can detect any dust spotsbeforeimaging and etching and thus can strip&relaminate if you find a dust speckle (which doesn't happen too often because the film has two protective films that are removed just before lamination and development). I never had such success ratios with spray type positive photoresist, but OTOH I was using NaOH developer which was very tricky; maybe the silicate would have worked better. I think my yield went from about 60% to 98% when I converted, but OTOH I had quite a strict criteria for success (which is exactly why I had to find something that really works).You still want proper, solid blacks in your mask film, but nothing super special really. A good inkjet printer works. And, this is the greatest thing in negative dry film photoresist: the development uses standard washing soda (sodium carbonate) and is extremely robust against differences in concentration, temperature and time. It's almost impossible to overdevelop negative dry film, or to mix the developer wrong. The film is also sturdy and you can speed up development and clear tightly packed areas using a toothbrush. It's typically something like 2 minutes at 30-35 deg.C with a little bit of brushing but you can double or triple that time no problem whatsoever if you are unsure. So yeah, dry film photoresist, go for it. It's not that expensive either. Just give it a shot, you may like it. Sometimes The Real Industry Thing also happens to work for a hobbyist.

author: dreggory
author_rank: Newbie
timestamp: February 11, 2015, 01:08:40 am
content: I have been thinking about using CLR Grease magnet as a silicate based developer, it contains the same "Sodium metasilicate - pentahydrate" that all the other "silicate based" developers have in common, although I'm not sure about the Alcohols C9 – 11, Ethoxylated that is listed as the only other ingredient in the MSDS.http://www.jelmar.com/msds/2014/GM-CH12215_Zero_VOC_RTU_Degreaser.pdfI would like to experiment though and see. does anyone know if this works/would work?I also like that the MSDS shows that it is a low health risk.

author: deanclaxton
author_rank: Regular Contributor
timestamp: February 13, 2015, 06:42:47 am
content: Hi all - I'm new here (1st post!) and would like to ask some advice on the whole DIY PCB process. I'm just getting back into electronics and I'd like to be able to quickly produce good quality (not sure yet on how I measure this - track width I guess) pcb's for prototyping before sending the board files off to be professionally made. I'm hoping to be able to have a board within an hour or two, which will help reduce the number of professional "spins" of the board till I get it right.First up, I've inherited a Kinsten double side UV exposure cabinet so I think I will be going the way of photographic transfer rather than the toner transfer method (which I did consider but don't have a laminator and it seemed difficult to find info on which laminator will pass a 1.6mm pcb through it). I also inherited a small PCB drill stand and pcb drill (RS branded drill stand). For cutting of bare pcb stock (or trimming of final boards) I've ordered from eBay a metal shear that will apparently cut 6mm steel bar (fingers clear!) - should be good for pcb work!My research so far has produced the following list of required items for the process :Film for printing positive layout - research has me picking up a block of Sihl Utoplex 90-95gsm tracing paper from Officeworks (http://www.officeworks.com.au/shop/officeworks/sihl-a4-tracing-paper-pad-90gsm-ja0036186)Blank PCB's with positive resist - Kinsten brand?? I'm not sure on the best source in Australia for positive photo resist boards in single and double sidedUV cabinet (tick!)Positive Photoresist Developer - research has pointed me in the direction of Sodium Metasilicate solution which is (apparently) fast acting with long shelf life and reusable (questions on this later)Etch Tank (tick!) - picked up a new-in-packet Altronics vertical etch tank with bubbler from Gumtree (cheap and cheerful)Etch Solution - research has me looking to use Hydrogen Peroxide + Hydrochloric acid - again fast and reusableCleaner for removing photoresist from etched boards - not sure on this one - acetone?Soldermask (if used ) - there seems to be some pots of UV activated soldermask paint on eBay - not sure how well this works or how to apply with even thickness?Tin Plating - tempted to do this to stop pads oxidising if not assembled immediately - if not using soldermask then I'd do the whole board - not sure on cheap source of solutionPCB cutter (tick!)PCB Drill (tick! - although I will need a supply of carbide bits)I think that will do it, so there are a number of items on the list I'm not sure of - mostly chemicals and sources of them.In regard to the developer solution, my googling turned up brewers detergent - a sodium metasilicate powder which is dissolved in water and used to clean brewing gear - would this work as a developer solution? It seems a lot cheaper ($8 for 500g) than a branded metasilicate developer from RS for example ($35 + gst for 500g).I'm very keen to get your feedback on the materials I plan to use, and any recommended sources in Australia (or elsewhere). I should also point out that I havent etched a pcb for 24 years so for all intent and purpose I'm starting from zero.Cheers!

author: Unknown
author_rank: Unknown
timestamp: February 13, 2015, 07:09:08 am
content: My only comments would be thatI've found Kinstenreallyeasy to overexpose, anddon't be surprised if your metal shear crazes, delaminates, or otherwise damages the presensitised coating within a cm or so of the cut.To remove the photoresist afterwards, I've always left it in the sun or under the UV light for 10 mins then run it through the previously-used developer again...

author: tautech
author_rank: Super Contributor
timestamp: February 13, 2015, 07:57:24 am
content: Welcome to the forumYour hope of an hour or two for expose, etch and drill is quite achievable IMO.For protection against oxidisation need not be plating for a prototype IMO.I use a Jaycar spray on PCB laquer. Cat NA-1002Keeps PCB's clean for months and easily solder through.Haven't tried it with reflow.Toner transfer and domestic Rexel laminator works fine for me.But I don't go below 15 thou tracks.HCL & peroxide works great, just don't expect the SAME etch times each time.Vertical bubbler tank is the way to go, with a lift out carrier to check progress frequently.I've not bothered with Carbide drills, HSS works OK if you are only doing a few.Dremel here, on slow-medium speed.Keep the hole pad hole sizes small to help centering of the drill bit.

author: sleemanj
author_rank: Super Contributor
timestamp: February 13, 2015, 08:37:36 am
content: Soldermask ink/paint is a pig to work with, really not worth the hassle, for reasonable results you'll need an air compressor and spray gun, and an oven capable of maintaining a low temperature like 100'c to "pre-dry" it (too hot and it no longer exposes, too cold and it never tack dries).

author: Fred27
author_rank: Unknown
timestamp: February 13, 2015, 10:05:00 am
content: Some opinions from my experience:Boards: Nice results with Bungard ones. Not tried Kinsten.Soldermask: Dynamask 500 works well. Needs a laminator though.http://www.instructables.com/id/Dry-Film-Solder-Mask/for all the details.Etchant: Some people rave about HCl (normally the same people who think toner transfer and Arduino shields are the pinnacle of PCB manufacturing). There are lots of downsides like the fumes will rust the tools in your lab. IMO Ferric Chloride is less nasty. Both will work though.Developer: Metasilicate based developer is so much more forgiving than the other one (sodium hydroxide? can't remember).Tin plating: definitely worth it. I will re -expose and re-develop the board (as Tac Eht Xilef does), the wipe with acetone and then immediately tin plate. Only make a small amount of the plating solution if you don't make many boars. It goes off quite quickly.Other: Ziplock vacuum food bags are great for pressing down your transparency on the PCB.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 13, 2015, 10:41:28 am
content: Quote from: deanclaxton on February 13, 2015, 06:42:47 amA better metric would be reliability and robustness against process deviations; finally, the yield. I managed to get high resolution out of piss poor processes such as spray-type positive photoresist (POSITIV 20 brand) and NaOH developer, but the yield was poor. Of course, by sacrificing resolution, the yield goes up, but not as much as you would like, so the right choice is to go for a process that works. As a side effect, it will work with small tracks/clearances, too. Again; dry film photoresist is the only process I have found really usable. It also supports the tenting process for through-hole plated boards if you ever need that (I didn't have that plan when I switched to dry film, but it came later). That's impossible with positive spray-type or pre-sensitized pcb's.QuoteThis is an extremely important point. I can make an almost production quality (8 mil/8 mil, almost 100% yield) pcb in just 2 hours, for almost free. It enables a completely different flow of prototyping compared to breadboards or production prototypes.QuoteI have used one. These are fine if:a) the vacuum table is working perfectly - the diffuse nature of light ruins the resolution if there is even a slight gap between the film and the pcbb) the UV tubes are in good condition - those wear off more quickly you would like, and you need to track the exposure manually.I ended up building my own using a 20W UV LED from the distance of about 40 cm, which gives a nice point light source, enabling high resolutions and giving more robustness against any distance between the pcb and artwork. The exposure time is about 5 minutes per side.QuoteYeah, life is too short on playing with toner transfer kludges, but you'll need a laminator anyway if you're going to go the real way with dry film photoresist. Any standard office laminator should work. I use a cheapest no-brand grocery store product.QuoteBubbling is indeed very important for high resolution work (without that, traces change their widths based on other stuff near them). And, bubbling should be as strong as possible. We have a proper compressed air line running here so I built a very powerful bubbler using that, but any bubbling is much better than nothing.QuoteGoogle instructions for cupric chloride process; it's HCl + H2O2 as you say, but you slowly convert to cupric chloride simply by not pouring the "waste" out but reusing it, adding a bit of new HCl (and H2O2) every time. You will see that you can slowly bring the H2O2 level down and finally eliminate it completely as cupric chloride takes over. This is the greatest thing since sliced bread. Formerly, we had problems getting new supplies (laziness, mostly). Now, we have had a totally uncontrolled etching tank with NOTHING added in whole TWO YEARS, and still running great; the etching time has increased from 10 minutes to 17 minutes because no one has added any new acid (as we should twice a year or so), but it still works and the amount of PCBs produced with this tank is running in hundreds.QuoteWe used tin plating solution and it was a nice little thing, but the solution went bad as quickly as in about 1 month. It was a huge monetary loss because of that.

author: Howardlong
author_rank: Super Contributor
timestamp: February 13, 2015, 10:53:56 am
content: Although I've been making my boards for some time, it's not every week, but I do it frequently enough that I appreciate being able to do it at home. Mostly it's for unit testing RF or other high speed stuff, or SMPS boards, and usually only a couple of square inches maximum. They tend to be designs requiring specific layouts not achievable by hand wiring. Almost universally I use surface mount parts, drilling is a PITA!Almost all of my artwork is etched single sided only, but done on double sided board, using the underside as a ground plane and using rivets for through hole connections. For the odd connection that would be needed for double-sided, I drill the vias, then do a small countersink in the ground plane and hand wire accordingly usually with wire wrap wire.When designing the boards I generally leave as much copper on the board as I can within reason. This is good practice anyway for high speed stuff, but it also saves you having to frequently renew your ferric chloride solution. The downside is that it will create potentially large areas of black toner on the film, which some laser printers may struggle to properly cover.My process, although I wasn't aware of it when I came up with it, closely follows Mike's herehttp://www.electricstuff.co.uk/pcbs.htmlI have the following:o 8" shear - megauk.com 700-400o Mini drill press - megauk.com 700-307o UV exposure box with timer - Megauk.com 300-001o Photo resist solution - Megauk.com 600-010o Ferric chloride solution - maplin WF10L (yes, really!)o Resist strip solutiono Plastic tweezerso CIF pre-sensitised FR4 in 0.4, 0.8 and 1.6mm double sided - ABC16, ABB16, AB16o Through hole rivets - megauk.com 700-025-4o HP Laserjet 1320o Laserstar film - Megauk.com 100-063I use sealable takeaway plastic containers for the chemicals. The ferric chloride is pre-mixed, saves you accidentally dropping a little grain into your stainless steel sink and turning it into a sieve - been there, done that, wife was not happy. I did have some bubble tanks but I never use them, waste of time money and effort if you're only making the odd board. I do all the work in the plastic containers.It will take quite a number of sessions to get your process right, you need to be patient and accept that you will fail, but once you have a process you will attain a pretty good yield. I can consistently do 0.4mm pitch and 6mil track and gap, but design to less demanding specs when possible, which is most of the time, no use busting a gut when you don't have to. I did once successfully do a BGA but I don't recommend it, without a solder mask you are largely pissing in the wind.For the film, which is like tracing paper, cut it as small as you can for the PCB and as small as the printer will accept to avoid wastage before printing. You can re-print on film that's already been through the printer, but there may well be some crap on the film from the previous run through which will degrade the transparency, so try to remember to pre-cut the film first before printing. Also print at as high resolution as you can. I use 1200dpi, the 300dpi default is not enough for the fine pitch stuff I do. I had to fiddle with the driver for my printer to make it accept the higher resolution. Print the top layer in mirror, and place the toner covered side of the film directly onto the presensitised copper.I warm up the UV exposure box for a couple of minutes first, then I put the film down onto the glass toner side up, and expose one side of the CIF presensitised board for 2.5 minutes. The other side (ground plane) I leave the self adhesive covering on until the resist strip. You will be able to see the yellowing of the board where the UV has done its stuff. It won't be hugely clear, but it should be visible.With the photoresist solution, once I've made some up I tend to use it for months and months before changing it, mostly because I have figured out the process with that batch, and trying to fiddle around with the solution will inevitably change the expected timings. However, it's as much to do with what you see with your eyes rather than how long it's swished about for. There needs to be a very clear definition on the board between the area that's staying (black) and the copper that's being removed.I put the ferric chloride solution in its plastic takeaway container in the microwave for about 40s, with the lid ajar, prior to use. I am sure it is not the recommended thing to do, but it works.After a few minutes of swishing the board about in the ferric chloride solution, it will be ready. I generally do a fair amount of swishing about holding the board with the tweezers, or, if I remember, drill a small hole in the board and put some plastic covered wire through the hole to make it easy to fish the board out and agitate it. If nothing else it gives you something to do while you wait for the board to etch. Don't be to afraid of taking it out occasionally, do a short rinse in a plastic takeaway container of water, and look under an illuminated magnifier. You can always put it back into the ferric chloride solution again as necessary.Then after thorough rinsing, I remove the remaining self adhesive covering on the ground plane side of the board and put it into the resist for a bit of further agitation for a few seconds, followed by wiping off the resist with some kitchen towel.I don't bother with tinning, I can't see the point for a prototype board that you're going to solder to right away.For the 0.4mm via rivets, I use 0.7mm drills. 0.6mm seems to be too tight a fit. The rivet mechanical press that mega do is a waste of time, the GBP100 tool for the GBP270 press will break after about two rivets. A steady hand, tweezers and a soldering iron are the best tools to the job.For vias where I use wire wrap wire, I use 0.5mm drills.I can usually turn around a board in half an hour.My best bit of advice is to always use the same raw materials and process once you have got it right. I had a lot of trouble with some presensitised boards from Mega (I'd bought about 25 of 400-034-1), it was as if the copper was not uniform thickness, I would get regular lines across the board every couple of mm or so where the copper wasn't dissolving as much as other adjacent areas. I assumed it was my laser printer until I tried the CIF boards where I never have the problem.Another way to keep consistency is to use premade solutions where possible rather than trying to dissolve your own. In my mind mixing your own is another reason to fail, and you have enough variables going on as it is.Regretfully, unless you are really very special, you will fail! But be patient, this is an experience thing, write down the timings that work for you, and note down your process. After a number of attempts (and probably some mild depression) your yield will improve, to the extent where you'll wonder what all the fuss was about.

author: deanclaxton
author_rank: Regular Contributor
timestamp: February 13, 2015, 11:55:25 pm
content: Thank you everyone - I can see already what an amazing resource this forum is!Lots of tips and tricks and things for me to investigate and research further. I'm now curious as to the use of dry film resist versus pre-sensitised boards. Is the same developer used etc?On that, has anyone tried the "brewers detergent" sodium metasilicate? Example here :http://www.ibrew.com.au/products/brewers-detergentIt sounds like I'm generally on the right track though. Many thanks again for your feedback - it is very much appreciated.

author: nadona
author_rank: Regular Contributor
timestamp: February 15, 2015, 03:23:04 am
content: Quote from: Fred27 on January 19, 2015, 10:25:29 amNice blog!

author: Scottjd
author_rank: Frequent Contributor
timestamp: April 15, 2017, 12:20:16 pm
content: So I'm giving this a try and bought the Samsung M2020. I never thought I would see the day of a laser printer under $100. Their was actually two others laser printers cheaper then the Samsung one, but also over twice the size and space in the lab is tight. Besides people have had success with this printer.My question to you is what setting are you using with your M2020?Do you increase the toner layer thickness in the web GUI settings?Thanks,Scott

author: madires
author_rank: Super Contributor
timestamp: April 15, 2017, 12:41:54 pm
content: In most cases disabling the toner Eco mode helps with large areas like a ground plane. It depends also on the toner and the paper. I'd try different settings to find the best result. If large black areas are still spotty you can use a toner enhancer spray. I use a label remover spray instead and it works quite well also, while being much cheaper.

author: David Chamberlain
author_rank: Frequent Contributor
timestamp: April 17, 2017, 11:00:19 pm
content: My first boards where made with positive photo resist prefabs from Dick Smith (stock developer and ferric chloride). I would go to the local library to print my designs on acetate, taking care to purchase the variety that would not melt in the photocopier. I was gifted a halogen desk-lamp that had a protective glass filter that I would just remove when I wanted to do an exposure. It worked well.I do remember passing the acetate through the printer a few times and setting the contrast to maximum to get a good black. Eventually I was able to do decent double sided boards.Regarding the exposure time - and this comes from having experience in a B&W photographic developing lab - just expose a test board with what ever light you have. Every minute move a mask (like a hard board) 1cm. This will give you exposure time gradients that you can use to judge the best time for your lamp.