I think we all hate how oxidized homemade PCB's get over time, and I also think we all love how easier it gets to solder SMD parts when you have a soldermask.
I myself tried to find a source for low quantities of soldermasking ink, better if photosensitive or UV curable, but I was unsuccesful. All I could find were buckets of the pro stuff for €€€,€€ in strange distributors.
Until I found this:
http://cgi.ebay.com/UV-Curable-Solder-M ... 2eb527251d (http://cgi.ebay.com/UV-Curable-Solder-Mask-PCB-Repairing-Paint-Green-New-/200607737117?pt=LH_DefaultDomain_0&hash=item2eb527251d)
I found it like a year ago, and I thought I had to give it a try. Bough a syringe and... my life has changed since then. Once you know how to use this stuff properly, your homemade PCB's will never look the same.
It's a bit hard to learn how to use that stuff, however.
The recommended way to apply it is to squeeze some drops in the centre of the PCB, cover it with a plastic film and extend the product with a squeegee all over the board forming a thin layer. But there is a problem: this stuff sticks to nylon, acetate and polyamides, so you can't use transparency films with the photolite already printed on them, because you'll mess up the board, so I'll tell you how I apply it.
The first thing you must find is a sheet of any thin but still quite rigid plastic. It must be as thin as possible but it must NOT form wrinkles, and be as smooth as possible. And it also must not stick to the stuff. Seems easy to find such plastics, but it isn't. I get mine from paper sheet packages. When you buy 500 sheet packs, they usually come wrapped in a kind of plastic that is just perfect for this job. You have to remove the prints from the plastic, I do it cleaning the plastic sheet with common ethil alcohol, until it's totally clear and transparent. Don't worry, plastic sheets are reusable and you won't have to buy a new 500 sheet pack every time you want to make a board.
Then, I apply a few drops of the product to the board, I put the plastic sheet on top and I extend the product all over the board with a plastic squeegee . The layer of product must be thin. If it looks too green then it's probably too thick. Once I have all the board covered with the product as uniformly as I can (a sandwich of board, layer of product and plastic sheet), I place the transparency film with the mask printed on top of the stack, and I align it with the board. Then I sandwich everything between two layers of glass and insolate the board for about 30 minutes with a 8 watt blacklight tube. Once it's done, the stuff that has been exposed to UV light will be hardened and stuck to the board, while the stuff that was covered by the mask will still be liquid. I peel off the plastic sheet that shouldn't be stuck to the ink (the plastic sheet shoudn't have rests of hardened ink attached), and the liquid ink that remains in the board can be easily removed wiping it with a towel and some alcohol or something. Then I clean the plastic sheet (which will have some rests of liquid ink) so it can be reused.
The results are pretty amazing, achieving very very high resolution masks that are really useful to protect the boards and facilitate soldering. Usually the coating won't be as uniform as one would want, and the texture and appearance of this solder mask isn't the same of an industry applied mask, but does its job perfectly.
I'll post pictures of the process if requested, but here's a sample of some homemade boards I did with the stuff applied:
http://lulzimg.com/i22/47ea9d.jpg (http://lulzimg.com/i22/47ea9d.jpg)
(I took the same image I used for my presentation thread, obviously the OLS and the BP boards aren't homemade :P) I don't have other pics right now. The robot you see has three LGA or QFN -packaged IC's (a buck voltage regulator, a dual H-bridge and an electronic potentiometer) and the mask was perfect for them.
Nice work, thanks for sharing. Please post some pictures! This would be a great wiki tutorial/blog post too!
Okay, i'll post pics the next time I make a board. You'll have to wait a bit because I'm on my final exams period and I can't play with boards in this moment, but I promise I will deliever.
I found this instruction with pictures from one ebay seller
(http://http://img8.imageshack.us/img8/4347/procedure2.jpg)
(http://http://img818.imageshack.us/img818/430/procedure3.jpg)
(http://http://img694.imageshack.us/img694/1885/procedure4.jpg)
(http://http://img41.imageshack.us/img41/3010/procedure5.jpg)
(http://http://img52.imageshack.us/img52/4177/procedure6.jpg)
Yeah, that's it. But what they don't say is that the stuff sticks to nylon, polyester, acetate and polyamides (learnt it the hard way) and most transparency films are made of any of these materials. Also, as transparency films are quite thick, it gets difficult to spread the paste correctly. So an intermediate layer other kind of plastic is required (say polyethilene or polipropylene film). There comes the paper sheet pack wrapping plastic trick ;). I screwed the first 2 or 3 boards I tried to soldermask because the stuff stuck to the transparency, and then screwed one or two more for not spreading the paste correctly. After that, all the PCB's have gone just fine. Don't worry, the PCB's I used for testing were small and cheap ;)
I just doesn't understand what stay in the pads, some soldermask? Or nothing?
I'm saying that because in the last picture i think i'm just seeing copper pads :s
you need to add a fotoresistive foil with your solder mask on top of the green gue, after you ligt it up, the part that was lit hardens and the part where you had your mask stays gue so you can then clean the board and remove green gue from the board.
The green stuff is really mostly for presentation, if you want to really protect and "better" your home made pcb's use the chemical tinning compound to apply layer of solder to your copper. It will protect your copper + it will strengthen it and make soldering easier. You can find some info here: http://www.aliatron.pt/download/Sur-Tin_manual.pdf (http://www.aliatron.pt/download/Sur-Tin_manual.pdf) .. also multi compound chemical tinner are better then ready made stuff as they all degrade in time so with multi compound (usually 3 parts) you can make smaller batches as you need them.
http://www.youtube.com/watch?v=MGbxrRmP-Zs (http://www.youtube.com/watch?v=MGbxrRmP-Zs)
or if you are american then you get something called "liquid tin" from MG Chemicals
http://www.youtube.com/watch?v=xnKRndxAo70&NR=1 (http://www.youtube.com/watch?v=xnKRndxAo70&NR=1)
Off-topic: the first link you post is from s shop in my country :)
Hmmm, ok. I tought that will make easy the solder process too.
[quote author="arhi"]you need to add a fotoresistive foil with your solder mask on top of the green gue, after you ligt it up, the part that was lit hardens and the part where you had your mask stays gue so you can then clean the board and remove green gue from the board.
The green stuff is really mostly for presentation, if you want to really protect and "better" your home made pcb's use the chemical tinning compound to apply layer of solder to your copper. It will protect your copper + it will strengthen it and make soldering easier. You can find some info here: http://www.aliatron.pt/download/Sur-Tin_manual.pdf (http://www.aliatron.pt/download/Sur-Tin_manual.pdf) .. also multi compound chemical tinner are better then ready made stuff as they all degrade in time so with multi compound (usually 3 parts) you can make smaller batches as you need them.
http://www.youtube.com/watch?v=MGbxrRmP-Zs (http://www.youtube.com/watch?v=MGbxrRmP-Zs)
or if you are american then you get something called "liquid tin" from MG Chemicals
http://www.youtube.com/watch?v=xnKRndxAo70&NR=1 (http://www.youtube.com/watch?v=xnKRndxAo70&NR=1)[/quote]
No, it's not only for presentation. In fact, the aesthetical part isn't important for me. The green stuff protects the board from oxidation and corrosion, and it's a really good protection. It's the same protection that industry uses for PCB's. And also, the biggest advantage you get with soldermask is that soldering gets much easier, specially for SMD's, as solder doesn't spread everywhere and gets confined to the pads, making things much easier and reliable. And I must say that this stuff is kinda "fragile" right after you apply it (with fragile I mean easy to scratch), but as it absorbs more and more light it gets harder and harder, and after a day or two it provides a very very good protection to the board.
I was trying to find chemical tinning compounds for a while, but they aren't easily available in Spain, at least not in small quantities. I wanted them for finishing the pads, but chemical tining isn't as good as people tends to think. It has some disadvantages. Tin melts at a higher temperature than solder, so the solder joint is no longer between copper and solder alloy, but between solder alloy and tin, which is chemically bonded to copper. Surely diffusion occurs and the intermetallic layer eventually diffuses through the solder joint blending with the alloy, but metallurgically speaking it isn't the best bond you can get.
That's something similar to what happens with electroplated gold finishes. As you can't directly plate gold to copper because it quickly diffuses, an intermediate barrier layer of nickel must be applied, so finally, what you get are solder joints between soldering alloy and nickel (gold diffuses almost instantly), and that nickel is plated to copper, and that's a weaker bonding.
Anyway, I'll post pics and document the process when I make my next board, which will be as soon as I finish my final exams.
nvm
I used lot lack many times and yes it does protect the board... and yes tin does chemically bond to the copper but that bond is as strong (and as low resistant) as the solder to copper so it really makes no difference that you have a solder-tin-copper "sanwich", not to mention that you have more then 50% of tin in your soldering wire. If you are doing lead-free soldering your solder wire will melt at roughly the same temp as the tin coating the copper etc etc ... so that story don't really stand ...
As for protection, the tin is protecting the copper as well as the lot lack, is much cheaper and easier to apply. Does not look as nice but who cares :D (unless you are selling the boards but for that you'd like to have metalized holes too). I have boards that were outside exposed to elements (only protected from direct snow/rain but in open wooden box outside) for 10+ years that still work :D and there are no issues with the traces ...
Don't get me wrong, I don't say "don't use lot lack", but chemical tin is cheaper+faster+simpler protection + I assume you already did tinned the pcb before you put lot lack over it so when you do that lot lack is really only visual protection ... but if you don't do chemical tinning (beats me why) then yes lot lack gives you some protection ....
As for "not having chemical tinner in Spain" it is hard to believe that, I live in piece of sht god forbidden backwards country where I can't get most of the stuff I need, and I have 2 types of chemical tinning solutions available (ready made and 3component one)... You just need to check proper shops :)
i have tried conformal spray with vinyl masks and is too time consuming.
i like the the solder mask ink idea. ill have to try it when i finish my uv-BOX!
No, I do not chemically tin any of my boards. They are "just" protected by the green paste. I don't know why, but I can't find chemical tinners in Spain in low quantities (yeh, checked pro stores, I live 100 meters away from the pro'st electronics store of Madrid), and what is available is quite expensive. Much more expensive than the green paste for the same results. A syringe of the green paste lasts a lot of time, you'll spend about 1/10th - 1/8th of the syringe to coat a double layer 100x160mm board. The layer required is very very thin, and 10ml's will last quite a bit. I'm starting my second syringe, and my first one lasted a bit more than a year.
The thing about the chemical tinning metallurgy isn't made up, it's a real problem. Sure it's a bit paranoid and most times it won't be a real problem at all, but happens. it was just written for informative pourposes. Another problem that might happen with high frequency signals is losses due to skin effect, because tin doesn't conduct electricity as good as copper. Again, paranoid but it happens :P
I honestly think that protection provided by soldermask is better than protection provided by chemical tining. In fact, industrially made PCB's aren't chemically tinned (they actually use a chemical tin coat as etchant resist, but it's then removed, and the soldermask is directly applied over bare copper, and then the uncovered areas are finished by HASL, ENIG or other coatings). It doesn't only protect against oxidation and corrosion, but it also provides mechanical protection against scratches, and it facilitates soldering a lot, as your solder stays confined to the pads and doesn't spread everywhere, and it's a "must" for QFN's, LGA's or other packages like those.
well the pro made pcb's get another layer of copper on top of what is originally there so they are different story :) ... but yes, if you can't get chemical tinner locally lot lack is the best solution. (locally ingredients to make 2.5L of chemical that last looooooooooooong cost ~30E)
Yeah, pro made PCB's start with a very very thin layer of copper, and then they electroplate another layer on top, which also electroplates the holes, but the total thickness of copper is most times 35um, the same thickness of copper that homemade PCB's have. Here it costs 20 € for the same amount of tinner (I consider 2.5l a large quantity), that is quite expensive for me, considering that the shelf lifes of these products are very reduced, and that you have to make new stuff every time you want to make a new PCB. As most of the PCB's I do are small...it is expensive.
The tip for the tinner - you get a multi part one. The shelf life is many years (of the parts). Then you mix only small amount (100cc for e.g.). The shelf life of the mixture is bit over 6 months (even after a year it works but too slow). after 6 months you throw those 100cc and make a new batch, thats many years of service for 20E :D
[quote author="arhi"]The tip for the tinner - you get a multi part one. The shelf life is many years (of the parts). Then you mix only small amount (100cc for e.g.). The shelf life of the mixture is bit over 6 months (even after a year it works but too slow). after 6 months you throw those 100cc and make a new batch, thats many years of service for 20E :D[/quote]
Didn't know that. Anyway, I'll keep soldermasking my PCB's. It's better for me.
I'm only vaguely familiar with MG Chemicals' liquid tin, and no other products. I didn't know you could get multi-part type.
Does anyone know what the shelf life of MG's liquid tin is? Their site only specifies "long shelf-life". Also PulsarProFX says that it has "no known shelf life expiration". I'm assuming it to be years, but i don't know.
Does anyone know of a brand name or supplier for the multi-part type in the states?
they all degrade over time and also you make the solution weaker every time you use it .. the "regular" shelf life of the pre-made solutions is cca 2 years (what I seen written on 2-3 different types I used to use earlier), the "long shelf-life" means that MG stuff can survive longer. The multi part stuff I use (SUR-TIN) after 6 months it start to take more then double time to get the same effect from the same concentration, but it still work (I once made two batches for test, used one for 6 months and kept the other one closed, after 6 months I tested them and they took approx same time to tin the board after 6 months, and it took cca twice as long as the day solution was made... I could of used it lot more then I did but .. in general I used it for maybe one board a week so that was not enough to "use it up", it desintegrated more from sitting then from being used)
erdabyz, do you know what kind of shelf life is there on the green gue from ebay (the link in your first post)? your boards look great, btw.
The price seems decent, especially for smaller boards. Assuming the 10ml (.6102374 inch^3) is applied 5 mils thick (this may be on the thick side), there should be enough for ~122 inch^2, or about a 10" x 12" PCB.
I agree, soldermask goes along with proper tinning to make the smaller SMD stuff easier to solder - it doesn't look too bad to apply.
[quote author="bearmos"]erdabyz, do you know what kind of shelf life is there on the green gue from ebay (the link in your first post)? your boards look great, btw.
The price seems decent, especially for smaller boards. Assuming the 10ml (.6102374 inch^3) is applied 5 mils thick (this may be on the thick side), there should be enough for ~122 inch^2, or about a 10" x 12" PCB.
I agree, soldermask goes along with proper tinning to make the smaller SMD stuff easier to solder - it doesn't look too bad to apply.[/quote]
Well, my first syringe lasted a year, and it was still like the first day. Of course, you have to store it in a opaque container, so it doesn't receive light. I think that as long as it doens't receive unnecesary light, it could last ages.
I also did calculations when I bough my first syringe and they were similar to yours, but reality is much much better than calculations. With a syringe, I coated A LOT of boards:four of five 100x160 double-side boards, like 5 or 6 50x50 to 50x100 boards, lots of 10x20 boards and I still wasted a lot of product when i didn't know how to use it. The yields are spectacular and totally unexpected, and the syringe is pretty big (maybe more than 10ml?) Give it a try!:P
Thanks again for the link! The only other item I've noticed was from LPKF (http://http://www.lpkf.com/products/rapid-pcb-prototyping/solder-masks-legend-printing/index.htm), Who knows what they were asking for it - they don't even provide pricing on their web site.
I was looking at some of the sellers on ebay that offer UV curable soldermask. One had this disclaimer:
International Buyers - Please Note:
Import duties, taxes, and charges are not included in the
item price or shipping cost. These charges are the buyer's responsibility.
Please check with your country's customs office to determine what
these additional costs will be prior to bidding or buying.
Just wondered if anyone has had to pay a tax or tariff or some other fee before they where able to receive there order? Especially since pretty much ALL of these vendors are in Hong Kong.
I've only ordered one thing via Hong Kong from ebay. It was labeled "gift" (I'm assuming so there weren't any import fees), so I only wound up paying for item + shipping. I imagine a "legitamate" seller/company would not do this, however.
single items tend to move OK.
pay for the extra shipping option, they tend to go through customs much quicker.
for inexpensive items the tax is all most nil anyway.
[quote author="sqkybeaver"]pay for the extra shipping option, they tend to go through customs much quicker.[/quote]
are you referring to something like DHL vs. just standard shipping?
I have heard that DHL, specifically, tends to move things more quickly through customs. A previous employer used them exclusively for shipping between the US and UK and it seemed to work quite well (note there was no monetary exchange).
Hong Kong post was extremely quick, shipped 6kilo package to states for $60. arived in 1 week.
[quote author="FourthDr"]I was looking at some of the sellers on ebay that offer UV curable soldermask. One had this disclaimer:
International Buyers - Please Note:
Import duties, taxes, and charges are not included in the
item price or shipping cost. These charges are the buyer's responsibility.
Please check with your country's customs office to determine what
these additional costs will be prior to bidding or buying.
Just wondered if anyone has had to pay a tax or tariff or some other fee before they where able to receive there order? Especially since pretty much ALL of these vendors are in Hong Kong.[/quote]
Spain recently approved a law to accomodate our customs laws to european directives, which if i'm not mistaken are followed by most countries in the european union.
You can import whatever you want without having to pay any tax or get involved in any custom clearance process as long as the declared value of the goods + shipping is less than 22€.
If it is between 22€ and 150€, you have to pay custom clearance fees (which vary from carrier to carrier) + VAT, which is 18% of the declared value here.
If it is worth more than 150€ then you have to pay VAT, clearance fees and customs taxes, which vary depending on the nature of the goods.
That's the theory, the practise is that 90% of the packages arriving through the official postal service pass whithout being stopped by the customs, and from the 10% that get caugh, 99% are big packages.
If you're unlucky, however, the custom clearance fees are high enough to remember you why adhering to the european union also has its bad things. (until this law, anything below 150€ passed without any tax)
It depends on where you are. USA has 400 exemption I think. Dhl fedex ups have own customs houses ans clear quick usually. Normal post gets no inspection in my experience
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Just found cheaper soldermasking ink, in more different colors and in much higher quantity:
http://cgi.ebay.com/PCB-UV-Curable-Sold ... 2eb6088535 (http://cgi.ebay.com/PCB-UV-Curable-Solder-Mask-Repairing-Paint-Green-100g-/200622507317?pt=LH_DefaultDomain_0&hash=item2eb6088535)
http://cgi.ebay.com/PCB-UV-Curable-Sold ... 2c5d833362 (http://cgi.ebay.com/PCB-UV-Curable-Solder-Mask-Repairing-Paint-Blue-100g-/190547440482?pt=LH_DefaultDomain_0&hash=item2c5d833362)
http://cgi.ebay.com/PCB-UV-Curable-Sold ... 2eb6089267 (http://cgi.ebay.com/PCB-UV-Curable-Solder-Mask-Repairing-Paint-White-100g-/200622510695?pt=LH_DefaultDomain_0&hash=item2eb6089267)
Now that's cheap!
I have experimented making soldering stencils in metal foil using soldermasking ink as the photosensitive mask for etching the metal, with very promising results. I'll try to refine the process to get something both usefull and durable, and if it works i'll post it here. I'm trying to find copper foil with a thickness of 0.1-0.15mm to make further testing, as aluminium is too soft.
Seeed started carrying them (http://http://www.seeedstudio.com/depot/solder-mask-ink-3-sets-pack-p-868.html?cPath=175_198) too, just saw it today but they are sold out.
I understood that this lot lacquer don't bond with PP (and does bond with thermal foil one would regularly use to print with laser printer on) ... have anyone tried paper? can you use tracing paper directly on the ink or you still need to add a layer of PP foil between?
If it's porous, it bonds to it. It's quite liquid and actually wets paper. Maybe waxed paper doesn't bond, but I haven't tested. It bonds to lots of materials, including glass, aluminium, copper and some plastics that I said before. It doesn't bond to polycarbonate, polyethylene (low density) and polypropylene as far as I've tested.. I think that for some reason it just bonds to polyamides and polyesters
I've seen that seeed also uses an intermediate layer of plastic on its tutorial.
PP and PE are nasty :) not many things bonds to them :D ..
[quote author="arhi"]The tip for the tinner - you get a multi part one. The shelf life is many years (of the parts). Then you mix only small amount (100cc for e.g.). The shelf life of the mixture is bit over 6 months (even after a year it works but too slow). after 6 months you throw those 100cc and make a new batch, thats many years of service for 20E :D[/quote]
I am really interested in this multi part tinning agent.
As a homebrew PCB maker, I use tinning agents not very frequently and expect something that would last me 5 years without shelling hundreds of dollars.
check your local electronics store, most of them sell one or another multi part chemical tinner ..
the pre mixed solution has a shelf life between 6 months and a year and are fairly cheap, there is also "extended shelf life" version with up to 5 years shelf life (I never tried those so ..)
[quote author="arhi"]check your local electronics store, most of them sell one or another multi part chemical tinner ..
[/quote]
Sure, but I would like to know which ones you use and recommend.
[quote author="arhi"]
the pre mixed solution has a shelf life between 6 months and a year and are fairly cheap, there is also "extended shelf life" version with up to 5 years shelf life (I never tried those so ..)[/quote]
I saw the MG Chemical bottle. Stores near me have it, but the shelf life of a year at best is a bummer - I don't use that much!
[quote author="KamalS"]
Sure, but I would like to know which ones you use and recommend.
[/quote]
I use SUR-TIN because it is the only multi part available in local store and I am super satisfied, basically because while in "non mixed" state the parts have super long shell life. Now if you mix all parts together you get 2.5L of stuff that will stop working in 6 months, but you don't mix it all up. What I do is I split all 3 parts in 4 measurements. I just approximate it I don't use some fine scale etc. So you mix in 1/4 of the liquid and 1/4 of the first powdery thing and 1/4 of the second salty thing with 625 (600 is fine :D ) mL of water. You can use regular tap water but if you can use demineralized / distilled water you will improve shelf life of newly made tinning solution. This 600mL of solution will last you some 6 months (or 0.5m2 of tinned copper whatever comes first).
I personally use this 600mL until it stops working, then I throw it away. I know some ppl who don't ever throw it away but just add a second batch of chemicals into same solution and top it with distilled water up to 650mL .. but I never tried that so can't say if it works better or worse then new solution..
[quote author="arhi"]
I use SUR-TIN because it is the only multi part available in local store and I am super satisfied, basically because while in "non mixed" state the parts have super long shell life[/quote]
Ah! I have watched many a video of Bungard Sur Tin :-)
Shipping it would kill the deal unless there is something similar here in SoCalifornia.
All I see here are those tinning liquids - nothing solid that I could use a bit now and then :-(
Would love to stand corrected!
Check out the prices of those liquids .. maybe they are useful too ... for e.g. those "long shelf life" ones claim to have 5 years shelf life.. that should be perfect solution, also check the package sizes.. I seen in Hungary some liquid tinning solutions (the box only said "chemical tinning solution" - no "brand") my friend uses and they come in 500mL packs for cca 5eur and last almost a year .. that would be more then ok solution imho ..