question for PCB homebrew types

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papasan

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after etching a pcb and removing all the resist, what do you do with the board?...do you, at this time, coat it with some sort of solder-friendly sealent?...i've heard of flux paste, floor wax, and other stuff to coat the board to keep it from oxidizing, but none of the descriptions are very exact as to what to use (any old floor wax?...i've seen flux paste but is there a spray on or a liquid that's easier to apply to a larger surface?)...

or perhaps do you wait until all of your components are soldered on before 'sealing' the board...then what do you seal it with?...

thanks...
 
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
after etching a pcb and removing all the resist, what do you do with the board?...do you, at this time, coat it with some sort of solder-friendly sealent?...i've heard of flux paste, floor wax, and other stuff to coat the board to keep it from oxidizing, but none of the descriptions are very exact as to what to use (any old floor wax?...i've seen flux paste but is there a spray on or a liquid that's easier to apply to a larger surface?)...

or perhaps do you wait until all of your components are soldered on before 'sealing' the board...then what do you seal it with?...

thanks...<HR></BLOCKQUOTE>

Hello papasan,


Well, so far I have not put anything on my boards. Yes, they some oxidization. I am not sure if it is clear laquer or clear enamel paint that is used. I plan to try spraying clear enamel on the etched copper side. If this doesn't work well, I'll try laquer. (Think furniture laquer). It should be coated with something. ?
 
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Wayne Johnson:
It should be coated with something?<HR></BLOCKQUOTE>

not sure...some of the sites i read say they use a solder friendly floor-type wax or they coat the whole copper side with flux paste (which, i suppose, is a type of wax) directly after etching...some don't mention any type of coating, neither pre-component mounting nor post...one specifically says thet it doesn't and had a picture of a board 'over 2 years old' that looked to be in pretty decent shape...

all of the stuff that i've seen does agree in that the copper *will* oxidize given enough time...just some folks say that it starts immediatly (and i'm sure it does, but to what extent?) and some say that it takes years to become visable and/or detrimental to the copper and soldering stuff to the copper...

i was just wondering what, if anything, other folks did...

i guess my current mode of thought is that unless the etched PCB is gonna sit around for longer than a few days then it doesn't need to be coated...even then it may be easier to just clean it off good...i'll probably just clean it and mount the stuff, since i won't have much to mount, then coat it later...anything that dries hard and doesn't conduct will probably work...maybe i'll dip it in lucite =)...
 
I've done several methods in the past. The copper will corrode if left exposed, eventually compromising the connections. The closest thing to a professionally made board would be to tin or gold plate the traces and then solder mask the board, essentially masking off the pads where the parts are going to be soldered and then spraying on a laquer type coating over the rest of the board. Tinning solution is available just about anywhere you can buy PC board etching supplies. The easiest way I have done it without having to buy tinning solution is to carefully drag my soldering iron across all the traces with a little bit of solder to put a thin layer of solder on all the traces. You don't need much, just enough to cover any visible copper. Not only does it help protect the board from oxidation, it just looks a heck of alot better.
 
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Lurch556:
The closest thing to a professionally made board would be to tin or gold plate the traces and then solder mask the board, essentially masking off the pads where the parts are going to be soldered and then spraying on a laquer type coating over the rest of the board.<HR></BLOCKQUOTE>

ahh...i've heard of solder masking but i never really knew what it meant...why not mount the components and then laquer the board and components together (after testing, of course)?...wonder how this afects heat dissapation...

soldering the copper sounds good...fairly easy to do on smaller boards...i've read some about the tinning stuff, the powder you mix with water then apply...sounds kind of wasteful as you can only use the solution once or twice and it goes bad after sitting around for awhile...supposedly, if you try to use a single solution too much the deposits in it will actually make soldering harder...
 
You can solder the parts to the bare copper and then coat the whole bottom, or even the whole thing if you like, with lacquer. You shouldn't have any problem with heat dissipation if you only coat the bottom of the board. If the whole thing is coated, there will most likely be a slight increase in temp as it can't dissipate as well. This has been know to happen with boards that have been potted or totally encapsulated in epoxy. I've used some stuff called Humiseal before and it works well. Typically, you would only need to apply a conformal coating if the board is going to be in a humid or dirty environment. The one drawback with conformal coatings is that if you need to rework the board, it's a pain to remove the coating to expose the solder connections. Most of the time, you just end up burning thru it with the soldering iron tip. I've thought about trying the tinning solutions but I just haven't made any boards lately. I did try out ExpressPCB. The miniboard service is pretty reasonable and the quality was good. One nice thing is that if you are making some real small boards, you can copy the layout as many times as it will fit on their board.
 
When you de-solder, save the used wick for instant tinning and its free! After you get a clean bare copper board with your traces on , clamp it down. With your soldering pen in one hand and your used wick in the other (hopefully held by a hemostat or pliers) 'mop' the wick over the traces with your hot pen tip. this makes the prettiest tinning.
 
papasan said:
after etching a pcb and removing all the resist, what do you do with the board?...do you, at this time, coat it with some sort of solder-friendly sealent?...i've heard of flux paste, floor wax, and other stuff to coat the board to keep it from oxidizing, but none of the descriptions are very exact as to what to use (any old floor wax?...i've seen flux paste but is there a spray on or a liquid that's easier to apply to a larger surface?)...

or perhaps do you wait until all of your components are soldered on before 'sealing' the board...then what do you seal it with?...
Click to expand...

If you are going to hand solder the board, you might as well tin the board right away. That'll stop the oxidation for sure.

If you're not going to build for a while, you might do nothing. A little bit of fine steel wool can be used to take the small amount of corrosion off just prior to soldering. Or... I sometimes use the wire wheel on my Demel tool. Storing the boards in a sealed bag (or bags) will slow the rate of oxidation.

Flux paste is used during the soldering process to clean oxidation off of the metal and prep the surface for the adhesion of the solder. I don't think that it is intended to prevent oxidation. In fact, most fluxes need to be cleaned off after soldering to prevent the flux from causing corrosion.

Once the board is built, the application of conformal coat will protect the board from most moisture and general dust and debris. For the electronics that I use on my bicycle, this is a critical step. At times, I've used Plasti-Dip in a similar way. I'm not sure that it seals as well, but does provide a bit more mechanical protection. Both coatings can be removed with a suitably nasty solvent.


regards,
Steve K.
 
When I worked at a small electronics development company we used clear Krylon after etching the board. When you solder to a pad or land, the Krylon burns off and the solder bonds OK.
 
When I have really cared, I bought tinning solution (i.e. something for a customer). I don't remember it being very expensive, maybe $15-20 a bottle. I will be honest, I don't make my own boards any more. Given how cheap you can buy them, it is not worth it I find.

That said, I have done tons of home made boards in my life.

Frankly, I rarely worried about a little oxidation. Light sanding with very fine steel wool is going to remove any oxidation. You do this right before you are going to solder your parts to the board. The solder will prevent any further oxidation wherever you have made a solder joint.

What is your concern? The oxidation is only going to make neglible changes to the copper. All the traces will conduct the same.

The only small ...very small effect may be in heat dissipation to the air, but even in this case, if you are mounting a heat sink, the best interface is bare copper with extremely thin thermal grease (which will also prevent oxidation). Tinning, etc. will add resistance and make the surface less flat.

Semiman
 
As soon as remove the resist I spray the entire pcb with Pure Shellac. Shellac has a low melting point, smells ok when heated and interacts very well when soldering. The melting point is lower than the lowest solder temp and you will find that soldering is much easier because the copper is unoxidised. Also works great with smd devices.

sbdwag

DCP_1271.jpg






digvolt2.jpg
 
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I used to use tin plating but the liquid would spoil, so I got some Cool Amp silver plating powder. Rub this on the board after etching and before drilling and silver plate the copper. One bottle is a lifetime supply for a hobbyist, and no spoilage problems. It solders nicely. I believe they are still in business.

http://www.cool-amp.com/
 
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