Old topic on flux...

[Lizard King]

I haven't soldered in years but am starting to build boards so I'm slowly re-learning.  I was reading through some old topics and came across this:

"When I etc boards, the first thing I do when they're drilled is to smear the entire board with flux.  That lets me tin the whole thing quickly and efficiently, and a fully tinned board lets me know that every solder joint will be good,"

I assume by tinning he means he adds a bit of solder to each pin pad.  Is that something that might be desirable?  Or just solder as you add components?

My first few flux-less attempts have been less than pretty so I'm going to go out and buy some flux...I was just wondering what the SOP was.

Thanks.

[Mark Hammer]

I assume by tinning he means he adds a bit of solder to each pin pad.  Is that something that might be desirable?  Or just solder as you add components?

"Tinning" means applying a thin layer of solder to the entire board.  The flux allows the solder to flow easily and widely, like a wave washing over a beach.

Depending on the time of year, where you live, how you clean your hands, etc., sometimes a freshly etched and buffed board can become tarnished faster than you would imagine.  It's not awful or irreparable, but it can make easy production of good joints hard to achieve.  Solder tarnishes too, just not as quickly as copper does.  If it's a nice dry day, and your hands are clean, there is no reason why you couldn't simply etch and solder the parts in without tinning the whole board first.  But, not all days are nice and dry, not all hands are clean, and not every component is in your parts bin when you want them.  I just find that tinning the board keeps the entire thing in more usable shape for when a hobbyist like me gets around to finishing something.  If you can figure out how to stuff 2/3 of a board right away, and then buff the tarnish off the unused pads to solder in the parts that just arrived in the mail, without tearing apart whatever you use to buff them, you're a better person than I.

Alternatively, if you can etch a board, and leave it alone until such time as you know you have every single needed part, buff it shiny again when it's time to build, and dedicate a block of continuous time to soldering in every single part and connection until it's done, you're also a better person than I.  I tin boards because I don't have that degree of self-restraint, a fully stocked parts bin, or enough continuous free time.  If I can't buff it ready and do it all in one shot - like a manufactuerer would - then tinning is the next best thing.

[Lizard King]

I get it.  I have some boards I etched but didn't get to and I noticed they are starting to tarnish already.  Our weather in the upper midwest has been more like that of Florida this summer with all the rain and humidity.  So I picked up some flux from R Shack over lunch.

Now when you "tin the board" do you rosin up your board, set your iron down on a trace, melt some solder and move the iron along the trace until it is covered?  Or do you melt up a big glob of solder and let it flow over the board - "like a wave".  I can comprehend the former but not the later.

Thanks!!!

[R.G.]

Both work, but it is very difficult to make a wave of solder with a standard iron.

I have this trick I keep posting, but I've seen a posting from anyone else trying it, successfully or not.

It's an adaptation of both the old sheer-mass soldering irons and a wetted-wax roller I saw being used to wax rental skis. The ideal solder coating is vanishing-thin, just enough solder to keep the air out. This is tough to do with an iron following the traces. It gets lumpy. Good technique makes it better, but not perfect.

I got a 6" length of brass water pipe from Home Depot, and then drilled and tapped a hole in the middle on one side to take a length of threaded rod. I set the threaded rod into the hole, locked it with a nut and lockwasher, and then put a handle on the end of the threaded rod. I then used steel wool to clean the non-handle side of the pipe to shiny. I coated the shiny side of the pipe in flux, then heated the inside with my propane torch, touching solder to the fluxed surface until I could tin the whole face of the pipe.

This is one of those operations you don't want to do either naked or in shorts, or without safety glasses. 

Once you have a layer of solder on the pipe, you can tin a board. You paint the board with flux, lay it down on a heat resistant surface that you don't mind getting marked up. You heat the pipe til it melts solder, load it with some solder, then slide the pipe over the fluxed surface of the PCB. If the flux is applied well, and the pipe properly heated, you will transfer a thin coating of solder to each trace. It is possible to lay snippets of cold solder on the PCB to be melted by the pipe as it moves along if you need more solder. The hot pipe holds enough heat for a PCB.

This also works to smooth out a soldering-iron-tinned board.

You can use steel pipe as well, but the tinning is tricker.

[Lizard King]

Interesting....thanks

[Mark Hammer]

I tend to do things the hard-headed stupid way, so I have a nice long pointy soldering iron tip (and you CAN get flathead kinds that would be better suited to the purpose...in fact I may just do that tomorrow) that I simply apply sideways.  It works fine...as long as your board is not a whole lot more than 2" x 2".  Anything bigger than that, and one needs to start pushing the solder along the traces with the tip.

You CAN get "tinning solution" in most well-equipped electronics stores.  I've used it, and didn't find the result thrilling.  It provides a consistent result, to be sure, but ultimately doesn't seem to be dramatically friendlier than slightly tarnished copper.

The question of whether to drill before buffing and tinning, or drill after tinning, is one I haven't made my mind up about yet.  Certainly one of the things that pre-drill tinning does is give you a slightly thicker "target" to poke a dimple into with your center punch so your bit doesn't wander and snap (something even carbide bits do). On the other hand, sometimes the little gap in the middle of an etched pad provides an excellent target.  I guess try it each way and see what you prefer.

[Lizard King]

Why not just tin the pads?  I'm not soldering all over the traces...

[Mark Hammer]

I tin the whole thing because it looks prettier, but also because I'm the sort that usually ends up poking new holes in boards for add-on parts or to accommodate oddball-sized caps and whatnot.  In a sense, for me the pad doesn't end where it says it does.    If one is content to useonly the circuit in the schematic, and all your parts fit the board, then you are most correct that only the pads need tinning.

[CodeMonk]

Both work, but it is very difficult to make a wave of solder with a standard iron.

I have this trick I keep posting, but I've seen a posting from anyone else trying it, successfully or not.

It's an adaptation of both the old sheer-mass soldering irons and a wetted-wax roller I saw being used to wax rental skis. The ideal solder coating is vanishing-thin, just enough solder to keep the air out. This is tough to do with an iron following the traces. It gets lumpy. Good technique makes it better, but not perfect.

I got a 6" length of brass water pipe from Home Depot, and then drilled and tapped a hole in the middle on one side to take a length of threaded rod. I set the threaded rod into the hole, locked it with a nut and lockwasher, and then put a handle on the end of the threaded rod. I then used steel wool to clean the non-handle side of the pipe to shiny. I coated the shiny side of the pipe in flux, then heated the inside with my propane torch, touching solder to the fluxed surface until I could tin the whole face of the pipe.

This is one of those operations you don't want to do either naked or in shorts, or without safety glasses. 

Once you have a layer of solder on the pipe, you can tin a board. You paint the board with flux, lay it down on a heat resistant surface that you don't mind getting marked up. You heat the pipe til it melts solder, load it with some solder, then slide the pipe over the fluxed surface of the PCB. If the flux is applied well, and the pipe properly heated, you will transfer a thin coating of solder to each trace. It is possible to lay snippets of cold solder on the PCB to be melted by the pipe as it moves along if you need more solder. The hot pipe holds enough heat for a PCB.

This also works to smooth out a soldering-iron-tinned board.

You can use steel pipe as well, but the tinning is tricker.

This is a GREAT idea.
As an alternative, maybe you could also attach the pipe to the type of soldering iron used for doing stained glass?
They are pretty big.
Whether they are large enough to heat up all that extra metal though, I have no idea.

One method I tried back in the 80's, just for the hell of it...
1. Give PCB a coating of flux (I used water based flux as it was far easier to clean up).
2. Dip PCB in solder pot.
3. Throw PCB on the floor. I don't mean just drop it, but throw it. Not like a Nolan Ryan fastball, but not just a "Oops, I dropped it" either.

I did it a few times and the results were fairly decent.
What kind of damage this may do to a PCB though, make it a less than ideal way to tin.

And I have used "Liquid Tin" (from MG Chemicals).
The results are less than stellar. Tends to leave a dull finish.
And you can't really polish it either. That just ends up removing the "tin" layer.

I have also used "Tin It" (I think that's what it is called).
Results were similar to Liquid Tin, without the ease of use that Liquid Tin has.

[R.G.]

The term "soldering iron" comes from the practice of using a chunk of iron/steel at the end of an insulating handle to solder. The chunk was heated in a fire and the mass held enough heat to heat the desired soldering to flow the solder. Electrical "irons" were developed so we could solder without a nearby fire.

I found that it was a common practice back in the 60s and early 70s to "roller-tin" PCBs. Today, boards are tinned by other methods. They used to be solder-plated. But roller tinning was an exact analog of roller-waxing skis. A biggish steel roller rotated in a solder pot. The PCB was fluxed, then passed over the top of the roller. The roller carried enough heat and solder to tin the PCB, on a continuous-production stream of PCBs.

I never wanted to get into PCB production, PITA that it is, so I thought I could get enough heat and solder onto a chunk of pipe to do one modest-sized PCB. Worked. It's probably less critical even if you tin the PCB first and then just reheat.

The throw-it-on-the-floor trick works. We used to call this "inertial solder removal" when we cleared PCB holes of solder with it. It requires some manual skills, but you can open up a hole by flowing the solder in a hole, then whacking the PCB on the workbench. Heavy liquid solder flies out of the hole. Same would work for the whole PCB clearing itself of all  but the alloyed/wetted layer of solder by throwing on the floor, although I've never tried that. Or seen it. 

I'm just really, really wimpy about being around a solder pot. I tended a type metal pot in my teen years, pouring type metal into inserts for a local newspaper that was still direct printed on a manually fed press. I still cringe when I think of the burns I might have received. This was before most of today's safety regs, and - well, I still cringe. I'm still sometimes amazed that I got through that without being in a burn ward.

[CodeMonk]

Come on R.G., its just molten metal

Back in "The Day" I ran a few wave solder machines, so working around small amounts of molten metal doesn't bother me much.
And yeah, I've been burned a few times.

I wanna get me a solder pot.

[R.G.]

I wanna get me a solder pot.

I understand that an electric skillet with the thermostat disabled or modified will melt solder.

Of course, that would be horribly dangerous, not only because it's mechanically unstable, but because it contaminates the skillet with lead and it must never again be used for food.

[J0K3RX]

https://www.americanbeautytools.com/site/models/sp/205

[R.G.]

That is a great way to tin wires, OK. I'd suspect that it's going to be limited in the size of the PCBs that could be tinned, though.

[greaser_au]

Come on R.G., its just molten metal

Back in "The Day" I ran a few wave solder machines, so working around small amounts of molten metal doesn't bother me much.
And yeah, I've been burned a few times.

I wanna get me a solder pot.

Been there, done that, got the T-shirt  - and a couple of minor spatter scars!!!   Interesting times working with a quarter of a tonne of molten metal being sprayed into a wave with a pump!  

Spent some time soldering with wave, drag and vapour phase (SMD) machines.   Used small and large solder pots (most of those were American Beauty) - that one that J0K3R pointed out is excellent. The older ones like this had a 100mm (4") base  and were about 150mm (6") or so tall - ours were fixed to a 300mm (1')  square wooden base for safety.
david