You need to supply more details about what you are trying to do.

Clean the surface and provide a light muriatic acid autistic wash at the joint. There are other compounds. Solder paste, and solder. Zinc coating is easy to solder.

Dik

Hi Swall,
I have a slot in a PCB which I push the metal through. I then solder the metal (kinda encase the metal) to the board in order to get connectivity from the board to the other end of the metal. Signal is then read from the metal back to the PCBA. I know there are better ways to do this but its a legacy design and I'm confined to this. Just need the solder to stick to the steel which is currently zinc coated.

Hi Dik,
Will give it a try.

Thanks all!

When I was about 10, I used to help my dad install eavestrough... cut my teeth with a soldering iron (actually copper).

Dik

Etang858--I have some concerns about your project. Using acid to prep the zinc or using an acid soldering flux could cause corrosion issues on your circuit board. The acid wash would be OK to remove the zinc, but then you need to neutralize the metal with something like NaOH, then rinse with distilled water. If you have clean,dry bare steel, you should be able to solder it with rosin core solder. Sometimes a scrubbing action with the soldering iron helps the solder to wet the steel in these situations.

Corrosion is an issue; and the muriatic acid is usually a 'killed' product to minimise this, there used to be a product called 'Flowzall' that also minimised corrosion. Caution to properly clean after. Thought the application was industrial.

If for circuit board, then just use a good soldering paste, non acid based.

Dik

HI all,

So it seems like I should just try to use some non-acid based soldering paste and see how that goes.

I've also done some reading about tin plating. There seems to be shelf life on the solder-ability of tin. I know it varies based on thickness, substrate, etc but is the shelf-life usually on the order of years or are we talking months when exposed to ambient air (not in a Nitrogen filled bag).

Thanks a bunch!

If the surface is 'dirty' then you may need something other than non-acid paste.

Dik

Hi All,

I was looking at the surface finish of the piece of zinc coated metal. I have one piece with a matte finish which solders fine, but the one with a more polished finish is the one which started this thread. Matte = solders OK, polished = solder does not stick as well.

I did a quick test and used low grit sand paper to abrade the polished surface. I then heated the surface and applied solder. The polished surface created a more bulbous solder ball while the sanded surface looked spread out more- better wetting. I think my issue may not be the zinc itself but an actual surface finish issue. I think the matte surface has more surface roughness therefore is better for soldering.

Matte finish on the left, polished on the right


Thoughts?

For Zinc coated steel, either galvanized, or electro-Galv you will need to use either Hydrochloric/muriatic acid which reacts with the zinc to form zinc chloride flux, or a proprietary acid soldering flux which contains free acid. The standard Rosin type fluxes have very poor performance on zinc coated parts. The soldering on the zinc case needs to be done away from the PCB to avoid acid flux contamination, once you have tinned the zinc pigtail with solder, you will then need to neutralize the soldered pigtail before coming back to the PCB, which you can then solder with a rosin core solder on the " Tinned" part. So tin the zinc part first , clean and neutralize it then assemble your PCB as before.
B.E.

You are judged not by what you know, but by what you can do.

I'm not sure where PCB came in, but, I've not encountered a PCB that is galvanised. If PCB, you definitely do not want acid based flux... rosin based solder or acid free paste is great for PCBs.

Dik

DIK,
From the OPs second post. " I have a slot in a PCB which I push the metal through. I then solder the metal (kinda encase the metal) to the board in order to get connectivity from the board to the other end of the metal. " . He has two opposing requirements he is trying to solder a galvanized part to a printed circuit board, the requirements for soldering one are death to the other. That is why I suggested " tinning" the zinc with regular solder and cleaning everything up. before coming back to the PCB and using regular rosin core to finish the job.
B.E.

You are judged not by what you know, but by what you can do.

Thanks... tinning it with 'solder'and then soldering it to the PCB might work... but, only use non-acid paste...

Dik

Maybe another solution:

https://www.masterbond.com/techtips/conductive-epo...

Dik

Thanks Dik, I have contacted the company

Masterbond is good... don't know about that product, but, I've used other products of theirs for decades... The product came as an eMail notification from them the same day...

Dik

Conductive adhesives are very expensive and really overkill for this application. Galvanized sheet metal is easily soldered or tinned with the correct solder and flux. Sal ammoniac is a common flux for sheet metal work

Hi all,

I looked into conductive epoxy and yes, its way too pricey for our application. Cleaning of the parts to expose the steel to make it solderable is too time consuming.

We are ready to just make a fresh run of parts with the proper plating. I've looked into tin plating and there is a shelf life due to oxidation of the surface and growing inter-metallics. We are not yet sure on how fast these parts will move so the shelf life concerns me a bit. I know we can ship them in nitrogen bags to slow this and keep parts in a temperature controlled room.

Do you all know of any other plating (over a stamped steel piece) that will promote wetting and solderability without the shelf life concerns? A shelf life of 2-3 years should be fine. Storage temperature will be ~20C.

Thanks!

I think you are best to stick with your existing zinc coating, If you pre solder the attachment areas with 60/40 tin lead solder and clean, the parts, before, you store them you should not have problems with oxidation that the standard rosin core soldering flux cannot handle.
You could use Terne plate, but a lot would depend on the amount of handling the part received, because of the high lead content.
B.E.

You are judged not by what you know, but by what you can do.

Hi Berkshire,

The problem is that the solder does not wet the existing zinc coating well enough. After soldering the metal part sometimes separates from the solder when adequate force is applied. Removing the zinc to expose the steel is too time consuming.

Thanks

Can you use a little more heat without melting something? Also use a good quality of soldering paste or rosin core. You shouldn't have difficulties if all is clean (famous last words).

I was going to add... maybe your propane torch is too far away <G>.

Dik

etang858
Ok two things, the non wetting of zinc plated or galvanized material is a function of the flux, you cannot easily solder zinc without a chloride flux .
If you paint the zinc where you want to solder with Hydrocloric acid the zinc will start to bubble, this is the acid cleaning the zinc and turning into zinc chloride, the flux you want. You can then solder this with either tin lead solder or 95/5 lead free solder, use a big enough iron to ensure you have thoroughly wetted the part. The zinc peeling off sounds like electrogalv zinc, what you need there is enough heat to reflow the coating. Now this is important having done this, you have to, clean the part, and neutralize the acid flux,( baking soda) before, you get that PC board anywhere near that.
You were saying you need to store these panels this would be a good time to do so.
Then for the second stage you can assemble the PCB onto the panel, however you may have to use a larger iron than the standard 25watt iron because of the size of the steel part, but use the rosin core solder or add rosin flux.
B.E.

You are judged not by what you know, but by what you can do.