PCB tinning, Liquid tin and paste tin not good?

Hello I have tried many times PCB tinning with liquid tin. It is in fact very convenient especially on big ground PCB traces and groundplanes, but I have some problems with it:

It does not solder very well, like pure solder tinning does.

If you leave the PCB tinned for a few weeks and then you decide to solder it, soldering is even worst as it does not solder well.

After a few weeks the "tin" gets a bit rusty, changing colour from silver to gray-silver.

This situation gets worst if you accidentally have touched the tin with your finger after tinning. It oxidizes after a few weeks.

When soldering a pad, the heat from the soldering iron oxidizes the pads near it!

If you decide to apply a cleaner, like alcohol, to clean the resin, then as you rub the PCB, some tin starts to be removed from adjacent traces and placed onto the PCB and other traces.


To overcome these problems, I do not touch the pcb with my fingers and I try not to heat it too much or clean it.
Are these "liquid tin" products really so crappy?

I do not think it is TIN that is applied on the PCB with these products. Tinning with the soldering iron and even using lead free solder makes a stable, super-easy to solder tin layer. The problem are big copped ground planes as they cannot be done with the soldering iron.

Any other ways or good chemicals to tin cheaply?

I use this stuff:

Just before plating I gently clean the board with an abrasive block, rinse it in clean water to remove any dust, dry it then leave it in plating solution for as long as possible. In theory it plates in around 10 minutes but I leave it overnight if possible. I have not had trouble soldering afterwards. I mix from crystals rather than using pre-dissolved solution. I find it works better if you use hot water too, although the steam smells bad!

Brian.

betwixt said:

I use this stuff:

Just before plating I gently clean the board with an abrasive block, rinse it in clean water to remove any dust, dry it then leave it in plating solution for as long as possible. In theory it plates in around 10 minutes but I leave it overnight if possible. I have not had trouble soldering afterwards. I mix from crystals rather than using pre-dissolved solution. I find it works better if you use hot water too, although the steam smells bad!

Brian.

Click to expand...

You leave it there all night?! I did not know it has to be that long, I leave it there for about 30 mins.
Have you ever noticed any rust (tin becomes not shiny) after a few months, or did you ever have problems with the soldering iron temperature rusting the tin?

A good way is after etching, to put the PCB back into the UV and then back into the developer to remove the protective coating. Then the PCB should be dead clean (or not?).
Do I need to sand paper my PCB prior to tinning? I see that the copper is too shiny and I did not bother to do so.

And something very important that I do not know, is it really tin that is put on the copper or some other metal that includes toxic lead as well?

I always remove the remaining resist with "Ultrasolve" (ULS). A cloth dipped in it will wipe the resist away without any hesitation. A 1L bottle lasts me more than a year.

I wouldn't use sand paper to clean the copper, it is far too abrasive, Mega sell cleaning blocks which are like pencil erasers but harder. They are useful to clean copper and other metalic surfaces too.

The plating process slows down as the tin (yes, it is just tin) bonds with the copper so the reaction stops by itself after a while. Leaving it longer than necessary does no harm and might result in a thicker coating. As I only make PCBs for prototyping and evaluation I rarely leave them for more than a day or so before populating them, as soon as the board is finished I wash any remaining flux away with ULS then spray the board with conformal coating to prevent contamination. I did make a spare PCB for a job about 2 years ago which was never built or sprayed. The tin coating on it still looks fine.

Brian.

betwixt said:

I always remove the remaining resist with "Ultrasolve" (ULS). A cloth dipped in it will wipe the resist away without any hesitation. A 1L bottle lasts me more than a year.

I wouldn't use sand paper to clean the copper, it is far too abrasive, Mega sell cleaning blocks which are like pencil erasers but harder. They are useful to clean copper and other metalic surfaces too.

The plating process slows down as the tin (yes, it is just tin) bonds with the copper so the reaction stops by itself after a while. Leaving it longer than necessary does no harm and might result in a thicker coating. As I only make PCBs for prototyping and evaluation I rarely leave them for more than a day or so before populating them, as soon as the board is finished I wash any remaining flux away with ULS then spray the board with conformal coating to prevent contamination. I did make a spare PCB for a job about 2 years ago which was never built or sprayed. The tin coating on it still looks fine.

Brian.

Click to expand...

These are the issues I am talking about https://www.delorie.com/pcb/liquidtin/ (end of page) and also https://www.turtlesarehere.com/html/making_pcbs.html (near the end of the page too).
It seems that these issues arise even with the use of different brands chemicals, since I have used another brand and I got these issues as well.
Have you got such issues with your liquid tin?

As I keep reading sites, I find that these issues present in all liquid tin products and in fact immersion tin is not such a good option (**broken link removed**). I believe that a roller tinning machine is the best copper protection option (after the HASL which is difficult to build at home) as it is like hand winning with the soldering iron, it can be made fully compatible with your solder (lead-free) etc. The plating never goes away or affected by heat and it is super-easy to solder even after 10 years using lead-free solder.

I think It is more worthy to try to build a roller tinning machine (since an HASL would be very complex), although the idea is simple, I have no idea if a homemade version will work or not...

Roller tinning is the best option but the machine is expensive, big and they need a lot of electricity to run them.
To be honest I have not had trouble with plating solution although as I pointed out earlier, I use it hot and leave it much longer than recommended. I was worried about the comment " It seems to be easily wiped off when it's fresh" which indicates the solution didn't bond to the copper properly, I have never had that problem, in fact I wash the boards vigorously under hot running water afterwards and the plating is unaffected. I find it easy to solder to, even on a board I modified a few days ago that was plated and constructed almost 5 years ago.

Brian.