Tinning traces for more current

[Poe]

Just watched the EEV blog #314 and noticed the tinned traces intended to increase a trace's current carrying capability. 

Since solder has something like ~1/10th the conductivity of copper, how effective would this be?   .

Has anyone looked into this technique?  I've seen it used quite a bit in older boards, but it never made much sense to me.

[Bloch]

Just watched the EEV blog #314 and noticed the tinned traces intended to increase a trace's current carrying capability. 

Since solder has something like ~1/10th the conductivity of copper, how effective would this be?   .

Has anyone looked into this technique?  I've seen it used quite a bit in older boards, but it never made much sense to me.

I also raised my eyebrows when Dave mentioned it.


Maybe it will even make it worse .... but right now i cant remember there i did read/hear that.

[Electr0nicus]

If you open a pretty standard desktop PC PSU and take a look on the main PCB, you'll see this technique all over the whole board.
The main intention is to reduce cost. 2oz or more copper thickness gets really expensive, as Dave said in the video.
I also don't think, that tinning the traces makes things worse. At least there is more conductive material available, so the resistance will go down  in any case, that's for sure. The only question that arises, is the effectiveness of such tinning, because you wouldn't be able to get a even thickness of tin along the whole trace.

[Bloch]

I also don't think, that tinning the traces makes things worse. At least there is more conductive material available, so the resistance will go down  in any case, that's for sure.

Yes the resistance will be a little bit lower. Anyone with a good low Z multimeter there want to make some test ?

But that if the track cant get rid off the heat. ? The Tin must act like an heat insulator or do you think it will be better to get rid off the heat ?

[Rufus]

Yes the resistance will be a little bit lower. Anyone with a good low Z multimeter there want to make some test ?

1oz copper is 35um. Putting 0.5mm of tin on a 1oz track would more than halve its resistance.

or do you think it will be better to get rid off the heat ?

More surface area, no solder resist, slight protrusion into air flow. I would say dissipation is likely improved slightly.

[EEVblog]

1oz copper is 35um. Putting 0.5mm of tin on a 1oz track would more than halve its resistance.

More surface area, no solder resist, slight protrusion into air flow. I would say dissipation is likely improved slightly.

Correct.
It can't do anything but help reduce the resistance and improve the dissipation (which is now lower thanks to the lower resistance)

Dave.

[EEVblog]

Since solder has something like ~1/10th the conductivity of copper, how effective would this be?   .

IIRC, copper is about 2-3 times better, not 10 times better.

Dave.

[Chasm]

The specific resistance (1m*1mm^2) of copper is 0,0178 ohm, tin is 0,1150. Thats a factor of 6,46.
For historic comparison: lead with a specific resistance of 0,2080 is even less condutive (11,68 times compared to copper), so the old Sn60Pb40 solder has a specific resistance of 0,1522 or 8,55 times worse than copper.

[amspire]

I do not think that the unmasked strips in the power supply were there to allow the solder to reduce resistance.

I think the track's design margin is so low, that they thought they may need to solder a length of copper wire on top of the tracks. That is why they only left a thin strip unmasked, rather then the whole track width.

They obviously decided they could get away with no copper wire, but if I owned the supply, I would add them.

[Chasm]

Soldering copper wired onto tracks actually works rather well but also has some potential drawbacks. (Say potential vibration problems over time.)

There are also options to embed such wires into or on top of the PCB, but that is rather expensive and thus only used in very high power stuff. (Copper Inlay PCBs)

[mikeselectricstuff]

Resistivity figures from Wikipedia, adjusted to have same exponent

Copper 1.68×10?8
Tin       10.9×10?8    
Lead       22×10?8

I've just done some actual measurements - short video uploading now..

[EEVblog]

I've just done some actual measurements - short video uploading now..

Poop, I was going to do that! 

Dave.

[Bloch]

I've just done some actual measurements - short video uploading now..

Thank you for taking time to do that. It will be very interesting info for me at least. 

[mikeselectricstuff]

[almoehi]

I've just done some actual measurements - short video uploading now..

Poop, I was going to do that! 

Dave.

Yesss!!! Battle of the tear down titans. 

[dda]

I would have thought that because of its low melting point, solder's conductivity would rise fairly fast as more current passed though it and heated it. But actual measurement is better than talk... time to watch the video.

edit: and of course I'm wrong, resistivity increases with temperature, not conductivity.

[Bloch]

Mike a great video as always.
40% improvement is not bad i must admit 


That about long term use. I think about bad soldering there can be seen at hot component in old pcb (TV). Just a thing to consider.

[nitro2k01]

Why is the video unlisted? Even the discussion originated here, I imagine the video can be interesting to "anyone".

[David_AVD]

It would be interesting to add fresh solder back to that track and see how much a heavy (manually added) solder coating affects the resistance.

[Bloch]

I would have thought that because of its low melting point, solder's conductivity would rise fairly fast as more current passed though it and heated it. But actual measurement is better than talk... time to watch the video.

edit: and of course I'm wrong, resistivity increases with temperature, not conductivity.

Yes the equation to calculate ohm is not as easy as with pure CU.

[mikeselectricstuff]

Why is the video unlisted? Even the discussion originated here, I imagine the video can be interesting to "anyone".

Because I forgot to change it - I always set unlisted during upload to check it's OK and select the thumbnail image before publishing.

[dda]

Is the 'normal' track there going to struggle with 1A? I would have thought it would have done ok, what happens at higher current?

[dda]

I now also realise that my solder wick is shithouse. What brand do you use?

[IanB]

I now also realise that my solder wick is shithouse. What brand do you use?

Equally importantly, ask what iron he used 

[David_AVD]

I now also realise that my solder wick is shithouse. What brand do you use?

I use Chemwick brand and find it very good.  Some of the cheap ones are rubbish.  The bigger issue is usually people putting their fingers all over the braid.  This contaminates it and really reduces its effectiveness.