# How to find out how much voltage and current a soldering agent can handle

Is there any way to find out the maximum voltage and current that a soldering agent can handle based on the material and/or the information that I find on the package?

For example, I have this soldering agent at home:

S-Sn60Pb40
DIN EN ISO 9453
DIN EN 29454
60% Sn
6g
1,0 mm ø

• You want to use it as 1mm diameter wire? Dec 28, 2020 at 19:43
• Yes, updated my question Dec 28, 2020 at 19:48
• Are you saying you want to use the solder as wire, or are you worried about it's abiliy to be used as normal solder in a high-current application? Dec 28, 2020 at 19:50
• Sorry, there might be a sloppy translation problem here on my side from German to English. My question is supposed only to consider the material itself so 'solder' / 'soldering agent' not 'solder wire' would be the appropriate term (updated my question). As for your question: I am especially interested in your second option, however, if the two options should lead to different answers, I am interested to hear both Dec 28, 2020 at 19:59
• The resistance of a solder joint is typically in the 10s to 100s of micro-ohms range. The resistance of any attached wires, device leads, or traces is usually much bigger, so the solder is not typically the limiting factor. Dec 29, 2020 at 2:19

Solder isn't wire.

Unless you are dealing with extreme voltages and currents, you shouldn't have to consider the conductivity of the solder at all.

The joints you make with solder are comparatively small. The resistance of such small volumes of solder isn't usually high enough to consider.

Do not try to use solder as wire. It is not made as a replacement for copper wire. Solder is only for joining things together.

It might be useful as a fuse. The voltage is unlimited by the conductor- it will be limited by whatever insulator(s) you are using.

The current will be limited by heating. According to the this Multicore datasheet the conductivity of 60/40 solder is 11.5% of that of copper. It won't be that good compared to a 1mm copper wire because a fair fraction of the solder is usually flux. It's only something like 3% by weight typically, but the density ratio is 8 or 9:1 so perhaps 25% of the cross-section area is flux. So if we assume an equivalent diameter of 0.85mm the resistance should be around 0.26$$\\Omega\$$/m. If you allow a maximum surface temperature of 90°C that implies a current of less than 2A. The fusing current will be considerably higher, of course.

In normal use the solder layer is a thin layer between copper and copper and the copper also draws heat away, so the solder does not tend to be limiting. And, of course, the diameter of the solder you use does not matter once it's melted in place.