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Electronics => Beginners => Topic started by: Jane on October 17, 2015, 05:19:45 am

Title: Why are soldering tips made of copper
Post by: Jane on October 17, 2015, 05:19:45 am
I know copper has very good conductivity, but very low resistance. It means it takes a longer time to heat properly.
Is the conductivity more important then time needed to heat up the soldering tip?
Or what are the most important reasons that CU ( alloy) is used for soldering tips?
Title: Re: Why are soldering tips made of copper
Post by: TheAmmoniacal on October 17, 2015, 05:40:08 am
Solder tips are not resistive elements in soldering tips, i.e. no electricity is flowing through the tip to make it hot. The tip is only thermally connected to a heating element (often placed inside it). Apart from that, I don't know why copper is used - or if better alternatives exist.
Title: Re: Why are soldering tips made of copper
Post by: DimitriP on October 17, 2015, 05:41:06 am
Quote
I know copper has very good conductivity, but very low resistance. It means it takes a longer time to heat properly.
Is the conductivity more important then time needed to heat up the soldering tip?

It  means the opposite, but the answer to your question is no.
Title: Re: Why are soldering tips made of copper
Post by: DimitriP on October 17, 2015, 05:46:28 am
Thermal properties of metals table

http://www.engineersedge.com/properties_of_metals.htm (http://www.engineersedge.com/properties_of_metals.htm)
Title: Re: Why are soldering tips made of copper
Post by: nanofrog on October 17, 2015, 05:59:33 am
Copper is a relatively inexpensive material that's an excellent conductor, is easy to form, and can be done quickly on simple tools, such as a lathes and belt sanders (reduces costs).
Title: Re: Why are soldering tips made of copper
Post by: PointyOintment on October 17, 2015, 06:14:14 am
Copper is used because it's an excellent conductor of heat. The fact that it's also an excellent conductor of electric current is irrelevant, because the heating element is generally a separate component, as others have said. The tip's job is to conduct the heat from the element to the joint.

Generally, the copper is plated with some other metal such as iron, because an uncoated copper tip would rapidly dissolve in the solder.
Title: Re: Why are soldering tips made of copper
Post by: alsetalokin4017 on October 17, 2015, 07:14:30 am
Because copper is cheaper than silver....
Title: Re: Why are soldering tips made of copper
Post by: tautech on October 17, 2015, 07:31:03 am
I know copper has very good conductivity, but very low resistance. It means it takes a longer time to heat properly.
Is the conductivity more important then time needed to heat up the soldering tip?
Or what are the most important reasons that CU ( alloy) is used for soldering tips?
Thermal recovery.
Title: Re: Why are soldering tips made of copper
Post by: TimFox on October 17, 2015, 02:40:03 pm
In soldering guns, as opposed to irons, a low-voltage secondary winding applies a very high current to a copper tip that then dissipates enough power to heat up.
Title: Re: Why are soldering tips made of copper
Post by: brobbuilder on October 18, 2015, 04:43:02 am
Copper wets out with lead/tin solder quite well, so you can get very good control over where the solder is flowing. IME it actually dissolves in the lead over time, hence why it's usually plated with something. Some people prefer plated tips, I personally like copper tips. Different strokes for different folks.
Title: Re: Why are soldering tips made of copper
Post by: SteveLy on October 18, 2015, 05:21:10 am
Thermal and electrical conductivities of materials are strongly correlated for physical reasons: both have to do with how easy it is for electrons to become excited. To a first approximation, they are proportional at a given temperature. But lattice vibrations complicate things so this is not strictly so, but it's a good rule of thumb for most metals.
http://www.electronics-cooling.com/2000/05/how-thermal-conductivity-relates-to-electrical-conductivity/ (http://www.electronics-cooling.com/2000/05/how-thermal-conductivity-relates-to-electrical-conductivity/)
Title: Re: Why are soldering tips made of copper
Post by: IanB on October 18, 2015, 06:26:50 am
I know copper has very good conductivity, but very low resistance. It means it takes a longer time to heat properly.

Copper has good thermal conductivity, and thus low thermal resistance.
Copper also has good electrical conductivity, and thus low electrical resistance.

But can you explain why you believe either of these makes it take longer to heat properly?

First of all, objects with higher thermal conductivity will tend to heat faster, since the heat can flow more quickly throughout the part. This is the opposite of your conclusion.

Secondly, the time to heat an object depends on the thermal capacity of that object. Objects with more thermal capacity take more heat to bring them up to temperature, so they will tend to heat up more slowly. Thermal capacity is not directly related to thermal conductivity.

It turns out that for metals the thermal capacity per unit volume doesn't change all that much between one metal and another. So for an object of fixed size like a soldering tip, the amount of heat required to bring it up to temperature will be similar whether it is made of copper, or say, iron.

However, copper is preferred since the better thermal conductivity makes it better at transferring heat from the heating element to the solder joint.
Title: Re: Why are soldering tips made of copper
Post by: crispy_tofu on October 18, 2015, 06:32:32 am
A less explanatory (more concise!) answer by Google:  :D

Quote
Soldering iron tips are made of copper core plated with iron. The copper is used for heat transfer and the iron plating is used for durability. Copper is very easily corroded, eating away the tip, particularly in lead-free work; iron is not.
Title: Re: Why are soldering tips made of copper
Post by: SteveLy on October 18, 2015, 06:38:48 am
^  :-+
Title: Re: Why are soldering tips made of copper
Post by: Simon on October 18, 2015, 12:07:10 pm
When you are using a soldering iron tip is acting as a buffer between the heater and your joint. The tip holds heat ready to go into your joint. When you make your joint you are sinking heat from the tip into the joint. When you do this but it gets colder and would not be able to make another joint. But the heater is there at the other end ready to feed more heating. So obviously you want your tip to be made of a material which will conduct heat quickly enough so that when heat is taken out the tip to make a joint it can be replenished quickly or you will have quite a stop start soldering experience.

Of course the other side of this is that when supplying heat to your joint you want the heat flow into a joint quickly. If your tip was made of a metal that does not conduct or relinquish heat easily you would end up with many dry joints as the heat would not be provided quickly enough and insufficient quantity.

And because of this you do need to size your tip to your joint sides. Small tips will not really do large joints for obvious reasons.
Title: Re: Why are soldering tips made of copper
Post by: dom0 on October 18, 2015, 01:38:20 pm
When you are using a soldering iron tip is acting as a buffer between the heater and your joint. The tip holds heat ready to go into your joint. When you make your joint you are sinking heat from the tip into the joint. When you do this but it gets colder and would not be able to make another joint. But the heater is there at the other end ready to feed more heating.

That depends on the soldering system. Low thermal mass systems only have a tiny amount of thermal energy in the tip.
Title: Re: Why are soldering tips made of copper
Post by: Richard Crowley on October 18, 2015, 01:55:29 pm
I know copper has very good conductivity, but very low resistance.
"Very good conductivity" MEANS "very low resistance". 
Resistance and conductivity are the inverse of each other by definition.

It is not clear that you have properly distinguished between ELECTRICAL resistance and THERMAL resistance.
Those are two very different things. Copper happens to have both good electrical and good thermal conductivity (i.e. low resistance)

Quote
It means it takes a longer time to heat properly.
How long it takes to heat is mostly a factor of mass, heat input, and heat sink (going out).
It has little to do with thermal resistance.

Quote
Is the conductivity more important then time needed to heat up the soldering tip?
They are BOTH important. As with most things, trade-off decisions are made at every step in the design process.

Quote
Or what are the most important reasons that CU ( alloy) is used for soldering tips?
Good thermal conductivity and convenient mechanical properties at low cost.
Title: Re: Why are soldering tips made of copper
Post by: G7PSK on October 18, 2015, 03:26:41 pm
Good thermal conductivity is essential to a soldering iron. It dose not matter if the iron is of the low or high mass type it has to be able to dump the heat into the work without too much of an internal heat gradient, if you tried making the iron tip from stainless (ignoring the fact that solder wont stick to stainless very well) the heat gradient will be so high that the tip will get to cold to melt solder when applied to the work while at the other end the heating element will be more than hot enough.