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I recently tried to use a soldering iron for the first time, but I don't seem to figure out how to use it properly.

In the articles I've read about how to solder properly, it is commonly stated that the process is quite short: you touch the connection you want to solder for a few seconds, then you apply the solder for another few seconds, and that's it.

This, however, is not what is happening in practice. When I apply the solder, nothing happens: the solder wire (provided with the soldering iron) just stays solid, and if I keep touching the solder with the soldering iron for, say, a minute or two, at some point it may start melting, sticks to the iron, and remains there in a solid form, then melts again a minute later.

I was thinking that this is due to the fact that the soldering iron is not hot enough, but the manual of the soldering iron says that the melting point of the solder wire is 215 °C and the general operating temperature is 270-320 °C, while I've set it up to 370 °C, and tried even a few times to push it up to 400 °C, even if the manual claims that “the temperature for general use should not exceed 380 °C.”

Since the problem is not the temperature, what am I doing wrong?

Notes:

  • The soldering iron is new. The tip is clean.
  • The temperature of the tip is reported on a small LCD screen (i.e. this is not the temperature I've set, but the actual temperature of the tip).
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  • \$\begingroup\$ Use leaded solder \$\endgroup\$
    – F.Ahmed
    Dec 15, 2019 at 12:08
  • \$\begingroup\$ @F.Ahmed: That's likely not the cause. Pure tin melts at 232°C \$\endgroup\$
    – Oskar Skog
    Dec 15, 2019 at 13:36
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    \$\begingroup\$ It could also be that the tip is corroded and has poor heat transfer. Make sure you clean it off with a standard soldering iron sponge or waterless cleaning pad. It is also helpful to dip the tip in soldering iron tip tinning flux. If none of that works, try a new tip. Some soldering irons can get out of calibration also. If your iron is the type that can be calibrated, you might be able to calibrate it with a thermocouple. \$\endgroup\$
    – user57037
    Dec 16, 2019 at 8:05
  • \$\begingroup\$ Maybe it is not called tinning flux. Maybe it is called tip activator. \$\endgroup\$
    – user57037
    Dec 16, 2019 at 8:24

4 Answers 4

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Are you sure the tip is actually getting hot? Not just what the stations sensor (which is probably nowhere near the actual tip) says. Try touching it to a small block of wood and see if it smokes/chars.

Does the solder melt if touched only to the iron tip, not to the joint? It sounds really that the tip is not getting hot enough, or, that the tip is too small for the joint being soldered (not enough thermal mass) and so applying it to the cold metals of the joint is robbing it of its heat capacity and cooling it down.

I would also obtain some good quality solder such as Kester or Multicore - the stuff supplied free with the iron (im going to guess its a chinese unit?) is likely rather poor.

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  • \$\begingroup\$ It is getting hot: I tried to desolder a capacitor from an old PCB, and the capacitor itself got hot enough that I couldn't touch it. If I touch a piece of wood, it chars (although there is no smoke). I tried to set the iron to the maximum 480 °C, it seems to work a bit better, although not much. I'll make a few attempts with a larger tip and with a better solder (the one I have now is indeed coming free with a chinese iron). \$\endgroup\$ Dec 15, 2019 at 11:41
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    \$\begingroup\$ It sounds then likely that the tip is just too small. What size tip are you using? A 0.5mm point tip looks great on a new iron, but its designed for no more than the tiny leads of a SOIC sized device. Almost anything bigger needs a much bigger tip (the exception being RF heated irons like some Metcal units). I have 3 irons (none 'intellegently controlled')- an 18W Antex, for normal everyday leaded parts and SMT, a 45W iron for larger parts and salvage, and a 150W for heavy duty items such as connectors for high current DC or high power RF. For normal components, a 2-3mm chisel tip is ideal. \$\endgroup\$ Dec 15, 2019 at 11:45
  • \$\begingroup\$ Consider the total mass of metal in the joint - that is, the PCB track area around it, the component lead, the solder itself (to a sensible distance, say 20mm around the joint) - all that will drain the heat from the iron tip. So, you need an iron tip with a much greater mass of metal already at that temperature, in order to rapidly heat the joint and melt the solder. \$\endgroup\$ Dec 15, 2019 at 11:50
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    \$\begingroup\$ One little trick with modern boards - if your just doing this as a hobby, you can still use leaded solder. If a modern lead-free joint is troublesome, add a little old-school leaded 60/40! It will bring the melting point down. Hobbyists dont have to be RoHS compliant! \$\endgroup\$ Dec 15, 2019 at 11:54
  • \$\begingroup\$ Or at least, get a premium lead-free solder - eg nickel-germanium alloyed. \$\endgroup\$ Dec 15, 2019 at 20:04
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Could it be that your display is showing Fahrenheit instead of Celsius? 350F would not melt the solder. I had a similar issue with the Weller WESD-51 which has a 'feature' where the default setting can be changed from Fahrenheit to Celsius. Since the display only shows digits, it's not clear whether Fahrenheit or Celsius is being displayed.

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The alloy composition isn't right. Normally a 63/37 or 60/40 would melt at 183 to 192°C.

If it is not melting at 375°C then the alloy composition is completely different and it might either Sn10PB90 or a Sn955Pb; please check at your end.

As many of us don't buy solder wire from retail shops there is a possibility that the alloy composition isn't right. Please buy from reputed solder manufacturers or authourised distributors only.

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  • \$\begingroup\$ The composition can't be the problem in this case, unless they bought something like "Aliexpress quality", or plumbing solder or whatever. \$\endgroup\$
    – Lundin
    Jan 18 at 9:20
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You could find likely 3 or four types of lead in circuits.
First one is simply known as lead. melts around 271°C. No problems dealing with it with the tip of iron.
Second known is nickel based lead which may need up to 475°C to melt. In general you won't need more than 410°C for a basic mix.
Third is some alloy we've observed in newer circuits which may be a triple alloy and its melting point is similar to nickel solder but it hardly mixes with conventional lead to reach a lower melting point[1]. It looks like conventional lead but with a porous surface structure at the microscope and it's less than malleable.
Fourth is likely a higher temperature lead for industrial circuits which may have a melting point beyond 500°C. Maybe around 550°C to 650°C.

You may want to add as much lead as possible to lower melting coefficient to reach target temperature faster in order to keep components cool while desoldering.

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    \$\begingroup\$ Are you using the word "lead" to mean solder? If so, please don't; that's needlessly confusing and nonstandard. \$\endgroup\$
    – Hearth
    Dec 16, 2019 at 3:35
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    \$\begingroup\$ Nickel based? Please share a reference. \$\endgroup\$
    – greybeard
    Jan 18 at 9:17
  • \$\begingroup\$ Are you talking about the high-temperature solder plumbers used for putting together pipes? I am quite sure that this is NOT the type of solder out comrade is using. \$\endgroup\$
    – Neppomuk
    Feb 18 at 15:39

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