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I've got a 48W Soldering iron which I'm using on PCB's, which I'm designing with Eagle and getting made up for me. I'm a hobbyist, so needless to say, I may well have the wrong tool for the job here.

My designs use surface mount components and my soldering iron is really struggling to melt the solder when I'm trying to solder to a surface mount pad which is connected to the ground plane.

Is 48W a bit on the small side? Should I replace the iron with a more powerful one or is that not the problem? I'd be very grateful for any help.

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    \$\begingroup\$ The wattage of the soldering iron means nothing unless you know the temperature of the iron, and can control it. You want to set the temp to the lowest possible and still get good results. When soldering to planes, you need to turn the heat up. But if you always solder with high temps then you will destroy PCB's. \$\endgroup\$
    – user3624
    Aug 13 '13 at 18:45
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You just need to heat the pad for a longer time. Use big flat tip on your soldering iron to maximize heat flow. If you still cannot solder you may try placing a hot plate under your board to preheat it.

And next time remember to use thermal reliefs:

enter image description here

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    \$\begingroup\$ I would recommend taking a knife (exacto blade) and cutting in some of my own. It's hacky but solid copper is too tough to deal with with a Radio Shack iron. \$\endgroup\$
    – scld
    Aug 13 '13 at 18:59
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    \$\begingroup\$ I've had luck using two soldering irons, in a pinch. Might be more likely to be lying around than a hot plate, depending on the world you live in. \$\endgroup\$ Aug 13 '13 at 20:55
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    \$\begingroup\$ Can't vote up as yet due to reputation but thanks for that, I'd never heard of "Thermal Relief" before now. \$\endgroup\$
    – jwhitmore
    Aug 14 '13 at 9:50
  • \$\begingroup\$ @Remiel Can't say enough about the two iron technique. It's definitely a bit more of an intermediate skill but two irons is a great step before going to hotplate/reflow oven. \$\endgroup\$
    – scld
    Aug 14 '13 at 13:00
  • \$\begingroup\$ @jwhitmore what PCB design software are you using? You should try to find one that automatically generates thermals when it pours copper planes. If, however, you are manually placing ground copper, you may be able to make small little keepouts around ground areas. Side note: The picture above is very pretty but you don't need to make it so symmetric if you're having trouble doing them manually. A few gaps in the copper will help a lot. \$\endgroup\$
    – scld
    Aug 14 '13 at 13:03
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I would recommend using a heat gun or hair dryer to raise the temp on the entire board. Then after 30 secs or so, reattempt to solder the component.

If that fails, buy a flux pen. Apply some flux to the pad to refresh the 'old' solder. Especially useful for re-work. https://www.sparkfun.com/products/8967

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Soldering iron wattage plays a role, but even more important is thermal recovery and capacity. For example, your iron may be at the proper temperature, but as soon as you transfer heat into a large wire or pad, that heat conducts away from the iron and it now must regenerate it. If the iron has a low thermal capacity, it might require that you hold the iron to the pin or pad in question for a long time, which could cause damage to components or pads.

I strongly recommend that you get an iron with good thermal recovery and temperature control. (See other threads for recommendations.)

As @Szymon mentioned, one way to reduce the heat requirement on the PCB is with thermal relief pads. But if you have a component that has a tab specifically designed to solder to a large copper pour as heat-sink, you will run into the issue anyway.

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  • \$\begingroup\$ Yet again can't vote up due to lack of reputation but thanks for that I'll have a look over other threads. Thermal Relief was new to me but like you say if I'm soldering to heat-sinks I'm going to have the same issue. \$\endgroup\$
    – jwhitmore
    Aug 14 '13 at 9:51

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