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I work with Sn 63 Pb 37, 1.8% flux solder which has a melting point of 187C, however, in order to reliably melt it I have to set my FX888D soldering station to 350C. Do I have a problem with my soldering station?

I measured the tip of the soldering iron at 258C when pressing into the temperature probe on my multimeter. Why is there such a difference between the specified and measured temperatures?

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The tip does have a bit of play on the heating element inside the iron - could this be the issue? Maybe I need a new heating element?

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    \$\begingroup\$ How quickly does ice melt at 1 degC? How quickly does it melt 50 deg higher? \$\endgroup\$ – Andy aka Apr 19 at 11:06
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    \$\begingroup\$ Immerse the thermocouple in a small blob of flux and measure again. Flux (and molten solder) transfer heat quite well ... point contact not so much. \$\endgroup\$ – Brian Drummond Apr 19 at 11:17
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The temperature the soldering iron is reading is from inside the iron body, the tip is removable so with this design there is no easy way to measure the temperature at that point, as such the temp will be slightly lower,

In the manual it tells you how to calibrate it if you need it spot on,

In reality most of the time the exact temperature of the iron is not a large concern, just that it can output a fair amount of wattage without cooking itself to death like the non station ones do,

having it at a high temperature mean the heat transfers to the solder quickly and has some margin to make up for other thermal loads such as the component and the PCB your in contact with while soldering,

For most jobs at my work I usually have essentially the same model iron as you set at 300-330C, if things melt quickly, you don't have to wait on a joint, so things are less likely to overheat.

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Why is there such a difference between the specified and measured temperatures?

Because there is a significant temperature gradient between the internal point where the iron measures the temperature and the point at the tip where you're measuring it. This gradient gets worse when you touch the tip to a cold joint that you want to solder.

350°C is actually a fairly typical setting for most types of soldering.

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