Soldering temperatures (resistors, caps, transistors)

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Hi all!

I've been thinking on the impact of different soldering temperatures.

When I'm in a hurry I don't really care about the resistors. They usually live after a 450 degrees Celsius blast, but what about different caps and transistors?

A more gentle approach is to solder just about everything at 380 degrees Celsius.

How about you? I've learned this by my self and haven't discussed it with anyone before. There are not so many sources on the net on the issue.

Generally, I've found everything I've ever done to be pretty forgiving. Most of my electronics experience is with digital stuff, so for them I have a 15 watt iron which tends to only last a few joints before getting too cold, but so long as the solder melts cleanly I can do the joints quite quickly.

With my P3A amp which I just finished a few days ago, there was no way that iron would cope (especially since it's really hot here at the moment, so I had a fan blowing over my work area). I used my dad's iron, which is pretty powerful - I'm guessing 40-50 watts, but I'm not sure. The tip is a 5mm wide chisel, sort of angled. Anyway, thanks to the width of the soldering iron tip and the small size of the pads on the PCB, I ended up heating up some areas for a lot longer than I felt I should have. But it worked. Nothing melted, not even one of the LED's which I was sure I'd killed.

And this is with an iron that I was regretting using PCB pins with, because when I'd try to solder the wire onto the pin, it'd melt the pin's solder and make it fall out of the board (and of course, the board was already bolted into the chassis and not worth the effort of removing).

Most stuff (semiconductors) are rated for 260 deg C for 10 seconds, at a certain distance from the package. SMT stuff is usually less. I've never seen ratings on passive parts, but I'm guessing they're probably more forgiving. I don't worry too much about overheating resistors or inductors. I usually take care with capacitors, especially electrolytics (which do nasty things if they get too hot, like leak carcinogenic goop).

If I had to give one tip though, it'd be to use an iron that's hotter than usual, but do your joints quickly. Keeping a cold iron on a joint for ages to try and heat it up properly is probably worse than a quick burst of heat (most of which will dissipate before it reaches the part, anyway).
Interest in lead free solder for industry has created some interesting developments, there is a 58Bi-42Sn that melts at 138°C, that means a soldering Iron temp of 180°C, much more comfortable for your components.

Cleaning the components leads and a clean copper surface on PCBs usually means a shorter exposure to the soldering temperature.

Sounds like a lot of good advice so far. What I normally do is load multiple components at one time, slightly bending their leads to hold them in place. I then solder one pin on all of them and then go back and do the other pin. This allows the device time to cool before I do the other side

With transistors I solder one leg and move on to the next. This holds the device on the pcb. When their all on I run back through them one pin at a time until there all done

For chips I always try to use a socket which eliminates the heat problem. I use a 40 watt weller and have never burnt anything up.

Be sure to keep your tip cleaned and tinned. I do this everytime I pick up the iron. By the time I've soldered up a pcb card I've cleaned and tinned my tip a hundred times.
Hello Magnus and all,

for soldering with good old old lead/tin solder i use 310 to 330°C, not more, for unsoldering components from PCBs i usually do not exceed 340, unsoldering 50 year old p-p wiring however asks for 380°C, in this case i used a redundant amount of flux and a desoldering pump. I prefer to solder quick and hot and do not apply any further thermal care. Never had a burnt components, including those i slaughtered out of old Tektronix scopes, only mechanical damges by being too rude with the soldering pencil :) .

An old friend of mine taught me how to solder (he was soldering around in military equipment and knew how to solder/unsolder in multilayer PCBs):

* Heat component lead and PCB trace simultaneously

* Apply solder, as few as possible and even sufficent

* Let the solder flow into gaps properly

* right in the moment before you remove the soldering iron, apply a second tiny amount (a faint kiss :) ) of solder and remove solder and iron immediately.

Using this technique, i never had a cold solder joint.

Using teflon tubing and ultrathin enamelled twisted copper wire i make top-notch interconnects which cost me a few $$.

Regulated heat also can be used to shape the end of teflon tubing which i use as mechanical protection for enamelled copper wire. Teflon tubing is so slippery that no strain relief based on friction works. I made a special solder tip to widen the tubing's end (shape of a trumpet funnel). The soldering iron is set to 355°C and the tip is put into the tubing end. The end softens and widens up and sometimes (i am happy if this happens) folds over itself, forming a circular bead. Then i switch the soldering iron off but leave the tip firmly pressed in the tubing's end and cool the tubings end using a wet soldering sponge. The tubing has a thick end now which can be hold by most strain reliefs (plugs, PCBs, whatever).

I thought buying a Weller WSD130 soldering station was incredible luxus; it is not. It is supporting two temperature-regulated soldering pencils, one with 80W and one with 25W. I almost never use the 25W pencil (knowing the 80W pencil annot overheat), except if i need a tiny solder tip or i solder copper wire to my phono cartridges pins. In this case i use a small cooling clip especially made for cartridge pins. Never had an internally unsoldered phono cartridge by doing this.
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