Electronic – For how long can one hold a soldering iron on a component pin when soldering


Somebody told me not to keep a soldering iron on the pin of a through hole package for more than 2 seconds. I am not aware of where he got this number from.

When soldering we come across discrete passive and discrete active components, then we have integrated circuits that connect the die to the package via very thin bonding wires. We have very passive tiny surface mount components like SMD resistors and also really huge power transistors.

How do we know for how long we can keep the soldering iron tip on the component without damaging it?
What temperature does one usually use when soldering, is it the same for all applications?
If this time duration is not enough and we need to put the tip back to complete soldering, how long do we need to wait so we can apply the soldering iron for full duration without damaging the component?
Finally what determines what shape of tip to use when soldering?

Best Answer

Like everything in engineering... IT DEPENDS

Time, by itself, is meaningless. There are a few competing concerns:

The temperature must reach the melting point of the solder material. This depends on the type of solder, the parts (mass and chemical composition), the soldering iron tip material and shape, power applied to the tip and its thermal conversion efficiency, and the ambient temperature (ex. preheaters).

It's not just about temperature, but how quickly you get there. If temperature rise is too slow, the total energy transferred past the pin to the internal part may be sufficient to damage or derate it. That is why all components come with either a JEDEC/IPC reference profile and/or a soldering temperature profile. This profile is an energy chart showing temperature vs. time.

If you ramp the temperature up too quickly you can get thermal fracturing of the part as the different elements inside expand at different rates breaking free of the ultrasonic bonding or lead frame.

If you leave the iron in contact for way too long you will overheat the part resulting in the destruction of the packaging (plastics don't fair so well, ceramics do much better) and the functional loss of the silicon die inside. There are many failure scenarios for microchips from overheating ranging from the obvious burn-out (physical fault) to the loss of function from ion-migration in the doped-semiconductors.

...but 2 seconds is a good average

The reason you hear 2-3 seconds as a "rule" is that for most parts and most irons and most situations and most PCB's and most... this time value works out safely.