SMD components and soldering temperatures?  Do they just handle it? - Page 1
Forum section: electronics / repair

author: Fried Chicken
author_rank: Regular Contributor
timestamp: March 06, 2025, 03:11:15 pm
content: These things are tiny, so they must have an equally tiny thermal mass.It's my understanding when soldering through hole or surface mount ICs, you want to go carefully on the legs: skipping every other one as you go so as not to heat a single part of the chip too much. Even regular through passive components, the rule of thumb is no more than 2-3 seconds of heating.It's also my understanding that heat (with time) kills these components, especially capacitors. It's why you want your electronics well ventilated, you don't want things running at a million degrees forever.Well in comes repair and rework of SMD components, especially stuff like hot air: literally oven bake the entire chip until it's hot enough that it melts the solder around it and to it. Even with regular soldering, the thermal mass of these chips is so small, just sticking a soldering iron and melting solder onto it, I don't see how that little component doesn't entirely heat up to the solder melt temperature.Now let's add lead-free solder that bumps the required temperatures up another 100°F or so.... are these components simply designed to handle these temperatures? If I have an SMD capacitor going in with lead-free solder, basted in flux, am I to understand that I can simply bake the whole thing until it sets with no harm no foul?Are there industry norms/standards on this? I don't get it.

author: benj38
author_rank: Frequent Contributor
timestamp: March 06, 2025, 07:03:04 pm
content: The short answer is: "Yes, these tiny components can take the heat".I have had SMD resistors and ceramic capacitors left on the tip of my iron for 15 minutes and then measure perfectly fine (I would obviously never use such an abused component just to be on the safe side).The extra fear of heat I think originates from the days transistors were made of germanium, which is much more heat sensitive than silicone-based semiconductors.I have yet to encounter an SMD component that was killed by soldering or rework unless it was super abused. In most cases the PCB will be damaged well before the component is. Note, of course, that I do not refer to SMD electrolytic capacitors which should be treated more gently, nor connectors which have to be soldered very carefully not to have their plastic bodies melt. Reworking such connectors is hard, and it is not uncommon that the more sensitive ones can not be removed without damaging them.Note that many manufacturers provide official soldering instructions for their components, sometimes in the datasheet, and sometimes in dedicated documents with titles like "recommended soldering profiles", so you can look at some of these to get a feel of things.BTW, the melting point of most SAC alloys is only about 60°F more than eutectic tin-lead.

author: Kurets
author_rank: Regular Contributor
timestamp: March 08, 2025, 01:41:25 pm
content: Solder stress does impact clmponents, but it is unlikely to do meaningful harm for hobbyists. Ceramic capacitors do take a big hit in reliability if they are hand soldered due to the uneven heat causing mechanical stresses.But, that is something which matters if you require that your build can take several years of daily thermal cycling etc. For a hobby project, it completely does not matter.