Soldering iron: do I need high power for desoldering? - Page 1
Forum section: electronics / beginners

author: rubenvann
author_rank: Newbie
timestamp: June 10, 2017, 12:33:59 pm
content: I've had an extremely cheap 48W soldering iron (Basetech ZD-99:image) for a while now that I always (more or less) happily used. Yesterday I decided to salvage an ancient motherboard for parts, using a desoldering pump and solder wick to get the old solder of. I was mainly interested in the coils and some of the connectors. Sadly, I didn't get that far. The desoldering was very frustrating. Initially, the solder just would not melt, even when I set the solder station to maximum temperature. Things worked a little bit better when I added some flux (although I have a flux syringe and not a marker like Dave always uses, it's not great) and fresh solder. It seemed to spread the heat a little better, and together with pulling the components and heating the joints (not recommended) I've had some success for some of the smaller components.However, some of the bigger inductors and capacitors have bigger joints. I was simply not able to melt the solder. After touching the joint for a few minutes with the hot soldering iron, I was able to scratch some of the solder of. I tried to get more solder of this way, but my soldering iron broke in half when I applied some pressure (I did apply more pressure than usual, but not excessively much: maybe just enough to break a pencil).So, I have no soldering iron and I still want to desolder these big joints with the next one I buy. Some things are clear. I want1. OK quality (e.g. doesn't break)2. A temperature indication on the thing (seriously, the one I bought did not have one) or maybe even a temperature regulated one.Do I also need higher power? The one I had before was slow to heat up (I'm not sure how slow because there was no way to know what temperature the iron was at or at what temperature it should be, but it took 10 minutes at least before solder showed some kind of reaction) and could not melt the solder on big joints. Is this normal? If not, the soldering iron might be miscalibrated.TLDR; Do I need a (more expensive) high power soldering iron for desoldering? Any other advice?

author: bktemp
author_rank: Super Contributor
timestamp: June 10, 2017, 12:42:11 pm
content: Even with a high power soldering iron it is difficult to desolder parts from a multilayer pcb with large ground and power planes.What you need is a preheater: If the whole pcb is at >100°C it is much easier to melt the solder and remove components.

author: P90
author_rank: Frequent Contributor
timestamp: June 10, 2017, 12:46:44 pm
content: Large pads and components act as a heat sink. Your iron needs to have more thermal mass, a bigger tip might help. that looks like a 30-40w iron and not the best. You need something that can revover thermally quickly.

author: Brumby
author_rank: Unknown
timestamp: June 10, 2017, 01:49:09 pm
content: Quote from: rubenvann on June 10, 2017, 12:33:59 pmThis was a clue. It is not good for it to take that long. The same time and temperature limits you use for soldering should also be applied when desoldering. Components can only survive so much heat for so much time - and they don't distinguish between soldering and desoldering. Since desoldering is far more challenging, you have to be more aware of these limits.Coils and connectors will still have limits. Excessive heat/time on connectors can result in softened plastic and deformed connectors - and coils aren't indestructible.As said above a preheat will help significantly. Also getting a desoldering unit - something like the ZD985 which has an 80W temperature controlled iron - which is purpose built for the job will make it amazingly easier.

author: madires
author_rank: Super Contributor
timestamp: June 10, 2017, 02:11:07 pm
content: If you got a heat gun you could use it for preheating the PCB, also for desoldering parts after gaining some experience. Practice with some junk boards first.

author: David Hess
author_rank: Super Contributor
timestamp: June 10, 2017, 02:22:40 pm
content: bktemp identified the problem and I have encountered it as well; the massive copper ground and power planes in the motherboard make it very difficult to apply enough heat to melt the solder.1. Preheat the board.2. Use more soldering irons.3. Use a higher heat capacity solder iron. Note that this has nothing to do with temperature.4. Maybe use something to lower the melting point of the solder likeChipquick.5. If you do not care about destroying the board, then use a propane torch.

author: P90
author_rank: Frequent Contributor
timestamp: June 10, 2017, 04:14:38 pm
content: a Hakko desoldering gun works good, but it's expensive!

author: Brumby
author_rank: Unknown
timestamp: June 11, 2017, 03:05:09 pm
content: Pre-heating is useful - but the question is how hot do you do that? Certainly not solder melting temperatures. Just enough to "take the chill" off the board (for electronic components) is what is being suggested. Somebody mentioned getting over the 100ºC mark, which is something to consider.Depending on the coil, some can take quite a bit of heat - but you can still damage them if not careful.It takes a bit of experience to get the feel of what you are trying to desolder - and to learn what works and what doesn't.Get some scrap boards and try your hand. Don't fret too much when things go wrong - you will learn a lot.Good components successfully salvaged will be a bonus.

author: innkeeper
author_rank: Unknown
timestamp: June 17, 2017, 06:46:44 pm
content: I've personally started looking for an iron with a large thermal mass, as the haako clones i use simply don't have the thermal mass to desolder multi plane boards well.I end up cranking up the heat to compensate, but that's not the right answer.I'll give the preheat a try in the mean time.