Connect with us

Desoldering

Discussion in 'Troubleshooting and Repair' started by somanshumehta, Nov 8, 2013.

Scroll to continue with content
  1. somanshumehta

    somanshumehta

    16
    0
    Jun 22, 2013
    Actually I have an old desktop motherboard and I am trying to desolder some comonents for a small project like capacitors,inductors and more.I cannot desolder using a 30W soldering iron,while the same can desolder components from usual PCB.I guess, the problem is with the temperature needed for desolder and also the solder wire composition.My solder wire is 60/40 Pb-Sn while industries use 67/37 Pb-Sn so the melting temperature is high.
    Can a 250W soldering iron solve my problem.
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    10,068
    2,150
    Nov 17, 2011
    A 250W soldering iron is likely to destroy the componens by overheating. A 30W soldering iron should suffice.
    Try adding some fresh solder to the joints you want to de-solder. The flux from the fresh solder helps liquifying the old solder. Also solder wick or a desoldering pump may come in handy.
     
  3. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    No electronics solder has more lead than tin. High lead solder was used by plumbers where pipe joints were wiped. This solder had quite a wide pasty phase. There is much confusion here since both electronic solder and plumbers solder are 60/40, just the opposite way round.

    60% tin 40% lead is at the eutectic where the solder is either liquid or solid with no pasty phase and is the minimum possible melting temperature.

    The rules have now changed and lead is banned so solder is almost pure tin and the melting point is higher. Some people suggest adding eutectic solder to bring the melting point down.
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,268
    Nov 28, 2011
    PC motherboards have at least eight layers, including two internal power plane layers, so the board itself absorbs heat very rapidly. That's why it's almost impossible to salvage components from them.

    I used to try; now I normally only try to salvage crystals and crystal oscillators, which are generic enough to be useful for other projects, and don't have many connections. Even then, most of them either won't come off, or break, so I've almost given up on them as well. (I only have a temperature-controlled soldering iron, no special desoldering equipment.)

    For SMD transistors and MOSFETs, you might find you can lift the leads one at a time if you can melt the solder first and use desoldering braid to remove most of it. Then the lead only needs to be raised slightly off the pad to detach it. Removing the heatsink pad is still going to be difficult, especially as it may have thermal vias to improve heat dissipation! (In that case, you might find heating it from below is effective. That's what the Chinese salvage people do. But you shouldn't re-label the salvaged components and sell them.)

    You could try adding low-melting-point solder and heating the board with hot air from above or below. There are commercial solutions for this. I haven't tried any of them. Google low-melting-point solder.
     
    Last edited: Nov 9, 2013
  5. somanshumehta

    somanshumehta

    16
    0
    Jun 22, 2013
    I got it will try next week.Meanwhile,Is it possible to desolder all components of a computer motherboard even with use of heat furnace for high teperatures.
     
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,268
    Nov 28, 2011
    Probably, but a lot of them will be damaged. Large surface-mount packages absorb moisture from the atmosphere (this is why they are packaged in airtight bags) and if heated (apart from during initial assembly when they are fresh out of the bag) they can crack! Even if they don't crack, their performance can be affected. They may appear to work but fail a parametric test, or they may seem to be OK but fail later. Motherboards are throwaway items :-(
     
  7. eKretz

    eKretz

    251
    27
    Apr 8, 2013
    That is definitely true. There are different grades of humidity sensitivity, but if you bake the boards in the oven at lower temps to drive out moisture before reclaiming components they will usually be alright.
     
  8. jpanhalt

    jpanhalt

    426
    4
    Nov 12, 2013
    Periodically someone seems to rediscover using a torch on the back side of a PCB to remove parts. It works. Just get the back good and hot. Then flick the board over something to catch the parts. If you are uncomfortable with a broad-flame torch, use an industrial hot-air gun.

    John
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,397
    2,777
    Jan 21, 2010
    A colleague of mine made a device with a fan heater on one side to heat the reverse side of the board to about 120C.

    This is cool enough not to damage too much (or to melt soldered components on the back of the board), and makes it easier to work on the top side.

    It makes it a lot easier to work with boards having large ground planes.

    I've not tried it with a motherboard, but I expect it would help.

    I guess it all depends on what you're doing. Are you trying to remove or replace just one component, or are you "working in bulk".

    This approach doesn't work well for through-hole components.
     
  10. Henrich111

    Henrich111

    1
    0
    Sep 19, 2019
    A lot has been said about soldering copper on the forum, but in pieces and fragments. Having been tormented to collect these grains of truth, I decided to scribble a consolidated posting, in which to combine knowledge from the forum, and a personal little experience of soldering. And I found a great article, read here.https://solderingironguide.com/blog/how-to-desolder/
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-