Hard Question, need an expert on soldering

Discussion in 'General Electronics Chat' started by jayjay1010, Jul 2, 2017.

  1. jayjay1010

    Thread Starter New Member

    Jul 2, 2017
    2
    0
    I have 15 years of all types of SMT and thou hole soldering/rework.

    I recency had an automotive part fail, idle control value in a BMW. straight forward circuit. It was sealed in some rubber type resin i manage to remove.

    I tried to remove a small sot-23 diode and could not, I then tried to solder some pins, nothing touched it.

    I then used hot air to just experiment and remove a basic 1206 cap, nothing touched it. My thoughts was lead free solder higher temp, so wacked up fuill hot air.

    So I basically put a serious amount of heat close up, the cap even slightly started to dis color. Nothing touched it or any of the 20 components on the small board.

    Has anyone ever come across an un solder able PCB? the components are standard IC;s and transistors. I manage to get some solder to stick to a leg of a mosfet and the side if the 1206 capacitor, but for 30 minutes of trying to solder or hot air remove a component I failed.

    dose anyone have any idea what on earth is going on? i though glue, but there not glued down. its just really strange. plenty of flux, heat etc nothing.

    Jason
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    15,654
    4,559
    Are you sure the potting compound was not between the SMT device and the board?
    Max.
     
  3. KeepItSimpleStupid

    Distinguished Member

    Mar 4, 2014
    2,772
    492
    yep. It wasn't solder. It was conductive Epoxy. See http://www.mouser.com/pdfdocs/FAQOtherConductiveEpoxy.PDF

    Quote:

    Conductive epoxies are mainly used in
    applications where the risks of mechanical and
    thermal cracking are very high, as well as when
    there are concerns about damaging heat
    sensitive components on the PCB during
    soldering
     
  4. jayjay1010

    Thread Starter New Member

    Jul 2, 2017
    2
    0
    Thanks very much - can you tell me if it's pitiable to rework small SO8 ic and Mosfets with the eproxy paste - do I need to smash them off? Do you have any tips for reworking please
     
  5. KeepItSimpleStupid

    Distinguished Member

    Mar 4, 2014
    2,772
    492
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