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Hot Air Soldering

Discussion in 'General Electronics Discussion' started by chillydk147, Jun 23, 2015.

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  1. chillydk147


    Jul 25, 2014
    Hello, I have had some boards manufactured, the PCBs have all other components soldered except for the MCU, which for cost reasons will be soldered by myself. I've recently acquired a Hot Air soldering station which I hope to use, on inspecting the PCBs, I noticed that there are what look like tiny bits of solder already on each of the contacts for the MCU. Would I be correct in assuming that I don't need to use anything like solder paste, that all I need to do is position the MCU and apply some heat, the pre-soldered should bind to the MCU pins, please see attached photo.

  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Yes, this is solder from the fabrication process - obviously the solder mask included the mcu as normally this part would be assembled in the same process as the other components.
    Soldering a part onto these bumps is going to be difficult:
    • The bumps are uneven, making it difficult to position the part exactly
    • The solder lacks flux as it has been heated and cooled during the first fabrication process. This will make it difficult to use the same solder for the mcu
    A hot air station, unless equipped for soldering all 4 sides of this package simultaneously, is not the perfect tool for this task.
    I recommend you remove the solder bumps as well as you can to get an even surface for placing the mcu. Instead of using hot air, use an iron with a fine tip and very fine solder wire to manually solder each pin.
    garublador likes this.
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