Need help disassembling LED flasher

Discussion in 'The Projects Forum' started by AndrejaKo, Sep 17, 2010.

  1. AndrejaKo

    Thread Starter New Member

    Sep 6, 2010
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    My first post here, so if I picked wrong forum, I apologize.

    Anyway, here's my story:

    Few days ago I decided to get needed equipment to get into electronics.
    I currently have available:
    250g of ELSOLD 1mm 60%Sn/40%Pb solder with ELTIN 3064 flux inside
    1.6m of 2mm wide amasan L20 desoldering braid
    SOMOGYI electronic SMA HSP 75 desoldering pump
    ERSA Multitip 25W soldering iron with 172BD tip (circular, 1.1mm diameter)
    some generic sponge

    For my first project I decided to disassemble a LED flasher. I hope to gain experience by disassembling it and to obtain some electronic components. Since I'm not very experienced, I don't expect to actually be able to desolder most of the components and have them work after.

    The flasher is LOUPI Electronic Art Gallery IL-ED01-v2.

    After all this exposition, I finally came to my problem.

    The flasher consists of basically three main components. A piece of plastic, one battery compartment and a printed circuit board.

    My first problem is the piece of plastic. The PCB and battery compartment are glued to it using white foamy adhesive pads (such pads are visible on pictures under LOUPI link) which I've often seen used in electronics but I do not know their name. I'm looking for a relatively easy way to destroy them without damaging the PCB and battery compartment. I managed to separate PCB form the plastic part, but remains of the pad are still on the PCB and seem difficult to scrape off.

    My second problem is PCB itself. The traces and terminals are mostly clearly visible and it looks like it's going to be easy to disassemble most parts, but there are two things which are problematic.

    The points where the battery compartment is soldered to the PCB are covered in what looks like silicon paste (looks like the one used in plumbing). I assume that it is not wise to poke it directly with soldering iron and would appreciate any tips on how to remove it. It does look like it could be scraped off without causing much damage.

    The second problem is that a part of the PCB is covered in some black mass. It looks like it was liquid at one time but is solid now. Again, I've seen it several times in electronic devices but I do not know its name. It looks solid and I do not believe that I could just scrape it off the PCB. Also, it looks like there are some components covered by it. I'm looking for tips on how to remove it.
     
    Last edited: Sep 17, 2010
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Why not make your own circuit instead of trying to take apart the one that has a "chip on board" (black mass which is a bare chip welded to the board and covered in black epoxy) and is glued together?
    The circuit is probably extremely simple.
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    As AG said, the components are extremely cheap, I figure the whole thing could be had for a $1. You can even buy LEDs that flash all by themselves.

    If you want to learn hang around, you will find lots of folks (like me) that like to teach. We also have a fairly good text book online, see the top of this page.
     
  4. AndrejaKo

    Thread Starter New Member

    Sep 6, 2010
    16
    0
    Actually, I've been lurking here for some time and I've read a big of the book itself. It looks nice and is easy to read. :)

    From parts of the circuit I can see, it does look very simple. My reasons for messing around with it are to practice desoldering and lack of time needed at the moment to design (or find designed) circuit and buy all needed components to assemble it.

    And yes I do know that simple electronic components are very cheap and that I won't gain much by using ones recovered form the circuit.

    As for the epoxy glue, can it be removed with acetone? They are rare in my country so I don't have any experience removing it.
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    Maybe, but probably not. It is meant to be forever. There used to be an active hacking industry for things like satellite receivers that opened up the chips, but I've been out of touch with that for decades.

    You could try it and see.

    With my job I see enough bare die to last me a lifetime.
     
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  6. Audioguru

    New Member

    Dec 20, 2007
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    Acetone melts plastic, not epoxy.

    The chip that is covered in black epoxy is extremely small and delicate. You will not be able to connect to it because it is tiny.
     
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  7. AndrejaKo

    Thread Starter New Member

    Sep 6, 2010
    16
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    OK. Thanks!
    Any ideas for the silicone? Or should I just scrape it off? EDIT: It came off easily with some scraping.
     
    Last edited: Sep 17, 2010
  8. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    You will find most technical people take things apart, it is part of the process. Putting it back together again, not so much. My advice is experiment, but don't expect to get anything salvageable. You want something salvageable, look for large items like TVs and VCRs. They will keep you in parts for months or years. The odds are this gadget you are messing with isn't built that way however.

    If it is raw chip on a PCB that has been bonded (with especially dedicated machinery called bonders) you do not have a chance, not even a small one, of recovering anything. Don't let it discourage you, because you will learn something look at the innards. I've been known to take small files and gently remove the tops of transistors. They will work, and eventually die because the hermetic seal is gone, but it is interesting to study meanwhile (and they make phototransistors meanwhile).

    Case in point, I just bought some SMT (surface mount technology) 2N2222A NPN transistors for 4¢ each. Resistors are 2¢ in quantity (3¢ if not), capacitors are the expensive parts at 19¢ and up. If you have a blank PCB, a fine point sharpie (a brand of magic marker), and some house hold chemicals you can etch your own board. While they didn't have SMT when I was a kid I did make my own PCBs with sharpies, that was very educational. This was a short while after my Dad gave my brother and me a 300 in 1 project kit, and I wanted to make some of the circuits in a more permanent setting.

    You may have to do some research, but the parts are out there.
     
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  9. AndrejaKo

    Thread Starter New Member

    Sep 6, 2010
    16
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    Thanks for the encouragement!
    I did eventually manage to remove everything except the contents of the area covered by epoxy.
     
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