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6656 Views 9 Replies Latest reply: Sep 11, 2014 2:10 AM by Scott594 RSS
Currently Being Moderated

Aug 11, 2014 12:42 AM

What's Happening To This Transistor

I haven't had the chance to do an in depth study of the circuit but I would like to ask what happened to this transistor? What is that yellowish goo that's coming out and why does it look like its shifting to the left side?

Could this be just an issue with poor soldering or is this a natural thing to expect in time.

 

Thanks!

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  • troubleshooter Novice 1 posts since
    Aug 11, 2014
    Currently Being Moderated
    Aug 12, 2014 1:05 AM (in response to Riley)
    What's Happening To This Transistor

    Hello Riley,

     

    My first impression is you're referring to the brownish flux residue. That's my opinion.

    Flux does not come out af a transistor, it is applied to the board prior to soldering.

    This part could have been out of place when it was assembled, but also it could have overheated and melted the solder, and slid.

    I would start by diode check the junctions in circuit, and careful visual to see if you can tell if the legs are still on the correct pads, and no shorts to adjacent pads, or the heatsink pad underneath (which might be same as the collector leg pad).

     

    Some fresh flux, and reflow it and position it square on it's pads would be good, by requires some experience.

     

    Is the circuit defective?

    If it is functioning normally, and was always like this, I would consider leaving it alone.

    (It would depend on your skill and other circumstances; if legs are close to shorting, heat dissapation, etc)

     

    If it's working, you might be best to leave it.

    Hard to advise on information given or knowing your skill level.

     

    Mr K L

  • depureanu Novice 1 posts since
    Aug 12, 2014
    Currently Being Moderated
    Aug 12, 2014 3:56 AM (in response to Riley)
    What's Happening To This Transistor

    Este flux,decapant la lipire. Curios este ca pozitia tranzistorului este anornala.Este posibil sa fii fost relipit !

  • cgervasi Novice 1 posts since
    Aug 28, 2014
    Currently Being Moderated
    Aug 28, 2014 1:08 PM (in response to Riley)
    What's Happening To This Transistor

    You could try cleaning it off with alcohol and a toothbrush.

  • AJ2X Novice 2 posts since
    May 29, 2014
    Currently Being Moderated
    Aug 28, 2014 2:52 PM (in response to Riley)
    What's Happening To This Transistor

    My immediate thought upon seeing the picture is, "that transistor has gotten VERY hot!"  I assumed it was soldered in place properly initially, but at some point it got so hot that it began to desolder itself, which is why it has moved from its proper location on the pads. (If the board is mounted vertically, gravity could well have moved it when the solder began to liquify.)  The flux has melted from areas around it and puddled on the pads.

  • StewartH Novice 2 posts since
    Aug 28, 2014
    Currently Being Moderated
    Sep 10, 2014 5:24 PM (in response to Riley)
    Re: What's Happening To This Transistor

    Yeah, it's the flux used in the solder operation, plus, they did not align the part very well. Poor alignment, poor cleaning, not a real pro-job. Leaving the flux there may be harmless, depending on the type and the use of the circuit - humidity and temperature cycling can cause the flux to spread over the board, contaminating more impedance and current sensitive parts of the circuit.  I have been trying to get Comcast to fix their screwed up remote controls - everyone of the 6 I have gotten from them have quickly stopped working due to contamination of the contact points in the remote due to their abject failure to remove the solder flux from the board: stupid and sloppy is no excuse.

  • Scott594 Novice 6 posts since
    Aug 21, 2013
    Currently Being Moderated
    Sep 10, 2014 4:25 PM (in response to Riley)
    What's Happening To This Transistor

    It HAS been severely overheated, to the point of melting the solder. This is confirmed by the outline of flux to the right of the pad, where the transistor was originally positioned, and the drag lines left in the flux as it slid to the left.

     

    I'd recommend identifying it's function, and determining why it overheated to such a degree, replacing it and any other components in circuit that may have been damaged as well. It seems there is an inadequate protection system, or it has failed.

     

    When it overheated, it approached fire hazard temperatures, and you should find out why and correct the malfunction. From there you should be able to put together the rest of the story.

     

    good luck!

    Scott

    • StewartH Novice 2 posts since
      Aug 28, 2014
      Currently Being Moderated
      Sep 10, 2014 5:48 PM (in response to Scott594)
      Re: What's Happening To This Transistor

      Interesting perspective. While the body of the part shows smeared flux that could arguably have been smeared from overheating, I do not think that explains the excess flux around the pins, which does not appear to be from the same effect. Most SMT parts are self aligning, but this one, if from original misplacement is skewed enough to possibly prevent it.If the part overheated and misaligned, assuming it was originally proper aligned, it would only misalign if the attitude of the board was not level  by a large anglular tilt, or if it got bumped: The part does look like its body has contacted the part to its right but there is no discoloring of the text or the body.

       

      I did not discuss overheating, as the original inquiry did not state the circuit is not working - his second post says it appears to be working fine. The.part is a power transistor, which can get pretty hot. The part datasheet does not list any internal thermal protection/shutdown. A temperature proble on cold start up would detect rapid heating.

       

      I am still persuaded it was from sloppy assembly.

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