TO-39 Can substitute

Discussion in 'General Electronics Chat' started by cmstratton, Jan 7, 2016.

  1. cmstratton

    Thread Starter New Member

    Jan 7, 2016
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    I have an application that uses a 2N3440 transistor, which is in a TO-39b package, in a very demanding environment, high temp 300 DEG F plus, and a lot of vibration. Eventually one of the leads will break. I've tried mounting it flush to the PCB, away from the PCB, buffered with silicone, etc, but eventually it will break. Does anyone know a substitute in a flat package like a TO-220? Thank you in advance



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  2. RichardO

    Well-Known Member

    May 4, 2013
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    The MJE340 might work. The biggest problem is that it is in a plastic packge that limits the operating temperature to less than 150 deg. C. A TO-220 packaged device would have similar temperature limits.
     
  3. crutschow

    Expert

    Mar 14, 2008
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    Staking it to the board flush with epoxy should prevent any lead breakage from vibration.

    Edit: The silicone you used likely had too much give and allowed the transistor to move under vibration, causing the lead breakage.
     
    Last edited: Jan 7, 2016
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  4. dl324

    Distinguished Member

    Mar 30, 2015
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    Part is readily available. Why are you looking for a substitute? Is it someone else's design?
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    300F is 149C. TIP47, 48, 49, 50 with 2 degrees F to spare. What gain do you need?

    ak
     
  6. cmstratton

    Thread Starter New Member

    Jan 7, 2016
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    Hi-Thanks. Not sure of the gain. here is a link to the circuit http://www.logwell.com/schematics/10/CCLSIEa.pdf Note: The circuit shows two different transistors, but I use the 2N3440 in other devices, and I have a lot of them on hand, and it works just fine

    Check out the name of the site: Analog Services, Inc. Why are you called the AnalogKid? These are tools that are lowered into oil wells, BTW
     
  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Few silicones have any structural strength at your operating temp. They will flex like the silicone is not even there. Use a high temp epoxy - contact masterbond.com for a recommendation.
     
  8. SLK001

    Well-Known Member

    Nov 29, 2011
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    I used to work in the design of Dual Laterallog down hole logging equipment. I am familiar with the temperature requirements. However, where is the vibration coming from? How is the device failing? Are the leads fracturing? Is the device breaking at the solder joint? Are you using high-temp tin-silver solder?

    Our tools precluded the use of any plastic package, as we had a design spec of 325 F. We never experienced any failures like this.
     
  9. cmstratton

    Thread Starter New Member

    Jan 7, 2016
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    Thank you for all of the input. These tools are lowered into water injection wells, and consequently there is a lot of lateral movement. The break usually occurs where the collector is welded to the can. I think that the mass of the can is too much for one lead, and consequently it breaks. Thanks again.
     
  10. SLK001

    Well-Known Member

    Nov 29, 2011
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    There is (at least used to be) a heatsink that mounted via a stud on a PC board in which a TO-39 can is inserted. The leads are then bent over into the PCB holes. If these don't exist any more, then have a hole (the diameter of the can)/pad made in the PCB, then mount the can into the hole and solder it to the board. Then bend the leads to their holes.
     
  11. PeterCoxSmith

    Member

    Feb 23, 2015
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    In some aerospace applications with high levels of vibration we used a transistor mounting pad and polysulphide glue.
     
  12. crutschow

    Expert

    Mar 14, 2008
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    I agree with Peter.
    Such a glue mounting procedure was also used on the aerospace boards I worked on that had to survive high levels of vibration.
    Staking the transistor with the proper glue should prevent the failures you've noted.
    If the transistor can't move, then vibration can't cause lead flexing and fatigue failure.
    No need to change the transistor or add some more complex mounting scheme.
     
  13. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Not always true. MIL-STD-810 and MIL-STD-901 have some extreme test requirements, and I have seen individual transistor leads and film and ceramic capacitor leads break, and relatively small aluminum electrolytics with a 360 degree continuous bead of RTV come flying off the board. For some magic reason, 1/4 W metal film resistors seem to be immune.

    ak
     
  14. crutschow

    Expert

    Mar 14, 2008
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    We're taking about adhesives much stiffer than RTV.
     
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  15. SLK001

    Well-Known Member

    Nov 29, 2011
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    Relatively small moments of inertia.
     
  16. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    And the tin can on this transistor likely has a simple butt joint to the brazed/soldered collector pin. I doubt there is any mechanical attachment (e.g. tapered pin) to the assembly.
     
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