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power dissipation capability

Discussion in 'General Electronics Discussion' started by electronicsLearner77, Jul 7, 2015.

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  1. electronicsLearner77


    Jul 2, 2015
    I very frequently hear the term power capability of an ic. what exactly is this? how an ic can dissipate its heat? suppose if it crosses the limits, does the bonds inside the ic gets separated? what exactly happens? on what factors does it depends like manufacturing etc. How heat sink is related with this? please help.
  2. Martaine2005


    May 12, 2015
    It's something to do with thermal resistance. And probably to do with manufacture.
    A good example would be a computer processor that gets so hot it needs a heatsink and fan.
    A calculator has a processor which can run all day without getting hot.
    It clearly has something to do with speed and what it handles too.

    I found this online and it's way above my understanding but interesting.
    Have a read here

  3. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    The thermal energy flows from the source (where the heat is "produced" within the ic) to the ambient air via the case and the electrical connections /pads) of the ic. This is where the thermal resistance comes into play. It describes how many Kelvins per Watt of dissipated power will develop across the thermal resistance.
    The concept is modelled after voltage sources, resistors and currents:
    • The source of thermal energy is equivalent to a voltage source.
    • The thermal resistance is equivalent to an Ohmic resistance.
    • The flow of thermal energy (heat) is equivalent to electrical current.
    Read Martin's link for more detail.

    Unlikely. The bonds are like welds and wil not easily melt from the thermal energy. The fine structures within the silicon and the metallization of the chips will break down from too much heat long before the bonds.

    Many. Choice of semiconductor material, size of the structures on the chip, how the chip is thermally coupled to the housing (e.g. housing with built-in heat sink) etc.

    The thermal resistance (see above) is a series connection of different smaller thermal resistances. For simplicity let's assume there are just two:
    • Rjc = thermal resistance from the junction(s) within the chip to the case
    • Rca = thermal resistance from the case to the ambient (typically air)
    Rca is typically rather high which means for a given power (in Watt) a rather high temperature will develop across this resistance (T=P*Rca). As the ambient typically has a more or less fixed temperature (e.g. room temperature of the surrounding air), this means that the interior of the chip heats up accordingly. By adding a heat sink, Rca is reduced from a high Rca to a smaller Rhsa (heat sink - air). Consequently the temperatre drop will be smaller, too, and the chip will not heat up as much as without heat sink.

    Note that this explanation deals with the thermal aspects of teh "power capability" only, as you specifically requested info on these details. The "power capability" of a component may be limioted by other factors as well (without coming even near to the thermal limit), e.g. by max. voltage or max. current.
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