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