Electronic components that contain a die require a path by which excess heat can be removed from the component package. In low-voltage plastic-encapsulated microcircuits, the heat may simply travel by conduction through the die attach and the die paddle for dissipation through the bottom of the package. In higher-voltage integrated circuit (IC) packages and in larger items such as insulated-gate bipolar transistor (IGBT) modules, a separate metal heat sink may be adhesively bonded to the package. The heat sink promotes conduction and prevents the temperature of the die from rising to a point where the circuitry on the die will fail. The bonding agent holding the heat sink in place may be solder, epoxy or another material. The heat sink is usually on the bottom of the component package, although some flip chips have a heat sink on the top side of the package.
In products where system longevity matters, it is worthwhile to inspect the bonding of the heat sink to the component in order to avoid components that have internal structural defects that will compromise the dissipation of heat from the die. The most frequent defects are gaps of some type in the bond holding the heat sink in place. The gaps may be voids (trapped air bubbles), non-bonds (where a factor such a surface contamination prevents adhesion of the bonding material) or cracks. The terms disbond and delamination may also be used for these defects.