question: Why do electronics get hot?
comment: Electronics work by taking electricity and doing work with it. As energy can’t be created or destroyed, the energy required to transform a physical object between two states that is greater than the energy it can contain at rest has to go somewhere. It ends up being released as atomic motion, which we call heat.
passages: Section::::Electrical engineering.
  
  Some electronic components develop lower resistances or lower triggering voltages (for nonlinear resistances) as their internal temperature increases. If circuit conditions cause markedly increased current flow in these situations, increased power dissipation may raise the temperature further by Joule heating. A vicious circle or positive feedback effect of thermal runaway can cause failure, sometimes in a spectacular fashion (e.g. electrical explosion or fire). To prevent these hazards, well-designed electronic systems typically incorporate current limiting protection, such as thermal fuses, circuit breakers, or PTC current limiters.
   Many electronic circuits contain special provisions to prevent thermal runaway. This is most often seen in transistor biasing arrangements for high-power output stages. However, when equipment is used above its designed ambient temperature, thermal runaway can still occur in some cases. This occasionally causes equipment failures in hot environments, or when air cooling vents are blocked.
  
  Section::::Electrical engineering.:Semiconductors.
   Section::::Radio-frequency heating.
   Heat generation in integrated circuits
  
  The heat dissipation in integrated circuits problem has gained an increasing interest in recent years due to the miniaturization of semiconductor devices. The temperature increase becomes relevant for cases of relatively small-cross-sections wires, because such temperature increase may affect the normal behavior of semiconductor devices.
  
  Section::::Joule Heating.
  
  Joule Heating is a predominant heat mechanism for heat generation in integrated circuits and is an undesired effect.
  
  Section::::Propagation.
   Thermal management (electronics)
  
  All electronic devices and circuitry generate excess heat and thus require thermal management to improve reliability and prevent premature failure. The amount of heat output is equal to the power input, if there are no other energy interactions. There are several techniques for cooling including various styles of heat sinks, thermoelectric coolers, forced air systems and fans, heat pipes, and others. In cases of extreme low environmental temperatures, it may actually be necessary to heat the electronic components to achieve satisfactory operation.
  
  Section::::Overview.
  
  Section::::Overview.:Thermal resistance of devices.
   For a certain definite purpose in a definite electrical equipment or a portion of it, definite type and size of materials (for boards,wires, insulators) with proper rating for voltage, current and temperature,are used. The circuit-resistance never kept too-low. Sometimes some parts placed inside the board and box, maintaining a proper distance from each-other, to avoid heat-damage and short-circuit-damage. To prevent short-circuit, on the wire-joints, appropriate type of electrical connectors and mechanical fasteners used.
  
  Section::::See also.
  
  BULLET::::- Wire gauge
  
  BULLET::::- Thermal resistance in electronics
  
  BULLET::::- Thermal management of high-power LEDs
  
  BULLET::::- Thermal design power
  
  BULLET::::- Heat pipe
  
  BULLET::::- Computer cooling
   Hot-carrier injection
  
  Hot carrier injection (HCI) is a phenomenon in solid-state electronic devices where an electron or a “hole” gains sufficient kinetic energy to overcome a potential barrier necessary to break an interface state. The term "hot" refers to the effective temperature used to model carrier density, not to the overall temperature of the device. Since the charge carriers can become trapped in the gate dielectric of a MOS transistor, the switching characteristics of the transistor can be permanently changed. Hot-carrier injection is one of the mechanisms that adversely affects the reliability of semiconductors of solid-state devices.
  
  Section::::Physics.
   High temperatures can also cause failure in connectors, resulting in an "avalanche" of failuresambient temperature increases, leading to a decrease in insulation resistance and increase in conductor resistance; this increase generates more heat, and the cycle repeats.
   Section::::Recent Innovations in ERH.:Controlled Low Temperature Heating.
   Resistors (and other elements with resistance) oppose the flow of electric current; therefore, electrical energy is required to push current through the resistance. This electrical energy is dissipated, heating the resistor in the process. This is called "Joule heating" (after James Prescott Joule), also called "ohmic heating" or "resistive heating".
  
  The dissipation of electrical energy is often undesired, particularly in the case of transmission losses in power lines. High voltage transmission helps reduce the losses by reducing the current for a given power.
   Electrical resistance (usually described as a material's opposition to the flow of an electric current) is used to convert electric energy into thermal energy as an electric current ("I") conducted through a material with resistance ("R") releases power ("P") equal to "P" = "I""R", where "P" is the power measured in watts, "I" is the current measured in amperes and "R" is the resistance measured in ohms.
  
  Section::::Processes.:Resistance soldering.
   Hot electrons arise generically at low temperatures even in degenerate semiconductors or metals. There are a number of models to describe the hot-electron effect. The simplest predicts an electron-phonon (e-p) interaction based on a clean three-dimensional free-electron model. Hot electron effect models illustrate a correlation between power dissipated, the electron gas temperature and overheating.
  
  Section::::Effects on transistors.
   An integrated-circuit chip contains many capacitive loads, formed both intentionally (as with gate-to-channel capacitance) and unintentionally (between conductors which are near each other but not electrically connected). Changing the state of the circuit causes a change in the voltage across these parasitic capacitances, which involves a change in the amount of stored energy. As the capacitive loads are charged and discharged through resistive devices, an amount of energy comparable to that stored in the capacitor is dissipated as heat:
   The term “hot electron” was originally introduced to describe non-equilibrium electrons (or holes) in semiconductors. More broadly, the term describes electron distributions describable by the Fermi function, but with an elevated effective temperature. This greater energy affects the mobility of charge carriers and as a consequence affects how they travel through a semiconductor device.
   Section::::Electrical engineering.:Batteries.
   Section::::Analogies.:Explanation from an electronics point of view.:Equivalent thermal circuits.
  
  The heat flow can be modelled by analogy to an electrical circuit where heat flow is represented by current, temperatures are represented by voltages, heat sources are represented by constant current sources, absolute thermal resistances are represented by resistors and thermal capacitances by capacitors.
  
  The diagram shows an equivalent thermal circuit for a semiconductor device with a heat sink.
  
  Section::::Analogies.:Explanation from an electronics point of view.:Example calculation.
   All electronic devices emit electromagnetic radiation. Because every wire that carries current creates a magnetic field, electronic devices create some small magnetic fields when in use. These magnetic fields can unintentionally reveal information about the operation of a device if not properly designed. Because all electronic devices are affected by this phenomenon, the term ‘device’ can refer to anything from a desktop computer, to mobile phone, to a smart card.
  
  Section::::Background.:Electromagnetic radiation.
   Overheating (electricity)
  
  Overheating is a phenomenon of rising of temperature in an electric circuit (or portion of a circuit). Overheating causes potential damage to the circuit components, and can cause fire, explosion, or injury. Damage caused by overheating is commonly irreversible; i.e. the only way to repair is to replace some components.
  
  Section::::Causes.
  
  On overheating, the temperature of the part rises above the operating temperature. Overheating can take place
  
  BULLET::::1. if heat is produced in more than expected amount (such as in cases of short-circuits, or applying more voltage than rated), or
   Section::::Microscopic description.
  
  Joule heating is caused by interactions between charge carriers (usually electrons) and the body of the conductor (usually atomic ions).
  
  A voltage difference between two points of a conductor creates an electric field that accelerates charge carriers in the direction of the electric field, giving them kinetic energy. When the charged particles collide with ions in the conductor, the particles are scattered; their direction of motion becomes random rather than aligned with the electric field, which constitutes thermal motion. Thus, energy from the electrical field is converted into thermal energy.
  
  Section::::Power loss and noise.
   Section::::Soldering of electronic products.:Reflow process.:Ramp-Soak-Spike.
   The power supply of an electrical system tends to generate much heat. The higher the efficiency, the more heat is pulled away from the unit. There are many ways to manage the heat of a power supply unit. The types of cooling generally fall into two categories -- convection and conduction. Common convection methods for cooling electronic power supplies include natural air flow, forced air flow, or other liquid flow over the unit. Common conduction cooling methods include heat sinks, cold plates, and thermal compounds. 
  
  Section::::Overload protection.
   Section::::Radiation effects on electronics.:Resultant effects.:Systems-generated EMP effects.
  
  SGEMP are caused by the radiation flash traveling through the equipment and causing local ionization and electric currents in the material of the chips, circuit boards, electrical cables and cases.
  
  Section::::Radiation effects on electronics.:Digital damage: SEE.
   A thermal interface material or mastic (aka TIM) is used to fill the gaps between thermal transfer surfaces, such as between microprocessors and heatsinks, in order to increase thermal transfer efficiency.
  
  It has a higher thermal conductivity value in Z-direction than xy-direction.
  
  Section::::Applications.
  
  Section::::Applications.:Personal computers.
  
  Due to recent technological developments and public interest, the retail heat sink market has reached an all-time high. In the early 2000s, CPUs were produced that emitted more and more heat than earlier, escalating requirements for quality cooling systems.
   "Hot electron"s can tunnel out of the semiconductor material, instead of recombining with a hole or being conducted through the material to a collector. Consequent effects include increased leakage current and possible damage to the encasing dielectric material if the hot carrier disrupts the atomic structure of the dielectric.
   Temporary heat sinks were sometimes used while soldering circuit boards, preventing excessive heat from damaging sensitive nearby electronics. In the simplest case, this means partially gripping a component using a heavy metal crocodile clip or similar clamp. Modern semiconductor devices, which are designed to be assembled by reflow soldering, can usually tolerate soldering temperatures without damage. On the other hand, electrical components such as magnetic reed switches can malfunction if exposed to higher powered soldering irons, so this practice is still very much in use.
  
  Section::::Applications.:Batteries.
  