Editing Surface-mount technology (section)

===Hot gas===
During hot gas soldering, the energy for heating up the solder joint is transmitted by a hot gas. This can be air or inert gas ([[nitrogen]]).

Advantages:

* Some systems allow switching between hot air and nitrogen
* Standard and component-specific nozzles allow high reliability and faster processing
* Allow reproducible soldering profiles (depending on the system used)
* Efficient heating, large amounts of heat can be transferred
* Even heating of the affected board area (depends on system/nozzle quality used)
* Temperature of the component will never exceed the adjusted gas temperature
* Rapid cooling after reflow, resulting in small-grained solder joints (depending on the system used)

Disadvantages:

* Thermal capacity of the heat generator results in a slow reaction whereby thermal profiles can be distorted (depending on the system used)
* Precise, sometimes very complex, component-specific hot gas nozzles are needed to direct the hot gas to the target component. These can be very expensive.
* Today, nozzles can often no longer be deposited on the PCB by neighboring components, which means there is no longer a closed process chamber and adjacent components can be blown on strongly from the side. This can lead to the blowing of adjacent components and even to thermal damage. In this case, adjacent components must be protected from airflow, e.g. by covering them with polyimide tape.
* Local turbulence of the hot gas can create hot and cold spots on the heated surfaces, resulting in uneven heating. Therefore, perfectly designed, high-quality nozzles are a must!
* Swirls at component edges, especially at bases and connectors, can heat these edges significantly more than other surfaces. Overheating can occur (burns, melting of plastics)
* Losses due to environmental influences are not compensated for since the component temperature is not measured in the production process
* Creation of a suitable reflow profile requires an adjustment and test phase, in some cases involving several stages
* Direct temperature control of the component is not possible because measuring the actual component temperature is difficult due to the high gas velocity (measurement failure!)