Selective soldering

Selective soldering is the process of selectively soldering components to printed circuit boards and molded modules that could be damaged by the heat of a reflow oven in a traditional surface-mount technology (SMT) assembly process. This usually follows an SMT oven reflow process; parts to be selectively soldered are usually surrounded by parts that have been previously soldered in a surface-mount reflow process, and the selective-solder process must be sufficiently precise to avoid damaging them.

Assembly processes used in selective soldering include:

Less-common selective soldering processes include:

Other selective soldering applications are non-electronic, such as lead-frame attachment to ceramic substrates, coil-lead attachment, SMT attachment (such as LEDs to PCBs) and fire sprinklers (where the fuse is low-temperature solder alloys).

Regardless of the selective soldering equipment used, there are two types of selective flux applicators: spray and dropjet fluxers. The spray fluxer applies atomized flux to a specific area, while the dropjet fluxer is more precise; the choice depends on the circumstances surrounding the soldering application.

The miniature wave selective solder fountain type is widely used, yielding good results if the PCB design and manufacturing process are optimized. Key requirements for selective fountain type soldering are:

...
Wikipedia