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30 SMT Magazine • November 2017 Using IR Rework There are two prevalent heating technolo- gies in use throughout most electronic assem- bly operations for advanced component re- work. The first method employs the use of hot air gas to heat up the component through the package—this may or may not include the in- jection of nitrogen. A second much-used heat- ing technology relies on infrared energy. This electromagnetic radiation, safe to the operators, is absorbed by the package, thereby sending the solder into reflow. Hot Air Rework A typical hot air rework system employs a heat source and an air source that forces the heated air through a nozzle (Figure 1) con- figured to the area of interest, which heats up the compo- nent to be reworked. There are numerous levels of such a hot air system, including a completely manual, a semi-automatic, and an automatic system, each with its own features. Why Hot Air? Hot air convection heating for PCB rework is advantageous for a variety of reasons. The ab- sorption of heat by the component and circuit board is independent of a material's color or texture. Additionally, inducing nitrogen to the site during component reflow has the advan- tage of making sure the metallurgical structure of the solder joint is the most reliable. In air-at- mosphere rework, an oxide layer forms around the solder sphere as it reflows. Inducing nitro- gen during this step displaces the oxygen and limits the oxide layer forming around the mol- ten solder. Finally, a hot air convection system quick- ly delivers heat energy into thermally massive boards. by Bob Wettermann BEST INC. Two Prevalent Rework Heating Methods— Which One is Best? KNOCKING DOWN THE BONE PILE Figure 1: Nozzle delivers hot air in and around the package during rework cycle.

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