Publication Date: 2005-Jun-15
The IP.com Prior Art Database
The present invention is directed to a method and device for reworking densely populated printed circuit boards. Specifically, the present invention is directed to an improved nozzle configuration for directing hot gas to a selected region of a printed circuit board.
The present invention is directed to a method and device for reworking densely populated printed circuit boards. Specifically, the present invention is directed to an improved nozzle configuration for directing hot gas to a selected region of a printed circuit board. Electrical and other surface mount components are typically soldered in place on a printed circuit board, which is also known as a hybrid. Sometimes, it is necessary to “rework,” (i.e., remove or reposition) a component on the hybrid. One method of reworking a component is to reflow, or melt, the solder holding the component in place. Typically, hot gas is directed at the component with a nozzle. The hot gas reflows the solder so that the component(s) needing rework can be removed with a pick-up tube while the other components are left in place on the hybrid. Typically, the outlet of the nozzle from which hot gas is emitted is centered over the component being reworked and sealed on to the hybrid to minimize the thermal stresses on components adjacent to the rework site. In other cases, where space allows, mechanical shielding or fluid cooling may be employed to minimize the thermal stresses on components adjacent to the rework site. However, as component size decreases and component density increases, the components in a particular region may be too tightly spaced to effectively shield them from thermal stresses during rework of an adjacent component within the region. The hot gas may inadvertently reflow the solder securing adjacent components, and adjacent components may be weakened from exposure to excessive heat, including heat that is insufficient to properly reflow the solder joint. In such cases, customized equipment is needed to adequately shield a component from the effects, or control the effects, of reworking a nearby component for each type and location of component intended to be reworked. This equipment included customized thermal profiles, which are the position and temperature of the hot gas source and how long the hot gas is applied, and customized tooling, which describes the nozzle arrangement and any mechanical shielding or independent cooling fluid control system. However, the use of customized tooling and thermal profile...