surrounding components

It is always a good idea to heat the entire board to 100C to 140C prior to reflowing the site to be reworked to reduce warp and localized stress. (Thermal uniformity of the preheater is key here). For a BGA, the laser is programmed to heat only the component package itself. The heat transfers to the solder joints by conduction through the component body. This is the same way solder joints on BGA�s are heated in a reflow oven. There is some conduction from the solder joints to the surrounding area but this is minimal. Some testing done has shown that the adjacent components maintain temperatures under 170C less than .010 inches from the site. Thermal imaging proved what was being registered by thermocouples attached to the site.

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