Yes, bottom preheating is worth it for RAM replacement.

Yes.

Soldered RAM replacement is a high-risk procedure even for experienced techs. The main cause of damage is thermal shock – heating one small area of the board while the rest stays cold. This creates mechanical stress that can crack traces or pop other components. Bottom preheating warms the whole board gradually, so the hot-air nozzle only has to handle the final bump to reflow temperature. It also prevents the board from warping under uneven heat.

A cheap preheater (or even a hot plate with temperature control) makes a huge difference. Without it, you’re gambling on the board’s ability to handle localised heat. With it, the risk drops from “very likely to break something” to “doable with patience.”

Don’t skip it unless you enjoy buying replacement motherboards.