It's also by design. Repeated heating and cooling cycles in consumer grade electronics eventually lead to micro fractures in the solder, which will make it so you have to replace it the future. Zero fail spec electronics (think space craft, aircraft, high heat applications, or other applications that would cause mass casualties if they fail) use leaded solder because it does not fracture. In it's intact form inside of your phone or computer, leaded solder really is harmless.