The components underneath shouldn't fall off. The surface tension of the solder should be enough to keep them in place. (That's how it's generally possible to r

The components underneath shouldn't fall off. The surface tension of the solder should be enough to keep them in place. (That's how it's generally possible to reflow solder components to two sides of a board.) Of course, reflowing the components in an ad-hoc way is quite likely to cause other problems, so it's probably still a good idea to avoid it.