Wave soldering

I am trying to understand how wave soldering works. Unfortunately the Wikipedia article has has left me unsure about the process:


Is the entire board with its components quasi-immersed in liquid solder while it passes through the wave? (If not, the following question probably make no sense.)
If the board cuts into the wave, how is the wave maintained?
Why does this not leave superflous solder residue on the board?


Double-Sided SMT soldering

How are double sided boards with SMT components soldered? How is it prevented that the components on one side fall off?


Question: Control 8V H-Bridge with microcontroller
Answer: You can't drive the PMOS transistor directly like that. Remember that the gate voltage is always referenced to the source terminal, so if you apply 8V to the source and 0-4V to the gate, the gate-source voltage varies between -8V and -4V. In other words, the PMOS can never shut off, because it's gats-source voltage never goes to zero.

To fix this, you need to create a "level shifter" for the PMOS gate signal. There are many ways to do this; one of the easiest is to purchase a driver chip designed specifically for the task.