Due to the adaptation of lead free soldering there is now increased temperature required in wave soldering of the circuit component to the PCB's. This can weaken them, PCB Stiffeners increase strength and rigidity.
There is now a much higher requirement for the use of different metals in PCB manufacture.These metals are often brittle and require higher temperatures in the assembly phases. This places stress on the circuit boards, stiffeners help combat this and add strength to the circuit boards.
They also help to keep circuit boards and back plates flat through manufacturing and assembly process. This is vital to ensure a good quality and reliable circuit board.
They are very good for use in harsh enviroments e.g. military grade products, aerospace products as they strengthen the circuit board itself.
The main purpose of a Bus Bar is to conduct a large current of electricity, more than can be provided by standard circuit board traces. They are used in distrubution boards, circuit boards, battery bank, power supply unit ETC. They do also provide structual rigidity to circuit boards.