Vragen over elektronische productie beantwoord

I have a batch of PCBs with SMT nuts which has been assembled onto a PCB – the nut has kapton tape on top to allow easy pickup for assembly.

My PCB manufacturer just informed me that he is facing PCB warpage issue in my simple, single sided, copper poured PCB. He says to avoid this issue he suggests to

The assembly note states: Bake bare PCBs in a clean and well ventilated oven prior to assembly at 125*C for 24 uren. Why is this necessary?

Although the adsorption of moisture by FR4 is quite low, what is the best way to minimize it or eliminate it completely?

On a Flex Printed Circuit (FPC) made out of Kapton polyimide, will anything bad happen if I put a VIA in a part of the FPC that has to bend?

Het is een mooi uitziende broodplank, maar de aansluitingen zijn te los om een ​​goede verbinding te maken met alle componenten. dus ik kon ze eigenlijk nergens voor gebruiken.

We receive a batch of PCB with scratches from my supplier, but they think it is acceptable. I have never seen such error on even an B stock boards parts.

I receive the samples BOM of our PCBA factory. It remarks that PCB is FR4 Isola 370HR. What is this and is it reliable materials?