Is it possible / good idea, to test dc-dc converters in breadboard before ordering the PCB.

 

You can always try but I have doubts. The manufacturers websites often give layouts. I say copy those.

Problem is, the current paths are critical on those circuits. How well can you imitate a copper path under a PC board with a wire?

 

Is it possible / good idea, to test dc-dc converters in breadboard before ordering the PCB.

define "breadboard". If you mean a proto "plug" board, it will never work right. We used to build them on copper PC boards where we used a Dremel to cut the trace paths. If the makers give a layout, just go with that. They are usually optimized.

 

Breadboard is a lot of effort, aren't these SMD chips?

I have made a small prototype circuit on prototype PCB, for one of these LM switcher IC's, working at 500 Khz. No problem.

I always use prototype PCBs with bottom side up now, kind of SMD.

For SMD components, adpater PCBs are used.

Breadboard is not relieable enough, most components don't fit.