If an unpatented PCB circuit board is found to be used by others, is it considered infringement?

Unpatented technology and unregistered layout designs are not protected by law and can be used by others without infringement.

If the technology has not applied for a patent and corresponding confidentiality measures have been taken, it is a technical secret. If others illegally obtain the technology or purchase the technology from the illegal acquirer, it is an infringement.