Functional resumes don't work, plain and simple. If you have one of these resumes it will be toxic to your charge search and do little more than to generate skepticism about your credentials and put your entire background under a cloud of suspicion.
So just what it is a functional resume. It's one that lists your skills, capabilities and functional experience but essentially camouflages where you worked and when. A typical functional resume will provide a list of skills and functional responsibilites that a person may have had over the years but not attribute or assign them to specific jobs or companies.
Where the person worked will probably not appear until the second page and only then may there appear a listing of the jobs that person held, quite often with no listing of dates. With some functional resumes, dates are not even used and the resume writer will simply include a list of the companies they worked at without any indication of chronology.