On my Pfaff Creative Performance Embroidery machine all was going well until half-way through the design when the bobbin thread started showing on my work. I immediately thought of tension problems so adjusted what controls I had, but to no avail. I did NOT touch the bobbin screw? Should I have to? On the more intensive embroidery parts I did not see the bobbin thread popping up. My needle size was a 90.

Normally, a problem on the top means an issue with the bobbin. Did you check the bobbin? Did the thread jump out of the bobbin tension spring, or maybe get wound around the spindle in the case? If you use prewounds, sometimes they go wonky half way thru. If the bobbin was partially used, I'd try another bobbin. Also, if the bobbin was working all right for the first part, I would not mess with the bobbin tension unless you tried everything else.

I bought a second bobbin and adjusted the tension so the thread wouldn't be visible on top. It worked.

Check your upper thread. Sometimes it wraps around the spool pin and gets too tight and that pulls the bobbin thread to the top.