Bubbles are ALWAYS squeegee technique. It doesn't matter what media, wet or dry, old or new squeegee. if you use proper squeegee technique there will seldom, if ever, be a bubble. What is proper squeegee technique?
It's easy to demonstrate but a challenge to describe. The principle is best summed up in "Never squeegee unplowed ground." Meaning, assuming you're right-handed and squeegeeing right to left, never EVER, let the left side of the squeegee start on un-squeegeed material and never, EVER, let the right edge of the squeegee be on un-squeegeed media. In other words, ALWAYS start a stroke with the squeegee COMPLETELY on the previous stroke and finish the stroke with 1/2 or so of the squeegee remaining on the previous stroke. If there is no previous stroke then start on whatever is to the right of the media. Be it hinge tape, substrate, or whatever.
Add to that the principle of ALWAYS let the squeegee put the media on the substrate. Try to never let the media come in contact with the substrate unless it's being squeegeed.
Use sufficient pressure to put the media down with authority. Never sketch at it, use complete strokes starting from off the media, to on the media, ending off the media.