All disc brakes squeal.
Learned that in a brake seminar many moons ago.
What we do is to mitigate the squeal as much as possible.
Membrane is something I always used in shops.
Blue or pinkish-orage, put it on the BACK, spread it around with your finger, set the pads in the sun to set up for a while, install.
Hardware helps, too, if old and collapsed springs.
Sanding cross hatch in rotors works sometimes.
Another trick is to bevel the leading and trailing edges of the pad proper (NOT the backing plate).
Think:
Fingernails on a chalkboard.
The sharp edges tend to create some of the vibration we hear as squeal.
Newer pads with no asbestos grind the edges, no problem.
Older pads with asbestos, best use a respirator.
You just try things until you find the mitigator for your particular circumstance.
Dave