Tried everything to stop brake squeal, what am I missing?

I am working on my project car and the brakes have been driving me absolutely insane. I installed new pads and rotors all around last month but I still get this annoying squeal at low speeds, especially when they are cold. I used the included hardware and even put brake grease on the contact points but the noise is still there. I was reading about different techniques for fixing noisy brake components and realized I might have forgotten to clean the caliper brackets properly or maybe I need to chamfer the pad edges. Some people also mentioned that certain pad materials just squeak no matter what you do. Before I take everything apart again this weekend, does anyone have a foolproof method for getting rid of brake noise? Is it worth trying those anti vibration shims or do they not really help?