Captain America's shield has been broken by godly powers. It’s also withstood impressive beatings by Hulk and Thor, etc. It has great abilities in helping deflect kinetic energy, but these tests don't include the quantum aspect that Ant-Man has.
talks about Ant-Man’s density becoming that of a white dwarf. The compactness changes things: quantum particles can pass through matter without issues.
So: has Ant-Man ever become small enough to pass through Captain America’s shield? And if so, is there any material that can stop him?