A package substrate may include a build-up layer. The build-up layer may include a dielectric material and one or more microspheres. The one or more microspheres may include a magnetic core that includes a first material that is a first oxidation-resistant material. Further, the one or more microspheres may include a shell to encapsulate the core, and the shell may include a second material that is a second oxidation-resistant material. The package substrate may further include a metal layer coupled with the build-up layer.