A method of preparing a semiconductor substrate with metal bumps on both sides of the substrate includes depositing a first-side UBM layer on a first surface of the substrate, and forming a plurality of first-side metal bumps on the first surface of the substrate after the first-side UBM layer is deposited. The method includes forming a second-side UBM layer on a second side of the substrate, and the first surface and the second surface are opposite of each other. The method includes forming a plurality of second-side metal bumps on the second surface of the substrate after the second-side UBM layer is deposited. The method includes removing exposed first-side UBM layer and exposed second-side UBM layer after the plurality of first-side metal bumps and the plurality of second-side metal bumps are formed. The method includes reflowing the plurality of first-side metal bumps and the plurality of second side metal bumps.