Packaging structure and forming method thereof

Packaging structure and method for forming a packaging structure are provided. A bonding layer is formed on the substrate. An improvement layer is formed on the bonding layer. The improvement layer contains openings exposing surface portions of the bonding layer at bottoms of the openings. Chips are provided and include functional surfaces. The chips are mounted on the substrate by bonding the functional surfaces of the chips to the bonding layer through the openings. Top surfaces of the chips are lower than or flush with a top surface of the improvement layer.