This invention provides a method and apparatus for manufacturing electronic devices. The method includes: providing a substrate having a first surface; providing an electronic device having bumps; mounting the bumps to the first surface to form an integrated unit; applying a capillary underfill to multiple sides of the electronic device, enabling the underfill to creep along and fill the gap between the electronic device and the substrate; placing the integrated unit into a processing chamber; raising the temperature in the chamber to a first predetermined temperature; reducing the pressure in the chamber to a first predetermined pressure of a vacuum pressure, and maintaining the vacuum pressure for a predetermined time period; raising the pressure in the chamber to a second predetermined pressure higher than 1 atm, and maintaining the second predetermined pressure for a predetermined time period; and adjusting the temperature in the chamber to a second predetermined temperature.