A method of injecting a sealing gel into a recess of a work piece, comprising steps of: injecting the sealing gel into the recess and stopping the injection of the sealing gel when the sealing gel reaches a first depth less than the total depth of the recess; after the sealing gel has cooled and solidified, continuing the injection of the sealing gel into the recess and stopping the injection of the sealing gel when the sealing gel reaches another depth higher than the first depth; and repeatedly performing the previous step until the cooled and solidified sealing gel in the recess has a top surface beyond a sealing interface surface of the work piece.