Patent ID: 8042261
Filing Date: 2011-10-25
Classification: C25D,H05K,Y10T

Abstract:
1. A method for fabricating embedded thin film resistors of a printed circuit board, comprising the steps of: (a) forming a circuitry required by a printed circuit board on a copper foil layer formed on the surface of a laminate made of an insulating material, and forming one or more corresponding resistor windows according to the locations and the sizes of resistors required by said circuitry; (b) coating a sensitized layer on said printed circuit board of step (a); (c) painting or attaching a photosensitive etching resist layer to the surface of said sensitized copper foil layer, and applying a photolithography technique to expose each resistor frame, said resistor frames exposing said sensitized layer on top of said copper foil layer; performing an activation technique using activation solution on said printed circuit board, said activation solution only reducing the surface of said resistor frames covered with said sensitized layer to an activated layer, the length of said resistor frames being the same as or slightly longer than said resistor windows in said circuitry direction to ensure the good contact condition of the contact endpoints; (d) immersing said printed circuit board in an electroless dip solution, said electroless dip solution only coating a resistor layer on said activation layer inside said resistor frames, depositing until the thickness of said resistor layer to a pre-defined thickness, said deposited resistor layer forming required resistor elements; and (e) stripping away said photosensitive etching resist layer on said copper foil layer.