Method for cleaning surface of resin layer
A method for cleaning a surface of a resin layer capable of sufficiently improving peel strength of a metal film formed by plating on a surface which is roughened by performing a desmear treatment on a resin layer containing a resin added with a large amount of filler is provided.
1. A method for cleaning a surface of a resin layer on which a metal film is formed by plating, comprising the steps of:
forming a resin layer on a substrate with a resin compounded with a filler in an amount of 20 wt % or more so that a difference of a coefficient of thermal expansion between the resin layer and the metal film formed on the resin layer is reduced;
dipping the substrate in a swelling liquid to swell a portion of the surface of the resin layer;
treating the surface of the resin layer with a desmear treatment to remove the swollen portion of the surface of the resin layer to thereby roughen the surface of the resin layer while at least some of the filler previously contained in the swollen portion of the surface of the resin layer remains on the roughened surface of the resin layer after the swollen portion is removed; and
removing only the filler remaining on the roughened surface of the resin layer such that the roughened surface of the resin layer is substantially the same as the roughened surface of the resin layer resulting from the desmear treatment, said filler being removed by ultrasonic cleaning in which ultrasonic vibration of a frequency of from 35 to 50 kHz is applied;
wherein a peel strength remains approximately constant even when a time period of applying the ultrasonic vibration changes.
2. The method of cleaning the surface of the resin layer according to claim 1 , wherein the metal film formed on the surface of the resin layer is a copper film formed by electroless copper plating, and the filler contained in the resin which forms the resin layer is a spherical filler made of silica.
3. The method for cleaning the surface of the resin layer according to claim 1 , wherein the ultrasonic cleaning is performed by using purified water as an ultrasonic cleaning liquid.
4. The method for cleaning the surface of the resin layer according to claim 1 , wherein the filler is a spherical filler and a maximum diameter of the spherical filler is 5 μm or less.
5. The method for cleaning the surface of the resin layer according to claim 1 , wherein the ultrasonic vibration is applied substantially perpendicular to the substrate.
6. The method for cleaning the surface of the resin layer according to claim 2 , wherein a maximum diameter of the spherical filler is 5 μm or less.