Copper clad laminate and method for producing the same

A copper clad laminate comprising:

• a low dielectric resin film having a relative permittivity of 3.5 or lower and a dissipation factor of 0.008 or lower at a frequency of 10 GHz;
• and
• an electroless copper plating layer laminated on at least one surface of the low dielectric resin film,
• wherein the copper clad laminate includes an electrolytic copper plating layer on the electroless copper plating layer,
• a weighted average size of crystallites in the electrolytic copper plating layer is 40 to 300 nm,
• assuming that a weighted average size of crystallites in the electroless copper plating layer is first crystallites and the weighted average size of the crystallites in the electrolytic copper plating layer is second crystallites, a ratio of the first crystallites to the second crystallites (the second crystallites/the first crystallites) is 2.0 or smaller, and
• an adhesion strength between the resin film and the electroless copper plating layer is 4.2 N/cm or more.

A method for producing a flexible circuit board by using a low dielectric resin film, the method comprising:

• an electroless copper plating step of forming an electroless copper plating layer on the low dielectric resin film having a relative permittivity of 3.5 or lower and a dissipation factor of 0.008 or lower at a frequency of 10 GHZ;
• a resist patterning step of applying a resist onto the electroless copper plating layer and patterning the resist;
• an electrolytic copper plating step of forming an electrolytic copper plating layer between portions of the patterned resist;
• and
• a heating step of, before the resist patterning step, heating the copper clad laminate in which the electroless copper plating layer has been formed, such that a weighted average size of crystallites in the electroless copper plating layer becomes 25 to 300 nm and an adhesion strength between the resin film and the electroless copper plating layer is 4.2 N/cm or more.