Substrate adhesion enhancement to film

#1. Field of the Invention

#The present invention relates to the manufacture of printed circuit boards having improved interlayer adhesion. More particularly, the present invention pertains to adhesiveless, flexible printed circuit boards having excellent thermal performance and useful for producing high-density circuits.

#2. Description of the Related Art

#A polyimide film substrate is plasma treated with a highly charged plasma etchant gas mixture of oxygen (O2) and tetrafluroromethane (CF4), the gas mixture containing 7% CF4. The plasma etchant bombards the film surface with positively and negatively charged species causing impurities on the film surface to degrade and ablating the film surface. This etching step removes approximately 0.7 μm of material from the surface of the film. Subsequently, the etched surface is coated with a continuous layer of polyimide to achieve a layer thickness of 8 μm. The coated substrate and a copper foil layer are then laminated together in a vacuum press at about 275° C., for about 30 minutes, under a vacuum of at least 28 inches of mercury, and maintained at a pressure of about 150 psi. The resulting laminate has a peel strength of about 4 lbs/inch.

#A polyimide substrate is plasma treated under similar conditions as in Example 1 using an etchant consisting of a gas mixture of oxygen (O2) and tetrafluoro methane (CF4), containing 7% CF4. However, the etching step is conducted to remove approximately 0.475 μm of material from the surface of the film. After coating the etched surface with a polyimide film and laminating the coated substrate together with a copper foil as in Example 1, the resulting laminate exhibits a peel strength of about 4.5 lbs/inch.

#Example 1 is repeated except using an etchant having only 3% CF4 and rather than limiting the etching step to remove approximately 0.7 μm of material from the surface of the film, the etching step is continued for about 15 minutes. This results in an overetched laminate having reduced peel strength. The peel strength of the laminate after fifteen minutes is only about 0.5 lbs/inch.