Method for Patterning Electroless Plated Metal on a Polymer Substrate

The present invention will be illustrated further by the following examples. These examples are meant to illustrate and not to limit the invention, the scope of which is defined solely by the appended claims.

A multi-chip packaging substrate, consisting of a silicon wafer coated with several layers of polyimide (total thickness approximately 30 microns) and copper features prepatterned by conventional methods, was cleaned in an oxygen plasma for 2.5 kW-minutes. The substrate was then covered with a 1 millimeter thick liquid film of 1% aqueous poly(acrylic acid) (molecular weight 250,000) and subsequently allowed to dry in a horizontal position in air for 1 hour. A solid layer of poly(acrylic acid) approximately 1.5 microns thick formed on the substrate. the substrate was covered with 0.1 M palladium sulfate for 3 minutes, then rinsed with deionized water for 20 seconds and then dried with pressurized nitrogen at room temperature for 10 seconds. The substrate was then irradiated in various patterns at a horizontal scan rate of 100 microns per second with a focused continuous-wave argon laser in all-lines mode with an incident beam power of 0.025 W and a 1/(e squared) beam radius of approximately 15 microns. The irradiated areas had complexed poly(acrylic acid) over both the polyimide and the copper features on the polyimide. The patterns were mostly configured to connect the previously isolated copper features. The substrate was next etched in 1 M aqueous NaOH at room temperature for 2 minutes and then rinsed with deionized water for 30 seconds. Finally the substrate was exposed to a Shipley "CUPOSIT 385" (trademark) copper electroless plating bath for 10 minutes, operated at 30 degrees C. with mechanical stirring. A copper pattern corresponding to the irradiated regions adhered tightly to the substrate.

A multi-chip packaging substrate similar to that in example 1 was cleaned in an argon plasma for 2.5 kW-minutes. The substrate was then immersed in 2% poly(acrylic acid) (molecular weight 250,000) in glycerol. Next the immersed substrate was irradiated in a crossed-line pattern at a horizontal scan rate of 100 microns per second with a focused continuous-wave argon laser in all-lines mode with an incident beam power of 0.025 W and a 1/(e squared) beam radius of approximately 15 microns. The substrate containing patterned polymer was then removed from the poly(acrylic acid) and rinsed with deionized water for 30 seconds, and then covered with 0.1 M palladium sulfate for 3 minutes, and then rinsed again with deionized water for 20 seconds. Finally the substrate was exposed to a Shipley "NIPOSIT 468" (trademark) nickel electroless plating bath operated at 66 degrees C. with mechanical stirring for minutes. The desired nickel pattern adhered tightly to the substrate.

The present invention is therefore well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While presently preferred embodiments of the invention have been described for the purpose of disclosure, numerous changes in the details of construction and arrangement of parts may be made without departing from the spirit of the present invention and the scope of the appended claims.