Catalysis of Electroless Copper Plating using Pd +2 /Poly(Acryilc Acid) TIIIN Films
- PDF / 1,609,014 Bytes
- 5 Pages / 420.48 x 639 pts Page_size
- 38 Downloads / 209 Views
CATALYSIS OF ELECTROLESS COPPER PLATING USING Pd +21POLY(ACRYIlC ACID) TIIIN FILMS ROBERT L. JACKSON IBM Almaden Research Center, San Jose, California 95120-6099 ABSTRACT A new method is described for initiating electroless copper deposition onto dielectric substrates. The method employs a thin poly(acrylic acid) film, applied to the substrate by dip-coating, to bind Pd+ 2 from PdSO4 solution. Uptake of Pd+2 takes place by It+/Pd +2 ion exchange at the carboxylic acid sites of 2 the polymer. Upon immersion of a substrate treated with Pd + /poly(acrylic acid) into an electroless 2 0 copper plating bath, reduction of Pd+ to Pd takes place, forming an active catalyst for the initiation of electroless copper plating. INTRODUCTION Electroless copper plating has been proposed as a method for producing circuit lines in printed circuit boards (PCB) (1). Fabrication of PCB's by electroless plating offers an important advantage over existing fabrication methods that employ chemical etching of a blanket copper layer to define the circuit lines. Because the chemical processes etch the copper isotropically, the sidewalls of the circuit lines are eroded as the desired thickness of copper is removed from the PCB substrate. Electroless deposition on the other hand is a totally additive process, so it is possible to form fine-pitch, high-aspect-ratio circuit lines with nearly rectangular cross sections. Electroless copper plating cannot be initiated on PCB substrates (typically glass fiber/epoxy composites) without first depositing a catalyst onto the substrate surface. In a common method used to initiate electroless copper plating on dielectric substrates, the substrate is dipped into an aqueous colloidal suspension of palladium to deposit 1-2 nm diameter particles of palladium on the substrate surface (2-6). This process is fairly simple, but has some problems. Because the colloid is prepared by reduction of Pd +2 to 0 Pd by SnCI2 , the palladium particles are surrounded by a tin chloride shell (7,8). Tin chlorides are not active catalysts for electroless copper deposition, and thus the shell inhibits the activity of the palladium particles. The shell can be dissolved away by an 'acceleration" step, which typically involves immersion of a catalyzed substrate in aqueous IICI or NaOlH (2-6). Acceleration must be carried out soon after applying the colloid, however, since the shell oxidizes in air to form tin oxides that are very difficult to remove. The acceleration step also causes agglomeration of the palladium particles on the substrate surface
(2-6). This paper describes a new process for initiating electroless deposition of copper onto dielectric substrates. In this process, the substrate is coated with a very thin film of poly(acrylic acid) and is then immersed in an aqueous solution of PdS0 4 . The carboxyl groups of the poly(acrylic acid) film complex with Pd+2 supplied by the PdSO 4 solution. Upon immersion in the clectroless copper plating bath, the complexed 0 Pd 2 is reduced to Pd , forming an active catalyst that init
Data Loading...
