Epoxy polymers are frequently used for electronic purposes, in particular for built up layers and micro-vias in advanced printed circuit boards. The adhesion of the plated metal layers to this polymer surface is of prime importance for the reliability of the interconnection. Chemical treatment of the polymer surface changes the chemical and physical nature of the polymer. This results in specific groups of the polymer chain present on the surface and changes the roughness of the polymer layer. The influence of swellers and oxidizing agents on the polymer surface roughness and the chemical properties of the surface are investigated. The surface is analyzed by atomic force microscopy, attenuated total reflectance-infrared ͑ATR-IR͒ spectroscopy, dynamic contact analyses ͑DCA͒, and peel strength measurements after electroless and electroplating of the surface. The changing of the chemical functionalities on the surface, which is detected by ATR-IR and DCA plays an important part in the adhesion strength of electrochemically plated copper. The combination of roughness and the presence of certain chemical groups, like alcohols, play an important role in the adhesion of electrochemically deposited metals to the polymer surface.

The adhesion of plated metals on top of chemically treated epoxy layers for build-up purposes was examined. Specifically, the influence of wet chemical pretreatments on the adhesion of plated copper to epoxy polymer is investigated. This adhesion is related to the surface roughness of the polymer and the chemical composition of its surface. The chemical composition of the surface was examined by X-ray photoelectron spectrscopy and placed in the context of the development of the interface during the wet chemical pretreatments and related to the theory developed in previous publications. Various combinations of pretreatments were followed by an identical electrochemical Cu deposition and peel strength measurement sequence. This allowed interpretation of the changes of the peel strength with pretreatments. Using this interpretation, the peel strength of build-up layers was maximized. We propose that the surface of the polymer layer develops into a fractal surface during wet chemical oxidation. Using this proposition, in combination with pore diffusion for the oxidizer, the evolution of peel strengths with chemical pretreatment times can be qualitatively understood. The peel strength of electrochemically deposited copper can be quantitatively related to the atomic force microscopy measurements for limited oxidation treatment times.

Epoxy polymers are frequently used for constructing buildup layers. Atop the dielectric polymer metal layers are plated by means of a wet-chemical electroless and/or electroplating process. The adhesion of the plated metal layers to this polymer surface is of prime importance for reliability of the interconnection. An increase in the roughness of the polymer surface plays an important part in the adhesion strength of plated metal layers by increasing the total area of interface between both layers. Hence, the evolution of polymer surface roughness with time due to the chemical treatment is of prime importance for determining the reliability of interconnections. A kinetic study of wet solution swellers and oxidizers is made, based on atomic force microscopy roughness measurements. Each chemical or combination of chemical treatments in a certain sequence has its influence on the evolution of roughness. The evolution of surface roughness also indicates the mechanisms that lead to the formation of roughness on the surface. Different models are proposed to explain the influence of sweller agents on polymer surface roughness. The kinetics of roughness formation under influence of swellers is modeled and the bases of the influence of swellers on oxidizing treatments are examined. Improvement of interconnection technology is essential for allowing increased signal frequencies and higher density of functions for future electronics. In order to meet the necessary improvements, sequential high-density buildup layers and microvia technology have been developed ͑Fig. 1͒. This research started in the late 1990s. 1 A wiring density of 100-150 m, defined as the sum of the width and the distance between copper interconnections ͑e.g., wires͒, is required in order to be able to mount unpackaged chips on the boards, through flip chip or wire bonding. 2 Most of the printed circuit boards ͑PCBs͒ used today are fabricated with a glass-epoxy resin on which metals ͑usually copper͒ are plated and patterned in order to realize interconnections between different components placed on top of the substrate. A good adhesion between the copper and the polymer is of prime importance for reliability of the interconnection. 3 By chemical treatment of the surface the characteristics ͑physical and chemical͒ of it can be changed in order to improve adhesion. It is obvious that the surface properties of the polymer are important for adhesion of the metal to the polymer. Hence, there is intense recent research into improving the adhesion of plated copper onto polymer surfaces. Many processes involve Ar plasma activation, followed by a surface graft polymerization. [4][5][6][7] Composites are also formed to improve adhesion. 8,9 However, because of the much lower prize of wet chemical treatments compared to composites or plasma ͑vacuum͒ processes, these treatments are preferred industrially. The adhesion strength of a solid-solid interface is largely determined by the bonding characteristics and structure of the interface. 10 The work required to pull an...

The adhesion of plated metal layers to epoxy polymer surfaces is of prime importance for the reliability of electronic interconnections. An increase in the roughness of the polymer surface, caused by chemical treatment, strengthens adhesion by increasing the total area of interaction between both layers. The evolution of the roughness at the polymer surface is studied through the kinetics of the chemical reactions on the surface. Sweller agents, that are able to diffuse through the free volume of the polymer, react with polar groups present in the bulk of the polymer and form channels. An increase in polar groups at the surface and the formation of channels facilitates the transport of water through the free volume of the polymer. The polar groups in these patches react with oxidizers and cause the formation of cavities as reported in literature. A mathematical model is developed to explain the influence of swellers and oxidizing agents on the development of polymer surface roughness. This model is based on atomic force microscopy measurements for the roughness and on attenuated total reflectance-infrared and electron spectroscopy for chemical analysis for the chemical changes on the polymer surface. Mass measurements are also used to record mass changes. The proposed model permits the prediction of roughness evolution.

The adhesion of plated metal layers to epoxy polymer surfaces is of prime importance for the reliability of interconnections in microelectronics. An increase in the roughness of the polymer surface, caused by chemical treatment, plays an important part in the adhesion strength of plated metal layers by increasing the total area of interaction between both layers. This kinetic study of the influence of chemical treatments on the surface of the polymer consists of two parts. In Part I the kinetics of sweller treatments and of the solvent were examined in detail and a kinetic model for the influence of sweller and solvent was developed. In this second part the kinetics of the formation of roughness at the polymer surface due to oxidative liquid treatments is examined. A kinetic model is developed based on experimental studies, compromising the combined effects of sweller-oxidizer treatments and the influence of diffusion of the different components. A number of examples are given and verified by experiment. The roughness of the treated polymer samples is measured experimentally by atomic force microscopy. Time-dependant mass measurements were used to record mass changes due to diffusion and reaction.The continuing striving in microelectronics to miniaturize and/or the necessity for electronic circuits to operate in harsh environments, together with the increased signal frequencies and higher density of functions necessary, necessitates further advances in interconnection technologies. A prime requirement for these is a good adhesion between polymers and plated copper layers. It is obvious that the surface properties of the polymer have a big impact on the adhesion of the metal to the polymer. By chemical treatment of the surface the characteristics ͑physical and chemical͒ of it can be changed in order to improve adhesion. Hence there has been intense recent research into improving the adhesion of plated copper onto polymer surfaces.A number of publications 1-3 exist on surface treatments with wet chemicals to improve adhesion strength of copper on epoxy resins. These authors made a phenomenological study on copper laminated foils but not on plated copper surfaces. Li and Tummala 4 studied the effect of wet chemical pretreatments on the interfacial adhesion between plated copper layers and epoxy polymers. According to these authors adhesion between two layers depends first on the physical and mechanical adhesion, caused by the roughness between both layers, and second on the chemical adhesion which is caused by interactions between polymer molecules and the plated metal. These findings are based on earlier work described by Wake. 5 The effects of wet chemical treatments on interfacial adhesion and roughness has not been well studied and understood, 6,7 Recently Ge et al. 8 studied the influence of surface modification on epoxy/copper systems. According to these authors wet-chemical treatments produce a large number of microcavities to anchor deposited electroless copper. Mechanical interlocking was found to have a do...