The present investigation represents a detailed study involving transmission electron microscopy and electron diffraction of surfaces treated by the catalyzing system false(SnCl2/PdCl2/normalHClfalse) in conjunction with various accelerating solutions and in some cases a subsequent electroless copper bath. Results give additional information demonstrating the proper procedure(s) necessary in the preparation of the catalytic system. In addition it was found the best plating results are obtained whenever Pd3normalSn is present on the treated surface prior to the metallization step.

A tin sensitizer solution has been developed which is useful with hydrophobic surfaces. Based on radiochemical tracer adsorption measurements and conventional analytical techniques, a chemical characterization of the surface was made following the sensitization and activation steps. Quantitative results relating to the surface concentrations of active components [tin (II), tin(IV), and palladium] have been established. The surface concentration ratio of tin (II) and tin (IV) was found to be about 3:1. It was also demonstrated that the tin(II) ‐palladium (II) redox reaction is of low efficiency.

In the electroless plating of dielectric substrates, sensitization and activation pretreatments are used to provide catalytic sites. The presence of the catalytic sites provides a path for the initiation of the electroless plating process. Based upon findings in this laboratory, a new sensitizing composition containing tin(II) and tin(IV) compounds was developed. This sensitizer was found to be particularly useful in the case of hydrophobic surfaces, and has resulted in good uniformity of metallic coverage on hydrophobic surfaces. In preparing the final sensitizer composition, the use of aged stannic chloride solution was responsible for the improved performance. The present investigation reveals the various chemical changes taking place during the aging of stannic chloride solution. Based upon the current findings, it is believed that during the aging process, a slow formation of a fl-stannic acid takes place. This material is a polymeric form, which causes a light scattering effect to take place. It is the presence of ~-stannic acid and its interaction with tin (II) that accounts for the improvement in sensitizer performance.It has been demonstrated (1-3) that contact angle measurements can be an effective technique by which sensitizer solutions may be evaluated. It was also demonstrated (1, 2) that the addition of stannic compounds to tin-type sensitizers can have a major influence on the effectiveness of such solutions, especially when hydrophobic substrates are employed. The results obtained (1, 2) employed sensitizers prepared by aging the stannic chloride stock solution prior to mixing with SnCl~ solution. Specially prepared and aged (4-6) stannic chloride solutions are most effective when added in low concentrations to solutions for the sensitization of dielectric substrates. By contrast, the startnic chloride normally present in typical stannous chloride does not result in improved wetting in spite of the fact that it is present in the same approximate concentration range as the added aged stannic chloride concentrations.However, according to Cohen et al. (7,8) the presence of stannic ions in conventional sensitizers (SnC12/ HC1) constitutes the basis for a proposed mechanism of sensitization. Employing the Mossbauer spectroscopy of tin, a model based upon colloidal stannic hydroxide (hydrated oxide) with bound stannous ions on the colloid surface was proposed. This colloid is present in bulk solution as well as on the sensitized surface. Sard (9), using electron diffraction had shown that sensitized films derived from conventional SnC12 sensitizers are adsorbed clumps of material several hundred angstroms in diameter. Luce et al. (10) and Drotar et al. (11) also described sensitizers in which excess stannic chloride was added to conventional sensitizer media (SnC1JHC1). However, in all cases, no attempt was made to precondition the stannic solution while in the present work, the stannic halide solutions are first prepared, allowed to age, and then mixed with the stannous chloride solution. Bernhardt (12...

A study of tin sensitizing solutions was made by contact angle measurements. Through the control of solution composition, i.e., stannous and stannic concentrations, major improvements in the effectiveness of such sensitizers on hydrophobic surfaces have resulted. The incorporation of excess sodium chloride was found to further improve the performance of such sensitizing solutions. The presence of the stannic ions facilitates the adsorption of the stannous ions necessary for the reduction of palladium.

A comparative study of the transmission electron micrographs in the different stages of the autocatalytic plating process has been made. The comparison was made between conventional SnC12/HC1 sensitizer solution and a n e w l y developed system based upon the incorporation of aged stannic component. Results have demonstrated an increase in catalytic site density of approximately one order of magnitude. This improved method has further resulted in the formation of finer and denser metal crystallites during the early stages of nucleation and growth.In the art of plating on dielectric substrates, chemical treatment of the surface is an essential step required for the initiation of the autocatalytic (electroless) plating processes. During the chemical treatment procedure, sites are formed which provide a chemical path for the initiation of the plating process. At present, there are two basic procedures used in the formation of the catalytic sites: (i) sensitization (via acidic stannous chloride) followed by activation (via acidic * Electrochemical Society Active Member. palladium chloride), or (ii) a colloidal system (via palladium chloride in excess acidic stannous chloride). Although both of the above procedures are widely utilized, this investigation is concerned with modifications related to the first approach only.In recent publications (1-4) it has been demonstrated that the effectiveness of conventional tin sensitizer solutions (SnC1JHC1) m a y be altered through proper solution modification. Specifically, the incorporation of aged stannic chloride solutions were found to provide the improvements in performance. During the Fig. 1. Electron micrographs of sensitized Formvar surface, at magnification I|6,000X (1 cm = 860,/~). A (left), conventional sensitizer; B (right), improved sensitizer. 875 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 157.182.150.22 Downloaded on 2015-03-09 to IP