High density printed circuit boards become indispensable with the miniaturization of electronic components. Conventionally, electroplating has been applied to the metallization of circuit patterns. However, the metallization by this method is not applicable for the isolated fine and concentrated patterns. Therefore, metallization technology by electroless plating is required in place of electroplating. Generally, copper as a circuit pattern is prepared by the pretreatment process and nickel is deposited on the copper pattern and followed by the deposition of gold for connection between printed circuit boards and electronic components. A palladium catalyst process is employed for initiation of electroless nickel plating on the copper substrate because copper is not catalytic for the oxidation of hypophosphite. In this case, palladium ions tend to be adsorbed on resist and resin surfaces. Therefore extraneous deposition is often observed on these surfaces. This phenomenon can be eliminated if electroless nickel deposition is initiated without palladium catalyzation treatment. Electroless nickel films without extraneous deposition can be obtained with hypophosphite and dimethylamineborane (DMAB) as the reducing agents. Selectivity of the nickel deposits on the copper patterns is improved by controlling the DO level and the addition of boric acid in the electroless nickel solution.

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A quantitative evaluation method of solder bridging in micro-soldering has been established using a printed wiring board with copper comb pattern conductors. Bridge tests were conducted by immersing the comb pattern board into molten solder bath. The total length of solder bridging between conductors against the total length between conductors was measured as a measure of the occurrence of solder bridging. The occurrence of bridging depended on the number of immersion, flux activity including solid content, conductor spacing, solder bath temperature and solder composition. The increase in number of immersion enhanced bridging. The rosin flux without activators showed higher bridging than the activated flux. Sn-37Pb solder showed lower bridging than Sn-3.5Ag-5Bi solder. Solder bridging was found to be closely correlated with wettability, therefore, the improvement of wettability could be effective to suppress solder bridging. The proposed method is believed to be suitable for the evaluation of solder bridging.

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BGA (Ball Grid Array) planar routing problem is formulated as a mapping problem of pads to pins. In this paper, we propose a BGA routing algorithm and incorporate it into our sketch layout system, which is based on a topological layout model. In our algorithm, since wires pass through adjacent pin pairs away from pins on the diagonal lines of the pin arrays, it reduces the wire congestion and maximum wire length. The algorithm obtains wiring results in which the number of wires passing through a adjacent pin pair on the pin ring differs by at most one. Experimental results show its efficiency and effectiveness.

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Dielectric/insulating properties were studied in connection with origin and development processes of ionic migration which was the main reason of the insulation deterioration on printed wiring boards. The results of this study were: from the measurements of insulation resistance, (1) when the settled migration originated, the resistance value had fell down at the regular level. (2) On the insulation resistance, ten minutes value was lower than one minute value. Its results showed to reverse against the normal value. (3) Also, that resistances showed voltage dependence characteristics. Secondly, from the measurement of the dielectric properties, dielectric absorptions on the low frequency range were showed, and its values were larger with the development of migration. On the other hand, its values change with the thermal humidity aging process, such as shows lower values in normal. Therefore, the dielectric properties should be evaluated with these differential values.

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