Displacement Au/electroless Ni-P double layer coatings were prepared on Cu plate. Effects of P content in lower Ni-P coatings on the structure and solderability of upper Au coating were studied with ESCA, EDS, SEM and meniscograph method. The Au coating consisted of pure Au layer and mixture of Au and Ni layer and the coating showed good solderability. During humid air aging test, Ni (OH) ₂ layer were formed on the Au/Ni-P coatings. Solderability for Ni-9.1% P/Au coating was superior to that for Ni-2.7wt%P/Au coating, because that the thickness of Ni (OH) ₂ layer was increased with decreasing P content.

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Recently, electronics industry requires to increase circuit density with downsizing of equipment. Especially, Flexible Printed Circuit (FPC) is becoming an indispensable material. In this report, we show the applications of polyamic acid film to prepunched adhesiveless FPC and adhesiveless coverlay, these materials have excellent electrical and thermal characteristics. By using polyamic acid film, we can make holes to the film easily by punching, and we can laminate it with copper foil or adhesiveless FPC under mild (100°C) conditions. Further polyamic acid film becomes usual polyimide by curing. Except these developments, polyimide ink was applied to adhesiveless coverlay, but has poor flexibility. On the other hand our developed material has good flexibility because it contains no filler. Adhesiveless FPC with via hole was also required. But the difficulty in making via hole by etching method is another problem in ordinary adhesiveless FPC that shows excellent chemical resistivity. Then we successfully developed punching method utilizing polyamic acid as the base or coverlay film.

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We have investigated the extraneous nodule deposition phenomenon in the formation of circuit pattern by electroless copper plating. The nodules are spherical and the sphere centers are on the resist wall. Small nuclei on the resist wall cause the electroless plating reaction. Small non-conductive particles like metal-oxides can act as the deposition nuclei. The growth of such nuclei is affected by diffusion of disolved oxygen. Measurement of diffusion parameters gives the critical size of a nucleus for nodule formation. We have made clear that particles result in nodule formation in the case of bigger than 4.2μm and located on the resist wall.

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[in Japanese]

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