No cleaning in fine pitch printed wiring boards (PWBs) after mounting the electronic devices, possibly deteriorates insulation reliability by ion migration, because the activator of flux remains on the surface of PWBs. The relationship between the solubility of copper ion and the insulation life of PWBs was examined. The insulation life depends on the kind and the concentration of the activator in the flux. It was proved that as the value of the solubility of copper ion increases, the insulation life of PWBs shortens further. The solubility of copper ion by the activator indicates that the flux could be use or not.

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Two modelling methods have been proposed and studied for analysing mechanism of ion migration at electrodes on printed wiring boards. First modelling method has targetted analysing basic reaction and visualization of ion migration phenomena. Second modelling method has targetted measurement of copper dissolving ratio according to resistivity change of thin film electrode. Both modelling methods have contented the targets as expected and have given some analytical results as follows : circumstance of electrodes changing to promote reaction of ion migration, chelating agent relating ion transfer, ion dissolving to resin in accordance with solubility principle, higher insulation resistance leading to less ion migration, and so on.

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In power electronics products, including general-purpose inverters and power module used 100-400V circuits, metal-base PWBs with superior thermal conductivity have come into wide use as high density mount PWBs to reducing size. Therefore, high electric strength of 1-3kV/mm have induced to insulated layer. Accordingly, we have been studied about copper ion migration phenomena by using some kinds of insulation materials. As a result, growth of copper ion migration is related to the amount of ionic element included in insulation. It becomes clear that NH₄⁺ is an important factor in addition to C1^- and SO₄^2- as the type of ion. It is possible to anticipate of the amount of ionic elements in insulation and the growth of copper ion migration by measuring dielectric loss tangent and the volume resistivity under enhanced condition.

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Thermosetting PPE resin S4100 was developed as an insulating material for printed circuit boards, which has both high glass transition temperature and excellent dielectric characteristics. S4100 laminate produced by using E-glass cloth was evaluated and found to have both superior dielectric properties, such as ε=3.36, tanδ=0.004 at 2GHz, and high Tg of 200°C which is comparable to polyimide laminate. The dependence of dielectric constant and dissipation factor on temperature, and their stability under humidified condition were evaluated and the results were compared with FR-4 and polytetrafluoroethylene (PTFE) laminate based on the idea that stability of dielectric characteristics at GHz region is an important measure of insulation reliability of insulating materials. Dielectric characteristics of S4100 laminate were found to be more stable than PTFE laminate having lower dielectric constant and dissipation factor, under temperature change ranging from -20°C to 80°C because of high glass transition temperature of S4100 laminate. Furthermore, S4100 laminate showed smaller change in dielectric constant snd dissipation factor under the condition of humidified in pressure vessel because S4100 had low water absorption of 0.2% by weight. Moreover, S4100 laminate had no blistering in solder bath after the test. On the other hand, FR-4 showed high water absorption of 0.9% by weight and blistering in solder bath under the above conditions. The measurement of transmission loss of laminate certified the fact that S4100 laminate has very low transmission loss, which is nearly equal to that of PTFE laminates in the frequency range of 0.8-4GHz. It is confirmed that S4100 is a useful material for the application to PWB's of high speed digital circuits and high frequency communication equipment.

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It is known that there is a difference of times from immersion to start deposition (Induction time: I.T.) in various electroless copper bath using formaldehyde. In case of glyoxylic acid using as a reducing agent for electroless copper plating at 25°C, the difference of I.T. with various chelating agents was bigger than formaldehyde bath. We have studyed about relation between I.T. and state of deposition. The potential on a sample just after immersed in long I.T.electroless copper bath was more noble than short I.T. bath. The anodic current density of glyoxylic acid on catalyzed copper surface in long I.T. bath was smaller than in short I.T. bath.I.T, of long I.T. bath was greatly affected by Pd density on substrate, i.e. higher Pd density substrate showed shorter I.T.. The appearance of deposition from ashort I.T. bath was uniformity and islands structure was obtained from a long I.T. bath.

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[in Japanese]

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