Cleaning and liquid contact with solids – Processes – For metallic – siliceous – or calcareous basework – including...
Patent
1998-05-18
2000-06-20
El-Arini, Zeinab
Cleaning and liquid contact with solids
Processes
For metallic, siliceous, or calcareous basework, including...
134 26, 134 32, 134 34, 134902, 134122R, 134131R, B08B 102, B08B 302, B08B 304, C23G 302
Patent
active
060773596
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of chemical and electrolytic treatment and rinsing of printed circuit boards and conductor films with high precision and velocity by means of a treatment liquid, and to a device for carrying out the method.
Among these treatment methods are counted particularly electroplating, film developing, film stripping, etching and stripping of metal resists, and the rinsing steps before and after these processes. A feature common to all processes is that an exchange of material is necessary at the surfaces. The intensity of the exchange of material has a decisive effect on the treatment time. Therefore attempts have been made to increase the exchange of material on the surfaces of the printed circuit boards while including the process-specific requirements. The said requirements are in particular increased by the technical development in the area of fine conductor technology with fine bore holes. In treating printed circuit boards with conductor track widths and intervals of an order of magnitude down to 0.05 mm, and bores with diameters of down to 0.15 mm, there is an addition hindrance to the exchange of materials. The precision (accuracy of the tolerances of the thicknesses of metal coatings to be observed, conductor track widths and intervals, cleanness of the surfaces treated) required in this technique however reaches the outer limits of what is industrially feasible when the treatment times are extended.
The following process-specific requirements are therefore as follows:
Drilled-through-contacted printed circuit boards are to be reinforced electrolytically. Furthermore, conductor tracks which are defined by resist, are to be reinforced. In both cases a uniform distribution of coating thickness is necessary over the entire surface of the printed circuit board, including in the holes. In addition, a short treatment time, i.e. a high current density, is sought after. The structures in fine conductor technology and the occurring fine holes and particularly the blind holes set narrow limits here. The precision of electrolytic treatment must be achievable with soluble and insoluble anodes.
The copper-lined, drilled and through-contacted printed circuit board is coated over the entire surface with photo-resist, which is also known as film. The coating thickness comes to 60 to 80 .mu.m. The unexposed points must be developed, i.e. must be freed from the film. In the case of structures 50 .mu.m wide, the channel to be developed out is narrower than its height. Due to diffuse light scatter during exposure, sides of the channels to be developed, particularly on the base, harden out in a more or less trapezoidal configuration. The total removal of the undeveloped resist and of the partly developed resist from the narrow channels is necessary. At the same time the exposed and thus hardened points must not be damaged or loosened at the base from the copper layer.
After electrolytic copper reinforcement, the hard and securely-adhering film must again be removed. What is required is a large-area detachment of the film, so that it remains industrially simple to filter it out of the bath solution. The trapezoidal cross-sections described above lead to an inclusion of the film by the deposited copper. The same is brought about by a copper layer which grows out in a mushroom shape over the upper edge of the resist. The resist areas so included must likewise be entirely removed. In this respect also detachment and to a lesser degree dissolution must be effected, so that it remains possible to filter the film out of the treatment liquid.
The copper areas from which photoresist has been removed are chemically etched off as far as the base material of the printed circuit boards. The other conductor tracks and holes are protected by an etching resist. The lateral sides of the conductor tracks, from which photoresist have been removed, and the sides occurring only during etching, are not protected. The copper layer must be entirely etched out with the minimum attack on the sides. Therefore there is
REFERENCES:
patent: 4789405 (1988-12-01), Blasing et al.
Baron David T.
Schneider Reinhard
Atotech Deutschland GmbH
El-Arini Zeinab
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