Cleaning and liquid contact with solids – Processes – Including application of electrical radiant or wave energy...
Patent
1997-07-03
2000-01-25
Gorgos, Kathryn
Cleaning and liquid contact with solids
Processes
Including application of electrical radiant or wave energy...
134 2, 134 64R, 134 15, 134 32, 134902, B08B 312, B08B 600, B08B 700, B08B 702
Patent
active
06016817&
DESCRIPTION:
BRIEF SUMMARY
SPECIFICATION
The invention relates to a method and a device for surface treatment of plate-shaped workpieces provided with extremely fine holes, particularly printed circuit board, by means of a liquid or gaseous treatment agent.
BACKGROUND OF THE INVENTION
The surface treatment of plate-shaped workpieces, particularly printed circuit boards, can provide problems when the latter contain holes which are extremely fine. In particular holes in which the ratio of hole diameter to hole length is extremely small, for example 1:10 or less, treatment with the treatment agents can only be carried out with difficulty as these can only be brought into the holes by means of special measures. Such holes are preferably located in multi-layer printed circuit boards, in which a plurality of electrical circuit layers are stacked one above the other and glued together. In this case the holes serve to provide a plurality of conductive connections between the inner and outer layers and if necessary also between the inner layers themselves. In most cases the ends of the printed circuit lines are for this purpose in the form of circular or rectangular plating surfaces. The holes pass through these plating surfaces. For purposes of electrical contacting of the individual circuits with one another, the walls of the holes are metallised. The copper sleeve bearing on the bore wall surfaces thus produced represents the electrical contacting between two or more associated contacting surfaces of the electrical circuits.
Various treatment steps are necessary for metallisation, such for example as cleaning, conditioning, activation, metallising and drying. When the holes are bored, for example, plastic emerges at the resin areas, each only a few micrometers thick, between the metallic surfaces of the electrical circuits in the interior of the printed circuit board; the plastic deposits as a smeared resin film on the bore surfaces of the metal layers to be contacted. In the case of the more usually used FR4 printed circuit boards (laminates with flame-retardant resin and glass fibre mats as reinforcement) the plastic consists of epoxy resins. When such smearing covers roughly 50% of the wall surface of the hole, the conductive connection at the contacting surfaces is already at risk. If a degree of smearing, even in one single plating hole, reaches about 80%, then the entire board should be rejected. When there are a plurality of plating holes for a larger multi-layer printed circuit board and in view of the extremely high manufacturing costs it is therefore clear that this smearing can lead to considerable costs due to waste, while in addition recognition of the smears after drilling is only possible with considerable outlay, and then only in individual holes.
Difficulties in the removal of resin smearing increase as an increasing proportion of small and extremely small holes (for example smaller than 0.4 mm diameter) have to be processed. For example, printed circuit boards are already being produced with a thickness of 7.3 mm and with holes of a diameter of 0.35 mm (ratio of the bore hole diameter to the length roughly 1:21).
Experience has shown that the flow speeds of treatment agent achievable in through plating holes with diameters with less than 0.3 mm and with lengths above 4.5 mm is no longer sufficiently high, so that sufficient exchange of materials at the wall surfaces of the holes is no longer guaranteed. In this case the holes behave almost like capillaries, which in the most favourable case are still wetted by the treatment agents, yet through-flow is only achievable with difficulty. Particularly when the peripheral surfaces of the holes are rough, wetting and through-flow are practically impossible. This is above all the case when operation is with liquid treatment agents, which have a higher viscosity than for example water.
In order to enable wetting and through-flow of such fine holes, it is therefore proposed among other things to pass the workpieces through the treatment plant in a horizontal operational positi
REFERENCES:
patent: 3989537 (1976-11-01), Sickmeier
patent: 4789405 (1988-12-01), Blasing et al.
patent: 5030293 (1991-07-01), Rich et al.
patent: 5593507 (1997-01-01), Inada et al.
Atotech Deutschland GmbH
Gorgos Kathryn
Nicolas Wesley A.
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