Metal working – Method of mechanical manufacture – Electrical device making
Patent
1996-09-23
1998-09-01
Arbes, Carl J.
Metal working
Method of mechanical manufacture
Electrical device making
174266, 427 97, H04K 310
Patent
active
057993939
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention related to a method for producing a plated-through hole on a printed-circuit board. In producing a plated-through hole on a multilayer printed-circuit board, it is possible to initially bore (drill) through the copper-clad printed-circuit board at the spots provided for the through-hole plating and, using a galvanic process, to plate (metallize) the inner wall of the bore through copper deposition. In so doing, the copper is not only deposited on the inner wall of the bore, but over the entire copper surface. The plated bores and the spots which will later form the interconnect traces (conductor lines) are subsequently coated with an etch resist or resist film. The uncoated copper surfaces are etched out, so that after removal of the etch resist, the desired interconnect traces, as well as the plated plated-through holes remain. When the inner wall is plated, copper is inevitably deposited on the copper surfaces of the printed-circuit board as well. However, this additional copper must later be removed again during the etching process, thus making the process for manufacturing the printed-circuit board more expensive. Another conventional method is used to imprint a conductive paste on an uncoated printed-circuit board using the screen printing technique, which at the same time fills in the bores, thus forming a plated-through hole. However, the disadvantage associated with this conventional method is that the plated-through hole provided for receiving a lead wire of an electrical component can no longer be used under the method of through-hole mounting, since the bores are sealed by the conductive paste. Additional bores must then be provided to insert the lead wires of the components. However, additional bores require additional space, which is not always available, particularly given a multilayer circuit wiring on the printed-circuit board.
SUMMARY OF THE INVENTION
The advantage of the method according to the present invention is that no additional metal is deposited on the copper-clad printed-circuit board that would then have to be etched away again. Another advantage is that the plated-through holes can be used for the through-hole mounting of the lead wires of the components, making it possible to omit additional bores and, thus, economize space on the printed-circuit board. In addition, the process for fabricating such a printed-circuit board is simplified, so that a cost saving is also realized.
According to another embodiment of the present invention, it is also advantageous that the catalyst is applied either after the boring operation or after the patterning of the printed-circuit board. As a result, the metal can be applied directly to the catalyst during the subsequent electrochemical plating without having to activate said catalyst once more.
It is further advantageous that the electrochemical plating is applied as such a thin-walled plating so as to leave open the remaining bore section, enabling the bore section to still receive the lead wires of the components.
Yet another embodiment of the present invention uses nickel or nickel compounds (alloys) for the electrochemical plating. Nickel layers are resistant to corrosion, so that the surface of the printed-circuit board does not need to be protected by an additional passivation layer.
It is also beneficial that not only the pads (eyelets) around the bores, but also parts of the printed-circuit boards are covered with the plating. As a result, these parts are also substantially protected from the effects of corrosion.
To improve the soldering process or the bonding of the printed-circuit board, the interconnect traces can preferably be coated with palladium, or the contact lands with a gold layer. As a result, thin bonding wires may also be advantageously used through application of the usual bonding methods, such as nailhead or thermocompression bonding. These bonding wires can then be bonded directly to a corresponding land of an integrated circuit, which is applied as a chip.
BRIEF DESC
REFERENCES:
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patent: 5539181 (1996-07-01), Sippel
Backasch Wolf
Hohmann Rolf
Arbes Carl J.
Blaupunkt-Werke GmbH
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