Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1998-03-13
2001-08-14
Young, Lee (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S846000, C029S832000, C029S837000, C174S262000, C174S264000
Reexamination Certificate
active
06272745
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to methods for the production of printed circuit boards with at least one electrically conductive through-plating which runs in a hole in an insulating base material from a first surface to a second surface.
BACKGROUND OF THE INVENTION
Such a through-plating of a printed circuit board serves, for example, to establish an electrically conductive connection between a conductive track running on the first surface and a conductive track running on the second surface, thereby enabling electronic components to be fixed to both surfaces, which electronic components can be inter-connected with one another in accordance with a circuit to be realized.
Through-platings are normally holes which are made in the printed circuit board at points which are pre-determined by the layout of the circuit to be realized, the inner sides of said holes being metallized.
As long as only components having connecting wires or legs (resistors, capacitors, coils, transformers, diodes, transistors, integrated circuits, etc.) were intended to be fixed to the printed circuit boards, it was possible to insert the connecting wires or legs directly into the metalized holes and solder them therein. Today's components, however, are almost exclusively SMD components. (The acronym SMD is formed from surface mounted device).
In contrast to components having connecting wires or legs, SMD components only have connecting pads. The latter are soldered in a planar manner on to conductive tracks of printed circuit boards. The holes which are not closed off by the metallization, in other words are open, are not closed off by this soldering and remain open.
If multilayer printed circuit boards with through-platings which pass only through some of the layers and are covered over by outer layers are to be produced, the air remaining in the open holes as a result of the latter being covered over would expand in the event of a temperature increase and might give rise to internal cracks.
SUMMARY OF THE INVENTION
It is therefore essential to close off the metallized holes. If this is done by means of screen printing, in which, as is known, a pasty material or material of similar consistency is forced through a stencil by a squeegee, materials available for this shrink on curing and a cavity forms on the material remaining in a hole. This cavity is likewise highly disruptive for the reasons mentioned in the context of covering over unfilled holes.
In order to solve the problems outlined, a first variant of the invention consists in a method for the production of printed circuit boards with at least one electrically conductive through-plating which runs in a hole in an insulating base material from a first surface to a second surface, having the following steps:
the base material is
either pressed on the first and/or the second surface with a first and/or with a second two-layered foil consisting of a Cu foil covered with a Cu layer, in such a way that the Cu foils adhere well to the base material,
or pressed with a first and/or with a second Cu foil, and a first and/or a second Cu layer is subsequently applied thereto,
the holes are produced,
these holes and the exposed surface of the first and/or of the second Cu layer are provided with a third Cu layer,
the metallized holes are completely filled with an insulating material or with a conductive material by spreading on with the a squeegee or by rolling on to the exposed surface of the third Cu layer,
the first and the second Cu layer are removed together with the third Cu layer,
portions of the insulating material or of the conductive material which project beyond the remaining Cu foils are removed after the curing of said material and, consequently, the surfaces of the Cu foils are planarized, and
the Cu foils are structured in a customary manner to produce a conductive pattern.
According to a preferred embodiment of the first variant of the invention the insulating material or the conductive material is cured already before the first, second and third Cu layer are removed.
Published Australian Patent Application AU-A 11 799/76 describes a method for the production of printed circuit boards with at least one electrically conductive through-plating which runs in a hole in an insulating base material from a first surface to a second surface, having the following steps:
the base material is a thin-film Cu laminate which has been covered by a first and a second Cu foil, respectively,
the holes are produced,
respective walls of the holes are covered by a first Cu layer and the exposed surface of the first and of the second Cu layer are provided with a second and a third Cu layer, respectively,
the first and the second Cu layer together with the second and the third Cu layer are removed by peeling, and
the first Cu layers in the holes are thickened using masks.
In this method, the holes are not filled, but are open after the Cu foils together with the Cu layers has been removed by peeling. As experiments showed this peeling results in irregular edges of the holes. But these irregular edges are unwanted.
U.S. Pat. No. 3,163,588 describes a similar method for the production of printed circuit boards with at least one electrically conductive through-plating which runs in a hole in an insulating base material from a first surface to a second surface, having the following steps:
on the first and the second surface, the base material is covered with a first and a second Cu foil, respectively,
these Cu foils are covered with a first and a second plastic film, respectively,
the holes are produced which runs in the base material, the Cu foils and the plastic films, so that a respective wall of the holes consists of a first portion covering the base material, a second and third portion covering the first and second Cu foil, respectively, and a fourth and fifth portion covering the first and second plastic film, respectively,
the walls of the holes and adjacent portions on the surfaces of the plastic films are metallized by plating,
the plastic films together with adjacent portions and the fourth and fifth portions of the walls are removed, and
the Cu foils are structured to produce a conductive pattern.
In this method, the holes are not filled, too, but are open after the Cu foils together with the Cu layers and the plastic films has been removed by peeling. As experiments showed again this peeling results in irregular edges of the holes. But these irregular edges are unwanted and are plated once again by a further metallizing step.
In order to solve the problems outlined, a second variant of the invention consists in a method for the production of printed circuit boards with at least one electrically conductive through-plating which runs in a hole in an insulating base material from a first surface to a second surface, having the following steps:
the base material is
either pressed on the first and/or the second surface with a first and/or with a second two-layered foil consisting of a Cu foil covered with a metallizable acrylonitrile-butadiene-styrene-copolymer film, in such a way that the Cu foils adhere well to the base material,
or pressed with a first and/or with a second Cu foil, and a first and/or a second metallizable acrylonitrile-butadiene-styrene-copolymer film is subsequently applied thereto,
the holes are produced,
these holes and the exposed surface of the first and/ or of the second acrylonitrile-butadiene-styrene-copolymer film are provided with a first Cu layer,
the metallized holes are completely filled with an insulating material or with a conductive material by spreading on with the a squeegee or by rolling on to the exposed surface of the first Cu layer,
the first and the second acrylonitrile-butadiene-styrene-copolymer film are removed together with the first Cu layer,
portions of the insulating material or of the conductive material which project beyond the remaining Cu foils are removed after the curing of said material and, consequently, the surfaces of the Cu foils are planarized, and
the Cu foils are structured in a c
Kersten Peter
Kiefer Jörg
Bose McKinney & Evans LLP
Photo Print Electronics GmbH
Trinh Minh
Young Lee
LandOfFree
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