Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1998-06-08
2001-06-12
Paladini, Albert W. (Department: 2841)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S250000, C361S750000, C428S209000, C428S901000
Reexamination Certificate
active
06246009
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the fabrication of multilayer combined rigid and flex printed circuits having flexible printed circuits extending from the rigid board. In particular, the present invention relates to an improved process for the fabrication of multilayer combined rigid and flex printed circuits, wherein two circuit boards having rigid and flexible sections can be prepared from a novel basestock composite.
2. Background of the Invention
Techniques for making multilayer rigid flex printed circuit boards are well known in the art. One early example of the prior art is disclosed in U.S. Pat. No. 3,409,732, assigned to the Assignee of the present application and whose teachings are incorporated by reference. Typically a rigid flex stacked printed circuit board includes flexible printed circuit cables extending from the periphery of the rigid section or sections. The rigid portions of the flex cables are typically used as sites for electronic components or mechanical hardware. It is important to note that the copper conductor in each plane or layer is fabricated from one continuous sheet of copper foil.
With improvements in electronic technology, there has been a constant need for advances in electronic packaging. This need has led to more complex multilayer rigid flex printed circuit boards with many boards now using up to twenty-five, or even more, layers of circuitry. However, severe problems developed when the rigid circuit portions included many layers of conductors and holes plated through with copper to provide conductor barrels connecting the conductor layers.
One particular problem, reported on and discussed in U.S. Pat. No. 4,800,461, assigned to the assignee of the present Application, and whose teachings are incorporated by reference, described the fact that in multilayer rigid flex boards which included insulator materials such as acrylic adhesive and Kapton (Kapton is a trademark of E.I. duPont de Nemours and Company Inc. for polyimide film), the insulating materials placed a “Z-axis” stress on plated through holes. The coefficient of thermal expansion, it was reported, of the acrylic adhesive (Z-axis expansion) was the dominate influence. It was observed that because of the amount of acrylic required in many multilayer rigid flex applications, all plated through holes are stressed, with many cracking, making the boards unusable.
To overcome this problem, the '461 patent reported on a novel process to provide a rigid section incorporating insulator materials which, when subjected to elevated temperatures, did not expand in the Z direction to cause difficulties, including delamination and cracking of plated copper barrels. Stated another way, in the '461 patent, the materials causing undesirable expansion in the Z direction in the multilayer rigid section of the board, and the materials absorbing excessive amounts of moisture, such as acrylic adhesives and Kapton, were eliminated from the boards rigid section.
However, although the '461 patent was extremely successful in addressing the various problems recited therein, and in particular, the problem of thermal stresses described above, the process for fabrication of the rigid flex printed circuits has remained limited to the fabrication of a multilayer combined rigid and flex printed circuit board wherein two circuit boards are always prepared from a basestock composition, and remain attached to one another via the prepreg. In other words, the process of fabrication according to the teachings of the prior art begin with the step of laminating two conductor layers (i.e. copper layers) to a single insulator layer (prepreg) followed by imaging and etching. Accordingly if one of the two bonded conductor layers was somehow improperly imaged, it was necessary to discard the entire lamination.
It is therefore an object of this invention to provide a process for the fabrication of a multilayer combined rigid and flex printed circuits, wherein two circuit boards having rigid and flex sections can be prepared and imaged from a novel basestock composite, followed by separation into two individual single sided basestock laminates.
It is also an object of this invention to provide a novel basestock composition of sufficient planarity and rigidity to permit adequate handling and further processing thereof, and which can be separated into two individual layers each comprising an imaged copper layer laminated to a fiberglass sheet which is impregnated with adhesives such as an epoxy.
SUMMARY OF THE INVENTION
The present invention provides a multilayer rigid flex printed circuit board fabricated by a novel process and from a novel basestock composite wherein two copper sheets are laminated to a prepreg and in-between said laminated copper sheets is placed a release material that is not coextensive with the boarders of the prepreg, such that the basestock can be imaged and processed in the usual manner, and such that cutting the edges of the basestock material, after imaging; at a location internal to the basestock border provides a cut into the release layer, thereby allowing for separation of the two individual imaged copper layers and their supporting prepreg, along with the removal of said release material.
The present invention also comprises in process form, a process for the fabrication of a rigid flex printed circuit comprising the steps of laminating a pair of conductor layers to respective opposite surfaces of an insulating layer wherein the insulator layers are both affixed to a release layer and wherein said release layer is not coextensive with the borders of the insulator layers, thereby forming a basestock composite. The basestock composite is then imaged and etched on the conductor layers to form conductor patterns. The basestock is then cut at a point internal to its borders and into the release layer thereby separating the two imaged and etched conductor layers and removing said release material from the insulating layer.
Alternatively, the novel basestock composite can be made without a release layer, and such a basestock composite which contains two copper layers permanently affixed to one another, or the single copper layer prepared from a basestock composite containing a release layer, can be converted into a novel multilayer rigid flex printed circuit board.
REFERENCES:
patent: 4634631 (1987-01-01), Gazit et al.
patent: 5095628 (1992-03-01), McKenney et al.
patent: 5144534 (1992-09-01), Kober
patent: 5175047 (1992-12-01), McKenney et al.
patent: 5288542 (1994-02-01), Cibulsky et al.
patent: 5505321 (1996-04-01), Caron et al.
patent: 5591519 (1997-01-01), Caron et al.
patent: 5723205 (1998-03-01), Millette et al.
patent: 5877940 (1999-03-01), Millette et al.
Caron A. Roland
Millette Lee J.
Thoman Joseph A.
Hayes Soloway Hennessey Grossman & Hage PC
Paladini Albert W.
Teledyne Industries Inc.
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