Etching a substrate: processes – Forming or treating electrical conductor article – Forming or treating of groove or through hole
Reexamination Certificate
2000-06-26
2002-10-08
Gulakowski, Randy (Department: 1746)
Etching a substrate: processes
Forming or treating electrical conductor article
Forming or treating of groove or through hole
C216S019000, C216S033000, C216S017000, C427S096400, C427S097100, C430S311000
Reexamination Certificate
active
06461527
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method for fabricating a flexible printed circuit board which has an access on both sides.
Flexible printed circuit boards or so-called “flexboards” are used as electrical connection elements and circuit carriers in a wide variety of technological areas.
The use of a cost-effective roll-to-roll process for producing flexible printed circuit boards with access on one side, i.e. with contact-making cutouts either only in the base sheet or only in the covering sheet, is already known. Base material, which is supplied in the form of a roll by the manufacturer of the base material and which includes a base sheet with a Cu sheet already applied thereto, is unwound continuously from the roll. The Cu sheet is patterned into conductor tracks and a covering sheet is rolled onto the patterned Cu sheet. The covering sheet is already provided with stamped-out portions at the contact-making locations that are to be formed subsequently. The material web thus fabricated is wound up onto a roll again at the end of the production line.
Printed circuit boards with access on both sides, i.e. with contact-making cutouts both, in the base sheet and in the covering sheet, cannot be fabricated in a roll-to-roll process, since this process, due to different expansion properties of the base material (base sheet with Cu sheet) and of the stamped covering sheet, does not have a sufficient positioning accuracy for the positionally highly accurate alignment of the stamped base film with the stamped covering film necessary in the case of a printed circuit board with access on both sides. For this reason, flexible printed circuit boards with access on both sides are not fabricated on a continuous material but rather in a comparatively cost-intensive method using individual-processing material sections or so-called “panels.”
German Published, Prosecuted Patent Application DE-AS 19 25 745 discloses a method for fabricating, in a roll-to-roll process, a flexible printed circuit board with access on one side.
U.S. Pat. No. 5,759,417 discloses a process for fabricating a flexible printed circuit board which has access openings on both sides. In this case, a base material which is in the form of a sheet and which is coated on both sides with Cu is used. A conductor track pattern is formed from one of the Cu layers, while fine holes are introduced into the other Cu layer at suitable locations through the use of a photolithographic step. The conductor track pattern formed from the first Cu layer is covered with a covering sheet having stamped-out portions at suitable locations. On the other side of the printed circuit board, the perforated Cu layer is used as a mask layer for a laser processing step, in which contact-making holes are burned into the base material. Access to the Cu layer forming the conductor track pattern is also enabled via the contact-making holes. The Cu mask layer is removed in a final step.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for fabricating a flexible printed circuit board with access on both sides which overcomes the above-mentioned disadvantages of the heretofore-known methods of this general type and which is cost-effective to carry out and allows a high flexibility in the process control.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for fabricating a flexible printed circuit board, which includes the steps of:
providing a base material having a base sheet and a metallic conductor track sheet disposed on the base sheet;
patterning the metallic conductor track sheet for producing conductor tracks;
providing a conductor track covering over the conductor tracks and providing a first contact-making cutout in the conductor track covering;
producing a second contact-making cutout in the base sheet with a laser irradiation by guiding, with an optical configuration, a beam of a laser, focused to a small-area laser light spot, along a predefined travel path across the base sheet and removing the base sheet in a region of the second contact-making cutout; and
performing the steps of patterning the metallic conductor track sheet, providing the conductor track covering, and producing the second contact-making cutout in at least one roll-to-roll process.
In other words, in accordance with the invention, a method for fabricating a flexible printed circuit board is provided, in which, on a base material including a base sheet and a metallic conductor track sheet provided thereon, in one or more roll-to-roll processes,
the conductor track sheet is patterned for the purpose of producing conductor tracks, and
a conductor track covering, in particular a covering sheet, is provided over the conductor tracks, first contact-making cutouts being provided in the conductor track covering, wherein the method is characterized in that
in the context of a roll-to-roll process, using laser irradiation, second contact-making cutouts are produced in the base sheet, by a laser beam, focused in a small-area, being guided by an optical configuration along a predefined travel path across the base sheet to be removed in the region of the second contact-making cutout to be produced.
With the objects of the invention in view there is also provided, a method for fabricating a flexible printed circuit board, which includes the steps of:
providing a base material having a base sheet and a metallic conductor track sheet disposed on the base sheet;
patterning the metallic conductor track sheet for producing conductor tracks;
providing a conductor track covering over the conductor tracks;
producing a first contact-making cutout in the conductor track covering and producing a second contact-making cutout in the base sheet with a laser irradiation by in each case guiding, with an optical configuration, a beam of a laser, focused to a small-area laser light spot, along a predefined travel path across the base sheet and the conductor track covering and removing the base sheet and the conductor track covering in regions of the first and second contact-making cutouts; and
performing the steps of patterning the metallic conductor track sheet, providing the conductor track covering, and producing the first and second contact-making cutouts in at least one roll-to-roll process.
A significant advantage of both methods according to the invention is that a cost-effective roll-to-roll process is used in the production of the flexible printed circuit board with access on both sides. The integration of the laser processing step into the roll-to-roll process, which uses a continuous material web, results in a maximum cost saving, since all the first and second contact-making cutouts in the printed circuit board layer structure have already been completed at the end of the cost-effective roll-to-roll process. Furthermore, in comparison with conventional methods which use a mechanical stamping step in order to form the second contact-making cutouts, both methods according to the invention have a high adaptability—which can be achieved in particular by the use of software—with regard to changes in the process configuration or process planning. Whereas a change in the desired stamping positions or patterns necessitates an exchange of parts of e.g. the stamping tool in the case of a conventional stamping process. In the case of the methods according to the invention on the other hand, only laser and/or laser positioning parameters have to be adjusted by software in such a case.
In accordance with the first method according to the invention, the laser processing step is preferably carried out after the application of the conductor track covering containing the first contact-making cutouts. In this case, it is appropriate to perform the process steps of patterning the conductor track sheet and providing or applying the conductor track covering, in a roll-to-roll process, on a continuous material web.
In accordance with the second method according to the invention, a
Franzen Frank
Haupt Detlef
Gulakowski Randy
Smetana Jiri F.
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