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Method for manufacturing a multilayer printed circuit board
| Details |
Inventors: Gales, Raymond; Michel, Damien;
Assignee: Circuit Foil Luxembourg Trading Sarl (Luxembourg, LU)
Primary Examiner: Arbes; Carl J.
Assistant Examiner: Phan; Tim
Attorney, Agent or Firm: McCormick, Paulding & Huber LLP
A method for manufacturing a multilayer printed circuit board includes providing a core board, a composite foil including a carrier foil, a functional copper foil and a non-reinforced thermosetting resin layer, the functional copper foil being electro-deposited with a uniform thickness of more than 4 .mu.m but less than 10 .mu.m on the carrier foil, the functional copper foil having a front side facing the carrier foil and an opposite backside which is coated with the non-reinforced thermosetting resin layer. The method further involves laminating the composite foil with the non-reinforced thermosetting resin layer on the core board and removing the carrier foil from the functional copper foil in order to uncover the front side of the functional copper foil. A CO.sub.2 laser source drills holes from the uncovered front side of the functional copper foil through the functional copper foil and the non-reinforced thermosetting resin layer to form microvias. |
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DETAILED DESCRIPTION U.
S.
Pat.
No.
3,998,601 discloses a composite foil and a method for manufacturing the latter.
The composite foil comprises an electrodeposited copper support layer and a second electrodeposited copper layer of a thickness which is-not self supporting.
Intermediate the copper support layer and the second copper layer is a thin layer of a release agent, preferably chromium.
The second copper layer has a thickness no greater than 12 .
mu.
m.
A laminate may be formed by superimposing this composite foil on epoxy impregnated fiberglass with the ultrathin copper surface in contact with the epoxy-glass substrate, and subjecting this assembly to a conventional laminating process.
After cooling of the laminate, the copper carrier coated with the release agent is peeled away to produce a thin copper clad laminate suitable for etching, etc.
in the production of printed circuit elements.
A method for manufacturing a multi-layer interconnected board is described in JP 10 190236.
According to a first step of this method, a circuit board with a desired circuit pattern formed thereon, a metal foil and an insulator layer are positioned, stacked up and laminated.
In the next step, a point on a conductor layer desired to be laser processed is subjected to a process to increase the rate of absorption of the laser.
In the following step a laser beam is impinged on the processed point so as to melt and sublime the metal foil and the insulator layer and thereby form a hole.
In a final step, electroless plating is performed to electrically connect conductors through the hole.
The possibility of laser drilling into copper clad epoxy-glass, in particular by means of a CO2 laser, is reported in "Laser drilling of microvias in epoxy-glass printed circuit boards" by A.
Kestenbaum et al.
, IEEE Transactions on components, hybrids and manufacturing technology, vol.
13, no.
4, Dec.
1990 (1990-12), pages 1055-1062, XP000176849 IEEE Inc.
New York, US ISSN: 0148-6411.
In one of the experiments, a CO.
sub.
2 laser was used to drill a through hole in a 0
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Metal Working 
