Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
1998-12-01
2002-11-05
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S315000, C430S329000, C216S015000, C216S016000, C216S020000, C427S404000, C427S405000, C427S471000, C427S532000
Reexamination Certificate
active
06475703
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to multilayer circuit boards, and more particularly to multilayer circuit boards having air bridge crossover circuits.
2. Disclosure Information
U.S. Pat. No. 4,404,059 to Livshits et al. (hereinafter “Livshits”), U.S. Pat. No. 3,801,388 to Akiyama et al. (hereinafter “Akiyama”), and U.S. Pat. No. 5,738,797 to Belke et al. (hereinafter “Belke”), all three of which are incorporated herein by reference, describe additive and subtractive plating and chemical etching processes for constructing multilayer (i.e., two-or-more-layer) circuit boards having air bridges. As typified in FIGS.
1
A and
2
A-F (and in
FIGS. 1
a-h
of Livshits), the additive process involves the following steps. First (FIG.
2
A), a thin metal foil
10
made of a first metal is provided having opposed top and bottom surfaces
12
/
14
. Second (FIG.
2
B), top and bottom etch-resist masks
22
/
24
are disposed on the respective top and bottom foil surfaces, wherein the top and bottom masks have apertures
23
/
25
therein which define respective first and second conductor patterns. Third (FIG.
2
C), top and bottom conductor networks
32
/
34
made of a second metal are electrodeposited through the mask apertures and onto the respective top and bottom foil surfaces. Fourth (FIG.
2
D), the masks are stripped off, fifth (FIG.
2
E), the structure is attached to an electrically insulative surface
61
of a substrate
60
, and sixth (
FIG. 2F
) the structure is exposed to an etchant which etches substantially only the first metal, so as to etch away substantially all of the metal foil except for those portions
16
sandwiched between the top and bottom conductor networks. These sandwiched portions
16
are much less aggressively etched because the top and bottom conductor networks act essentially as etchresist masks, since the metal of these networks is not appreciably etched by the aforementioned etchant. After etching, these sandwiched portions
16
typically assume an hour-glass-like shape, and may be referred to as “pedestals”, “support elements”, or the like.
Air bridge crossover circuits are advantageous in that they facilitate high density circuits—that is, they permit the arrangement of a high number of circuit traces and other circuit elements into a small circuit board area. However, such circuits sometimes suffer from at least one of the following two problems: (1) susceptibility to mechanical damage, from impact, thermal excursions, and the like; and (2) poor electrical performance, caused by the use of certain metals having poor electrical conductance characteristics as the conductor network material. It would be desirable, therefore, to provide a way of creating such multilayer air bridge circuits without these drawbacks.
SUMMARY OF THE INVENTION
The present invention overcomes the disadvantages of the prior art approaches by providing a multilayer air bridge circuit structure, and method for producing the same, which has special metallic fortifying layers which mitigate the aforementioned disadvantages.
It is an object and advantage that the present invention includes such fortifying layers made of a metal selected such that the air bridge structure is mechanically and/or electrically fortified.
Another advantage is that the present invention may be easily and economically incorporated into the conventional air bridge circuit construction process.
These and other advantages, features and objects of the invention will become apparent from the drawings, detailed description and claims which follow.
REFERENCES:
patent: 3801388 (1974-04-01), Akiyama et al.
patent: 4404059 (1983-09-01), Livshits et al.
patent: 5738797 (1998-04-01), Belke, Jr. et al.
patent: 5976391 (1999-11-01), Belke, Jr. et al.
Achari Achyuta
Belke, Jr. Robert Edward
Goenka Lakhi Nandlal
Li Delin
McLeskey Edward
Brinks Hofer Gilson & Lione
Chacko-Davis Deborah
Huff Mark F.
Visteon Global Technologies Inc.
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