Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2000-02-02
2002-07-16
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S031000, C430S317000, C430S318000, C430S330000, C427S058000, C427S372200
Reexamination Certificate
active
06420093
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for making additional interconnect layers on commercially available printed circuit boards using toughened benzocyclobutene based polymers and metal foils coated with such polymers. This invention also relates to such toughened benzocyclobutene-based polymers.
BACKGROUND OF THE INVENTION
Various printed wiring boards or printed circuit boards (referred to herein as “PWBs”) are known and frequently have two to eight layers of laminates. Occasionally, it is desirable to add additional layers to these board structures (see, e.g., H. T. Holden,
In Printed Circuits Handbook,
4
th
ed., C. F. Coombs, Jr., Ed.; McGraw-Hall: New York, 1996, Chapter 4). For high frequency applications, the insulating materials typically used in the PWBs (e.g., epoxy materials) may not provide the desired low dielectric loss. Therefore, it would be desirable to have a process and materials which could provide the desired low dielectric loss.
Benzocyclobutene-based polymers (hereinafter referred to as “BCB polymers”) are thermosetting polymers. Certain of these polymers have low dielectric constants and thus, are desirable as insulating coatings in various electronics applications (see, e.g., “Benzocyclobutene (BCB) Dielectrics for the Fabrication of High Density, Thin Film Multichip Module,”
Journal of Electronics Materials, Vol.
19, No.12, 1990 and G. Czornyl, M. Asano, R. L. Beliveau, P. Garrou, H. Hiramoto, A. Ikeda, J. A. Kreuz and O. Rohde,
In Microelectronic Packaging Handbook, Volume
2; R. R,.Tummala, E. J. Rymaszewski and A. G. Klopfenstein, Eds.; Chapman & Hall: New York, 1997; Chapter 11). However, for certain applications, BCB polymers may not have sufficient toughness. Therefore, it would be desirable to have a BCB polymer with increased toughness without significant loss or degradation of other desirable properties.
JP 8-60103 discloses an adhesive sheet comprises a compound having a benzocyclobutene group and a binder polymer. The preferred binder polymers have carbon-carbon unsaturated bonds. The reference indicates that from about 1-95 percent of the composition may be the binder polymer.
SUMMARY OF THE INVENTION
According to a first embodiment, the present invention is a process comprising
providing a printed wiring core board, which comprises a glass fiber reinforced board with conductive metal circuitry,
laminating to the printed wiring core board a sheet comprising a foil of a conductive metal and, on the foil, a dielectric layer of a curable composition comprising (a) at least one precursor compound selected from arylcylobutene monomers, arylcyclobutene oligomers, and combinations thereof; and (b) a polymer or oligomer having a backbone comprising ethylenic unsaturation (i.e., carbon-to-carbon double bond(s)), wherein, during the lamination step, the dielectric layer is in contact with the printed wiring board, and
processing the laminated article to form additional electrical connections.
According to a second embodiment, this invention is a preferred composition comprising
a) at least one precursor compound selected from arylcylobutene monomers, arylcyclobutene oligomers, and combinations thereof; and
b) a polymer or oligomer having a backbone comprising ethylenic unsaturation (i.e., carbon-to-carbon double bond(s)) and terminal acrylate or methacrylate groups. The invention is also the partially polymerized (b-staged) reaction product of this composition and the cured reaction product of the b-staged material.
According to yet a third embodiment, the invention is a sheet comprising a metal foil and a film comprising the composition of the second embodiment or the partially cured product of that composition.
DETAILED DESCRIPTION OF THE INVENTION
The core board to which the BCB coated metal foil is laminated is characterized by having various insulating layers laminated together and separating various metal interconnect lines. Processes for making such PWBs are well-known (see, e.g.,
Printed Circuits Handbook,
4
th
Ed., C. F. Coombs, Jr., McGrall-Hill: New York, 1996). Typically, the insulating layers are glass reinforced epoxy. The metal foil is a very thin layer of a conducting metal, such as Cu or Cu alloy, and is preferably copper. The thickness of the metal foil is preferably about 3 to 50 microns. The BCB dielectric layer is preferably coated from a solvent onto foil. Suitable solvents include mesitylene xylenes, toluene, methyl ethyl ketone, cyclic ketones and a mixture of these solvents. After coating, the composition is preferably baked at temperatures from 100° C. to 200° C., more preferably 120° C. to 180° C. in air for 5 to 30 minutes, most preferably at 140° C. to 160° C. for 10 to 20 minutes.
Lamination to the core board may occur according to standard processes, preferably by vacuum hot press at temperatures of 200° C.-250° C. and pressures of 10-40 Kg/cm
2
.
Additional patterning steps may then be performed to the laminate according to known procedures. For example, the metal foil could be stripped or pattern etched followed by via formation with a laser drilling (e.g. with a CO
2
laser), or the entire laminate could be mechanically drilled through. Electroless plating of additional conductive metal, such as copper, followed by electroplating (e.g. with copper) could be used to form the desired electrical connections.
As stated above, the precursor is either an arylcyclobutene monomer, a b-staged oligomer of one or more arycyclobutene monomers, or some combination of b-staged arylcyclobutene oligomers and/or monomers.
Preferably, the monomers are of the formula
wherein
B
1
is an n-valent organic linking group, preferably comprising ethylenic unsaturation, or B
1
is absent. Suitable single valent B
1
groups preferably have the formula —CR
8
═CR
9
Z, wherein R
8
and R
9
are independently selected from hydrogen, alkyl groups of 1 to 6, most preferably 1 to 3 carbon atoms, and aryl groups, and Z is selected from hydrogen, alkyl groups of 1 to 6 carbon atoms, aryl groups, —CO
2
R
7
wherein R
7
is an alkyl group, preferably up to 6 carbon atoms, an aryl group, an aralkyl group, or an alkaryl group. Most preferably Z is —CO
2
R
7
wherein R
7
is an alkyl group, preferably up to 6 carbon atoms, an aryl group, an aralkyl group, or an alkaryl group. Suitable divalent B
1
groups include —(CR
8
═CR
9
)
o
—(Z′)
o−1
, wherein R
8
and R
9
are as defined previously, o is 1 or 2, and Z′ is an alkyl group of 1 to 6 carbon atoms, an aromatic group, or a siloxane group. Most preferably o is 2 and Z′ is a siloxane group.
Ar
1
is a polyvalent aromatic or heteroaromatic group and the carbon atoms of the cyclobutane ring are bonded to adjacent carbon atoms on the same aromatic ring of Ar
1
, preferably Ar
1
is a single aromatic ring;
m is an integer of 1 or more, preferably 1;
n is an integer of 1 or more, preferably 2-4, more preferably 2; and
R
1
is a monovalent group, preferably hydrogen, lower alkyl of up to 6 carbon atoms.
The synthesis and properties of these cyclobutarenes, as well as terms used to describe them, may be found, for example, in U.S. Pat. Nos. 4,540,763; 4,724,260; 4,783,514; 4,812,588; 4,826,997; 4,999,499; 5,136,069; 5,185,391; 5,243,068, all of which are incorporated herein by reference.
According to one preferred embodiment, the monomer (a) has the formula
wherein
each R
3
is independently an alkyl group of 1-6 carbon atoms, trimethylsilyl, methoxy or chloro; preferably R
3
is hydrogen;
each R
4
is independently a divalent, ethylenically unsaturated organic group, preferably an alkenyl of 1 to 6 carbons, most preferably —CH
2
═CH
2
—;
each R
5
is independently hydrogen, an alkyl group of 1 to 6 carbon atoms, cycloalkyl, aralkyl or phenyl; preferably R
5
is methyl;
each R
6
is independently hydrogen, alkyl of 1 to 6 carbon atoms, chloro or cyano, preferably hydrogen;
n is an integer of 1 or more;
and each q is an integer of 0 to 3.
The preferred organosiloxane bridged bisbenzocyclobutene monomers can be prepared by methods disclosed, fo
Achen Albert Charles Marie
Akimoto Hideki
Garrou Philip E.
Kaliszewski Britton Lee
Martin Brian
Barreca Nicole
Huff Mark F.
The Dow Chemical Company
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