Multilayer hybrid integrated circuit

A multilayer circuit device comprises a substrate having a plurality of metallized patterns thereon said patterns being separated by a photodefined polymeric dielectric film formed from a polymeric photodefinable triazine base mixture including a photosensitive acrylate moiety. The various circuit patterns are interconnected by means of microvias through the polymeric film or film layers.

TECHNICAL FIELD 
This invention relates to multilayer hybrid integrated circuits and more 
particularly to the novel dielectric layer employed as part of the 
circuit. 
BACKGROUND OF THE INVENTION 
In the evolution of hybrid integrated circuits for switching systems and 
high performance processes as well as other electronic devices one of the 
most critical system packaging needs is the capability of utilizing 
effectively high I/O pin-out devices with high speed interconnections. To 
meet this goal multilayer ceramic hybrid integrated circuits have been 
developed. However, the currently available multilayer ceramic circuits 
require a complex manufacturing system and are relatively expensive. 
Consequently, in order to meet the packaging needs of such hybrid 
integrated circuits while retaining quality, reliability and performance 
demands, especially in conjunction with the use of very large scale 
integrated circuit chips, in a cost competitive package, further 
improvements are necessary. 
To meet this goal, I believe that a multilayer polymer hybrid integrated 
circuit configuration is one approach to solving the problem. The polymer 
layer must act as a dielectric material between layers containing thin 
film circuitry and must meet many other stringent requirements including a 
high T.sub.g, a high thermal stability and hybrid process compatibility. 
It would also be preferred if such a polymeric material were 
photodefinable. 
SUMMARY OF THE INVENTION 
A multilayer circuit device comprising a substrate having a metallized 
pattern thereon and a plurality of polymeric dielectric film layers each 
having a metallized circuit pattern thereon with metallized microvias 
interconnecting the metallized patterns of one layer with that of at least 
one other metallized layer thereunder, said polymeric dielectric layer 
being formed from a photodefinable triazine base mixture including a 
photosensitive acrylate moiety.

DETAILED DESCRIPTION 
It should be understood that the novel device as summarized above is 
suitable for use as a multilayer printed circuit board employing 
substrates which are commonly used and are well known in the printed 
circuit board industry. Also, because of the characteristics of the 
triazine based dielectric layer employed, the device is especially suited 
for use in what is known as a multilayer hybrid integrated circuit device 
generally employing a ceramic substrate. 
To meet the requirements of advancing technology involving hybrid 
integrated circuits for switching systems and high performance processes, 
a multilayer hybrid integrated circuit must be capable of employing a high 
number of I/O pin-out devices with high speed interconnections. Due to the 
heat developed and the electrical requirements, minimum requirements for 
the dielectric material employed to separate conductor layers include a 
glass transition temperature (T.sub.g) of at least 140.degree. C. and good 
thermal stability to about 220.degree. C., a dielectric constant of no 
greater than 3.5 and preferably, the material should be capable of being 
imaged by means of actinic radiation so as to be able to achieve fine line 
features and an aspect ratio approaching 1. In addition, the dielectric 
materials must be tough enough to withstand thermal cycling specifications 
with severe mismatch in dimensional stability between the ceramic 
substrates and the dielectric materials; the dielectric must be compatible 
with typical ceramic resistors and conductors under accelerated life 
testing and the surface of the dielectric must be metallizible so as to 
form at an adherent circuit pattern thereon. In addition, the dielectric 
material must have chemical resistance to all chemicals used in further 
processing steps and should be in a form that can be coated reproducibly 
and efficiently. The polymeric dielectric material must also have good 
high voltage breakdown characteristics and be compatible with all other 
components and materials employed. Preferably, for commercial purposes, 
good shelf stability and shelf life of the uncured polymer is required. 
Heretofore, polymeric dielectric materials meeting these requirements were 
not available. 
I have now discovered that a polymeric mixture having a triazine resin as 
its primary constituent and including a photosensitive acrylate moiety 
crosslinking agent can be used to achieve the necessary goals. The 
acrylate moiety can be on a separate compound or on the triazine itself. 
More particularly, a suitable polymeric dielectric formulation giving the 
ranges of its constituents in weight percent is as follows: triazine, 
40-65%; rubber resin, 0-30%; an epoxy-acrylate hybrid resin or individual 
epoxy and acrylate resins totaling from 0-50%; a hardener, 0-12%; a 
crosslinking agent, 0-8%; a coupling agent, 0-5%; and a photoinitiator, 
1/2-3%. 
The preferred rubber resins are acrylonitrile butadiene resins. It is 
preferred that a hybrid epoxy-acrylate resin be employed rather than 
individual separate epoxy resin and acrylate resin. Such hybrid resin may 
be epoxy terminated or vinyl terminated. For example, the half acrylate of 
the diglycidyl ether of bisphenol-A is suitable. A particularly suitable 
hardener is N-vinylpyrrolidone. Further, a particularly suitable 
crosslinking agent is trimethylolpropanetriacrylate. Also a particularly 
suitable coupling agent to enhance the adhesion of the polymeric 
dielectric material to the underlying material is a silane coupling agent 
such as glycidoxypropyltrimethoxysilane. Coupling agents, and in 
particular silane coupling agents, are well known in the art for enhancing 
adhesion between dissimilar layers. A suitable photoinitiator is 
2,2-dimethoxy-2-phenylacetophenone. In addition to the above, one may also 
add small amounts of pigment, surfactant and copper chelate thermal 
stabilizer, e.g., copper benzylacetonate. Such additives are generally 
included, if desired, in amounts of up to about 1%. 
Generally preferred formulations of the triazine mixture are as follows: 
(A) triazine 50-60 weight percent; epoxy acrylate hybrid 20-30 weight 
percent, hardener 5-12 weight percent, crosslinking agent 2-6 weight 
percent, coupling agent 2-5 weight percent, photoinitiator 1-3 weight 
percent; or 
(B) triazine 50-60 weight percent; acrylated rubber 10-25 weight percent, 
epoxy acrylate hybrid 5-15 weight percent, hardener, crosslinking agent 
and photoinitiator as in (A); or 
(C) triazine 50-55 weight percent; acrylated rubber 20-30 weight percent 
and the remainder of the ingredients as in (B) plus pigment, surfactant 
and stabilizer up to 1 weight percent. 
More specific examples of suitable photodefinable resin mixtures utilized 
to form the polymeric dielectric are as follows: 
EXAMPLE I 
______________________________________ 
Component Weight Percent 
______________________________________ 
Triazine 56% 
Half acrylate of the 25% 
diglycidyl ether of bisphenol-A 
(Celanese) 
N--vinylpyrrolidone 9% 
Trimethylolpropanetriacrylate 
4% 
Glycidoxypropyltrimethoxysilane 
4% 
2-2-dimethoxy-2-phenylacetophenone 
2% 
______________________________________ 
EXAMPLE II 
______________________________________ 
Component Weight percent 
______________________________________ 
Triazine 52% 
Acrylated acrylonitrile butadiene 
16% 
rubber 
Half acrylate of the 9% 
diglycidyl ether of bisphenol-A 
N--vinylpyrrolidone 9% 
Epoxy propylacrylate 3.5% 
Trimethylolpropanetriacrylate 
4% 
Glycidoxypropyltrimethoxysilane 
4.5% 
2,2-dimethoxy-2-phenylacetophenone 
2% 
______________________________________ 
EXAMPLE III 
The basic formulation of this example is as follows: 
______________________________________ 
Component Weight Percent 
______________________________________ 
Triazine 50% 
Acrylated acrylonitrile 
26% 
butadiene rubber 
Half acrylate of the 9% 
diglycidyl ether of bisphenol-A 
N--vinylpyrrolidone 9% 
Trimethylolpropanetriacrylate 
4% 
Glycidoxypropyltrimethoxysilane 
2% 
Added to this basic formula is the following: 
2,2-dimethoxy-2-phenylacetophenone 
2% 
Magenta pigment 0.5% 
Surfactant 0.2% 
Copper benzyl acetonate 
0.5% 
______________________________________ 
The various photodefinable triazine resin mixtures as set above are 
employed, as previously indicated, in the manufacture of multilayer 
circuit devices such as multilayer hybrid integrated circuits. A typical 
multilayer fabrication process is shown with reference to FIG. 1 A-E. FIG. 
1A shows the bare substrate 10 such as an alumina ceramic substrate. FIG. 
1B is a representation of the substrate 10 after a conductor pattern 12 
has been placed on one surface thereof. This metallized pattern can be 
formed by any of the well known techniques including thin film technology, 
thick film technology, vacuum evaporation and electroless plating 
techniques. Further, while the layer is shown to be patterned to form a 
circuit one may employ a blanket metallized layer which may be used as a 
ground plane or power plane for the devices to be attached. FIG. 1C 
depicts the substrate 10 and first metallized layer 12 with a 
photodefinable dielectric 14 applied thereover. This dielectric 14 may be 
applied by any of the well known techniques including screen printing, 
brushing, spraying, dipping or the like. Subsequent to application of the 
photodefinable dielectric 14, as shown in FIG. 1D, the photodefinable 
dielectric 14 is subjected to actinic radiation so as to define microvias 
16 which, upon development, are formed therethrough. These microvias 16 
allow additional metallization 18 as shown in FIG. 1E to form a contact 
between adjacent metallized layers. In this way, any desired portions of a 
top metallized layer may be made to electrically contact any lower 
metallized layer. Steps 1C to 1E can be repeated to build as many levels 
as needed or desired. Discrete devices such as integrated circuit chips, 
resistors, capacitors or the like can be mounted such as by surface 
mounting techniques or any other available techniques known to the art to 
any of the metallized layers or preferentially to the top layer. Upon 
completion, a complete hybrid integrated circuit package is formed. In 
order to achieve a commercially feasible hybrid integrated circuit for 
high density packaging of integrated circuit devices and a large number of 
I/O pin counts, the polymeric dielectric material should have the 
following properties. Where, however, the use is not so stringent and a 
high number of I/O pin counts is not necessary and lower power is to be 
used the following requirements may be relaxed. The various requirements 
and the performance of the photodefinable triazine mixtures as set forth 
herein with respect to those requirements are given in the table below. 
______________________________________ 
Specific Material Requirements 
Photodefined 
Triazine 
Parameter Requirement Performance 
______________________________________ 
T.sub.g &gt;130.degree. C. 
150-190.degree. C. 
Thermal stability 
Long term 100.degree. C. 
180.degree. C. 
Short term 125.degree. C. 
210.degree. C. 
Spikes 300.degree. C.-10-15 sec. 
Passes 
Dielectric constant 
&lt;4.0 3.4-3.6 
Resistor compatibility 
Yes Yes 
Thin film 
Via-resolution 
.about.3 mil minimum 
.about.3 mil min. 
Chemical resistance 
Not sensitive to 
Passes 
any of the process 
chemicals 
Leakage current 
&lt;1 micro amp &lt;1 micro amp 
Thermal cycle 5 cycles Pass 
140.degree. C.-40.degree. C. 
______________________________________ 
EXAMPLE IV 
This example sets forth the essential steps in preparing a multilayer 
integrated circuit employing one of the novel triazine mixtures as the 
photosensitive dielectric layer. In accordance with this process, which is 
just one example of many variations of processes which can be used for 
preparing a multilayer integrated circuit employing the novel 
photodefinable dielectric, a substrate is first sputter metallized to form 
a very thin base metal layer thereon. A photoresist such as Dupont Riston 
is then applied to the surface and the Riston is exposed and developed so 
as to form an image of the desired conductor pattern thereon. The exposed 
metallized layer is then electroplated such as with copper followed by 
nickel and gold and thereafter the Riston is stripped from the surface and 
the substrate is etched so as to remove the initially applied sputtered 
layer. Thereafter the photodefinable dielectric triazine mixture is 
applied to the surface of the substrate by any of the known coating 
techniques, e.g., spray coating and is warmed so as to prevent bubble 
formation. The triazine mixture is then imaged by exposing to actinic 
radiation in a desired pattern and then developed so as to create 
microvias in the triazine dielectric layer. The dielectric is cured, e.g., 
by heating at temperatures from 100.degree. C. to 210.degree. C. 
Preferably, the surface of the dielectric layer is then treated such as by 
means of an argon etch so as to enhance the adhesion of that surface for 
subsequent metallization. Thereafter a metal layer is sputtered onto the 
surface of the triazine dielectric layer, another layer of Riston is 
applied over the sputtered layer and the Riston is imaged in a desired 
pattern and a second metallization layer is built up by electroplating 
techniques. The Riston is thereafter stripped such as with methylene 
chloride and the underlying thin sputtered metal layer over which there is 
no electroplate is removed by etching. By this technique, interconnections 
between the first and second pattern layers of electroplated conductors 
are made through the microvias in the triazine dielectric layer. These 
steps can then be repeated as many times as required to build as many 
layers as is necessary. Also interconnections can be made between any 
lower and any upper layer skipping any middle layer if desired. Such 
techniques would be obvious to one skilled in the art. Subsequent to 
completing the last layer, circuit devices such as capacitors, resistors 
and the like can be mounted or formed so as to interconnect with the top 
conductive layer or pattern. Further, where desired, the pattern may 
include a ground plane or power plane or both. 
The utilization of these materials will also be important in other circuit 
material applications, such as encapsulants, cover coats and for single 
polymer layer circuits. 
It is to be understood that the above-described embodiments are simply 
illustrative of the principles of the invention. Various other 
modifications and changes may be devised by those skilled in the art which 
will embody the principles of the invention and fall within the spirit and 
scope thereof.