Note: Descriptions are shown in the official language in which they were submitted.
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LAGER WELDABLE HERMETIC CONNECTOR
Cross Reference to Related Application
This application is a National Phase Canadian
application of co-pending United States Patent Application
Serial No. 727,668, filed on July 9, 1991, which is set to
issue on May 5, 1992, as U.S. Patent No. 5,110,307.
Field of the Invention
This invention relates to electrical connectors, and
more particularly, to manufacturing methods for maintaining
hermeticity and providing metallurgical compatibility between
connectors and microelectronic housings.
Backq_round of the Invention
Microelectronic modules, such as those containing
electronic circuit components, fiber optics, or pressure
sensing devices, rely on hermetic sealing, i.e., gas-tight
seals, to protect these sensitive components from the
corrosive effects of the environment. As is often the case,
these modules contain a mosaic of materials having various,
and often less than compatible, physical properties.
The art has typically relied upon hermetic
connectors disposed through a side wall of the housings of
such modules to provide input-output electrical access for
cables and the like. In the past, such connectors included a
connector body made of a low coefficient of thermal expansion,
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Fe-Ni-Co alloy, such as Kovar~, and one or more connector pins
axially disposed through the connector body. These pins are
usually hermetically sealed with glass through small pin-
receiving holes disposed through the center of the connector
body. The glass insulates the pins from the rest of the
connector and is relatively compatible with the Kovar~ base
metal, so as to provide an air-tight hermetic fit around the
connector pins during severe temperature cycles, such as those
experienced by aircraft during flight.
The module housing, for a number of years, was also
made of an iron-based alloy, such as Kovar~, which enabled
thermal expansion compatibility with the connector during
these wide temperature cycles as well as weldability, such as
by fusion welding or brazing, for providing a hermetic seal
between the connector body and the housing.
With the advent of cost cutting measures, including
weight reduction efforts aimed at conserving fuel in the
military and commercial aircraft industries, module housings
have recently been made from light weight metals, such as
aluminum. Although aluminum is easier to machine, is less
expensive, and is lighter in weight than iron-based alloys, it
is not very compatible with Kovar~, both in regard to
weldability and thermal expansion.
In an effort to accommodate the use of aluminum
housings in microelectronic modules, the art has resorted, in
certain instances, to plating the connector-receiving window
regions of aluminum housings and the matching surface of the
Kovar~ connectors with nickel, or a similar metal, and then
soldering or brazing the nickel-plated surfaces together.
Since these metal joining techniques require heating the
plated metal surfaces to at least about 200°C (and as high as
360°C), and since aluminum and Kovar~ have drastically
different coefficients of thermal expansion, stress is created
in the joint upon cooling the module to room temperature.
Such stress can lead to joint failure and a loss of
hermeticity when the module component undergoes subsequent
manufacturing operations or is placed in service, especially
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if such service requires exposure to severe temperature
cycling, for example, in aerospace applications.
Summary of the Invention
Electrical connectors suitable for providing
electrical access through a side wall of a microelectronic
package or module and methods for preparing such connectors
are provided by this invention. The connectors are designed
to maintain hermeticity, or gas impermeability, throughout the
manufacturing and service life of these components.
In a first embodiment of this connector, the housing
of the microelectronic package includes a first coefficient of
thermal expansion. The connector has a connector body having
an aperture therethrough and a second coefficient of thermal
expansion. A connector pin is disposed through the aperture
in the connector body and hermetically sealed to the connector
body with an insulating composition. In an important aspect
of this invention, flange means are provided for joining the
hermetic electrical connector to the housing. The flange
means includes upper and lower flanges metallurgically bonded
together and comprising first and second metallic compositions
respectively. The first composition is hermetically bonded to
the connector body, preferably by fusion welding thereto, and
is metallurgically compatible (i.e., Kovar~ to Kovar~,
stainless steel to Kovar~, Kovar~ to stainless steel,
stainless steel to stainless steel, etc.). This fusion weld
is produced by progressive spot laser welding or progressive
spot resistance welding having a heat--affected-zone ("HAZ")
small enough such that it does not significantly affect the
hermeticity provided by the insulating composition, i.e.,
glass or ceramic. The second layer is similarly compatible
with the housing package, (i.e., aluminum to aluminum, etc.).
Accordingly, this invention provides sound hermetic
joints between Kovar~ connectors or iron or steel connectors
and aluminum modules (or zinc modules, or titanium modules,
etc.) by employing cladded flange members and low HAZ welding
procedures. Unreliable soldering or brazing techniques can be
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avoided altogether, thus minimizing resulting residual
stresses to internal sensitive electronic components sensors
or optics, etc. Greater reliability of the microelectronic
module can be afforded by the carefully orchestrated process
steps of this invention, which take into account both
weldability and thermal expansion compatibility of the various
sealing compositions and base metals of electrical connectors
and electronic modules.
In a further embodiment of this invention, a method
of manufacturing hermetic electrical connectors is provided.
This method includes providing a connector body having an
aperture therethrough, disposing a connector pin through the
aperture and hermetically sealing this pin to the connector
body with an insulating composition. A flange means is
further provided by this method for joining the hermetic
electrical connector to a microelectronic package housing.
The flange means includes upper and lower flanges
metallurgically bonded together and comprising first and
second metallic compositions respectively. The first
composition is weldable to the connector body with a low HAZ
welding technique and the second composition is weldable to
the microelectronic package housing.
In a further aspect of this invention, an electrical
connector is provided for accessing a microelectronic elements
within a package housing through a side wall of the housing.
The connector includes a connector body having a cavity
therethrough and a coefficient of thermal expansion which
differs from the coefficient of thermal expansion of the
housing. This connector also includes an insulating body
having a pin receiving hole therein. The insulating body is
hermetically sealed to the connector body and disposed
substantially within its cavity. The connector further
includes a pin disposed through the pin receiving hole and
hermetically sealed to the insulating body and flange means
for joiizing the hermetic electrical connector to the
microelectronic package housing. The flange means, like the
ones described above, includes upper and lower flanges
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metallurgically bonded together and comprising first and
second metallic compositions respectively. The first
composition is hermetically bonded to the connector body with
a fusion weld having a HAZ which does not significantly affect
5 the hermeticity between the connector pin and the insulating
body, and the second composition is bonded to the
microelectronic package with a fusion weld having a low HAZ,
so as to provide a sound hermetic seal without high
temperature brazing or soldering which are known to affect the
temperature sensitive components therein.
Brief Description of the Drawings
The accompanying drawings illustrate preferred
embodiments of the invention according to the practical
application of the principles thereof, and in which:
FIG. 1: is a side elevation plan view of a
preferred electrical connector of this invention;
FIG. 2: is a top plan view of the preferred
electrical connector of FIG. 1;
FIG. 3: is a side cross-sectional view, taken
through line 3-3 of FIG. 2, illustrating the sealing of the
input-output connector pins of this embodiment;
FIG. 4: is a side cross-sectional view of an
alternative embodiment electrical connector having a ceramic
insulating member; and
FIG. 5: is a top plan view of the alternative
embodiment of FIG. ~.
Detailed Description of the Invention
This invention provides electrical connectors
suitable for providing input-output access through a side wall
of a microelectronic package housing while maintaining
hermeticity. This connector utilizes a dual layer flange
having layers of relatively incompatible metal compositions
which are metallurgically bonded together, preferably by high
compression cladding, without the introduction of interface
stress or elevated temperatures. The upper portion of the
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flange of this invention contains a metallic composition which
is compatible with the connector body metal. As used herein,
the term "compatible" refers to an approximate matching of the
metallurgical and fusion welding properties of metallic
compositions.
The other portion of the flange of this invention is
manufactured with a metallic composition which is compatible
to the module housing. By matching the metallic compositions,
fusion welding can be employed to attach the flange to the
connector body and in turn to the microelectronic package
housing to provide sound, hermetic joints, which are less
susceptible to stress during large temperature cycles.
With reference to FIGS. 1-3, there is shown a
preferred electrical connector of this invention. This
connector 10 preferably includes a connector body 12 having a
'°male pinned" connector mate which can engage via a coupling
flange, which preferably includes bored threaded engagement
holes 24. The connector body 12 is preferably made of an
iron-based alloy, more preferably a Fe-Ni-Co alloy, such as
Kovar~ alloy. Alternatively, the connector body 12 can
include a material having a thermal expansion similar to
borosilicate glass, i.e. about 5.5ppm/°C.
As illustrated in FIG. 2, a plurality of conducting,
connector pins 20, are shown which are disposed through pin-
receiving apertures in the middle portion of the connector
body 12. These pins 20 are also preferably made of the same
metal as the connector body 12, for example, Kovar~ alloy, and
are hermetically attached through the apertures by an
insulating composition. The connector pins 20 are preferably
sealed by melting or fusing a glass, such as a borosilicate
glass, into the spaces around the pins 20 to produce highly
reliable glass seals 26. Alternatively, a single glass
preform having pin receiving holes therein can be placed into
the connector body interior as a substitute for the metal
through-hole section. The pins can then be fused into the ,
glass preform upon heating. Glass sealing or fusion, as it is
known in the art, consists of heating a glass mixture to a
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temperature of at least about 900°C, and ideally about 950°C,
to produce, upon cooling, a hermetic bond between the pins 20
and the connector body 12 or a glass preform. This is a very
highly reliable seal since Kovar~ has a coefficient of thermal
expansion similar to that of the glass, which together with
the glass, provides a gas-tight intergranular attachment
around the connector pins 20 throughout a wide range of
temperatures.
The flange means of this invention, generally
represented by composite flange 21, comprises an upper flange
14 and lower flange 16 metallurgically bonded together to form
joint 18. The upper flange 14 preferably contains a metallic
composition which is compatible with the base metal of the
connector body 12. Preferably, the coefficients of thermal
expansion for alloys of the upper flange 14 and the connector
body differ by less than about 5 ppm/°C, and more preferably,
differ by less than about 10% of the coefficient of the
connector body alloy. Most importantly these alloys are
compatible to allow fusion welding with a narrow HAZ.
Ideally, the upper flange 14 includes a substantially similar
base metal as connector body 12, for example, Kovar~. The
upper flange 14 is preferably hermetically bonded to the
connector body 12 with a fusion weld having a HAZ which does
not significantly affect the hermeticity provided by the
insulating composition, or glass seals 26, which bond the
connector pins 20 to the connector body 12. Such low HAZ
fusion welding processes include, for example, plasma,
electron beam, and laser welding techniques, which are known
in the art.
In a preferred method of manufacturing the
electrical connectors of this invention, the upper flange 14
is laser welded to the connector body 12, using known laser
welding processes and equipment, following the glass sealing
operation. This can be accomplished through the application
of a small local laser spot which produces a metallurgical
fusion weld in a small local area at the joint between the
upper flange 14 and the connector body 12.
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In an important aspect of this invention, the laser
melt heat is restricted to the joint area, which is
preferably, less than about 1 mm at its widest point, and more
preferably, is less than about .33-.5 mm in width and depth.
The weld path of the laser is moved, after the initial
starting point, to produce a thin continuous and reliable
laser welded joint 22 around the connector body. This process
does not produce heating of the metallurgical joint 18 or the
glass seals 26. Accordingly, thermal stresses at these
critical hermetic sealing areas are thus avoided. Thus, both
the laser welded joint 22, the glass to metal seals 26, and
the integrity of the composite flange 21 can be hermetic and
highly reliable.
The lower flange 16 of the composite flange 21
preferably contains a second metallic composition which is
weldable to the microelectronic package housing 23.
Typically, the choice of alloy will be compatible with the
alloy of the housing 23, preferably, the differences between
the thermal conductivity of the lower flange 16 and the
housing 23 are less than 5 ppm/°C, or less than 10% of the
coefficient of the housing 23, and most preferably the alloys
are substantially similar. Good choices for both the housing
23 and the lower flange 16 include aluminum, for its iow
weight and good thermal conductivity (coefficient of thermal
expansion of about 24 ppm/°C), brass or copper, for their
solderability and good thermal conductivity (coefficient of
thermal expansion of about 18 ppm/°C), titanium, for its high
strength to weight ratio (coefficient of thermal expansion of
about 10 ppm/°C), and stainless steel (preferably, 400
series), for its high strength and good corrosion resistance
(coefficient of thermal expansion of about 14 ppm/°C). In a
certain situations these alloy selections could also be used
for the connector body 12 and pins 20.
In a preferred detailed embodiment of this
invention, the microelectronic package housing includes 6061
aluminum, and the lower flange includes 4047 aluminum. The
lower flange and microelectronic package housing are
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9
preferably fusion welded with a low HAZ welding technique, and most
preferably, by laser welding.
The metallurgical bond 18 between the upper and lower flanges
14 and 16, respectively, of this invention, is ideally the result of a
cladding
technique. One common technique is to metallurgically bond an aluminum
plate to a steel or Kovar~ plate with an explosive charge. Such a technique is
known as explosive bonding or cladding and is described in U. S. Patent Nos.
3,233,312; 3,397,444; and 3,493,353. A wide variety of dissimilar metals may
be
bonded together in this manner without the constraints imposed by other
bonding methods which require compatibility between the materials. The
resulting laminate exhibits a bonding zone which includes multi-component,
inter-atomic mixtures of the metals of the two dissimilar materials. Such
explosion cladded materials have been known to exhibit a shear strength of
greater than about 75% of the weaker metal in the composite.
In an alternative embodiment of this invention described in
FIGS. 4 and 5, and electrical connector 30 is provided having a single
insulating body 33, preferably a ceramic or glass preform, disposed in a
cavity
of the connector body 32 and hermetically bonded thereto. In this
embodiment, preferred Kovar~ or 52 Alloy connector pins 40 are disposed
through a plurality of pin receiving holes in the insulating body 33. If a
ceramic preform is employed, a preferred high temperature braze is used to
bond to the metalized surfaces of the ceramic to form hermetic seals 46
between the connector pins 40 and the ceramic, as well as between the ceramic
and the connector body 32. If a solid glass preform is used, the connector
pins
40 are inserted into the preform holes and then fused with the glass at high
temperatures to form hermetic seals 46. As with the embodiment of FIG. 1,
the connector body is preferably a low expansion alloy compatible with
ceramic and glass, such as Kovar~ alloy. The connector body 32 of this
embodiment can conveniently be laser welded to the clad flange 31 with a
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laser welded joint 42. The clad flange can include an upper
flange made of Kovar~ alloy and a lower flange 36 made of
aluminum, preferably 4047 aluminum. The upper and lower
flanges 34 and 36 respectively, can be explosion cladded to
5 form metallurgical bond 38 as earlier described.
Connector embodiment 30 employs a clad flange 31
which has a slightly different configuration than the
composite flange 21. As described in FIG. 4, the upper flange
portion 34 of the clad flange 31 includes threaded holes 44
10 and the connector body 32 is disposed concentrically within
the clad flange 31 and laser welded along the lower seam.
Nevertheless, the fundamental concepts and principles of this
invention are equally applicable to this embodiment.
From the foregoing, it can be realized that this
invention provides highly reliable hermetic connectors which
provide for compatibility between microelectronic aluminum
package housings and Kovar~ alloy connector bodies hereto-
fore not achievable. Low HAZ welding techniques are employed
to avoid breaking hermetic glass seals around the connector
pins. Additionally, explosion clad flange members provide
adequate compatibility between housing alloys and connector
body alloys for enabling highly reliable, laser welding of
these members. Although various embodiments have been
illustrated, this was for the purpose of describing, but not
limiting the invention. Various modifications, which will
become apparent to one skilled in the art, are within the
scope of this invention described in the attached claims. ,
