Hermetic sealing of flexprint electronic packages

A hermetically sealed electronics package in which an electronic element located on a support is hermetically sealed using a cover comprising the top layer of a multilayer flexprint or a separate flexprint. The top layer of the flexprint or the separate flexprint is supported above the electronic element by a frame structure. When the cover comprises the top flexprint layer, the top layer is only partially bonded to the underlying flexprint during fabrication of the package. After circuit placement, the flap portion of the top flexprint layer is bonded to the flexprint to provide hermetic sealing of the underlying electronic elements. The frame structure provides support for the flexprint cover to prevent deformation of the cover and resulting damage to the underlying circuit. A cooling system is also disclosed for use in combination with the hermetic seal configuration to provide an electronic package which is protected from both contaminants and built-up heat.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to hermetically sealing electronic 
elements associated with electronic circuitry. More particularly, the 
present invention relates to providing hermetically sealed packages of 
flexprints and chips, integrated circuits, and other electronic elements. 
2. Description of Related Art 
Flexprint electronic blanket packages are widely used to house and 
interconnect electronic elements including integrated circuit chips. The 
flexprint package generally includes a support wafer or base onto which 
the flexprint blanket is placed. The flexprint blanket or body is made up 
of one or more layers of flexprint. Flexprint is the term commonly used to 
describe flexible layers of plastic which are laminated with alternating 
layers of a metal and having an outer metal coating. The most common 
flexprints are made from polyimide laminated with copper. 
The plurality of layers of flexprint which form the blanket package are 
laminated onto the underlying silicon wafer. Usually between 5 and 15 
flexprint layers are used to form the blanket body which generally is on 
the order of 0.050 inch (0.12 cm) thick. Openings or cavities are made in 
the blanket body for housing various electronic integrated circuits (IC's) 
and other elements. The silicon wafer forms the bottom of the well with 
the electronic element typically being attached to the silicon wafer by 
eutectic bonding. Electrical connections are made between the chip and the 
various metallic pads present on the flexprint layers. 
A typical problem with any electronic package is the prevention of 
contamination or corrosion of the integrated circuit chips and electrical 
connections. In order to avoid premature failure of the electronics 
package, it is important that the package assembly be hermetically sealed 
to prevent such corrosion and contamination of the integrated circuit. 
Accordingly, there is a continuing need to provide flexprint blanket and 
other flexprint assemblies wherein the cavities in which the electronic 
elements are located are hermetically sealed. Preferably, the hermetic 
sealing of the cavities is achieved quickly, simply and efficiently, at a 
minimum of cost. Although adequate hermetic seals may be obtained 
utilizing a variety of metallically sealed packages, there is still a 
continuing need to simplify and reduce the cost, weight and volume of 
electronic assemblies. 
The dissipation of heat from electronic package assemblies is also an 
important consideration. Without adequate cooling systems, the electronic 
package will quickly overheat and destroy or shorten the life of the 
temperature sensitive electronic elements contained therein. This problem 
is especially critical in devices which operate at power levels of 50 
watts and beyond. There is a continuing need to provide systems and 
methods which efficiently cool and transfer the generated heat away from 
IC's, to prevent overheating. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a flexprint electronic package is 
provided wherein the chips and other electronic elements located within 
the package are hermetically sealed in a simple and efficient manner. 
The present invention is based upon an electronic package which includes an 
electronic element support, which may comprise a wafer and which has a top 
surface for receiving and supporting one or more electronic elements. One 
or more electronic elements are located on the top surface of the wafer or 
support. These electronic elements are located in cavities within a 
flexprint or a blanket body which is made up of one or more flexprint 
layers. As a feature of the present invention, a frame structure is 
provided which extends over the electronic elements and their leads to the 
flexprint and which is resistant to deformation forces in order to protect 
the electronic elements and their leads from damage. The frame structure 
includes a base which is located on the top surface of the flexprint or 
the flexprint blanket body. A cover is provided over the frame structure. 
The cover also includes a base which is located on the top surface of the 
flexprint or the flexprint blanket body to provide hermetic sealing of the 
electronic elements and their leads therein. This sealing configuration 
provides a simple and efficient hermetic seal surrounding the electronic 
elements and their leads. 
As a feature of the present invention, the cover which is placed over the 
underlying frame structure also forms the top layer of the flexprint or, 
alternatively, is a separate flexprint. When the cover is a flexprint 
layer, it initially is only partially attached to the upper layer of the 
remainder of the flexprint. After installation of the electronic elements 
into the flexprint/blanket body, the unattached flexprint flap is used to 
cover the frame structure. The flexprint flap is then bonded to the 
remainder of the flexprint in order to provide a hermetic seal. When the 
cover comprises a separate flexprint rather than an upper layer of a 
flexprint, the separate flexprint is similarly bonded to the underlying 
flexprint. The use of the flexprint or a layer thereof as the hermetic 
seal cover provides a simple, inexpensive and efficient hermetic seal. 
As another feature of the present invention, the hermetically sealed 
package is cooled during high power usage by providing a series of 
conduits through the wafer or by securing separate conduits to the 
support. The conduits are connected to an external cooling fluid. The 
cooling fluid is continually passed through the conduits to absorb heat 
and remove it from the sealed electronics package. In this way, a simple 
and efficient cooling system is provided. When the cooling system is 
combined with the hermetic sealing of the electronics package in 
accordance with the present invention, the result is an electronics 
package with significant protection against moisture, contaminants and 
built-up heat to thereby protect and prolong the life of the electronic 
elements. 
The above-discussed and many other features and attendant advantages of the 
present invention will become better understood by reference to the 
following detailed description when taken in conjunction with the 
accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
An exemplary hermetically sealed electronics package in accordance with the 
present invention is shown generally at 10 in FIG. 1. The electronics 
package 10 includes silicon wafers 12 and 14. The silicon wafers are 
typically between 0.030 and 0.050 inch (0.08 to 0.13 cm) thick. Although 
it is preferred that wafers 12 and 14 are made of silicon, any other 
suitable electronic wafer support material may be used. 
An exemplary electronic element in the form of an integrated circuit is 
shown at 16. The integrated circuit 16 is attached to the top surface of 
wafer 14 by eutectic bonding. The eutectic bond is shown at 18. Although 
eutectic bonding of the integrated circuit 16 to the silicon wafer 14 is 
preferred, any other conventional bonding technique may be utilized. 
In FIG. 1, a single integrated circuit 16 is depicted for demonstration 
purposes only. As is well known, typical electronic packages include many 
integrated circuits attached at spaced locations on the silicon wafer, 
such as illustrated in FIG. 6. As indicated by gap 20 in FIG. 1, only a 
portion of the electronics package is depicted, with it being understood 
that many other integrated circuits are typically present on the silicon 
wafer 14. 
A blanket body or a flexprint 22 is located on top of the silicon wafers 12 
and 14. The blanket body 22 includes a plurality of flexprint layers. The 
preferred exemplary blanket body 22 shown in FIG. 1 includes 5 flexprint 
layers 24, 26, 28, 30 and 32. The flexprint layers 24-32 are conventional 
flexprint layers made from polyimide laminated with a suitable metal. Such 
flexprint films are commonly referred to as H film. These films are widely 
available from Dupont Corporation which markets these films under the 
trademark Kapton.RTM.. The flexprint films 24-32 are preferably between 
0.002 to 0.003 inch (0.002 to 0.008 cm) thick. As is well known, the 
flexprint layers include a metal coating. The metal coating is relatively 
thin compared to the overall thickness of the flexprint layer. Copper is 
the preferred metal coating for the flexprint layer. Other suitable metal 
coatings include aluminum, nickel and gold. 
As shown in FIG. 1, the blanket body 22 has an encircling interior 
perimeter surface 34 which defines a cavity 36 in which the electronic 
element 16 is housed. The cavity 36 is fabricated in the blanket body 22 
by etching or other conventional electronic board fabrication technique. 
The top surface 38 of the blanket body 22 is preferably located above the 
height of integrated circuit 16. The relative heights of the integrated 
circuit 16 and blanket body 22 will depend for the most part upon the 
number of flexprint layers utilized for the circuit board. The number of 
flexprint layers will vary between 1 to more than 10 depending upon the 
complexity of the circuitry. The integrated circuit 16 is connected to the 
conductive metal coating present on the flexprint layers by way of 
connectors 40 and 42. This connection is made by solder or any other 
electrically conductive connection. The integrated circuit 16 is shown 
being connected to only the upper flexprint board 30 for demonstration 
purposes only. It will be understood by those skilled in the art that the 
integrated circuit 16 will be connected via numerous interconnections 
between various different flexprint layers. The flexprint layers 24-32 are 
laminated together in accordance with conventional lamination procedures. 
In accordance with the present invention, the integrated circuit 16 is 
hermetically sealed by providing a plastic frame structure 44 and a cover 
46 over the cavity 36. The plastic frame structure 44 may be made from any 
plastic material which is inert, structurally strong, does not outgas, and 
has electrostatic isolation. By structurally strong, it is meant that the 
structure 44 is able to resist deformation forces to prevent collapse onto 
and damage to the chip and its leads. Suitable plastic materials include 
polyimides, epoxy resins or other polymers. Other frame structure 
materials, such as ceramics and other non-conductive materials may be 
utilized provided that they are structurally strong, non-reactive in an 
electronic package environment and non-conductive to provide protection 
from electromagnetic interference. 
The size and shape of the frame 44 is such that a dome is provided over the 
integrated circuits to be sealed. The frame structure 44 terminates in a 
base 48 which is attached securely to the top surface 38 of the blanket 
body 22. Attachment or bonding of the frame structure 44 to top surface 38 
is preferably accomplished by using a suitable adhesive, such as an epoxy 
material. The frame structure 44 may be a solid piece of material or it 
may be perforated to reduce weight. The important criteria for the frame 
structure 44 is that it be suitably strong to prevent the more flexible 
cover 46 from being compressed downward onto the interconnections 40 and 
42 resulting in damage to the circuits and the wire bonds on the 
electronic elements. 
The cover 46 is preferably formed from the upper flexprint layer 32. FIG. 5 
shows the preferred exemplary electronics package 10 as the flap portion 
46 of the top flexprint layer 32 is lowered into position to form the 
cover 46 on top of frame structure 44. In the preferred embodiment, the 
top flexprint layer 32 is initially only partially bonded to the other 
laminated flexprint layers 24-30. The top flexprint layer 32 is not bonded 
to the rest of the blanket body at those locations where support frame 
structure 44 is to be placed. After the support frame is in place, the 
unbonded flap portion 46 of upper flexprint layer 32 is placed over frame 
44 and then bonded to the flex body at 50 (as shown in FIGS. 1 and 5) in 
order to provide a hermetic seal. Bonding of the flap 46 to the blanket 
body 22 can be accomplished using any of the known laminating adhesives 
procedure for printed wiring flexprints such as using an epoxy resin 
prepreg under increased temperature and pressure. Alternatively, a dry 
film prepreg may be used. 
Although other possible cover materials can be utilized to provide an 
appropriate cover 46, it is preferred that the cover material be an 
unbonded flap portion of the top flexprint layer. By using the top 
flexprint layer as a cover, a quick, effective, and inexpensive cover is 
provided which is capable of maintaining a hermetic seal over extended 
periods of time. 
However, the cover 46 may also comprise a flexprint which is independent 
from the flexprint 22, but hermetically sealed thereto, In this 
configuration, additional electrical connections to other hermetically 
sealed electronic elements similar to the chip 16, may be obtained. 
It is preferred that some means be provided for removing heat generated by 
the integrated circuits during operation of the electronics package. 
Preferred exemplary means for cooling the integrated circuit 16 includes 
conduits 52 and 54 located in wafers 14 and 12 respectively. The conduits 
are preferably configured as shown in FIGS. 3 and 4. The conduits 52 and 
54 are preferably etched into the silicon wafers 12 and 14. The conduits 
may be formed by other procedures such as imbedding suitable glass or 
ceramic conduits into the silicon or forming the conduits by 
micromachining. The conduits 52 and 54 are connected to an external 
cooling system (not shown). The cooling system cycles cooling fluid to the 
conduits. Suitable cooling fluids include carbon tetrafluoride, water or 
other known gases or liquids utilized as heat exchange fluids. The 
conduits 52 and 54 may be located throughout the wafers 12 and 14 if 
desired. However, it is preferred to locate the cooling conduits 52 and 54 
only directly under each integrated circuit to maximize heat removal while 
minimizing the cost and complexity of providing conduits throughout the 
entire body of each of the wafers. 
The conduits preferably have a diameter in the range of about 0.005 to 
0.015 inch (0.013 to 0.038 cm). Although the internal diameter of the 
conduits and the size of the conduit patterns may be the same for each 
wafer 12 and 14, it is preferred that conduit 52 located in wafer 14 be 
smaller than the conduit 54 located in wafer 12. For example, if conduit 
52 has an internal diameter of 0.010 inch (0.025 cm) and a lateral spacing 
between conduit turns of 0.040 inch (0.14 cm), then the preferred size of 
conduit 54 would be an internal diameter of 0.02 inch (0.05 cm) and a 
lateral spacing between conduits of about 0.08 inch (0.20 cm). Further, 
the relative positioning of the conduits 52 and 54 are preferably 
perpendicular to each other so that the straight lengths of conduit 
intercept each other at right angles. This angle relationship is believed 
to provide maximum cooling capacity for the electronic element. 
Referring now to FIG. 6, a hermetically sealed package 110 is formed on a 
portion of a flexprint or flexible electric cable 122, which extends 
beyond the package 110 and which can be bent or otherwise configured in 
accordance with the system in which the hermetically sealed package 110 
and the flexprint 122 are parts. 
The package 110 is similar to the package 10 depicted in FIGS. 1 and 5. In 
FIG. 6, the flexprint 122 includes a plurality of cavities 136 cut into 
flexprint layers 124-130 so that each cavity is bounded by an interior 
perimeter walled surface 134. A plurality of integrated chips or other 
electronic elements 116 are housed within the cavities 136, preferably 
below top surface 138 of the flexprint, and are coupled electrically to 
the electric leads or traces of the flexprint 122 by connectors 140 and 
142. 
A deformation resistant frame structure 144, which is constructed like the 
frame 44 of FIGS. 1 and 5, is positioned over all electronic elements 116 
and their electric connections 140 and 142 to protect them from being 
squashed or otherwise damaged. The frame 144 is positioned on and bonded 
at its base 148 to the flexprint top surface 138. 
A cover 146 is positioned over the frame 144 and is hermetically sealed by 
bonds 150 also to the flexprint top surface 138. The cover 146 may be 
formed like the flexprint 146 of FIGS. 1 and 5, e.g., as a separate 
plastic film, as a separate flexprint, or as a top layer of the flexprint 
122. Thus, the cover 146 may terminate at the bonds 150 or extend 
therebeyond along the flexprint 122, such as is shown in FIGS. 1 and 5. 
Unlike the package 10 of FIGS. 1-5, however, the package 110 of FIG. 6 
replaces wafers 12 and 14 by a support 112, to which the electronic 
elements 116 and affixed by eutectic bonds 118. The support 112 has 
sufficient rigidity to support the electronic elements 116 and to protect 
them from bending forces and possible fracture or other breakage. A 
plurality of coolant passages or conduits 152 are thermally and 
mechanically secured to the support 112 for removal of heat therefrom to a 
heat sink. The mechanical securement of the conduits 152 to the support 
112 may be provided by a laminate 156 of plastic or other material by 
conventional bonding techniques. 
Having thus described exemplary embodiments of the present invention, it 
should be noted by those skilled in the art that the within disclosures 
are exemplary only and that various other alternatives, adaptations, and 
modifications may be made within the scope of the present invention. 
Accordingly, the present invention is not limited to the specific 
embodiments as illustrated herein, but is only limited by the following 
claims.