Abstract:
A millimeter wave transceiver package is provided. Housings for electronic, RF, and support components of the transceiver with an RF transparent cover are stacked vertically in a multilayer structure. The channelized RF housing affects a reduction of 5:1 by minimizing the components placed on the housing. The design and position of the regulator/controller allows the use of surface mount parts and simplified DC and RF interfaces further contributing to design efficiency and reduced costs. Additionally, costs are reduced through the appropriate selection and application of materials. The generic housing for the millimeter wave module assembly accommodates frequencies from 20 to 40 GHz without design change, thus improving the modular character.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present device is directed generally to the packaging for an electronics module. More specifically, the present invention is directed to the architecture of the packaging that houses a single module, either a transmitter or a receiver, of a millimeter wave device. 
     2. Background Information 
     The main components in millimeter wave (MMW) transceivers are monolithic millimeter wave integrated circuit (MMIC) chips, connective substrates, housings, and DC regulators/controllers. It has traditionally been difficult to design and build very wideband amplifiers that display consistent performance across the entire passband. Gain irregularities and peaks, large variations of input and output impedance, and spurious oscillations are examples of the problems encountered. 
     Monolithic millimeter wave integrated circuit (MMIC) devices are low-cost solutions to the problems. The cost of MMIC chips and substrates have been steadily falling in the last few years due to improved yield and increased demand for commercial telecommunication applications. However, the two areas of housings and regulators/controllers have not enjoyed similar cost reductions because, for example, Coefficient of Thermal Expansion (CTE) matching and thermal conductivity requirements limit the material choices for packaging and make it difficult to reduce costs. 
     U.S. Pat. No. 4,490,721, issued to Stockton et al., the disclosure of which is hereby incorporated by reference, discloses the fabrication of MMIC components and their interconnects onto a single substrate by using thin film and IC fabrication techniques. 
     U.S. Pat. No. 5,945,941, issued to Rich, III et al., the disclosure of which is hereby incorporated by reference, discloses a pulsed radar apparatus and method for employing a power distribution system having reduced cost and weight and enhanced efficiency and reliability. The power distribution system is provided in a radar apparatus to distribute power from a 270 VDC source through an intermediate power converter and very high frequency (VHF) regulator/modulator units. Costs are reduced through the use of electrical components with increased efficiency. 
     U.S. Pat. No. 5,493,305, issued to Woodbridge et al., the disclosure of which is hereby incorporated by reference, discloses a vertical, multi-layer arrangement of MMIC chips to facilitate automated assembly and increase yields. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to reducing the cost of MMW housings through the appropriate selection and application of materials. The cost of the regulator/controller can be reduced through the use of surface mount parts and simplified DC and RF interfaces. Exemplary embodiments provide a generic housing for MMW module assemblies that accommodate frequencies from 20 to 40 GHz without changing the design, thus improving the modularity. 
     An exemplary millimeter wave transceiver package in accordance with the present invention comprises a multilayered structure of planar housings stacked vertically. A cover to an electrical housing and a surface mount board is positioned at a first edge of the vertical stack. A surface mount board is positioned as a second layer. The third layer is an electrical housing made from aluminum and comprising a regulator/controller. The RF components are housed in a fourth layer made from copper tungsten. A plurality of interconnected channels are recessed into a planar surface of the housing, either by machining or by the joining of a channelized layer and flat base layer. Only MMIC chips and connective substrates are disposed in the plurality of channels. An RF cover made from Kovar is disposed at a second edge of the vertical stack and forms a seal over the MMIC chips and connective substrates. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     Other objects and advantages of the invention will become apparent from the following detailed description of preferred embodiments thereof in connection with the accompanying drawings in which like numerals designate like elements and in which: 
     FIG. 1 is an exploded perspective view of a channelized housing as seen from the top and front. 
     FIG. 2 is an exploded perspective view of a channelized housing as seen from the bottom and back. 
     FIG. 3 is an exploded perspective view of a flat plate housing as seen from the top and front. 
     FIG. 4 is an exploded perspective view of a flat plate housing as seen from the bottom and back. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a perspective view of an exemplary MMW transceiver package in which a multilayered structure is stacked vertically. In a first embodiment, a channelized MMW housing  2  has on first edge  4  of the vertical stack, a RF cover  6 . The RF cover  6  is transparent to the frequency of the transceiver which will be placed within the housing  2 . In the illustrated embodiment, the RF cover  6  is shown in the form of a substantially rectangular and planar sheet  8  which is positioned above a second layer which is the RF housing  10 . Examples of suitable materials for the RF cover  6  are Kovar, nickel, cobalt, and iron. The RF housing  10  can be made of a suitable material that provides the appropriate thermal conductivity and coefficient of thermal expansion. In the illustrated embodiment, a suitable material is copper tungsten. The RF housing  10  is a monolithic structure and has a first planar surface  14  positioned toward the RF cover  6 . On the first planar surface  14  is formed an internal recessed edge  16  corresponding to the shape of the RF cover  6 . The recessed edge  16  is provided to allow for mating of the RF cover  6  to the RF housing  10 . On the first planar surface  14  of the RF housing  10  are channels  12  and wells  13  which provide locations for the positioning of channelized connectors and MMIC chips, respectively. 
     The third layer of the vertical MMW housing  2  is the electrical housing  24 . The electrical housing  24  can be made of suitable materials, such as aluminum, to provide engineering strength as well as appropriate thermal and conductivity properties. The first planar surface  26  of the electrical housing  24  abuts the second planar surface  18  of the RF housing  10 . The second planar surface  28  of the electrical housing  24  is provided with a recessed edge  30  for the positioning of the subsequent layer, a surface mount board  32 . The surface mount board  32  houses such components as the signal conditioning circuits and the control functions. Components are surface mounted using conventional techniques. Finally, positioned at a second edge  5  of the channelized MMW housing  2  is an electrical housing cover  34 . 
     The multilayered channelized MMW housing  2  is assembled and held together by connectors (not shown) positioned at each of the four corners of the individual layers. The RF housing  10  has through holes  36  positioned at its corners which correspond to through holes  38  in the electrical housing  24  and through holes  40  in the electrical housing cover  34 . DC feedthroughs  42  are provided between the RF housing  10  and the electrical housing  24  to provide electrical connections. These feedthroughs  42  mate with corresponding through holes  44  in the electrical housing  24 . An interface  46  is provided to provide connections between multiple channelized housings  2  and/or other components. The interface  46  may be in the form of a waveguide  48  which is mounted to the RF housing  10  with, for example, bolts  50 . Alternatively, an interface  46  may comprise of a coaxial interface  52 . The coaxial interface  52  is also connected to the RF housing  10 . 
     FIG. 2 is an expanded perspective view of the channelized MMW housing  2  of FIG.  1 . The view in FIG. 2 is from the lower back edge. In this view, the recessed edge  30  on the second planar surface  28  of the electrical housing  24  is clearly visible. Additionally, a connector  54  is visible which is housed in the electrical housing  24  and provides a point of connection for dc signals and ancillary equipment such as a computer interface, which is used to control functions within the MMW module. 
     FIG. 3 is an expanded perspective view of a second embodiment of a channelized MMW housing  102 . The housing  102  comprises a multilayered structure stacked vertically. On a first edge  104  of the vertical stack, a RF cover  106  is provided. The RF cover  106  is transparent to the frequency of the transceiver which will be placed within the housing  102 . In the illustrated embodiment, the RF cover  106  is shown in the form of a substantially rectangular and planar sheet of Kovar  108  which is positioned above a second layer which is the RF housing  110 . The RF housing  110  is comprised of two individual sections—a channelized RF section  160  and a flat plate  170 . Both the RF section  160  and the flat plate  170  can be made of a suitable material that provides the appropriate thermal conductivity and coefficient of thermal expansion, such as copper tungsten. The RF section  160  has a first planar surface  114  positioned toward the RF cover  106 . An internal recessed edge  116  corresponding to the shape of the RF cover  106  is formed on the first planar surface  114 . The recessed edge  116  is provided to allow for mating of the RF cover  106  to the RF housing  110  and form an environmental seal when assembled. Channels  112  and wells  113  within the body of the RF section  160  receive channelized connectors and MMIC chips, respectively. 
     Additional embodiments can include components in addition to MMIC chips and connective substrates on the RF housing  10 , 110 , such as capacitive and resistive elements. 
     An independent RF section  160  and flat plate  170  affords the use of surface mounting techniques for installing the RF components in the RF housing  110 , which reduces costs and facilitates production by simplifying deposition of the epoxy for securing the MMIC chips and assembling the module  102 . Additionally, the individual components  160 ,  170  of the RF housing  110  may be cast, further providing cost reductions over more expensive material preparation techniques. 
     There is a protruding lip  172  on the first planar surface  171  of the flat plate  170 . The lip  172  mates to an inner recess  162  of the second planar surface  115  of the RF section  160 . An outer recess  164  correspond to the outer dimension of the flat plat  170 . The RF section  160  and the flat plate  170  may be joined by mechanical or adhesive means. 
     The third layer of the vertical housing  102  is the electrical housing  124 . The electrical housing  124  may be made of suitable materials, such as aluminum, to provide engineering strength as well as appropriate thermal and conductivity properties. The first planar surface  126  of the electrical housing  124  abuts the second planar surface  174  of the flat plate  170  of the RF housing  110 . The second planar surface  128  of the electrical housing  124  is provided with a recessed edge  130  for the positioning of the subsequent layer, a surface mount board  132 . Finally, positioned at a second edge  105  of the channelized MMW housing  102  is an electrical housing cover  134 . 
     The multilayered channelized MMW housing  102  is assembled and held together by connectors (not shown) positioned at each of the four corners of the individual layers. The RF housing  110  has through holes  136  positioned at the corners of the RF section  160  which correspond to through holes  138  in the electrical housing  124  and through holes  140  in the electrical housing cover  134 . DC feedthroughs  142  are provided between the flat plate  170  of the RF housing  110  and the electrical housing  124  to provide electrical connections. These feedthroughs  142  mate with corresponding through holes  144  in the electrical housing  124 . An interface  146  is provided to form connections between multiple channelized housings  102  and/or other components. The interface  146  may be in the form of a waveguide  148  which is mounted to the RF section  160  of the RF housing  110  with, for example, bolts  150 . Alternatively, an interface  146  may comprise of a coaxial interface  152 . The coaxial interface  152  is also connected to the RF section  160  of the RF housing  10 . 
     FIG. 4 is a expanded perspective view of the channelized MMW housing  102  of FIG.  3 . The view in FIG. 4 is from the lower back edge. In this view, the inner recess  162  the outer recess  164  and the second planar surface  115  of the RF section  160  are more easily seen. In addition, the feedthroughs  142  may be seen on the second planar surface  174  of the flat plate  170 . The recessed edge  130  on the second planar surface  128  of the electrical housing  124  is clearly visible. This recess is provided for mating the surface mount board  132  to the electrical housing  124 . Additionally, a connector  154  is visible which is housed in the electrical housing  124 . 
     The regulator/controller on the electrical housing  24 ,  124  can be constructed from larger surface mount parts. It also can serve as a secondary heat sink due to its large volume and high thermal conductivity. 
     Due to the relocation of some devices from the RF housing, the RF channels  12 ,  13  of the MMW housing  2 ,  102  can be made larger to accommodate frequencies from 20 to 40 GHz without any changes to the housing module. This allows the MMW housing to be flexible in its applied uses. 
     One method by which the MMIC die and thin film substrates are attached to the housing  10 ,  110  is by the use of silver-based conductive epoxy. Excessive epoxy can cause shorts, while lack of adequate epoxy can allow the chips to fall off and impacts module reliability. 
     Different methods have been used to control the amount of epoxy. The use of automatic epoxy deposition in the fine tolerances of a monolithic housing with small channel widths has been very challenging. In tight RF channels, spiral and dot patterns have been utilized to overcome the difficulties and are among the most popular methods of epoxy deposition. The proposed flat plate housing  30  allows the use of epoxy screening, which has the advantage of being easily controlled which helps to reduce costs. 
     Housing 
     GaAs MMIC chips expand and contract over the temperature ranges encountered during use requiring the surface on which the chips are mounted to expand similarly over the same temperature range. Failure to have a closely matched coefficient of thermal expansion between the chip and the housing results in chip cracking, separation from the surface, and damage. In addition, the chips generate a large amount of heat and require a housing and packaging material with sufficiently high thermal conductivity to rapidly remove the heat. The efficient removal of heat contributes toward extending the life of the MMIC chips. 
     These characteristics limit the choices of possible materials. Several examples of suitable materials include Copper Tungsten (CuW), Aluminum Silicon Carbide (Al—SiC), Aluminum graphite (Al-graphite), and Copper Molybdenum (CuMo). 
     One example of a material for use as the housing is CuW. The raw material for CuW has the advantages of relatively low cost and the alloy has a high thermal conductivity, typically 180-200 W/mK. Additionally, the coefficient of thermal expansion of CuW is closely matched to both the coefficient of thermal expansion of the MMIC chips and the coefficient of thermal expansion of the materials typically utilized in other areas of the housing. However, this material is very hard, making it difficult to machine. To reduce costs, the machining operations required for this material should be minimized. 
     Regulator/Controller 
     Minimizing the amount of CuW material used in the housing  2 ,  102  serves to reduce costs. The use of the assembly  2 , 102  of the present invention results in a 5:1 reduction in the amount of CuW used for the RF housing  10 , 110 . A similar reduction in material is achieved when the housing is made from any of the other suitable materials discussed previously. 
     For example, to reduce the amount of CuW used, the present invention moves the regulator/controller board out of the RF section  10 ,  110  and places it in the electronic section  24 ,  124  adjacent to the second planar surface  18 ,  118  of the RF section  10 ,  110 . The DC and control signals are carried to the sealed RF MMIC area through glass feedthroughs  42 ,  142  in the electronic section  24 ,  124 . The feedthroughs are glass conductors which are placed in vias in the RF section and soldered in place. The feedthroughs  42 , 142  extend out of the second planar surface  18 , 118  or the RF section  10 , 110  for a distance of approximately 250 to 280 mils. The use of feedthroughs  42 ,  142  is independent of the choice of interface  46 ,  146  and allows the module  2 ,  102  to have either a coax interface  52 ,  152  or a waveguide interface  48 ,  148  with no changes to the module housing or internal circuits. This interchangeability improves modularity and further reduces costs. 
     In addition to the low cost advantage of the surface mount technology, the architecture of the housing  2 ,  102  of the present invention allows the DC signals to be available in very close proximity to where they are being used inside the RF section  10 ,  110 . The proximity of the DC signals and the RF section  10 , 110  is important to minimize signal attenuation associated with traveling between widely spaced parts and for power management. Typically, the distance of separation is typically 2 to 5 mils and should be minimized to below a preferred maximum of 10 mils. 
     Fabrication 
     A MMW housing consistent with the present invention can be made by the following method. The MMIC and connective substrates are epoxied onto the channelized RF housing  10 , 110  and the electronic components are surface mounted on the electronic housing  24 , 124 . The electronic housing  24 , 124  is gold plated on a first planar surface  26 , 126  and the monolithic RF housing  10  is gold plated on a second planar surface  18 . Alternatively, the RF housing  110  comprised of a channelized RF section  160  and a flat plate  170  is gold plated on the second planar surface  174  of the flat plate  170 . The respective gold plated surfaces are then joined with the DC feedthroughs  42 , 142  being placed into corresponding holes  44 , 144  in the electrical housing  24 , 124 . A thermal sheet is placed between the electrical housing  24 , 124  and the RF housing  10 , 110  and provides both a thermal contact and a seal. In one embodiment, the thermal sheet is a metal foil. The use of a thermal sheet compensates for any tolerances in the dimensions and surface finish of the components. Next, a RF cover  6 , 106  is disposed in the recessed edge  16 , 116  on the first planar surface  14 , 114  of the RF housing  10 , 110 . A surface mount board  32 , 132  is then placed in the recessed edge  30 , 130  on the second planar surface  28 , 128  of the electrical housing  24 , 124 . An electrical housing cover  34 , 134  is placed over the surface mount board  32 , 132 . The assembled housing  2 , 102  is then fastened together by the use of connectors placed in threaded holes  40 , 140  in the corners. Finally, the interface connector  46 , 146  is attached by threaded fasteners. 
     Exemplary embodiments of the present invention provide unique solutions for a housing assembly and for the integration of the regulator/controller into the assembly that reduces costs. Housing solutions are provided using a combination of metals designed to meet requirements at a fraction of the cost. The material used for the housing is matched to the function of the feature within the housing. Additionally, only features requiring the benefits of a material of high cost are housed within an area constructed from high cost materials. 
     The regulator/controller, which has traditionally resided in the RF section, has also been relatively expensive because it is made out of micro-electronic circuits. The proposed packaging concepts moves the regulator/controller out of the small RF section which allows the use of larger low cost surface mount parts for this application. 
     The design also provides a common package capable of supporting frequency ranges from 20 GHz to 40 GHz. 
     Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without departing from the spirit and scope of the invention as defined in the appended claims.