Abstract:
A package for a semiconductor device includes a base having a flat surface with an edge of a predetermined shape for abutting against a similar edge of another object. Conductors are placed on the flat surface of the base and extend to but do not overlap the edge of predetermined shape. The base along with a frame and a cover cooperate to provide a package which encloses and protects the semiconductor device. The package can be placed adjacent a similarly shaped package so that the overall structure takes up a minimal amount of space. Ground planes located on the base can be readily interconnected.

Description:
This application is a continuation of prior application Ser. No. 121,720, filed Nov. 16, 1987, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to packages for high frequency semiconductor devices and more specifically to housings suitable for protecting Monolithic Microwave Integrated Circuit die (MMICS). 
     At the present time, much effort and expense is going into research and development relating to MMIC-type galium arsenide circuitry. Chips including this circuitry tend to provide advantages of high speed and high power operation while taking up minimal space. The space reduction can be as much as 50:1 as compared to other methods. These semiconductor chips are not usable for practical applications unless they can be enclosed in and protected by proper packages or housings. 
     Prior art packages for MMIC semiconductor chips which operate up to or even above 12 gigahertz (GH z ) tend to be expensive and they are generally presently available from only a limited number of suppliers. While some prior art packages allow mounting of MMIC chips within the package in a small area, the packages themselves require excessive amounts of space. This is because some such packages utilize leads that extend beyond the boundaries of the package. These leads often must be tied down to conductors on a substrate surface and then brought from the conductors on the substrate to an adjacent package. This requires that sufficient space be maintained between the prior art packages to facilitate the required electrical and mechanical connections. 
     Moreover, some prior art packages require that ground plane connection between devices be provided on bottom surfaces of their substrates. This complicates the construction and manufacture of products including such packages. Furthermore, some prior art packages have heat dissipating buttons for removing heat from the chips. Such buttons are difficult to reliably attach to heat sinks. Additionally, some prior art packages have leads which are only suitable for being grounded. The layout of products including such packages is thereby complicated. Furthermore, some prior art packages cost on the order of Fifty Dollars ($50.00) each which makes them unsuitable for many high quantity production items. 
     SUMMARY OF THE INVENTION 
     Accordingly, one object of the invention is to provide packages for high frequency semiconductor devices which enable compact final product configurations by allowing the packages to be mounted side-by-side with substantially no wasted space therebetween. 
     Another object of the invention is to provide packages for wide bandwidth, high frequency semiconductor devices operating in the gigahertz region which allows for ground plane interconnection on the top of the structure rather than on the bottom and which provides a plurality of leads. 
     Still another object of the invention is to provide high frequency, hermetically sealed packages for high frequency semiconductor devices which efficiently conducts heat from the semiconductor chips mounted therein. 
     A further object of the invention is to provide low cost, easily manufactured packages for MMIC or other high frequency semiconductors which can be placed in abutting relationship to minimize the required space. 
     A package for a semiconductor device in accordance with one embodiment of the invention is suitable for abutting against an adjacent object so that the resulting structure takes up a minimum amount of space. The package includes a base having a flat surface with an edge of predetermined shape for abutting against a similar edge of the other object. Conductors are provided on the flat surface of the base and extend to but do not overlap the edge of predetermined shape. A semiconductor die pad for a semiconductor die is also provided on the flat surface of the base. A frame is affixed to the base and surrounds the semiconductor die pad. A cover is affixed to the frame for covering the semiconductor die. The base, frame and cover cooperate to provide a package which encloses and protects the semiconductor die. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the present invention may be derived by reference to the detailed descriptions and the claims considered with the accompanying drawings wherein like reference numbers designate similar parts. 
     FIG. 1 is an exploded isometric view of a MMIC package in accordance with one embodiment of the invention; 
     FIG. 2 is a top view of the package of FIG. 1 illustrating the dimensions and the relationship of some of the parts thereof; 
     FIG. 3 is a cross-sectional view of the structure of FIG. 2; 
     FIG. 4 is an isometric view part of another package showing the location of the semiconductor chip and additional ends; and 
     FIG. 5 is an isometric view of an electronic subassembly having two packages in accordance with the invention which had been mounted in abutting relationship to one another to minimize the size of the resulting product. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates an exploded isometric view of package 10 for MMICS or other high frequency semiconductor devices. Package 10 includes cover 12, seal frame 14 and base 16. These parts can have rectangular, square or other shaped top views and these parts can be made of a ceramic material such as alumina. Ceramic base 16 has all surfaces thereof at least partially covered by a thin gold layer which may be applied in a known manner such as by sputtering along with the well-known technique of silk screening to provide desired patterns in the top surface 17 and end surfaces, eg. 18. Alternatively, top surface 17 and the end surfaces, eg. 18, can be completely coated with a gold layer and then masked and etched in a known manner to provide the desired gold patterns. Gold layer 19 on the flat bottom surface of ceramic base 16 is not patterned. A cross section of package 10 including layer 19 is shown in FIG. 3. End portions of base 16 such as surfaces 18 and 20 are covered with gold except for exposed ceramic areas such as 22 and 24 beneath leads or conductors 25 and 26, respectively. These exposed ceramic areas 22 and 24 prevent the leads or conductors from being shorted out. Leads 28 and 30 also have exposed end areas (not shown) of ceramic material beneath them to prevent shorting. 
     Holes 31 are plated through base 16 to facilitate heat flow from a semiconductor chip or chips mounted on rectangular pad 32. Gold plated ground plane portions 33, 34, 36 and 38 are connected by the gold on the end surfaces of base 16 to the gold plated bottom surface 19. Coplanar waveguide lines 25, 26, 28 and 30 on the top of base 16 are designed to provide 50 ohm impedances at the input and output terminals or ports thereof to facilitate maximum power transfer and to minimize interface problems. The thickness of base 16 and the thickness an spacing of conductor 25, for instance, relative to metallized ground plane areas 36 and 38 are selected in a known manner to provide the desired impedances. 
     FIG. 2 is a top view of the structure of FIG. 1 without cover 12. Seal frame 14 is positioned on ceramic base 16 and sealed into place by sealing glass, for instance, which is applied in a known manner. Lines 25, 26, 28 and 30 run underneath seal frame 14. Ceramic base 16 has a square shape having approximately 350 mils (thousands of an inch) along each side dimension, eg. 40. The top view of ceramic seal frame 14 is likewise square having sides of length 46 of approximately 250 mils. Holes 31 have diameters of 10 mils. Base 16 has a flat top surface with straight edges for abutting against the straight edge of another object. Lines 25, 26, 28 and 30 extend to but do not overlap the straight edges of base 16. 
     FIG. 3 shows a cross-sectional view along leads 25 and 28 of the structure shown in FIG. 2. The thickness of flat, square cover 12 as indicated by distance 52 is on the order of 10 mils. The height or thickness of seal frame 14 is 100 mils as indicated by distance 54 and the thickness of base 16 as indicated by distance 56 is 10 mils. Furthermore, as indicated by distance 58, the thickness of seal frame 14 is 15 mils. Semiconductor die pad 32 is located centrally on the flat top surface of metallized base 16. 
     FIG. 4 is a top view of package 69 which is similar to package 10 described in FIGS. 1, 2 and 3 without cover 12, but with additional microstrip lines 62, 64, 66 and 68 radially extending from pad 32 toward the edges of base 16. Furthermore, semiconductor chip 70 is shown in FIG. 4 as being diebonded to pad 32 in a known manner using epoxy or solder bonding. Conductive pads 71 on chip 70 are wirebonded in a known manner to the ends of conductors 25, 26, 28, 30, 62, 64, 66 and 68 by respective wirebonds 80, 81, 82, 84, 87 and 88. After chip 70 has been diebonded and wirebonded, the chip is electrically tested. If the test is satisfactory, cover 12 is glass sealed to seal frame 14 by sealing glass 90 as indicated in FIG. 3 so that base 16, frame 14 and cover 12 enclose and protect semiconductor die 70. 
     FIG. 5 shows MMIC coplanar waveguide packages 93 and 92 which have common edges abutted against each other. These packages are fastened to flat copper carrier 94 of module or subassembly 95. Input stripline conductor 96 provides input signals for the devices in cascaded packages 93 and 92. Rounded surfaces 97 provide matching compensation between stripline 96 and the coplanar waveguide conductor 100. Conductor 96 is connected to waveguide 100 by silver ribbon 98 which can be soldered or welded to the top surfaces of conductor 96 and input conductor 100 of package 90. Similarly, silver ribbon 102 provides connection between coplanar ground planes 103 and 105 on the top surfaces of packages 93 and 92. This simplifies fabrication as compared to if the bottoms of the packages had to be interconnected as is the technique in some prior art applications. Thus, coplanar packages 93 and 92 allows mounting in a smaller area than such other available packages. Some of the conductive lines, eg. 100 and 106, of packages 90 and 92 can conduct RF and others, eg. 110 and 112, can conduct DC power supply potentials and currents. These lines have similar widths and thicknesses to facilitate product layout. Output signal conductor 104 is connected to output line 106 of package 92 by silver ribbon 107. Aligned conductors 120 and 122 of respective packages 93 and 92 can also be connected by silver ribbon (not shown). 
     As further illustrated in FIG. 5, the close proximity of packages 92 and 93 allow designers to take advantage of the reduction in size inherent in MMIC circuits by also reducing the size of the final product configuration. Packages 92 and 93 of the invention do not have external leads which otherwise would increase the size of the final product configuration because they must be brought down upon carrier 94 and then brought back up into adjacent packages thus requiring space between the adjacent packages. This would undesirably increase the sizes of modules and hence the size of final product configurations using prior such art packages. 
     The disclosed packages 10, 69, 92, and 93 are suitable for use with modules, subassemblies, subsystems and systems employing MMIC technology. Nearly all types of MMIC circuits such as amplifiers, phase shifters, attenuators, etc. can be mounted in packages 10, 69, 90 and 93. These packages can be hermetically sealed using ceramic glass sealing 12 between cover 90 and frame 14 and glass sealing 91 between frame 14 and base 16 as shown in FIG. 3 so that these packages meet MIL SPEC 883, for instance. The disclosed packages have low cost and a capability of operating over wide frequency ranges such as from DC to 20 gigahertz. Although package 69 of FIG. 4 has 8 leads, it is apparent to those skilled in the art that an even greater number of leads can be accommodated by the package shown. Plated through holes 70 enable heat transfer between the chip 70 and carrier 94. 
     Thus, it is apparent to one skilled in the art that semiconductor packages in accordance with the invention have been described that fully satisfy the objects, aims and advantages as set forth above. More specifically, packages 10 and 69 can enclose high frequency, semiconductor devices and enable fabrication of compact final subassembly 95 by allowing the packages thereof to be mounted side-by-side with substantially no space therebetween. Either of packages 10 or 69 is capable of operating with wide bandwith, high frequency semiconductor die. Top surfaces of ground planes 103 and 105 are easily connected together. Plated through holes 70 facilitate heat flow from a semiconductor chip 70 mounted on pad 32. The resulting packages facilitate the manufacture of subassembly 95, for instance, by low cost techniques. 
     While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alterations, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, the invention is intended to embrace all such alterations, modifications and variations in the appended claims.