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Home , Planar transmission line

United States Patent (19) 11) Patent Number: 4,626,805 Jones 45) Date of Patent: Dec. 2, 1986

54) SURFACE MOUNTABLE MCROWAVE IC 4,543,544 9/1985 Ziegner ...... 333/238 X PACKAGE Primary Examiner-Paul Gensler (75) Inventor: Keith E. Jones, Aloha, Oreg. Attorney, Agent, or Firm-Francis I. Gray (73) Assignee: Tektronix, Inc., Beaverton, Oreg. 57 ABSTRACT 21 Appl. No.: 727,946 A surface mountable IC package uses 22) Filed: Apr. 26, 1985 printed transmission lines on a in 51 Int, C...... H01P 5/00 lieu of plumbing between milled packages. A backside (52) U.S.C...... 333/33; 333/246; co-planar is connected to a topside micro 333/260 strip line by a through-hole in a carrier . To (58 Field of Search ...... 333/33, 238, 246; compensate for inductance added by the hole and trans 339/17 M, 17 LM; 361/414 mission line ends, a gap is adjusted to provide compen sation capacitance. Hermetic sealing of the package is 56) References Cited. assured by brazing a lead frame over the through-hole U.S. PATENT DOCUMENTS and using a solder sealed lid. The lid provides both a 3,842,360 10/1974 Dickens ...... 333/238 X hermetic seal and shielding. 3,848, 198 11/1974 DeBrecht et al...... 333/238 X 4,110,712 8/1978 Morris...... 333/238 X 9 Claims, 7 Drawing Figures

U.S. Patent Dec. 2, 1986 Sheet 1 of 5 4,626,805

U.S. Patent Dec. 2, 1986 Sheet 2 of 5 4,626,805

F. G.3 U.S. Patent Dec. 2, 1986 Sheet 3 of 5 4,626,805 U.S. Patent Dec. 2, 1986 Sheet 4 of 5 4,626,805

U.S. Patent Dec. 2, 1986 Sheet 5 of 5 4,626,805

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y 4,626,805 1. 2 substrate 12. Ground pads 18 are located on the top SURFACE MOUNTABLE MCROWAVE IC surface of the substrate 12 near the end 20 of the trans PACKAGE mission line 16, each pad having a metallized through hole 22 to connect the pad with the 14 on BACKGROUND OF THE INVENTION 5 the opposite side of the substrate. A controlled impe 1. Field of the Invention dance taper of the end 20 brings the The present invention relates to transmission line width down to a geometry commensu (IC) packages, and more particularly to a surface rate with the surface mount package pinout 19. mountable microwave IC package which provides high A surface mountable package 24 has a carrier sub performance at a reasonable cost. 10 strate 26, typically of a material well-known in 2. Description of the Prior Art the art, with a metallization layer, or ground plane, 28 The application of microwave gallium-arsenide on the bottom. A portion of the ground plane 28 is (GaAs) integrated circuits is limited by package perfor removed to form a co- 30. The mance and/or complexity. Typical packages using co-planar transmission line 30 has a lead end 32 and a milled metal enclosures with ceramic substrates are 15 termination end 34. The co-planar transmission line 30 expensive and rarely hermetic. Hermetic enclosures, may be composed of an etched lead frame brazed to the such as Kyocera or NTK multilayer ceramic carriers, substrate metallization. A transmission line are limited to one to two gigahertz with reasonable 36 has a termination end 38 and is located on the top performance. High performance carriers, such as the surface of the substrate 26. A metallized through-hole Hypcon described in U.S. Pat. No. 4,255,003 issued 20 40 connects the termination ends 34, 38 of the respective Mar. 10, 1981 entitled "Electrical Connector" by Wil transmission lines 30, 36. An IC 42 is mounted on a liam E. Berg, are expensive and complex. mounting pad 43 on the carrier substrate and is electri What is desired is a low cost, hermetic or semi-her cally connected to the microstrip transmission line 36. metic, high performance, surface mountable GaAs mi The pinout 19 is formed by a lead frame 21 which ex crowave IC carrier. 25 tends beyond the edge of the surface mount package 24. SUMMARY OF THE INVENTION A lid 25 may be solder sealed to the package 24 for both Accordingly, the present invention provides a sur a hermetic seal and shielding. face mountable microwave IC package which uses The equivalent circuit for the circuit on the surface printed transmission lines on a printed circuit board in 30 mountable package 24 is represented in FIG. 2. The lieu of plumbing between milled packages. A back side co-planar transmission line 30 is represented as a coaxial co-planar waveguide line is connected to a topside mi cable, as is the microstrip line 36. The inductance XL crostrip line by a through-hole in a carrier substrate. To represents the portion L of the coplanar transmission compensate for inductance added by the hole and trans line 30 which crosses the gap G between the ground mission line ends, a gap is adjusted to provide compen 35 plane 28 and the through-hole 40 metallization, con sation capacitance. Hermetic sealing of the package is necting with the termination end 34. Likewise, the in assured by brazing a lead frame over the through-hole ductance XU represents the portion U of the microstrip and using a solder sealed lid. The lid provides both a transmission line 36 which also crosses the gap G, con hermetic seal and shielding. necting with the termination end 38. The capacitance The objects, advantages and novel features of the XG represents the gap G, and can be altered by adjust present invention will be apparent from the following ing the width of the gap to compensate for inductances detailed description when read in conjunction with the introduced by the transmission lines 30, 36 and the appended claims and attached drawing. through-hole 40. For standard 50 ohm transmission lines the co-planar line 30 is 10 mils wide with a three BRIEF DESCRIPTION OF THE DRAWING 45 mill gap on each side. The substrate 26 is typically 10 FIG. 1 is an exploded perspective view of an IC mils thick of alumina (AlO3) or the like. For a hole 40 of surface mountable microwave package according to the 10 mils diameter a 15 mil annulus forms the gap G, present invention. determined empirically. For thick substrates 26 of 25 FIG. 2 is a schematic view of an equivalent circuit for mils or greater the microstrip transmission line 26 may the package of FIG. 1. 50 be replaced with a co-planar transmission line to keep FIG. 3 is a plan view for the hybrid circuit of the the line width small. surface mountable microwave package. Another embodiment is shown in FIG. 5. A co-planar FIG. 4 is a plan view of a lead frame for the hybrid transmission line section 44 is in the form of a pad, and circuit of FIG. 3. a microstrip transmission line 46 is in the form of a "t' FIG. 5 is an exploded perspective view of an alterna 55 terminated in a coplanar line connected to IC42. Refer tive embodiment of an IC surface mountable micro ring to the equivalent circuit of FIG. 6 XG represents wave package according to the present invention. the capacitance of the gap G, XH represents the induc FIG. 6 is a schematic view of an equivalent circuit for tance of the through-hole 40, XU represents the portion the package of FIG. 5. U of the transmission line 46 across the gap G, and XT FIG. 7 is a graphic view of a time domain reflectome 60 represents the capacitance introduced by the width step ter output for the package of FIG. 1. T. The capacitive reactances XG and XT provide shunt capacitance to compensate for the inductance of the DESCRIPTION OF THE PREFERRED through-hole 40. EMBODIMENT For both embodiments the surface mountable pack Referring now to FIGS. 1, 3 and 4 a printed circuit 65 age 24 is placed on the printed circuit board 10 so that board 10 is shown having a substrate 12 and a ground the ground plane 28 contacts the ground pads 18 and plane 14 on the bottom of the substrate. A microstrip the co-planar transmission lines 30, 44 contact the end transmission line 16 is located on the top surface of the 20 of the micro-strip transmission line 16 on the printed 4,626,805 3 4. circuit board. The package 24 is then connected to the 3. A package as recited in claim 1 wherein said sec board 10 using conventional techniques such as reflow ond microwave transmission line comprises a co-planar soldering. Preferably the co-planar transmission line 30, transmission line. 44 and hole 40 are bonded to a lead frame 21 of a mate 4. A package as recited in claim 1 further comprising: 5 a lead frame brazed to said co-planar waveguide rial such as Kovar which provides a hermetic seal and transmission line for sealing the electrical connec ease of inspection of the reflow solder connections. The tion via said metallized through-hole and for con etched leads 19 give a measure of compliance which necting with said first microwave transmission line; compensates for the difference in temperature coeffici and ents of expansion between the ceramic substrate 24 and 10 a solder sealed hermetic lid enclosing said carrier the material of the PCB substrate 12, typically Teflon or substrate. glass fiber. 5. A package as recited in claim 1 wherein said co The values for the various inductances and compen planar transmission line further comprises capacitive sating capacitances caused by the gap G are solved means for compensating for inductive reactances intro empirically simultaneously as described below such that 15 duced by said co-planar and said second microwave transmission lines at the metallized through-hole. 50=XL-XU=XG or 50=XH--XU=XG for the two 6. A package as recited in claim 5 wherein said capac embodiments, respectively. As shown in FIG. 7 for the itive means comprises a gap surrounding the end of said first embodiment the portion of the graph which is co-planar transmission line and said through-hole, the positive represents inductance and the portion which is 20 width of said gap being adjusted to provide a required negative represents capacitance. For compensation the compensation. negative area should equal the positive area. 7. A package as recited in claim 6 wherein said capac Thus, the present invention provides a hermetic, sur itive means further comprises a width step integral with face mountable microwave IC package which is opera and near the end of said second microwave transmission ble at frequencies up to 20 gigahertz and is relatively 25 line. inexpensive. 8. A surface mountable microwave IC package for What is claimed is: mounting on a printed circuit board having a first mi 1. A surface mountable microwave package compris crowave transmission line, said IC package comprising: ing: a carrier substrate; 30 a co-planar waveguide transmission line on the a printed circuit board having a first microwave bottom of said carrier substrate configured for transmission line thereon with ground pads adja connection to said first microwave transmission cent the end of said microwave transmission line; line; and a carrier substrate; a second microwave transmission line on the top of a co-planar transmission line on the bottom of said 35 said carrier substrate, electrically connected to said substrate situated so as to make electrical contact co-planar waveguide transmission line via a metal with said first microwave transmission line on said lized through-hole, to which an integrated circuit is printed circuit board; electrically connected; and a second microwave transmission line on the top of said package, during operation, having said carrier 40 substrate placed on and connected to said printed said carrier substrate connected to said co-planar circuit board. transmission line via a metallized through-hole, an 9. A package as recited in claim 8 further comprising: integrated circuit being connected to said second a lead frame brazed to said co-planar waveguide microwave transmission line; transmission line for sealing the electrical connec said package, during operation, having said carrier 45 tion via said metallized through-hole and for con substrate placed on and connected to said printed necting with said first microwave transmission line; circuit board. and 2. A package as recited in claim 1 wherein said sec a solder sealed hermetic lid enclosing said carrier ond microwave transmission line comprises a microstrip substrate. transmission line. 50 se s as

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