Erratum to: New Horizons in Electrochemcial Science and Technology

JOM, May 1987

Richard C. Alkire, Stanley M. Wolf

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Erratum to: New Horizons in Electrochemcial Science and Technology

JOURNAL OF METALS. May 1987 MMC Microwave Packaging Components Years Since Baccalaureate Degree C. Thaw R. Minet J. Zemany C. Zweben Space Systems Division General Electric Company Vears Since Baccalaureate Degree - over the last two years, educator salar­ ies still lag behind private industry pay scales. Other factors such as assign­ ment of research contracts can sub­ stantially raise compensation in the academic sector. Overall increases in faculty compensation are associated with appointment to higher rank rather than increased experience within ranks. Compensation among engineers working at research organizations and those employed as consultants is de­ picted in Figures 4a and 4b. Finally, the effects of socio-economic changes and shifting industrial emphasis are de­ picted in Table I, which lists regional variations in median salary. The complete 1986 EMC study can be obtained by writing to: The American Association of Engineering Societies, Inc., 415 2nd Street, NE, Suite 200, Washington, D.C. 20002. 70000 1--+-+-+-+--+--+--+-+---1--1------1 -'" .. ...' ----- - - ~ 64000 1-+-+-+-+--b.-t=.,:•.•+-+-+--+-.-4 ;§?i 5582000000 ~ljjj2t~tt:tl~ 2 /~~:.""""'" _' - .- --1-- « 46000 I-+-,""l/O+'/"...,.v.. ~,,;ro.I"'.,:::'.+-.=_.:-J:.,. ,._..,j......j.....1=-:1 40000 ,~~/'... ,. 34000 /1.1',/ ,. ~ .' 28000 ~~.:..'+-"-+-+--1-1--+-+-+--+--+--1 == 880001-+-...J...-,c:',.""....l.--+-t-l_t-+-+--I ;:::,;;~::.:" 1-+--+-+-+--+--1 ___ 1.'wr""I,,~"II' .-.-.- I '..Hlf.', II' ~ 640001-+-+--+--+--+-+-I-1-+-+--I ;?'"i 580001-+-+--+--+-+-t-l-t-+-+--I ~ 52000 I-+-+--+--b-'f.:.,..-•±•-::.;-:j.::,,';;--1:0..-.-.........-.=-.::3 Figure 4b. Compensation for non-supervi­ _sory consultants. Requirements for aircraft and space­ craft microwave devices (e.g., radar and communication systems) under devel­ opment exceed the capabilities of ex· isting packaging materials. With mechanical and physical properties which can be tailored to the application, metal matrix composites (MMC) give engineers unprecedented opportunities for efficient and reliable packaging de­ signs. The unique properties of metal matrix composites were used to de­ velop new microwave packaging com­ ponents that, compared to the baseline Kovar, are 65% lighter, have a 600% greater thermal conductivity, and do not distort during or after machining. This obviously represents a major break­ through in packaging technology. Microwave circuits use carriers and packages (small boxes) to support ce­ ramic circuit substrates and microwave devices such as field effect transistors. These packages must be machined precisely to avoid misalignment of sig· nal connections with conductors on the substrate, and to prevent bending stresses which can fracture the fragile ceramic substrates and microwave de­ vices mounted on them. Kovar, a high nickel steel, commonly has been used in this application, pri· marily because of its low coefficient of thermal expansion (CTE), which is sim­ ilar to that of alumina ceramic sub· strates. This CTE match is necessary to avoid both debonding and breakage of the ceramic substrate during the thermal cycling (- 65 to 125°C) expe­ rienced by military specification elec­ tronics. Although the CTE of Kovar is suitable, it has several major deficien­ cies, including low thermal conductivity, high density, and frequent distortion during and after machining. The trend to increasing component density means that more heat per unit area must be dissipated. The thermal conductivity of Kovar is only 10 BTU! hr.·ft.·oF, less than 10% of that of pure aluminum. This is a major problem, be­ cause the failure rate of microwave de­ vices increases with increasing operating temperature. The density of Kovar is 0.3 Ib.lin.,3 about three times that of alu­ minum. Kovar packaging components often are a major part of the weight of microwave devices, which is a major design consideration for aircraft and spacecraft systems. Kovar parts typi­ cally have high internal stresses which can cause them to distort both during and after machining. The long-term dis· tortion (creep) displayed by Kovar fre­ quently results in parts that exceed tolerances, even though their initial di­ mensions met specifications. These deficiencies were remedied by developing microwave packaging com­ ponents using metal matrix composites. The particular material selected was a 6061 aluminum alloy reinforced with sil· icon carbide particulates. This material has a low coefficient of thermal expan­ sion, high thermal conductivity, and does not distort during or after machining. The material was purchased from DWA Composite Specialties, Inc. Alumina ceramic substrates bonded to Kovar and metal matrix composite gold-plated blocks have been thermal cycled without demonstrating bond fail­ ure. This success has prompted the de­ velopment of a variety of microwave packaging components. Identical Kovar and MMC packages were fabricated and tested, and no difference in electrical response was shown. The demonstrated advantages of the metal matrix composite components represent a major breakthrough in packaging technology. Soldered and welded jOint integrity is maintained. Since . thermal conductivity is increased 600% over Kovar, the result is cooler, more reliable devices. Packaging weight is reduced by 65%. This weight savings results in further reductions in the weight of supporting structures and fuel. For example, the rule of thumb for fighter aircraft is that each pound of weight saved in avionics decreases takeoff weight by seven pounds. Use of metal matrix composites eliminates the ma­ chining and post·machining distortion exhibited by Kovar, reducing scrap rates, rework and schedule problems. If you want more Information on thll lubJect, pleale circle reader lervlce card number 71. Correction


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Richard C. Alkire, Stanley M. Wolf. Erratum to: New Horizons in Electrochemcial Science and Technology, JOM, 1987, 55-55, DOI: 10.1007/BF03259001