Hermetic packages for hybrid circuits

Redistribution of dopant impurities in oxidising ambients ANTHONY C, HILL, ROY BRADLEY and WILLIAM G. ALLEN Solid St. Electron, 22,633 (1979). The redistribution of dopant impurities in an oxidising ambient is considered using a new series method. The results obtained are valid for a wide class of oxide growth functions including as special cases the parabolic and linear laws. More importantly, the method copes readily with the practically useful mixed linear-parabolic growth law. The solution retains the flexibility of the related Chen and Chen series and is applicable for a wide range of initial dopant profiles and for different boundary conditions at the oxide-semiconductorinterface. As an example of the power of this new technique results are presented for the previously analytically unsolved problem of redistribution from an initial eric profile, with a segregation type boundary condition, assuming a linear-parabolic growth law. The convergence difficulties of our general series solution have been surmounted by the use of the Euler transformation, providing solutions which are valid for realistic diffusion times. Our analysis permits a comparison with the earlier work of Guckel and Hall on the redistribution from a step profile. On the splitting of the exciton ground state in silicon N. O. LIPARI and M. ALTARELLI SolidSt. Commun. 32, 171, (1979). The exciton ground state in silicon is calculated taking into account the effect of the split-off valence band. We show that this effect is very important. The anisotropy splitting of the ground state is found to be 0.32 meV, while a previous analysis, which neglected the split-off band, gave 0.46 meV. The new resuh is in good agreement with recent experimental data. Monolithic M1Cs gain momentum as gallium arsevide MSI nears FRANK J. MONCRIEF Microwaves p. 42 (July 1979). Gallium Arsenide ICs are reaching MSI complexity, and LSI circuits will soon follow. The arrival of high-speed GaAs subsystems-on-a-chip could change this industry radically. Electron-exciton inelastic collision cross sections for different semiconductors S. G. ELKOMOSS and G. MUNSCHY J. Phys. Chem. Solids40, 431 (1979). The electon-exciton inelastic collision cross sections for the different semiconductors CdS, ZnO, CdSe, St, CuzO, CuCI, CuBr and CuI have been calculated in the Glauber approximation. The transitions ls-2s, ls-3s, ls-2p and ls-3p have been considered. The calculations are carried out as function of the different available values of o" = m~/m~ where m ' a n d m~ are, respectively, the electron and the hole effective masses for the corresponding semiconductors.

2.

Memories

E-Prom doublesbit densitywithoutaddinga pin BOB G R E E N E and FRANK LOUIE

Electronics p. 126 (16 August 1979). Multiplexing makes room for the extra address bit, keeping the 32-K memory compatible with 16-K devices and 64-K ROMs. Scaled process adds new life to bipolar RAMs RAYMOND P. CAPECE Electronics p. 39 (30 August 1979). Static random-access chips made with new process hold off fastest MOS parts; 16-K density is next target.

3.

Microprocessors

Peripheral chips shift microprocessor systems into high gear JOHN G. POSA Electronics p. 93 (16 August 1979). Support devices, peripheral controllers make short work of functions that microprocessor software toils over, says this special report.

Evaluation delay cut by low-cost microprocessor development CHRIS BAILEY andTRACY KAHL Electronics p. 121 (30 August 1979). Universal prototyping instrument standardiscs command and data entry; data ports allow expansion to include development system, cassette storage.

4.

Hybrids

Echo-cancelling chip opens way to increased use of satellite channels H A R V E Y J. HINDIN Electronics p. 41 (2 August 1979). Bell Labs' n-channel MOS chip, in production at Western Electric, will be installed in fourth quarter. Hermetic packages for hybrid circuits M. G. HARWOOD Proc. lnternepcon, Brighton U.K., October 1978, p. 97 Hermetic packages should be used for hybrid circuits where one or more components need to be protected from the ambient atmosphere to prevent unacceptable rates of degradation setting in. Devices which are most sensitive to this degradation are unpassivated semiconductors, surface acoustic wave filters and oscillators, and those passive components which need to be very stable to maintain close circuit tolerances. The component of the atmosphere which is chiefly responsible for device degradation is moisture particularly in the presence of alkalies and/or halides. Packages are tested for hermeticity in various ways but MIL STD 883 is widely regarded as a standard for military applications. This does not involve a test of the permeability to water or to any elements found in appreciable quantities in the atmosphere but of the permeability to helium. This gas was chosen because it is easy to detect with a mass spectrometer, is not known to affect the circuit components and has a permeability higher than most other gases. A lower leak rate can be detected with it than, for example, with moisture. One method in MIL STD 883 is to submit the sealed package to an overpressure of 4 atmospheres of helium for one hour, and after leaving it in air for a half hour to allow the helium attached to the outside to be removed to place the package in a mass spectrometer and test for helium coming out. If there is a substantial leak in the package helium will go in during the pressure test and will come out during the mass spectrometer test. The helium leak rate considered to be acceptable in the MIL STD is 5 × 10-r at ccs/sec. This is regarded by some, including ourselves, as too large to be acceptable; a more desirable leak rate of < 10-~0at ccs/sec is essential for good packaging. The moisture leak rate is not revealed by these measurements. Hybri d IC structures using solder reflow technology TSUNEAKI KAMEI, MASANORI MAKAMURA, HISASttl ARIYOSHI and MASANOBU DOKEN IEEE Trans. Components, Hybrids, Mfg TechnoL Chmt-2, (2) 208 (June 1979). A study of hybrid IC's produced by solder reflow technology was carried out to achieve optimum miniaturisation and substantial cost reduction. Thin-film resistor and capacitor network (R-C) chips and silicon integrated circuit (SIC) chips are mounted on a multilaycred thick-film conductor substrate and connected to the substrate by solder joining. The chips are first supported by solder bumps, and then they are self-aligned by the surface tension of the solder through the fellow process. This process results in a joint that compensates for the deviation and undulation of the substrates. Mechanical supports and electrical contacts of hybrid IC's are accomplished through a single reflow process. These hybrid 1C's have proven to be completely satisfactory and reliable. New generation of electronic components and how they influence printed circuit boards D. WEINERTH Circuit WIdS, (4) 29 (1979). The approach to reduce the cost of electronic circuits will be the transition of LSl-circuits to VLSl-circuits, introducing another order of magnitude to the complexity and density of these circuits. The 37