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Method of characterizing gallium arsenide crystals
WORLD
ABSTRACTS
ON MICROELECTRONICS
various stages, the engineer is ready to implement a screening program that economically minimizes risks of failures.
*Literature survey of s o m e surface and subsurface processes affecting materials in thermionic diodes. L. K. TOWER. Nat. Aeronaut. Space Admin., Washington, U.S.A., March (1971), pp. 39, P-174485, NASATM-X-2187. Cites references and presents a summary of work done on the surface and subsurface chemical and physical processes affecting materials in the thermionic diode. T h e processes considered were the evaporation and condensation of substrate materials, the bulk diffusion of metallic substrate materials, reactions between insulators and metals and the surface selfdiffusion and reconstrnetion of clean surfaces, faceting and other surface reconstruction caused by contaminants or additives, solution and oxidation.
Method of characterizing g a l l i u m a r s e n l d e crystals. A. M. HUBER and G. CHAMPIER. R~3. Tech. Thomson-CSF 3, No. 2 (1971), p. 225. (In French.) A comparison between different methods of characterizing gallium arsenide crystals (metallographic microscopy, electron microscopy with photoemission, X-ray topography and ion micro-analysis) shows that it is possible to identify the flaws associated with the six shapes of the figures observed after chemical attack. The flaws detected in this preliminary study are microprecipitates, decorated or non-decorated dislocations and variations in the concentration of the dopant and impurities. The results obtained suggest that metallographic microscopy should permit satisfactory evaluation of a material. Study of the validity of electronic parts stress m o d e l s . J. M. GRANGE. IEEE Trans. Reliab. R-20, No. 3 (1971), p. 136. By using data on the failure rates of electronic components collected by a European bank, we try to form an idea on the validity of the various models (Bazovsky model, M I L HDBK-217A standard model, exponential model, RADC TR-67 models) that represent the variations of the failure rate with respect to the thermal and electrical stresses. Two different approaches have been programmed on a computer: (1) conventional, using the linear regression analysis; (2) more modern using the Fletcher-Powell method or methods derived from it (Fletcher-Reeves or Davidon). The results are given for four types of components. The models studied reflect, more or less accurately, what happens in real life. We define and give a value to a criterion, allowing the model to be chosen closest to reality. This paper, apart from its practical interest on the validity of currently accepted models and its theoretical interest on the use of methods for seeking extremes, shows how the computer can assist the reliability engineer with the filing of data, the statistical processing of these data, etc., right up to the automatic tracing of the network of curves.
*Solder-circuitry separation problems associated with plated printed circuit boards. A. M. PASCIAK. Nat. Aeronaut. Space Admin., Washington D.C., U.S.A.,
AND
RELIABILITY
113
May (1971), pp. 48. P-176139 NASA-TM-X-2290. This report covers a detailed investigation of the problem of solder-circuitry separation associated with plated printed circuit boards. Gold and copper platings were studied and various circuitry conditions were evaluated, including tinned laminated copper, plated copper with brightener additives over laminate copper and gold overplate. The laboratory test programme included a technical survey, failure analyses, metallographic examinations, chemical analyses and thermal conditioning. Factors pertinent to the separation mechanism were isolated and ageing/strength studies were performed.
Performance and reliability aspects of current trends i n t , t . l . R . H . MURPHY. New Electronics, 20 April (1971), p. 30. Just as the production of commercially viable m.s.i, demanded a revolution in attention to details of yield-improvement, so the reliability specifications of equipments with circuit or sub-system densities as high as previously-employed discrete component densities demanded a revolution in inspection, test and screening procedures. Failure rates of less than 0-001 per cent per 1000 hr (approximately one failure every 40 yr for a 300-circuit system) have been predicted and verified in commercial applications; at the component level this represents at least two orders of magnitude improvement on failure rates of the most pedantic aerospace programmes for discrete component reliability assurance (e.g. early Minuteman).
N e w aspects of failure m e c h a n i s m in g e r m a n i u m t u n n e l d i o d e s . A. G. Rmm~sz, J. REYNOLDS and J. LIrCDMhY~R. Solid St. Electron. 14 (1971), p. 1137. Commercially available germanium tunnel diodes, fabricated with ball alloying technique and planar technology, respectively, have been investigated. It was found that ball alloyed diodes degrade gradually during heat treatment between 50 and 230°C but planar diodes do not. Planar diodes showed greater tendency toward degradation under forward bias than ball alloy diodes, especially those with higher speed index (1p/C1). In both cases the primary effect of degradation is an increase of the valley current, and the temperature independent component of the excess current is mainly responsible for degradation. This indicates that the defect states giving rise to the increased excess current are located near one of the band edges. It is proposed that in ball alloy diodes these defects originate from slight plastic deformation (creep) as due to the inherent stress at the junction. Variations in this built-in stress can qualitatively explain the effects of heat treatment. Due to their construction, the internal mechanical stress is greatly reduced in planar diodes, hence this type of degradation is not prevalent. However, injectionrecombination current during forward biasing beyond the valley voltage may increase the density of defects in planar diodes. Neither ball alloy nor planar diodes degrade under reverse bias or at the valley voltage, showing that tunneling current does not create defects. Based on these results, a new selection procedure is suggested for improving the reliability of ball alloy diodes.
ABSTRACTS
ON MICROELECTRONICS
various stages, the engineer is ready to implement a screening program that economically minimizes risks of failures.
*Literature survey of s o m e surface and subsurface processes affecting materials in thermionic diodes. L. K. TOWER. Nat. Aeronaut. Space Admin., Washington, U.S.A., March (1971), pp. 39, P-174485, NASATM-X-2187. Cites references and presents a summary of work done on the surface and subsurface chemical and physical processes affecting materials in the thermionic diode. T h e processes considered were the evaporation and condensation of substrate materials, the bulk diffusion of metallic substrate materials, reactions between insulators and metals and the surface selfdiffusion and reconstrnetion of clean surfaces, faceting and other surface reconstruction caused by contaminants or additives, solution and oxidation.
Method of characterizing g a l l i u m a r s e n l d e crystals. A. M. HUBER and G. CHAMPIER. R~3. Tech. Thomson-CSF 3, No. 2 (1971), p. 225. (In French.) A comparison between different methods of characterizing gallium arsenide crystals (metallographic microscopy, electron microscopy with photoemission, X-ray topography and ion micro-analysis) shows that it is possible to identify the flaws associated with the six shapes of the figures observed after chemical attack. The flaws detected in this preliminary study are microprecipitates, decorated or non-decorated dislocations and variations in the concentration of the dopant and impurities. The results obtained suggest that metallographic microscopy should permit satisfactory evaluation of a material. Study of the validity of electronic parts stress m o d e l s . J. M. GRANGE. IEEE Trans. Reliab. R-20, No. 3 (1971), p. 136. By using data on the failure rates of electronic components collected by a European bank, we try to form an idea on the validity of the various models (Bazovsky model, M I L HDBK-217A standard model, exponential model, RADC TR-67 models) that represent the variations of the failure rate with respect to the thermal and electrical stresses. Two different approaches have been programmed on a computer: (1) conventional, using the linear regression analysis; (2) more modern using the Fletcher-Powell method or methods derived from it (Fletcher-Reeves or Davidon). The results are given for four types of components. The models studied reflect, more or less accurately, what happens in real life. We define and give a value to a criterion, allowing the model to be chosen closest to reality. This paper, apart from its practical interest on the validity of currently accepted models and its theoretical interest on the use of methods for seeking extremes, shows how the computer can assist the reliability engineer with the filing of data, the statistical processing of these data, etc., right up to the automatic tracing of the network of curves.
*Solder-circuitry separation problems associated with plated printed circuit boards. A. M. PASCIAK. Nat. Aeronaut. Space Admin., Washington D.C., U.S.A.,
AND
RELIABILITY
113
May (1971), pp. 48. P-176139 NASA-TM-X-2290. This report covers a detailed investigation of the problem of solder-circuitry separation associated with plated printed circuit boards. Gold and copper platings were studied and various circuitry conditions were evaluated, including tinned laminated copper, plated copper with brightener additives over laminate copper and gold overplate. The laboratory test programme included a technical survey, failure analyses, metallographic examinations, chemical analyses and thermal conditioning. Factors pertinent to the separation mechanism were isolated and ageing/strength studies were performed.
Performance and reliability aspects of current trends i n t , t . l . R . H . MURPHY. New Electronics, 20 April (1971), p. 30. Just as the production of commercially viable m.s.i, demanded a revolution in attention to details of yield-improvement, so the reliability specifications of equipments with circuit or sub-system densities as high as previously-employed discrete component densities demanded a revolution in inspection, test and screening procedures. Failure rates of less than 0-001 per cent per 1000 hr (approximately one failure every 40 yr for a 300-circuit system) have been predicted and verified in commercial applications; at the component level this represents at least two orders of magnitude improvement on failure rates of the most pedantic aerospace programmes for discrete component reliability assurance (e.g. early Minuteman).
N e w aspects of failure m e c h a n i s m in g e r m a n i u m t u n n e l d i o d e s . A. G. Rmm~sz, J. REYNOLDS and J. LIrCDMhY~R. Solid St. Electron. 14 (1971), p. 1137. Commercially available germanium tunnel diodes, fabricated with ball alloying technique and planar technology, respectively, have been investigated. It was found that ball alloyed diodes degrade gradually during heat treatment between 50 and 230°C but planar diodes do not. Planar diodes showed greater tendency toward degradation under forward bias than ball alloy diodes, especially those with higher speed index (1p/C1). In both cases the primary effect of degradation is an increase of the valley current, and the temperature independent component of the excess current is mainly responsible for degradation. This indicates that the defect states giving rise to the increased excess current are located near one of the band edges. It is proposed that in ball alloy diodes these defects originate from slight plastic deformation (creep) as due to the inherent stress at the junction. Variations in this built-in stress can qualitatively explain the effects of heat treatment. Due to their construction, the internal mechanical stress is greatly reduced in planar diodes, hence this type of degradation is not prevalent. However, injectionrecombination current during forward biasing beyond the valley voltage may increase the density of defects in planar diodes. Neither ball alloy nor planar diodes degrade under reverse bias or at the valley voltage, showing that tunneling current does not create defects. Based on these results, a new selection procedure is suggested for improving the reliability of ball alloy diodes.