- Email: [email protected]
Hybrid circuit technology keeps rolling along
382
World Abstracts on Microelectronics and Reliability
well as the methods which are still in a state of infancy have been included. Requirements for the ideal adhesion test are outlined and, apparently, there does not exist any test which fulfils all the virtues. Many of the techniques may not provide absolute quantitative values of adhesion strength but these can profitably by used to follow changes in adhesion strength due to process variables, ageing weathering, etc. The principle, merits, potentialities and limitations of each technique are outlined, and the difficulties associated with measuring adhesion strengths and their relationship to "basic adhesion" are discussed.
High reliability Ta/AI thin-film hybrid circuits. R. G. DUCKWORTH. Microelectron. and Reliab. 15, 141 (1976). This paper outlines a manufacturing sequence for reliable thinfilm hybrid circuit production, from bare substrate to final encapsulation. The reasons why particular processes are used are given, and the choice of all materials of construction discussed. Chemical processing of the thin film has been eliminated during the manufacture of the basic resistor networks, to minimise the risk of contamination whilst the film is in a reactive state. This has been done by employing an efficient R.F. sputter etching process to form the resistive film pattern, and an "incontact" masking method for the contact film deposition. For good long term performance, "as fired" high alumina ceramic substrates are preferred to glass. The R.F. sputter etching with argon ions allows accurate patterns to be easily produced, on the relatively rough ceramic surface, from films which have been previously thermally stabilised in air. The circuits are designed for use in gas turbine engine control equipment, where difficult environmental conditions exist. Of equal importance to long term stability of component value, is the ability of the assembly to withstand high levels of shock and vibration. R.F. sputter cleaning of contact areas, together with the use of controlled hot gas reflow soldering, and a specially designed package, has allowed these conditions to be met. Fluid abrasive trimming of thin-film resistors. THOMAS J. FAITH and JOHN W. JENNINGS. IEEE Trans. Parts, Hybrids and Packaging. PHP-12 (2), 133 (1976). Thin-film nickelchromium resistors have been trimmed using the fluid jet from an air brush. Micrometerized distilled water droplets impinge on the resistor surface at high velocity, eroding away resistor material, thereby increasing resistance. The need for top hats is eliminated. Substrate damage and the hot spots which result from trim-line cuts are avoided. Trimming up to 230 per cent has been achieved on narrow (0.0012-in.) resistors. Test results at power densities up to 6000 W/in 2 indicate that power density ratings as high as 2400 W/in 2 are feasible.
R.F. relaxation oscillations in polyerystalline TiO 2 thin films. G. TAYLOR and B. LALEVIC. Solid-State Electron. 19, 669 (1976). Negative resistance oscillations were studied in polycrystalline TiO 2 thin films in the T-TiO2-Cr device structure. Stable oscillations were readily produced in the 1 3 MHz frequency range and showed lifetimes of more than 8 x 1011 cycles. A simple equivalent circuit model for current controlled negative resistance (CCNR) devices was used to interpret the bias voltage and temperature dependence of amplitude and frequency of negative resistance oscillations. Bias voltage dependence was found not to involve changes in the device parameters. Temperature variations produced changes in the device threshold and minimum (holding) voltages and the "on" and "off" state resistances. The "on" state and "'off" state resistances showed thermal activation energies of 0.006 and 0.052 eV respectively. I V characteristics for these devices are shown to be in agreement with the theory of filamentary double injection space charge limited currents.
Hybrid circuit technology keeps rolling along. JERRY LYMAN. Electronics p. 91. (July 1976). Riding high on a surge of technological innovation, improved hybrids are triumphing in new fields as a cost-effective circuit-assembly technique.
Thick-film hybrid techniques offer new hope for the blind. DAVID HETHERINGTON. Electronic Engng. p. 27 (August 1976). Hybrid thick-film circuits of the type developed for avionic applications are now finding important uses in the medical field. Two independent groups of workers are well advanced in developing aids which will enable blind people to see. The author describes these developments and some associated work that is likely to benefit an even wider audience.
Techniques of adjusting thin- and thick-film resistors in hybrid microelectronic circuits. AWATER SINGH. Microelectron. and Reliab. 15, 123 (1976). The film resistors are formed on a substrate by both thin-film vacuum deposition and thick-film paste screening. The tolerance to which a resistor is manufactured depends on such factors as fabrication method, material and operator skill. Thin-film resistors can be deposited [1] through precision masks to a tolerance of ±570 and photoetched [2] to a tolerance of +10°~. Thick film resistors can be screened to an as-fired tolerance of ±20"/o. It is, therefore, an accepted fact in hybrid circuit industry that to achieve film resistors with tolerances of better than _+1 21!~,(and down to 0.590) the resistors must, in some manner, be trimmed. There are several methods which have been developed for such resistor trimming, each with its own advantages and disadvantages. In this paper we will describe a number of these methods and indicate their advantages and shortcomings.
Statistical interpretation of meniscograph solderability tests. JAMES L. JELLISON,D. R. JOHNSON and F. MICHEAL HOSKING. IEEE Trans. Parts, Hybrids and Packaging. PHP-12 (2), (June 1976). As part of a thick-film characterization study, a solderability test program was initiated utilizing the meniscograph. The meniscograph test measures the changes in wetting force as a function of time, and thus affords a description of the kinematics of the wetting phenomenon. Difficulty was encountered in the derivation of unique parameters which provide consistent statistical comparisons. As an alternative to selecting a time interval from the meniscograph trace as a measure of wetting rate or only qualitatively comparing traces, as some investigators have done, we have evaluated the approach of measuring the slope of the trace replotted so as to yield a straightline fit. A plot of the logarithm of a normalized wetting force vs time has generally afforded the best fit. To evaluate the analytical techniques, a large number of meniscograph tests were conducted employing copper nickel, and Kovar substrates using both tin-lead and lead indium solders; and rosin flux with varying activity. With the wetting rate estimated on the basis of the logarithmic line fit, the tests have consistently ranked solder systems with regard to substrate solderability and the activity of fluxes. Calculated equilibrium contact angles were found useful in interpreting the meniscograph traces.
Thin-film deposition techniques and design of thin-film passive components. AWATAR SINGH. Microelectron. and Reliab. 15, 233 (1976). Cathode sputtering and vacuum evaporation considered to he the important methods of thinfilm depositions are described and their advantages and short-comings pointed out. The state of the art in the design of thin-film passive components such as resistors, capacitors, inductors, interconnection and cross-over is also described.
World Abstracts on Microelectronics and Reliability
well as the methods which are still in a state of infancy have been included. Requirements for the ideal adhesion test are outlined and, apparently, there does not exist any test which fulfils all the virtues. Many of the techniques may not provide absolute quantitative values of adhesion strength but these can profitably by used to follow changes in adhesion strength due to process variables, ageing weathering, etc. The principle, merits, potentialities and limitations of each technique are outlined, and the difficulties associated with measuring adhesion strengths and their relationship to "basic adhesion" are discussed.
High reliability Ta/AI thin-film hybrid circuits. R. G. DUCKWORTH. Microelectron. and Reliab. 15, 141 (1976). This paper outlines a manufacturing sequence for reliable thinfilm hybrid circuit production, from bare substrate to final encapsulation. The reasons why particular processes are used are given, and the choice of all materials of construction discussed. Chemical processing of the thin film has been eliminated during the manufacture of the basic resistor networks, to minimise the risk of contamination whilst the film is in a reactive state. This has been done by employing an efficient R.F. sputter etching process to form the resistive film pattern, and an "incontact" masking method for the contact film deposition. For good long term performance, "as fired" high alumina ceramic substrates are preferred to glass. The R.F. sputter etching with argon ions allows accurate patterns to be easily produced, on the relatively rough ceramic surface, from films which have been previously thermally stabilised in air. The circuits are designed for use in gas turbine engine control equipment, where difficult environmental conditions exist. Of equal importance to long term stability of component value, is the ability of the assembly to withstand high levels of shock and vibration. R.F. sputter cleaning of contact areas, together with the use of controlled hot gas reflow soldering, and a specially designed package, has allowed these conditions to be met. Fluid abrasive trimming of thin-film resistors. THOMAS J. FAITH and JOHN W. JENNINGS. IEEE Trans. Parts, Hybrids and Packaging. PHP-12 (2), 133 (1976). Thin-film nickelchromium resistors have been trimmed using the fluid jet from an air brush. Micrometerized distilled water droplets impinge on the resistor surface at high velocity, eroding away resistor material, thereby increasing resistance. The need for top hats is eliminated. Substrate damage and the hot spots which result from trim-line cuts are avoided. Trimming up to 230 per cent has been achieved on narrow (0.0012-in.) resistors. Test results at power densities up to 6000 W/in 2 indicate that power density ratings as high as 2400 W/in 2 are feasible.
R.F. relaxation oscillations in polyerystalline TiO 2 thin films. G. TAYLOR and B. LALEVIC. Solid-State Electron. 19, 669 (1976). Negative resistance oscillations were studied in polycrystalline TiO 2 thin films in the T-TiO2-Cr device structure. Stable oscillations were readily produced in the 1 3 MHz frequency range and showed lifetimes of more than 8 x 1011 cycles. A simple equivalent circuit model for current controlled negative resistance (CCNR) devices was used to interpret the bias voltage and temperature dependence of amplitude and frequency of negative resistance oscillations. Bias voltage dependence was found not to involve changes in the device parameters. Temperature variations produced changes in the device threshold and minimum (holding) voltages and the "on" and "off" state resistances. The "on" state and "'off" state resistances showed thermal activation energies of 0.006 and 0.052 eV respectively. I V characteristics for these devices are shown to be in agreement with the theory of filamentary double injection space charge limited currents.
Hybrid circuit technology keeps rolling along. JERRY LYMAN. Electronics p. 91. (July 1976). Riding high on a surge of technological innovation, improved hybrids are triumphing in new fields as a cost-effective circuit-assembly technique.
Thick-film hybrid techniques offer new hope for the blind. DAVID HETHERINGTON. Electronic Engng. p. 27 (August 1976). Hybrid thick-film circuits of the type developed for avionic applications are now finding important uses in the medical field. Two independent groups of workers are well advanced in developing aids which will enable blind people to see. The author describes these developments and some associated work that is likely to benefit an even wider audience.
Techniques of adjusting thin- and thick-film resistors in hybrid microelectronic circuits. AWATER SINGH. Microelectron. and Reliab. 15, 123 (1976). The film resistors are formed on a substrate by both thin-film vacuum deposition and thick-film paste screening. The tolerance to which a resistor is manufactured depends on such factors as fabrication method, material and operator skill. Thin-film resistors can be deposited [1] through precision masks to a tolerance of ±570 and photoetched [2] to a tolerance of +10°~. Thick film resistors can be screened to an as-fired tolerance of ±20"/o. It is, therefore, an accepted fact in hybrid circuit industry that to achieve film resistors with tolerances of better than _+1 21!~,(and down to 0.590) the resistors must, in some manner, be trimmed. There are several methods which have been developed for such resistor trimming, each with its own advantages and disadvantages. In this paper we will describe a number of these methods and indicate their advantages and shortcomings.
Statistical interpretation of meniscograph solderability tests. JAMES L. JELLISON,D. R. JOHNSON and F. MICHEAL HOSKING. IEEE Trans. Parts, Hybrids and Packaging. PHP-12 (2), (June 1976). As part of a thick-film characterization study, a solderability test program was initiated utilizing the meniscograph. The meniscograph test measures the changes in wetting force as a function of time, and thus affords a description of the kinematics of the wetting phenomenon. Difficulty was encountered in the derivation of unique parameters which provide consistent statistical comparisons. As an alternative to selecting a time interval from the meniscograph trace as a measure of wetting rate or only qualitatively comparing traces, as some investigators have done, we have evaluated the approach of measuring the slope of the trace replotted so as to yield a straightline fit. A plot of the logarithm of a normalized wetting force vs time has generally afforded the best fit. To evaluate the analytical techniques, a large number of meniscograph tests were conducted employing copper nickel, and Kovar substrates using both tin-lead and lead indium solders; and rosin flux with varying activity. With the wetting rate estimated on the basis of the logarithmic line fit, the tests have consistently ranked solder systems with regard to substrate solderability and the activity of fluxes. Calculated equilibrium contact angles were found useful in interpreting the meniscograph traces.
Thin-film deposition techniques and design of thin-film passive components. AWATAR SINGH. Microelectron. and Reliab. 15, 233 (1976). Cathode sputtering and vacuum evaporation considered to he the important methods of thinfilm depositions are described and their advantages and short-comings pointed out. The state of the art in the design of thin-film passive components such as resistors, capacitors, inductors, interconnection and cross-over is also described.