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Properties of die bond alloys relating to thermal fatigue
tracking and small size make possible better performance at higher packaging densities. This article discusses the advantages and disadvantages of thin film chip networks. Aspects of hybrid design with chip networks and chip design are outlined. Several hybrid converters and an active flter are discussed to illustrate the thick film/thin film hybrid combination.
Application of tape automated bonding technology to hybrid microcircuits Dr R U D O L P H , G. OSWALD and W. R. de MIRANDA Solid State Technology, p.33 (March 1977). There is currently a major effort underway to adapt tape automated bonding (TAB) to hybrids. This effort involves pursuing tasks which seek to: (1) adapt available inner lead bonding (ILB) technology to hybrid circuits and, (2) develop a form of outer lead bonding (OLB) to single and multilayer ceramic substrates. Conventional hybrid fabrication steps of wire bonding and die attach may then be replaced by steps which involve gang bonding of tape-supported leads to the chip pads and subsequent simultaneous positioning and bonding of the chip and leads to a ceramic substrate. A significant advantage of this assembly procedure is that electrica[testing of chips is possible prior to mounting to the substrate. This results in minimised rework, corresponding high first pass yield, and lower hybrid cost. Process steps within the TAB technology include tape manufacture, bumping (raising) of the pads on the integrated circuit chip, inner lead bonding, chip testing, and outer lead bonding. Optional process steps now being considered are high and low temperature electrical testing and burn-in of the chips while on tape. Screening procedure for adhesion degradation due to solder leaching in thick-film hybrid microcircuits S. S. LEVEN Solid State Technology, p.39 (March 1977). The results of an experiment to determine practical screening and quality assurance procedures to preclude excessive adhesion degradation, due to solder leaching, in gold alloy/solder systems in thickfilm hybrid microcircuits are described. These results include a comparative rating among the materials tested, along with criteria for rating different materials. Four environmental stresses were compared to determine which one to use a quality assurance test for adhesion decay. The test method consisted of soldering copper pins to conductor pads on the substrate, and then pull-testing the pins to the destruction of the conductor/substrate bonds, both before and after environmental stresses. This method provides a measurement of both tensile adhesion between the soldered conductor and the substrate, and adhesion degradation promoted by the environmental stress. Seven thick-film conductor materials and three solder compositions were used, making a total of 21 conductor/solder systems tested. Pins were soldered to each of the seven conductor materials with each of the three solders. Adhesion measurements were made immediately, again after a minimum three-day shelf life, and also after each environmental stress. The median force-per-unit area values for each conductor/solder/environmental stress combination were tabulated and plotted. The results are presented tO show the relative degradations of the differerit materials. Based on the results of the experiment, the temperature cycling stress appears to be the most practical stress to use a. screening procedure for solder leaching. Guidelines are presented for performing the screening test and determining a rating for any material combination.
5.
Discrete Devices
Analytical technique for the design of DMOS transistors T. M A S U H A R A and R. S. MULLER Proceedings of the 8th Conference (1976 International) on Solid State Devices, Tokyo, 1976; Japanese Journal of Applied Physics, 16, Supplement 16-I, pp.173-178 (1977). A n analysis of doubt-diffused MOS (DMOS) transistor that features an accurate forecast of the current-voltage behaviour in various DMOS structures is presented. The specific DMOS transistors analysed include both p-n and p-p- type asymmetrical devices and p-n-p and p-p--p type symmetrical devices. The analysis is based on one-dimensional approximate theory and is carried out by a computer using numerical calculation of the charge and the potential along the channel. The program is efficient and c:alculations are accomplished rapidly. The results of the analysis correlate well with measurements
on n-channelp-n type andp-p--p type DMOS transistors. The analysis allows comparisons to be made between the various DMOS structures and is demonstrated as an effective tool for optimising device structure, channel lengths and doping profiles in DMOS transistors.
A mathematical study of space-charge layer capacitance for an abrupt p-n semiconductor junction D. P. KENNEDY SolidState Electronics, 20, p.311 (1977). Simple approximation equations are presented for the space-charge layer capacitance of an abrupt p-n semiconductor junction. By direct comparison with exact capacitance calculations, this approximation method is shown to yield a maximum error of about 3.5% throughout the wide range of impurity atom density and reverse biasing voltage. In addition, calculations are presented to show the magnitude of error associated with several approximation equations presently available in the technical literature.
6.
Materials
Organics used in microelectronics: a review of outgassing materials and efforts R. K. T R A E G E R Proc. Electron. Components Conf., Arlington, Va., p.408 (May 1977). Versatility, ease of application, and low cost make organic materials attractive for adhesive bonding, chip die down, and coatings for microelectronic systems. However, negative past experiences and lack of knowledge about the organic materials have raised many concerns; one concern being the effect of outgassing materials on devices and interconnections. This paper documents some of the concerns, briefly reviews the chemistry of organics commonly used with respect to possible detrimental materials, summarises the outgassing data obtained at Sandia and that reported in the literature, and makes recommendations for the selection and application of organic materials. The results show that outgassing need not be a concern if materials are chosen carefully and processed under conditions used for handling the other parts of microcircuits..Water and carbon dioxide, the major contaminants, absorbed in the organics from the environment during handling and storage. " " Properties of die bond alloys relating to thermal fatigue D. R. OLSEN and H. M. BERG Proc. Electron. Components Conf., Arlington, Va., p. 193 (May 1977). The differing performances of hard soldered and soft soldered power devices under thermal cycling stresses are well understood. Hard soldered dice are often under considerable stress and may even fracture in extreme cases, but 'the solder alloy itself does not degrade by fatigue after many temperature cycles. This fatigue free behaviour is due to the very high mechanical strength of the Au-eutectic hard solders over the normal range of po,,fei= cycling temperatures. Soft soldered die bonds exhibit an opposite behaviour, transmitting very little stress to the chip but exhibiting considerable degradation during temperature or power cycling by a process known as thermal fatigue. This behaviour is related to the much lower mechanical strengths and higher ductilities of the soft solders. In this study, the mechanical properties of the Au-eutectic alloys, Au-Sn, Au-Ge and Au-Si, and two common soft solders, Pb-5%Sn and Sn-3.5%Ag-l,5%Sb', have been measured between - 6 5 and 20(PC. In addition, several physical properties were measured as well as their fatigue perforrnance. An alloy was developed with mechanical properties intermediate to those of hard and soft solders, and its performance in power cycling approached that of the Au-eutectics. Models are presented which relate the fatigue behaviour of hard, soft and intermediate solders to their mechanical properties.
Electrically conductive epoxies for screen printing applications G. W. BRASSELL and D. R. FANCHER Proc. Electron. Components Conf., Arlington, Va., p.226 (May 1977). The use of conductive epoxies in the electronic industry is becoming more common as the number of new epoxy systems on the market increases. Private and government laboratories have evaluated many of the new adhesives on today's market, and as a result, a few articles in the areas of materials properties and reliability have been published. However, the number of articles published on manufacturing-related applications is relatively small. Thus, the primary purpose of this study 39
Application of tape automated bonding technology to hybrid microcircuits Dr R U D O L P H , G. OSWALD and W. R. de MIRANDA Solid State Technology, p.33 (March 1977). There is currently a major effort underway to adapt tape automated bonding (TAB) to hybrids. This effort involves pursuing tasks which seek to: (1) adapt available inner lead bonding (ILB) technology to hybrid circuits and, (2) develop a form of outer lead bonding (OLB) to single and multilayer ceramic substrates. Conventional hybrid fabrication steps of wire bonding and die attach may then be replaced by steps which involve gang bonding of tape-supported leads to the chip pads and subsequent simultaneous positioning and bonding of the chip and leads to a ceramic substrate. A significant advantage of this assembly procedure is that electrica[testing of chips is possible prior to mounting to the substrate. This results in minimised rework, corresponding high first pass yield, and lower hybrid cost. Process steps within the TAB technology include tape manufacture, bumping (raising) of the pads on the integrated circuit chip, inner lead bonding, chip testing, and outer lead bonding. Optional process steps now being considered are high and low temperature electrical testing and burn-in of the chips while on tape. Screening procedure for adhesion degradation due to solder leaching in thick-film hybrid microcircuits S. S. LEVEN Solid State Technology, p.39 (March 1977). The results of an experiment to determine practical screening and quality assurance procedures to preclude excessive adhesion degradation, due to solder leaching, in gold alloy/solder systems in thickfilm hybrid microcircuits are described. These results include a comparative rating among the materials tested, along with criteria for rating different materials. Four environmental stresses were compared to determine which one to use a quality assurance test for adhesion decay. The test method consisted of soldering copper pins to conductor pads on the substrate, and then pull-testing the pins to the destruction of the conductor/substrate bonds, both before and after environmental stresses. This method provides a measurement of both tensile adhesion between the soldered conductor and the substrate, and adhesion degradation promoted by the environmental stress. Seven thick-film conductor materials and three solder compositions were used, making a total of 21 conductor/solder systems tested. Pins were soldered to each of the seven conductor materials with each of the three solders. Adhesion measurements were made immediately, again after a minimum three-day shelf life, and also after each environmental stress. The median force-per-unit area values for each conductor/solder/environmental stress combination were tabulated and plotted. The results are presented tO show the relative degradations of the differerit materials. Based on the results of the experiment, the temperature cycling stress appears to be the most practical stress to use a. screening procedure for solder leaching. Guidelines are presented for performing the screening test and determining a rating for any material combination.
5.
Discrete Devices
Analytical technique for the design of DMOS transistors T. M A S U H A R A and R. S. MULLER Proceedings of the 8th Conference (1976 International) on Solid State Devices, Tokyo, 1976; Japanese Journal of Applied Physics, 16, Supplement 16-I, pp.173-178 (1977). A n analysis of doubt-diffused MOS (DMOS) transistor that features an accurate forecast of the current-voltage behaviour in various DMOS structures is presented. The specific DMOS transistors analysed include both p-n and p-p- type asymmetrical devices and p-n-p and p-p--p type symmetrical devices. The analysis is based on one-dimensional approximate theory and is carried out by a computer using numerical calculation of the charge and the potential along the channel. The program is efficient and c:alculations are accomplished rapidly. The results of the analysis correlate well with measurements
on n-channelp-n type andp-p--p type DMOS transistors. The analysis allows comparisons to be made between the various DMOS structures and is demonstrated as an effective tool for optimising device structure, channel lengths and doping profiles in DMOS transistors.
A mathematical study of space-charge layer capacitance for an abrupt p-n semiconductor junction D. P. KENNEDY SolidState Electronics, 20, p.311 (1977). Simple approximation equations are presented for the space-charge layer capacitance of an abrupt p-n semiconductor junction. By direct comparison with exact capacitance calculations, this approximation method is shown to yield a maximum error of about 3.5% throughout the wide range of impurity atom density and reverse biasing voltage. In addition, calculations are presented to show the magnitude of error associated with several approximation equations presently available in the technical literature.
6.
Materials
Organics used in microelectronics: a review of outgassing materials and efforts R. K. T R A E G E R Proc. Electron. Components Conf., Arlington, Va., p.408 (May 1977). Versatility, ease of application, and low cost make organic materials attractive for adhesive bonding, chip die down, and coatings for microelectronic systems. However, negative past experiences and lack of knowledge about the organic materials have raised many concerns; one concern being the effect of outgassing materials on devices and interconnections. This paper documents some of the concerns, briefly reviews the chemistry of organics commonly used with respect to possible detrimental materials, summarises the outgassing data obtained at Sandia and that reported in the literature, and makes recommendations for the selection and application of organic materials. The results show that outgassing need not be a concern if materials are chosen carefully and processed under conditions used for handling the other parts of microcircuits..Water and carbon dioxide, the major contaminants, absorbed in the organics from the environment during handling and storage. " " Properties of die bond alloys relating to thermal fatigue D. R. OLSEN and H. M. BERG Proc. Electron. Components Conf., Arlington, Va., p. 193 (May 1977). The differing performances of hard soldered and soft soldered power devices under thermal cycling stresses are well understood. Hard soldered dice are often under considerable stress and may even fracture in extreme cases, but 'the solder alloy itself does not degrade by fatigue after many temperature cycles. This fatigue free behaviour is due to the very high mechanical strength of the Au-eutectic hard solders over the normal range of po,,fei= cycling temperatures. Soft soldered die bonds exhibit an opposite behaviour, transmitting very little stress to the chip but exhibiting considerable degradation during temperature or power cycling by a process known as thermal fatigue. This behaviour is related to the much lower mechanical strengths and higher ductilities of the soft solders. In this study, the mechanical properties of the Au-eutectic alloys, Au-Sn, Au-Ge and Au-Si, and two common soft solders, Pb-5%Sn and Sn-3.5%Ag-l,5%Sb', have been measured between - 6 5 and 20(PC. In addition, several physical properties were measured as well as their fatigue perforrnance. An alloy was developed with mechanical properties intermediate to those of hard and soft solders, and its performance in power cycling approached that of the Au-eutectics. Models are presented which relate the fatigue behaviour of hard, soft and intermediate solders to their mechanical properties.
Electrically conductive epoxies for screen printing applications G. W. BRASSELL and D. R. FANCHER Proc. Electron. Components Conf., Arlington, Va., p.226 (May 1977). The use of conductive epoxies in the electronic industry is becoming more common as the number of new epoxy systems on the market increases. Private and government laboratories have evaluated many of the new adhesives on today's market, and as a result, a few articles in the areas of materials properties and reliability have been published. However, the number of articles published on manufacturing-related applications is relatively small. Thus, the primary purpose of this study 39