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Epoxy bonding in hybrid microelectronic circuits
World Abstracts on Microelectronics and Reliability be expensive and physically large for microelectronic realisation an alternative method has been developed at the AUWE. This method only requires small cheap, wide tolerance capacitors, but necessitates resistor adjustment of the filter sections as working circuits. A Laser must be used for thick film adjustment but spark erosion can be used if the filter sections are manufactured in this film. The design techniques are currently used for frequencies up to 100 KHz, (a) Cascaded 2nd order factors using the Lim circuit (b) Inductance simulation of ladder L-C filters using positive impedance converters (PIC). Thin film, or Precision thick film circuits, are ideally suited for producing active filters in hybrid form as this type of technology enables convenient adjustment of the resistors. By careful design of the film circuit it is possible for the discrete components (chip capacitors and operational amplifiers) to be arranged in such a way that the resistors which have to be actively adjusted are easily accessible.
The application of hybrid integration techniques to microwave transistor amplifier design. N. R. HOWARD. Proc. Internepcon. (Microelectron.) p. 89 (Oct. 1975). Silicon bipolar transistors can now be with fr's of around 5 GHz, providing useful gain and low noise in the 1-4 GHz range. This paper describes the application of these transistors in low power amplifiers in L and S bands using stripline hybrid integration techniques. Two types of amplifier are discussed; first, one based on conventional alumina substrates and using packaged transistors and discrete capacitors and resistors, and then a more integrated form using sapphire substrates, unencapsulated transistors and MOS capacitors, and deposited thin film resistors.
Microwave hybrid integrated circuit technology. ROBERT DAVIESand BARRIEH. NEWTON Proc. Internepcon. (Microelectron.) p. 66 (Oct. 1975). The microwave portion of the electromagnetic spectrum extends from 1 GHz to 300 GHz (30cm to 1 mm wavelength). However, this article considers the technology of microwave hybrid integrated circuits (M.I.C.) and since such techniques have influenced mainly the lower portion of this frequency range we shall be concerned only with frequencies between 1 GHz and about 40 GHz. The application of thick film techniques to microwave components in the range 10-20 GHz. D. C. RICKARD. Proc. Internepcon. (Microelectron.) p. 159 (Oct. 19-21, 1976). At microwave frequencies, thin film processing has been generally utilised to satisfy small quantity precision circuit requirements. The lower cost thick film technique has been restricted to relatively simple circuits, mainly below 10GHz. Recent refinement of thick film materials and technique has, however, led to significant improvements in obtainable definition and low loss, warranting application at the higher microwave frequencies. Results are presented for microstrip lines and typical circuits realised using high content conductor compositions and operating in the frequency range 10-20 GHz.
Volume production of hybrid circuits. JOHN B. KNOWLES. Proc. lnternepcon. (Microelectron.) p. 16 (Oct. 19-21, 1976). "Volume production" is defined as any quantity of circuits where the economics of production would be improved by automatic machine feed and mechanical handling of the substrates during the manufacturing process. Because the processing times of the various stages vary, it is not practical, or economic, to synchronise the performance of all the operations. Another factor is the continuous
121
belt furnace used for sintering metal films. For stability reasons, this must be maintained at a constant temperature throughout the 24 hours. Ideally, therefore, it should be kept fully loaded. For these reasons, our particular concept of volume production includes not only automatic feed of substrates to each machine and their transfer from machine to machine, but also the provision of reservoirs to store them temporarily between operations, wherever and whenever the machine loading situation makes this necessary. A review of thick film conductors. R. H. CALEY. Proc. Internepcon. (Microelectron.) p. 54 (Oct. 1975). Thick film conductors have reached a stage where numerous products are available from many manufacturers. The increase in the prices of precious metals between 1972 and 1974 has seen the emergence of new conductor systems without always proper emphasis being put on the relationship between these new materials and existing products. A survey has been conducted by ERA Limited to collate product performance data and to critically discuss the types of metallisation available. The survey provides a comprehensive assessment of the most important thick film conductor properties. The current presentation has selected information from this survey which describes 300 different products. A general commentary on the performance of various conductor types is described in the following sections.
The techniques and applications of high rate sputtering. G. N. JACKSON.Proc. Internepcon. (Microelectron.) p. 30 (Oct. 1975). The use of epoxies in hybrid microelectronic circuits is becoming more widespread. As more information about epoxies is disseminated, the apprehensions long felt by hybrid manufacturers about their use are vanishing. The major impetus of this sudden burst of activity was the development of epoxies with 100~o solid systems which contained no volatile solvents. Outgassing of the solvent during the curing cycle which resulted in voids in the epoxy bonds was the major reason why manufacturers were reluctant to specify epoxies. Such voids reduce the mechanical strength of the bond, and increases both the electrical and thermal resistance of the bond. The solvent vapors also attacked certain metallization systems at the elevated temperatures required for curing. Modern epoxies can be used with confidence that no significant outgassing will occur either during or subsequent to cure. It is important to realize that the epoxy bond is strictly a physical bond. When heat is applied, the mixture of epoxy and catalyst changes chemical structure and becomes solid. The bonding mechanism is a result of the epoxy filling crevices and scratches in the device and the mounting pad. The strongest mechanical bond occurs, therefore, between two rough surfaces. Epoxies are available in both conductive and non-conductive and in both one- and two-component forms. The scope of this paper is to discuss the advantages and disadvantages of each type and to discuss the reliability of epoxy bonds in general.
Epoxy bonding in hybrid microelectronic circuits. DR. JERRY E. SERGENT. Proc. Internepcon. (Microelectron.) p. 45 (Oct. 1975). Both d.c. and r.f. glow discharge sputtering has been around for quite some time and have found fairly wide acceptance in the electronics industry. However the slow rates of deposition that are obtained have restricted the range of uses to those areas where the high precision of the technique is necessary or the coatings cannot be obtained by any other means. Competitive technologies such as electron beam evaporation and electro-plating have been preferred by production engineers because higher deposition rates and throughputs were possible together with lowbr costs. Even so sputtering holds many
122
World Abstracts on Microelectronics and Reliability
attractions as a surface coating technique. These include extremely high adherence of the coating to the substrate, good controllability, good material utilisation, and an ability to cope with an almost limitless range of materials. The only significant limitation in many potential applications has been the deposition rate. Typically metals could be deposited at rates of up to about 1000/~ rain -a and dielectrics at rates of up to a few hundred A m i n - ~. Higb,er rates are possible in conventional systems by simply applying more power but the substrates tend to suffer. For example, the author was able to obtain a deposition rate of approaching 2000 A m i n - 1 for silica but the substrate temperature very quickly exceeded 80&C.
Manufacturing process for hybrid microcircuits containing vias. D. NORVV(~D. A. LAUDEL and P. BLESSNER. IEEE Trans. Parts, Hyhrids. Packayinq. PHP-12, (4) 323 (Dec. 1976). Hybrid microcircuits designed for use in radars require metallized vias to interconnect front-side tantalum-nitride chromium-gold thin-film networks with metallized backside ground planes on 95 x ll4-mm alumina substrates. Processes were developed for fabricating precision holes in alumina substrates, metallizing substrates on both sides and through the via, and dry-film lithographing 6-/tm-thick gold to linewidths and spacings of 127 #m. Front- and back-side resistance measurements through the via were used to determine the surface finish and metallization thickness on the via wall. Hole fabrication methods investigated included ultrasonic drilling in already-fired alumina and punching or drilling holes in green alumina before the firing. Photolithography techniques were developed which protect both sides of the substrate and the vias from etchants and delineate a thin-film network consistent with critical hybrid-microelectronic-circuit (HMC) linewidth tolerances for RF circuits. A metallization technique was developed, using a planetary system, to evaporate chromium-gold on the front and back side (while simultaneously depositing the metallization on the via wall). Front-side-to-back-side resistance measurements through the via showed that the manufacturing methods used were compatible with a stable low-resistance connection for RF circuitry in hybrid microcircuits. 9. E L E C T R O N ,
ION
AND
Wiggly phase shifters and directional couplers for radiofrequency hybrid microcircuit applications. J. L. TAYLOR and DAVID D. PRIGEL. IEEE Trans. Paris, ttybrids, Packaging. PHP-12, (4) 317 (Dec. 19761. A packaging technique which makes use of a wiggly (sawtooth) conductor-edge geometry between adjacent conductors has been developed for the fabrication of microwave hybrid microcircuit-directional couplers and phase shifters. The new technique provides approximately a 20-percent space saving as well as a significant improvement in circuit fabrication. A technology of thin-film hybrid microwave circuits. J. E. CURRAN, R. V. JEANES and H. SEWELL. IEEE Trans. Part,s, Hybrids, Packaging. PHP-12, (4) 304 (Dec. 1976). This paper describes the various thin-film processes that arc being used to produce microwave integrated circuits, both microstrip and lumped element systems. The technologies described involve a combination of vacumn evaporation or RF sputtering, photolithographic, electrochemical, and microbonding processes used in sequence to achieve integrated resistor, capacitor, and conductor networks. Stable thin-film integrated nickel-chromium resistors are achieved with good microwave behavior. The usual conduclor and interdigital capacitor systems are gold with either nickelchromium or titanium underlay. The microwave circuits are produced on a variety of substrates which include alumina, ferrite, quartz, and sapphire. Some of the ancillary amplifier networks are produced on glass. A successful scheme for the fabrication of integrated anodized aluminium capacitor structures, compatible with the nickelchromium/gold resistor conductor system, is outlined as well as preliminary results of such systems at GHz frequencies. Assembly techniques used for incorporating add-on components including chip capacitors overlay couplers, chip resistors and microwave semiconductor devices are included. Substrate preparation and the packaging of prototype assemblies are also included. Examples are shown of components and systems where the various technologies have been successfully applied. Data on the manufactured components are given~ showing that good reliable performance can be achieved. While the processes are typically operated in the environment of a workshop for circuit development, they are adaptable for large-scale manufacture.
LASER
Ion beam sputtering for thin film deposition and high-precision micromachining. H. J. GARVIN. Electron. Prod. p. 36 (Dec. 1976/Jan. 1977). High-current density ion sources, resulting from the development of electrostatic thrusters for deep-space missions requiring ion propulsion, provide an alternative to plasma sputtering as a production tool. An inert gas ion beam produced in an ion source can be accelerated through a high-vacuum chamber and with, or without, final focusing can be directed to impinge on a target surface. By means of contact masking, or by shadow masking, or by precise beam focusing and deflection, patterns can be ion beam micromachined into the surface of the target. The directed beam permits etching of patterns which are more sharply defined than can be accomplished by chemical etching processes and, because no material is impervious to sputtering attack, high resolution patterns can be produced in a broad variety of thin film materials. Electron-beam system makes masks for integrated circuits. JOWL STRATTE-MCCLURE. Electronics. p. 17E (January 6, 1977). Pattern generator combines with step-and-repeat camera to bridge gap between optical and fully electronic systems. Investigations on the damage caused by ion etching of SiO2 layers at low energy and high dose. HANS R. DEPPE,
BEAM
TECHNIQUES
BARBARA HASLER and JOACHIM HOPFNER. Solid-St. Electron. 20, (1) 51 (1977), The radiation damage caused by argon ion bombardment during ion etching of thermally grown SiO2 films at an energy below 1 keV and a dose of about 1018cm 2 has been studied by evaluating MOS C-V curves, FET characteristics, as well as Rutherford ion backscattering spectra. The bombarded samples revealed that ion beam etching in this energy range causes a damaged layer of 5 10nm thickness at the single crystal silicon surface. Moreover, traces of metal atoms are found in the damaged layer together with argon atoms (~ 1021 cm 3).
Implanted silicon layers as strain sensors. E. IGRAS and J. RVmNSKI. Electron. Technol. 9, (2) 109 (1976). The implantation of boron or phosphorus was carried out to fabricate low resistance surface layer on high resistance silicon plates. The resistance of these layers as a function of strains and temperature was measured. In the case of boron implanted silicon layers the strain gauge factor was equal to about 70. The use of high energy ion beams for surface and thin film analysis. J. M. POATE. Proc. IEEE Reliab. Phys. p. 297 (April 1976). The object of this brief review is to introduce the subject of surface and thin film analysis by the use of high energy ion beams. This field has grown consider-
The application of hybrid integration techniques to microwave transistor amplifier design. N. R. HOWARD. Proc. Internepcon. (Microelectron.) p. 89 (Oct. 1975). Silicon bipolar transistors can now be with fr's of around 5 GHz, providing useful gain and low noise in the 1-4 GHz range. This paper describes the application of these transistors in low power amplifiers in L and S bands using stripline hybrid integration techniques. Two types of amplifier are discussed; first, one based on conventional alumina substrates and using packaged transistors and discrete capacitors and resistors, and then a more integrated form using sapphire substrates, unencapsulated transistors and MOS capacitors, and deposited thin film resistors.
Microwave hybrid integrated circuit technology. ROBERT DAVIESand BARRIEH. NEWTON Proc. Internepcon. (Microelectron.) p. 66 (Oct. 1975). The microwave portion of the electromagnetic spectrum extends from 1 GHz to 300 GHz (30cm to 1 mm wavelength). However, this article considers the technology of microwave hybrid integrated circuits (M.I.C.) and since such techniques have influenced mainly the lower portion of this frequency range we shall be concerned only with frequencies between 1 GHz and about 40 GHz. The application of thick film techniques to microwave components in the range 10-20 GHz. D. C. RICKARD. Proc. Internepcon. (Microelectron.) p. 159 (Oct. 19-21, 1976). At microwave frequencies, thin film processing has been generally utilised to satisfy small quantity precision circuit requirements. The lower cost thick film technique has been restricted to relatively simple circuits, mainly below 10GHz. Recent refinement of thick film materials and technique has, however, led to significant improvements in obtainable definition and low loss, warranting application at the higher microwave frequencies. Results are presented for microstrip lines and typical circuits realised using high content conductor compositions and operating in the frequency range 10-20 GHz.
Volume production of hybrid circuits. JOHN B. KNOWLES. Proc. lnternepcon. (Microelectron.) p. 16 (Oct. 19-21, 1976). "Volume production" is defined as any quantity of circuits where the economics of production would be improved by automatic machine feed and mechanical handling of the substrates during the manufacturing process. Because the processing times of the various stages vary, it is not practical, or economic, to synchronise the performance of all the operations. Another factor is the continuous
121
belt furnace used for sintering metal films. For stability reasons, this must be maintained at a constant temperature throughout the 24 hours. Ideally, therefore, it should be kept fully loaded. For these reasons, our particular concept of volume production includes not only automatic feed of substrates to each machine and their transfer from machine to machine, but also the provision of reservoirs to store them temporarily between operations, wherever and whenever the machine loading situation makes this necessary. A review of thick film conductors. R. H. CALEY. Proc. Internepcon. (Microelectron.) p. 54 (Oct. 1975). Thick film conductors have reached a stage where numerous products are available from many manufacturers. The increase in the prices of precious metals between 1972 and 1974 has seen the emergence of new conductor systems without always proper emphasis being put on the relationship between these new materials and existing products. A survey has been conducted by ERA Limited to collate product performance data and to critically discuss the types of metallisation available. The survey provides a comprehensive assessment of the most important thick film conductor properties. The current presentation has selected information from this survey which describes 300 different products. A general commentary on the performance of various conductor types is described in the following sections.
The techniques and applications of high rate sputtering. G. N. JACKSON.Proc. Internepcon. (Microelectron.) p. 30 (Oct. 1975). The use of epoxies in hybrid microelectronic circuits is becoming more widespread. As more information about epoxies is disseminated, the apprehensions long felt by hybrid manufacturers about their use are vanishing. The major impetus of this sudden burst of activity was the development of epoxies with 100~o solid systems which contained no volatile solvents. Outgassing of the solvent during the curing cycle which resulted in voids in the epoxy bonds was the major reason why manufacturers were reluctant to specify epoxies. Such voids reduce the mechanical strength of the bond, and increases both the electrical and thermal resistance of the bond. The solvent vapors also attacked certain metallization systems at the elevated temperatures required for curing. Modern epoxies can be used with confidence that no significant outgassing will occur either during or subsequent to cure. It is important to realize that the epoxy bond is strictly a physical bond. When heat is applied, the mixture of epoxy and catalyst changes chemical structure and becomes solid. The bonding mechanism is a result of the epoxy filling crevices and scratches in the device and the mounting pad. The strongest mechanical bond occurs, therefore, between two rough surfaces. Epoxies are available in both conductive and non-conductive and in both one- and two-component forms. The scope of this paper is to discuss the advantages and disadvantages of each type and to discuss the reliability of epoxy bonds in general.
Epoxy bonding in hybrid microelectronic circuits. DR. JERRY E. SERGENT. Proc. Internepcon. (Microelectron.) p. 45 (Oct. 1975). Both d.c. and r.f. glow discharge sputtering has been around for quite some time and have found fairly wide acceptance in the electronics industry. However the slow rates of deposition that are obtained have restricted the range of uses to those areas where the high precision of the technique is necessary or the coatings cannot be obtained by any other means. Competitive technologies such as electron beam evaporation and electro-plating have been preferred by production engineers because higher deposition rates and throughputs were possible together with lowbr costs. Even so sputtering holds many
122
World Abstracts on Microelectronics and Reliability
attractions as a surface coating technique. These include extremely high adherence of the coating to the substrate, good controllability, good material utilisation, and an ability to cope with an almost limitless range of materials. The only significant limitation in many potential applications has been the deposition rate. Typically metals could be deposited at rates of up to about 1000/~ rain -a and dielectrics at rates of up to a few hundred A m i n - ~. Higb,er rates are possible in conventional systems by simply applying more power but the substrates tend to suffer. For example, the author was able to obtain a deposition rate of approaching 2000 A m i n - 1 for silica but the substrate temperature very quickly exceeded 80&C.
Manufacturing process for hybrid microcircuits containing vias. D. NORVV(~D. A. LAUDEL and P. BLESSNER. IEEE Trans. Parts, Hyhrids. Packayinq. PHP-12, (4) 323 (Dec. 1976). Hybrid microcircuits designed for use in radars require metallized vias to interconnect front-side tantalum-nitride chromium-gold thin-film networks with metallized backside ground planes on 95 x ll4-mm alumina substrates. Processes were developed for fabricating precision holes in alumina substrates, metallizing substrates on both sides and through the via, and dry-film lithographing 6-/tm-thick gold to linewidths and spacings of 127 #m. Front- and back-side resistance measurements through the via were used to determine the surface finish and metallization thickness on the via wall. Hole fabrication methods investigated included ultrasonic drilling in already-fired alumina and punching or drilling holes in green alumina before the firing. Photolithography techniques were developed which protect both sides of the substrate and the vias from etchants and delineate a thin-film network consistent with critical hybrid-microelectronic-circuit (HMC) linewidth tolerances for RF circuits. A metallization technique was developed, using a planetary system, to evaporate chromium-gold on the front and back side (while simultaneously depositing the metallization on the via wall). Front-side-to-back-side resistance measurements through the via showed that the manufacturing methods used were compatible with a stable low-resistance connection for RF circuitry in hybrid microcircuits. 9. E L E C T R O N ,
ION
AND
Wiggly phase shifters and directional couplers for radiofrequency hybrid microcircuit applications. J. L. TAYLOR and DAVID D. PRIGEL. IEEE Trans. Paris, ttybrids, Packaging. PHP-12, (4) 317 (Dec. 19761. A packaging technique which makes use of a wiggly (sawtooth) conductor-edge geometry between adjacent conductors has been developed for the fabrication of microwave hybrid microcircuit-directional couplers and phase shifters. The new technique provides approximately a 20-percent space saving as well as a significant improvement in circuit fabrication. A technology of thin-film hybrid microwave circuits. J. E. CURRAN, R. V. JEANES and H. SEWELL. IEEE Trans. Part,s, Hybrids, Packaging. PHP-12, (4) 304 (Dec. 1976). This paper describes the various thin-film processes that arc being used to produce microwave integrated circuits, both microstrip and lumped element systems. The technologies described involve a combination of vacumn evaporation or RF sputtering, photolithographic, electrochemical, and microbonding processes used in sequence to achieve integrated resistor, capacitor, and conductor networks. Stable thin-film integrated nickel-chromium resistors are achieved with good microwave behavior. The usual conduclor and interdigital capacitor systems are gold with either nickelchromium or titanium underlay. The microwave circuits are produced on a variety of substrates which include alumina, ferrite, quartz, and sapphire. Some of the ancillary amplifier networks are produced on glass. A successful scheme for the fabrication of integrated anodized aluminium capacitor structures, compatible with the nickelchromium/gold resistor conductor system, is outlined as well as preliminary results of such systems at GHz frequencies. Assembly techniques used for incorporating add-on components including chip capacitors overlay couplers, chip resistors and microwave semiconductor devices are included. Substrate preparation and the packaging of prototype assemblies are also included. Examples are shown of components and systems where the various technologies have been successfully applied. Data on the manufactured components are given~ showing that good reliable performance can be achieved. While the processes are typically operated in the environment of a workshop for circuit development, they are adaptable for large-scale manufacture.
LASER
Ion beam sputtering for thin film deposition and high-precision micromachining. H. J. GARVIN. Electron. Prod. p. 36 (Dec. 1976/Jan. 1977). High-current density ion sources, resulting from the development of electrostatic thrusters for deep-space missions requiring ion propulsion, provide an alternative to plasma sputtering as a production tool. An inert gas ion beam produced in an ion source can be accelerated through a high-vacuum chamber and with, or without, final focusing can be directed to impinge on a target surface. By means of contact masking, or by shadow masking, or by precise beam focusing and deflection, patterns can be ion beam micromachined into the surface of the target. The directed beam permits etching of patterns which are more sharply defined than can be accomplished by chemical etching processes and, because no material is impervious to sputtering attack, high resolution patterns can be produced in a broad variety of thin film materials. Electron-beam system makes masks for integrated circuits. JOWL STRATTE-MCCLURE. Electronics. p. 17E (January 6, 1977). Pattern generator combines with step-and-repeat camera to bridge gap between optical and fully electronic systems. Investigations on the damage caused by ion etching of SiO2 layers at low energy and high dose. HANS R. DEPPE,
BEAM
TECHNIQUES
BARBARA HASLER and JOACHIM HOPFNER. Solid-St. Electron. 20, (1) 51 (1977), The radiation damage caused by argon ion bombardment during ion etching of thermally grown SiO2 films at an energy below 1 keV and a dose of about 1018cm 2 has been studied by evaluating MOS C-V curves, FET characteristics, as well as Rutherford ion backscattering spectra. The bombarded samples revealed that ion beam etching in this energy range causes a damaged layer of 5 10nm thickness at the single crystal silicon surface. Moreover, traces of metal atoms are found in the damaged layer together with argon atoms (~ 1021 cm 3).
Implanted silicon layers as strain sensors. E. IGRAS and J. RVmNSKI. Electron. Technol. 9, (2) 109 (1976). The implantation of boron or phosphorus was carried out to fabricate low resistance surface layer on high resistance silicon plates. The resistance of these layers as a function of strains and temperature was measured. In the case of boron implanted silicon layers the strain gauge factor was equal to about 70. The use of high energy ion beams for surface and thin film analysis. J. M. POATE. Proc. IEEE Reliab. Phys. p. 297 (April 1976). The object of this brief review is to introduce the subject of surface and thin film analysis by the use of high energy ion beams. This field has grown consider-