Microelectronics International

Manca, J.V.; De Schepper, L.; De Ceuninck, W.; D'Olieslager, M.; Stals, L.M.; Barker, M.F.; Pickering, C.R.; Craig, W.A.; Beyne, E.; Roggen, J.

1993 Microelectronics International

doi: 10.1108/eb044494

In this paper, it is shown that the socalled insitu electrical measurement technique is a valuable tool for understanding failure mechanisms in thick film dielectrics. The technique makes it possible to measure important electrical characteristics of thick film dielectric systems in the temperature range from room temperature up to 900C. This information is essential to understand failure mechanisms and to optimise the system with respect to quality and reliability. Mainly two electrical properties have been investigated i the electrical resistance of the dielectric as a function of temperature and ii the spontaneous electromotive force occurring at higher temperatures between two metal layers with the dielectric in between. A significant result of the work is the observation of a close correlation between the leakage current measured through the dielectric at elevated temperatures, and the ability of the dielectric to resist shorting and blistering effects during the preparation of circuits. Secondly, from insitu voltage measurements, it was confirmed that the mixed metallurgy system AubottomdielectricAgtop acts at 850C as a spontaneous battery, and the battery voltage i.e., the spontaneous electromotive force was measured. Depending on the type of dielectric, a battery voltage up to 200 mV between the two metal layers was observed. As a result of this spontaneous electromotive force, blistering occurs. The battery voltage was shown to be much smaller in unmixed metallurgy systems with AgbottomdielectricAgtop or AubottomdielectricAutop. However, if an external voltage of 300 mV is applied to such a system during a temperature profile up to 850C, blisters can also be induced. This shows unambiguously that blistering is a voltage driven effect.

Kos, A.

1993 Microelectronics International

doi: 10.1108/eb044495

This paper deals with the computation of thermal fields of power hybrid circuits using the finite difference method FDM. The FDM is one of the classical methods used for temperature calculation of microcircuits having any shape and any boundary conditions. The equation written in the matrix form, describing thermal equilibrium, is solved using Choleski's method. The need for sufficient computer memory capacity is one of the main problems when using a small personal computer. This work attempts to show how to reduce the necessary computer memory capacity as much as possible. A compromise between memory capacity and CPU time is achieved.

Baggerman, A.F.J.; Kessels, F.J.H.

1993 Microelectronics International

doi: 10.1108/eb044496

Tape automated bonding TAB is an interconnection technique for integrated circuits ICs with a small lead pitch and a thin assembly thickness. During inner lead bonding the flying Au plated Cu leads of the TAB foil are connected to the Au bumps on the bondpads of an IC. The Au bumps are deposited in the openings of a thick Novolac based resist layer by electroplating. The resist is coated on a sputtered TiWAu metallisation TiW is the barrier layer between Au bump and Al bondpad. Bonding of the leads to the Au bumps requires substantial plastic deformation of the bump and lead. As a result of this deformation, the TiW barrier layer underneath the bump may crack easily. A theoretical model has been used to describe the occurrence of these cracks. This theoretical model is compared with experimental results of deformation and cracking behaviour by visual inspection of the TiW barrier and the etched crosssections. Separate single point and simultaneous gang bonding techniques, different gold plating baths and TAB tapes are used to study the cracking behaviour.

Mather, J.C.; Minogue, G.R.

1993 Microelectronics International

doi: 10.1108/eb044497

The advent of novel advanced packaging technologies such as multilayer thinfilm interconnect, combined with continuous improvements in IC clock speed and circuit performance, has placed extreme demands on electronics packaging and package materials. Aluminium nitride AIN ceramic offers significant opportunities and advantages for package design, particularly where the effective thermal management and overall reliability of large devices are a high priority. AIN has already been successfully employed at the substrate level for the enhanced thermal relief of power devices. Examples of these applications include heat sinks and device mounts for thyristor modules, power transistors, solid state relays, power SCRs, switching modules, LEDs and various RF package configurations. Both bare and metallised AIN substrates are beginning to find application as a substitute for beryllia BeO in mass market and high reliability automotive electronics applications. Successfully implementing AIN in a high level electronics packaging application requires a systems approach in which the intrinsic properties of AIN are considered as first principles in shaping the package design process. The unique physicochemical and mechanical properties of AIN require the development of specialised metallisation and cofiring processes to fabricate the advanced components necessary for hermetic packaging of complex devices and multichip modules. This paper presents a practical and mass manufacturable AINbased package tailored to these high level applications. The package design is unique in that it provides for the total separation of the electricalsignal conduction from the mechanical supportmounting functions of the package. Such a separation of the functions improves both the package durability and reliability relative to currently available electronics packages of conventional designs.

Spalding, O.

1993 Microelectronics International

doi: 10.1108/eb044498

An important disadvantage of conducting adhesives is their inferior heat conductivity when compared with soft solder such as Sn60Pb40. Thermal simulations, however, show that, by using thinner layers of adhesive than of solder, the module's thermal resistance does not increase greatly. Test modules with four different silver filled epoxy adhesives and tinlead solder were manufactured. These test modules contained power diodes, 30 A, 1000 V, die bonded onto AgPt thick film conductors on alumina. The die bond adhesive layer thicknesses were typically 30 or 40 m. For die bond solder layers the thickness was 90 m. The alumina substrates were connected to 3 mm thick copper plates with filled epoxy or silicone adhesive. The thickness of these layers was 150 m or 50 m, respectively. Thermal resistance of the structures was measured. The results showed that good adhesion between joined surfaces is essential for optimised heat flow. The heat conductivity of an adhesive was only a secondary factor affecting the structure's thermal resistance. When the adhesive joint is of good quality, the replacement of solder with conductive adhesives does not increase the module's thermal resistance any more than as shown by the simulations. It should, however, be remembered that the printing of thin < 20 m uniform layers is not always possible.

Wiedemann, M.

1993 Microelectronics International

doi: 10.1108/eb044499

This paper will describe how methods developed in structural dynamics may be used to solve a problem of microsystem technologies. In microsystem simulation, determination of the physical properties is of considerable interest. The method of thermal wave measurement is often used today to describe the thermal behaviour of microstructures. The simulation of thermal wave effects based on thermal mode vectors and followed by a sensitivity analysis enables the correction of primarily estimated thermal parameters by fitting calculated results with measured information. Model description and sensitivity analysis offer an effective tool for determining thermal parameters by thermal wave measurement in a fast and clear manner. Thermal wave measurement, simulation and sensitivity analysis together may be used for device design as well as for testing.

Adell, J.A.; Molina, M.; Cavero, J.M.

1993 Microelectronics International

doi: 10.1108/eb044500

This paper describes the results of an analysis carried out on thermally conductive and electrically conductive adhesives, in order to characterise their behaviour for electronics and telecommunications applications.

Liu, F.T.

1993 Microelectronics International

doi: 10.1108/eb044501

Despite great developments in silicon technology over the past decade, hybrid microelectronics continue to survive for a number of reasons. One reason is the difficulty of achieving acceptable component tolerances for resistors and capacitors in silicon. Another reason is the ability to trim resistors in thick film, which makes it more attractive for use in analogue circuits. Furthermore, if the volume of production is not high enough to justify a high nonrecurring expense NRE, a hybrid circuit would be a feasible solution. The rediscovery of the advantages of multichip modules MCMs will further boost the growth of the hybrid microcircuits market in the '90s. MCMs offer the advantages of high reliability, performance high speed and miniaturisation size and weight. This paper briefly outlines the activities of certain government bodies and tertiary institutions in the field of microelectronics. Emphasis is given to the areas of activity where hybrid industry professionals may participate. Perceptions of trends in the '90s are explored in a way that should inspire and generate enthusiasm among microelectronics professionals.

ElshabiniRiad, A.; Moore, D.J.

1993 Microelectronics International

doi: 10.1108/eb044502

The Hybrid Microelectronics Laboratory in the Bradley Department of Electrical Engineering at Virginia Polytechnic Institute and State University VPI & SU, also named Virginia Tech, was established during the 19791980 academic year in order to provide classroomlaboratory instruction and research capabilities in the area of hybrid microelectronics. The laboratory was initially designed for the hybrid and thick film areas of microelectronics. Thin film design and fabrication capability was added in the Fall Semester, 1987. Currently, efforts are under way to develop the area of monolithic diffusion and processing of semiconductor wafers using both elemental and compound materials, initiated in the Fall Semester, 1991.

1993 Microelectronics International

doi: 10.1108/eb044503

The majority of visitors to the Kingdom of Fife probably arrive there by the 2.5 kilometres long Forth Road Bridge, the southern gateway to Fifeshire, which is geographically bound north and south by the Firths of Tay and Forth. Glenrothes, less than 30 minutes' drive from the Bridge on a modern dual carriageway, was planned as a New Town with the original aim of establishing a selfcontained and balanced community for working and living. The town's site has a long history radiocarbon dating revealing 3000 BC as the construction date of Balfarg Henge but since 1948 has been developed along Garden City principles featuring lowrise suburban layouts with a good interlinking road network and spacious parking areas. A recent visit to this region took Hybrid Circuits to the Southfield Industrial Estate, which sadly reflects the signs of the times with several deserted factory units a situation that has played into the hands of Coors Ceramics Electronics Ltd who in December 1992 announced a major expansion of their Glenrothes operation. The acquisition in October 1992 of adjacent property will enable the company to treble its existing manufacturing facility to occupy 30,000 ft2. This move will create significant new jobs in a phased programme that will see expansion of the core business and the introduction of a number of new ceramic and ceramicrelated products. With a presence in Scotland since 1981, the company was reorganised in July 1988 to form Coors Ceramics Electronics Ltd CCEL as a laser machining operation for the processing of thick and thin film ceramic substrates. It also acts as the sales and marketing facility for Europe for these products and for the US Electronic Products Group of the parent company. CCEL is a wholly owned subsidiary of Coors Ceramics Company of Colorado, USA, whose activities are divided over three units the company's headquarters in Golden, Colorado, a unit in Grand Junction, Colorado, and the Glenrothes facility.

Hemansk, Vojtch; Bilinski, M.; Binner, H.; Lee, Joon; Lowrie, Dave; Whiteside, M.

1993 Microelectronics International

doi: 10.1108/eb044504

The members of the chapter at the annual meeting held on 27 November 1992 in Brno decided not to split after the separation of Czechoslovakia. It was suggested to organise a larger chapter from the Central European States to provide greater cooperation and better functioning of the smaller chapters. A new name for the chapter was proposed Central European Chapter CEC to express neutrality and to point out that the chapter is open to other neighbouring chapters and to new members from the states where no national chapter yet exists.

1993 Microelectronics International

doi: 10.1108/eb044505

Rob Knowles has been appointed Technical Service Specialist by MetechRonal to support the company's rapidly expanding Thick Film Materials business throughout Europe.