Abstract: The chip carrier industry and the mounting of chip carriers with solder paste are growing rapidly. Recent papers have covered the advantages of increased board density and design flexibility. This paper addresses how percent metal, paste viscosity, paste constituents, pad dimensions and spacing, print thickness, chip carrier weight, and reflow profile correlate with the incidence of undesired pad bridging and solder balls. This information can be used in circuit design and process optimisation.

Abstract: A finite difference method is presented to calculate the potential distribution in a trimmed resistor. The numerical results are used to study the influence of trimming on the power density distribution and the noise performance.

Abstract: A historical review of the development of metal‐cored substrates is given, together with a detailed account of glass‐ceramic coated metal substrates as currently manufactured by Wade plc. The advantages over monolithic ceramics are discussed, and an indication is given as to future developments in this technology.

Abstract: In this study a multilayer hybrid circuit for high frequency digital systems using Cu conductors was fabricated. The available Cu pastes were evaluated in terms of their applicability and a complex multilayer interconnection circuit was realised and optimised using both the DuPont and Heraeus Cu thick film systems. Also, AI‐1% Si wedge bonding on Cu thick film was investigated. The pull strengths were measured before and after ageing (high temperature storage). Results indicate that Al wire bonding on Cu is technologically feasible and gives no reliability problems.

Abstract: The increase in semiconductor integration level has led to complex Integrated Circuits (ICs) characterised by an increasing number of I/O, such that dies with 40 to 84 metallised pads are currently manufactured and frequently used in modern electronic systems. The advent from 1980 onwards of these LSI‐VLSI semiconductors requires new economical micropackages to be devised that can be adapted to surface mounting techniques on Hybrid Integrated Circuits (HICs) and Printed Circuits Boards (PCBs). Plastic encapsulation using a transfer moulded epoxy resin is a widely used method for packaging silicon devices because of the reduced manufacturing cost for large volumes. This economic criterion, which is considered with widespread interest in the electronics industry, has recently led the major semiconductor manufacturers to produce Plastic Leaded Chip Carriers (PLCCs) with up to 84 J bend connections on 1·27 mm pitch, and Mini Quad Packs with 40 to 84 Z bend pins on 0·75∼0·80mm centres. However, until now, a si...

Abstract: Laser welding of Kovar (54% Fe, 16% Co, 29% Ni, <1% Mn, Cr) has been evaluated in order to develop a reliable welding method for hermetic encapsulation of hybrid packages. In particular, the design of the welding joint and the impact of Au/Ni plating on the joint quality have been examined. It has been found that for the specific combination of case and lid used, the sealings are hermetic (leak rate <2 × 10−9 mbar l/s) if the following requirements are fulfilled: the contact area of the case against the lid is ground; the case and the lid are unplated or Ni electroplated (2–5 µm); when using a Nd‐YAG laser the pulse time is relatively long (furthermore the pulse power shall be low in order to avoid splatter of molten metal into the case); the welding is performed in a pure N2 gas flushed covered chamber; the joint is formed in such a manner that the molten metal ‘runs over’ the edge of the case. In addition, it was found that Au plating increases the probability of gross point leaks. When there is an increasing percentage of Au in the joint, the number and size of the leaks also tend to increase. Finally, material analysis including SEM and EDX is reported together with details of weld schedules, equipment and a comparison with the reviewed literature.

Abstract: Demanding technical requirements of thin film electroluminescent display modules and hard competition in electronic display markets set boundaries for the setting of goals in the development of an extremely thin display module. To meet the targets the problems of electronic packaging concepts had to be considered from the point of view of total optimisation. As a result, a packaging concept was developed which had an influence on all design decisions starting from the end user's requirements and extending to the selection of a special semiconductor manufacturing process. A set of customised high voltage integrated driving circuits was developed. High density interconnection problems were solved by the tape automated bonding of semiconductors and a single‐sided two‐layer polymer thick film circuit board. Throughout the assembly process surface‐mounted components and reflow soldering methods were applied to form a large area printed polymer hybrid module. Viable volume production methods for a flat dot‐matrix display could be suggested.

Abstract: Platinum gold conductors, used as solderable terminations, contain a glass frit which reacts with the minority constituents in debased alumina substrates forming an adhesive bond. Some conductor inks also contain copper and cadmium, in addition to the glass frit, which react directly with the alumina to form a chemical bond. Dielectric inks contain a crystalline filler, such as alumina or zirconia, in a glass matrix. The effect on the physical and electrical properties of platinum golds on various dielectrics was examined in comparison with the behaviour on alumina. Composition and surface structure of the dielectric affects the adhesion strength, solderability and solder leach resistance of the conductor inks. Interaction between the glasses in the dielectrics and conductors was determined by analysis in the SEM. Interdiffusion between the conductor and solder metals occurs and brittle intermetallic compounds are formed. The effects of the intermetallic formation on the adhesion strength and modes of failure, especially after thermal ageing at 150°C, have been examined. Thick film resistors printed and fired onto dielectrics rather than onto alumina substrates generally have different electrical properties. Chosen resistor systems, terminated with a gold conductor, were evaluated on different dielectrics. The values of electrical parameters such as resistance, TCR and noise index were compared with those on alumina. Interactions between the glasses in the resistors and dielectrics were examined as for the conductors. Thermal ageing on various resistor/dielectric combinations was carried out in order to determine the long‐term stability. The activation energies and time dependences of the ageing mechanisms for each combination were found. Corresponding ageing equations were calculated in order to predict the likely behaviour during life.

Abstract: The separation of thick‐film resistor temperature characteristics into two components is presented. One of the components is a function of the resistive material, the other a function of the linear expansion coefficient mismatch between the substrate and the resistive layer. The analysis has been carried out by two methods: by taking the temperature characteristics of the resistive material in the form of pearls, and by generating compressive stress in the resistive layer corresponding to the stress created by the temperature rise.

Abstract: Plasma chemistry is employed almost exclusively for etching, cleaning and deposition processes in semiconductor device fabrication technology. As a natural expansion of this successful technique, attention has been directed at similar processes for thick film ceramic, thin film hybrid and more generally printed circuit board electronic assemblies. This paper discusses a variety of applications, some established and some experimental, where plasma is offering the benefits which semiconductor engineers have enjoyed for many years. Such applications include general organic removal, i.e., flux residues, finger print contamination and the removal/reduction of oxides and glass on thick film conductors to promote improvements in solderability and wire bondability.

Abstract: This study attempts to quantify the loss of accuracy that arises after packaging and during the life of the IC device. To identify a solution to the problem of mismatch in voltage dividers, the characterisation of the amount of stress associated with commercially available moulding compounds was performed by means of silicon integrated strain gauges. In addition, the influence of the voltage divider lay‐out was measured with a specifically designed test pattern. The possibility of producing circuits with an accuracy level better than 0·1% without trimming was demonstrated.

Abstract: The paper describes the physical phenomena which influence the electrical and mechanical characteristics of low temperature coefficient, high stability thin metal resistive films. Emphasis is placed on the Matthiensen and Arrhenius rules in respect of resistivity and time‐temperature stabilities. The phenomena outlined are highly dependent on the deposition methods used and film properties are discusssed in terms of the film formation kinetics, substrates, and deposition technologies. The production of thin metal film resistive films based on these principles readily achieves temperature coefficients of <5 ppm/°C over the temperature range −55°C to + 155°C with load stress stabilities of <300 ppm with full dissipation, 155°C, 2000 hours, which is as good as bulk nickel‐chromium alloy foil.

Abstract: Output rates with multicircuit printing techniques on different sizes of substrate are examined. Hand load/unload is then compared with the autofeed systems now becoming available for larger sizes. High yield is shown to be more important than high cycling rates, and increasingly so the larger the substrate. The factors important to achieving high yield are examined, and some of the improved techniques for substrate handling and registration are described.

Abstract: Increasing interest in surface mount technology has led to a growth in the use of adhesives for attachment of SMDs. This paper reviews the properties of an adhesive which make it suitable for use in attachment of SMDs. Visibility, rheology and cure speed are of primary importance but the need for one‐part stable materials is stressed. The existing adhesives offered are generally based on epoxy or acrylic technology. Though these products are effective in attachment they have many features which make them less than ideal, e.g., mixing of multi‐component systems, high cure temperature, etc. One‐part acrylic anaerobic adhesives offer the benefit of low cure temperatures with good strength and product stability. Curing data, adhesive properties and cured polymer properties are reported for a new acrylic anaerobic adhesive which has been specifically designed for attachment of SMDs to substrates.

Abstract: Present and future development of laser processing as a production technique for modifying semiconductor devices, improving yields, and decreasing development times are described. Current applications covered include thick‐ and thin‐film resistor trimming, deposited film and polysilicon resistors on silicon trimming and redundant memory repair. Emerging applications include microcircuit mask making and capacitor trimming. Examples of processes still under development include selective annealing, minority‐carrier lifetime doping, and device diagnostics by laser imaging.

Abstract: This paper is an introduction to a personal approach to Electronic Thermal Design and Temperature Prediction. The approach described is essentially one of reducing the problems to manageable proportions. The designer should then probe around the boundaries of the problem and establish a temperature envelope. The envelope can then be trimmed until its extent is within the required accuracy. An additional point that comes from the paper is that perfection is the enemy of good and that sufficient is all that is required.

Abstract: New resistor compositions prepared by using special kinds of glass, CdO, RuO2 and Nb2O5, have been developed. This system is typical in containing only a small amount of RuO2, ranging from 2 wt% to 8 wt%. The properties of resistors prepared from various compositions were tested in relation to peak firing temperature varying in the range from 720°C up to 800°C. In this way conditions were found for resistor preparation with low TCR and high long‐term stability at 95% relative humidity and at 40°C. By adding very small amounts (0·4–0·9%) of Nb2O5 the TCR was very drastically reduced and could achieve almost zero value. The resistance changes after 4,000 hours ranged from 0·1% to 0·8%. Further new types of dielectric compositions were prepared. The bulk insulation resistance of fired layers reached values in the range of 1012ohms/cm2; the dielectric constant (≈7) and dissipation factor (≈10−3) were also measured. This composition is well suited to applications in both oxidation and inert atmosphere.

Abstract: In general, sputtered ruthenium films attain platinum‐group properties that make them candidates for various uses in electrical, thermal and decorative areas. Advanced communications devices are one of these areas. Ruthenium could possibly be used as a diffusion barrier and adhesive layer, as a suicide former for low ohmic contacts, and as a final metallisation over platinum suicide for very large scale integration (VLSI) applications.

Abstract: This paper is aimed at Engineers involved in production wire‐bonding processes and system maintenance. It traces the development of microbonding from its origins to the present day. Principles and techniques are examined and some approaches to fault diagnosis are explored.