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A review is given of the several heat transfer phenomena occurring in hybrid circuits. Most attention is devoted to the non‐linear properties. Some theoretical simulations and experimental results are discussed.

The reliability of thick film multilayer systems, based on palladium‐silver conductors, and obtained from several suppliers, is evaluated. A test structure is presented and the impact of different parameters, such as humidity, temperature, voltage bias and presence of overglaze, on the data is discussed. A SEM analysis of the failed samples allows identification of the failure mechanisms as due to flaws (pinholes and inclusions) in the dielectric.

The evolution of today's high speed electronic systems has resulted in the need for modules which are able to provide all chip‐to‐chip interconnection with very fine top level and buried conductor traces, and a dielectric with a very dense via grid pattern. As standard thick film technology is capable of pitches only down to 250 µm, new photoimageable thick film pastes have been developed in order to achieve a higher resolution. These materials allow one to combine the advantages of screen printing as a deposition technique with photolithography for the patterning. The image is produced by exposing the printed paste through a photomask to define either lines or vias, so that a very high resolution (50 (µm pitch), similar to that available in MCM‐D or MCM‐L, can be achieved. This paper describes the processing of the photoimageable dielectric and conductor pastes. As an example of the capability of this technology, a module for electro‐optical interconnection is presented.

A new method of studying the accelerated ageing of interconnection materials is applied to a high‐stability thick film resistor system (the Du Pont HS‐80 system). The new method, referred to hereafter as the in‐situ method, allows measurement of the electrical resistance of a thick film resistor to a resolution of a few ppm during accelerated ageing. With the in‐situ technique, the electrical resistance measurements are performed at the elevated ageing temperature during the ageing treatment, whereas with the conventional ageing method the resistance measurements are carried out at room temperature, between subsequent annealing steps. The measuring resolution obtainable with the in‐situ method is orders of magnitude better than with the conventional method. The ageing kinetics can therefore be studied on a shorter time scale and in greater detail than with the conventional method. In this paper, the authors use the in‐situ method to study the accelerated ageing of the Du Pont HS‐80 thick film resistor system, encapsulated with a proper glaze. It will be shown that kinetics of the resistance drift observed in this system cannot be described by an Arrhenius‐type equation. The ageing data can only be interpreted in terms of a kinetic model incorporating a spectrum of activation energies for the ageing process. Such a model is given, and is shown to provide a good explanation of the observed ageing behaviour. The physical process that causes the observed ageing is most probably diffusion of silver from the contacting terminals into the amorphous matrix of the thick film resistor.

This paper describes a simple test configuration which allows an analytical solution for thermal analysis. Comparison with experimental measurements has been undertaken and complete agreement has been found.

An investigation to evaluate the suitability of anodised aluminium as a substrate material has shown that the relatively high coefficient of thermal expansion of the aluminium caused the brittle cermet resistors to craze giving rise to unstable resistance values whereas PTF resistors appeared to suffer no ill effects. The work was implemented in conjunction with selection of low temperature thick film conductor and resistor inks to achieve the optimum combination of anodised aluminium substrate and ink system. These inks were then printed and fired on anodised aluminium, aluminium nitride and alumina substrates, and the physical and electrical properties of the inks and substrates compared. A combination of modest success, employing polymer resistors and cermet conductors, produced viable circuits with resistors of reasonable stability. A low power hybrid device, with surface mounted components, was employed to further validate the substrate/ink combinations in ongoing tests.

ISHM (UK) presented a technical meeting on this topic on the 23rd October 1982 at the Cunard International Hotel, London. The meeting was attended by some 50 engineers, both those involved in the field of hybrids and potential users. It was generally felt that this was a useful meeting but more especially that it would have appealed to many potential users of hybrids, had the right people been able to be contacted.

In this contribution a linear thermal model for hybrid circuits is presented. Both the heat dissipated in screen printed resistors and in mounted components such as transistors and integrated circuits is taken into account.

In this paper the temperature distribution in hybrid circuits will be studied in two different ways. First of all the results of numerical simulations obtained with the programs PROMETHEE and HYBRITHERM will be shown. Secondly, experimental temperature plots obtained with infra‐red thermography will be compared with the theoretical results. The influence of the substrate material (epoxy, glass, Al2O3, AlN and BeO) on the temperature distribution will be demonstrated. Various ways of cooling will also be considered. It will be shown that using high quality substrates such as AlN or BeO is not always useful from a thermal point of view.

In this contribution a short review is given on thermal analysis of hybrid circuits using 2‐D, 3‐D and time‐dependent models. It will be shown which models are necessary to be included in a CAD system for hybrid circuit design.