A computer-aided topological hybrid layout-design procedure is proposed, that yields the wanted principal routing
in the form of a geometrical planarization graph. A so-called grid-embedding of a circuit graph into the Euklidean
plane enables us to observe all except one of the various technological constraints. The real problem is reduced to
finding a proper arrangement of &#8220;nets&#8221; and &#8220;flocks&#8221; in the plane in order to meet the omitted cross-capacity
constraint. The solution is accomplished by a constructive and implicit enumeration procedure, which is used within
an interactive man-machine design process.

Walter  Ulbrich

Rudolf  Van Der Leeden

A New Approach to the Topological Design of Hybrid Circuits

During the past decade, the thick film process has become a viable technology for the production of numerous
varieties of electronic circuits. Improvements in the quality of the substrates, the thick film inks, and the
manufacturing equipment have all been significant. In addition, the quality of the stencil screens has also been
improved to aid the process. New types of mesh material, improved emulsion systems and better control of the
screen parameters have all been realized. These refinements in the screen making materials and processes have all
contributed to the feasibility for printing complex resistor and conductor networks, hybrid circuits, multilayer
arrays, and sophisticated watch and display patterns.This paper will present the critical parameters of the screen mesh materials and compare the characteristics of
the screen mesh materials and compare the characteristics of the nylon, polyester, stainless steel and metalized
polyester fabrics. A new fine-wire 325 mesh stainless steel will be discussed and the significant impact on the
technology of fine-line printing will be illustrated. In addition, recent developments in screen emulsions will be
offered and pictures of fine-line patterns will be shown.

Stewart G. Stalnecker, Jr.

Stencil Screens for Fine-Line Printing

D. S. Campbell

Editorial

The problems of heat conduction in hybrid thin and thick film circuits have been investigated using both
analytical and numerical approaches.The calculations were restricted to two dimensions by assuming zero temperature gradient across the thickness
of the substrate (slightly more than half millimeter).All normally recognized parameters were taken into consideration, such as film temperature, power dissipated,
substrate area, etc.Allowances have also been made for lead conduction and connection technology, for horizontal or vertical
circuit assembly, and for flush or stand-off mounting on the mechanical support.The measured results for practical cases show close agreement with the theoretical calculations.This approach provides a simple tool for the calculation, at an early design stage of power handling capacities
of hybrid circuits using composite resistive configurations.Very little difference was found between temperatures predicted from the theoretical approach and those
measured in practical cases of circuits under load.The availability of such accurate design information means that the stability, life, and reliability of hybrid
circuits can be predicted with considerable accuracy at an early design stage.

G. P. Ferraris

M.  Tudanca

The Solution of Two-Dimensional Heat Conduction Problems for Predicting Operating Temperature and
Power Handling Capabilities of Hybrid Circuits

The quality and reliability of hybrid circuits is examined, with particular reference to the BS9000/CECC systems.
It is shown that the capability approval approach developed within the BS9000/CECC systems is appropriate to
hybrid circuits where only small quantities of each circuit are produced and the steps involved in obtaining
capability approval are discussed.

R. F. Read

Quality and Reliability in Hybrid Circuits
  

In order to minimize drift in a thick film resistor both printing and trimming parameters have to be optimized
carefully.With the aid of a linear theoretical model it is shown how the resistance drift in the bulk transition zone
and terminals of the resistor can be calculated for both trimmed and untrimmed resistors.The theoretical results are used for optimization of laser trimmed high ohmic resistors. The experimental
results are in good agreement with the theoretical predictions and confirm that thick film resistors can be
optimized for low drift.

Gunnar  Bj&#246;rklund

Lars  Linde

Optimization of Thick Film Resistors for Low Drift

This paper presents a screen printing process for the metallization of silicon solar cells. The physics and construction
of a classical solar cell are reviewed. The results obtained with a screen printing process are comparable with other,
more expensive technologies. This technology does not introduce an additional contact resistance on silicon. The
process optimization and the influence of different parameters are discussed.

L. Frisson

Ph. Lauwers

R. Mertens

R. Van Overstraeten

R. Govaerts

Screen Printed Metallization of Silicon Solar Cells

Porcelain enameled steels have had a long history of industrial, structural and related applications. Recent interest
in such materials has centered on electrical uses as a substrate for hybrid circuits, additive printed wiring, and
packaging. A study of some of the critical properties of available enameled steels was undertaken.Five types of enameled steel substrates from three manufacturers were tested. The electrical properties studied
included dielectric constant, dissipation factor, voltage breakdown, surface and bulk insulation resistance. The
effect of humidity on the insulation resistance of the enamel coatings themselves was compared. The influence of
the thermal conductivity of the substrates was also examined.The properties of a thick film resistor system was determined on the various enamel steel substrates. The
properties tested included resistivity and TCR firing sensitivity.The effect of the type of substrate on the properties of a selection of thick film conductors was determined.
Conductivity and gold and aluminum wire bond strength were compared on the various substrates.The dielectric properties of a multilayer/crossover dielectric thick film material were compared among 96&#37;
alumina, soda-lime glass and the various enameled steel substrates.Many individual differences between the enameled steel substrates were found. However, all of the substrates
could be utilized to produce satisfactory thick film circuits when the proper choice of thick film materials was made.Continuing changes, improvements and additional sources of supply are expected to overcome some of the
present shortcomings. These should enhance the use of such substrates for large area uses and lower cost applications.

S. J. Stein

C.  Huang

A. S. Gelb

Comparison of Enameled Steel Substrate Properties for Thick Film Use

The process of ball/wedge bonding and its advantages are described. A capacitor discharge technique for the
formation of balls on 25 and 75 <mml:math id="E1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>μ</mml:mi></mml:math>m diameter aluminium wires is discussed. Ultrasonic welding trials were carried
out and the bonds subjected to pull tests with good results. Bonds of good strength were made between 25 <mml:math id="E2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>μ</mml:mi></mml:math>m diameter Al-1% Si wire and Al thin films, Pd-Au thick films and Au flashed Kovar.

C. J. Dawes

K. I. Johnson

M. H. Scott

Ultrasonic Ball/Wedge Bonding of Aluminium Wires

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Active and Passive Electronic Components provides a forum for the science and technology of all types of electronic components, and publishes experimental and theoretical papers on topics such as transistors, hybrid circuits and sensors.

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