Advanced thick-film material
meets microwave, MCM circuit needs

The Cermalloy Div.of Heraeus (West Conshohocken, PA) has developed
a thick-film material consisting of a gold conductor and borosilicate-based
dielectric that overcomes the geometrical and electrical performance limitations
of conventional thick-film materials. Called KQ, the new thick-film material
offers performance equal to that of thin-film materials, but at significantly
lower cost.

Up to now, only thin-film materials have exhibited the low dielectric
losses and tight impe-dance control required for high- performance applications
involving microwave and RF circuits and multichip modules. Existing thick-film
materials are largely unable to achieve conductor gap and line widths of
finer than 100 µm. Moreover, these materials have high dielectric
constants of 8 to 10 and loss factors exceeding 1 x 10^–3 .

The KQ thick-film material instead offers low resistivity, high density,
a low dielectric constant, and a low loss factor. And it can be patterned
in the fine-line geometries required in microwave and MCM applications.

The material's thick-film gold conductor comprises 0.3 to 1-µm-thick
particles that have been printed and fired to a very smooth surface with
no agglomeration of particles. The smooth nature of the resulting conductor
allows the use of well-established photoresist and etch processes to give
superior line definition. Table 1 shows the properties of the etched
gold conductor.

The high-purity borosilicate glass used for the dielectric in the KQ
material allows a firing temperature in the 870°C range, while preserving
the electrical performance inherent in the glass material. To achieve the
fine-line geometries required in MCM and microwave applications, Heraeus
developed a photoimageable dielectric film that is patterned by conventional
screen-printing processes using a photomask and collimated light source.
This film allows 50- and even 25-µm vias to be easily fabricated.

Table 2 shows the performance characteristics of the photoimageable
dielectric.

For more information on the KQ material, contact Chuck Sabo of the Cermalloy
Div.of Heraeus at 610-825-6050, send e-mail to , or circle
473.