Substrates

The Materials employed tor insulating substrates of thin-film circuits are commonly glasses, ceramics and glass ceramics. Glazed alumina is most popular. Substrates are usually rectangular or square in shape. The thickness of substrates is 0.6, 1.0 and 1.6 mm.

The substrate of an 10 must have a high mechanical strength, low electrical conductivity, and good thermal conductivity. The substrate surface must be mirror-like. The degree of surface finish determines the thickness of deposited films. The process of fabrication of substrates includes several stages: blank cutting, lapping, polishing, cleaning, washing, etching, drying, and last, ion bombardment using a glow descharge. She treatment gives the desired surface finish and thus ensures a good adhesion of films to the substrate. Minute crystal defects cause appreciable changes in the properties of thin-film elements.

XI. Прочитайте текст Д и задайте 10 вопросов по содержанию текста.

Conductors and Contact Pads

Conducting films serve as interconnections, inductors, and capacitor plates.

The conductivity of a metal film depends on the film thickness. A film conducts well at a thickness of 0.1 The materials for metallized current-carrying stripes interconnecting circuit elements and contact pads must fill the following requirements.

1.High adhesion to a substrate. Contact pads are subject to thermal shocks during soldering or welding and
support the leads of active elements.

2. High conductance. The circuit designer usually specifies a lower level of connection pattern conducance
that ensures the adequate performance of the circuit.

3. Chemical stability. The factors affecting the quality of films are corrosion, structural changes leading to
disturbances in film layers are in contact with resistive elements, capacitor plates, and dielectrics. It is, thus,
essential to avoid chemical interaction of all circuit components both during the manufacture of a film microcircuit
and in the operating conditions.

4. Good solderability to enable adequate circuit assembly. Contact pads serve to connect the circuit to input,
output, and power supply lines and also to interconnect active elements through film stripes and jumpers.

5. The parameters of contact pads are a contact resistance, current-voltage characteristic, and noise
voltage induced by contacts.

6. The materials for thin-film conductors are commonly gold and aluminum vaporized in a vacuum.