Print thickness

Fig. 6.2. Screen-printed (thick-film) sensors for decentralized metal testing. WE working reference RE reference electrode CE counter electrode.

Screen-printing allows the fast mass production of highly reproducible electrodes at low cost for disposable use. A variety of screen-printed thick-film devices can be produced and in Fig. 25.2 an example of carbon screen-printed electrode is shown. 

Process Binders Solvent Boiling range/ °C Viscosity Poise Ink thickness/ pm. Print thickness/ pm... 

The solvent is the vehicle to produce a homogenous mixture for the silk-screen printing. It is essential that the prepared ink or paste is homogenous in nature to obtain a uniform thick film. The printed thick films are not limited to metallic film insulation materials, carbon, and other nonmetallic films can also be silk-screened using appropriate inks and pastes. 

MenU, F., Debeda, H., and Lukat, C., Screen-printed thick films From materials to functional devices, J. Eur. Ceram. Soc. 25 (2005) 2105-2113. 

Device structures adopted for resistor type sensors in practice, (a) Sintered block, (b) thin alumina tube-coated layer, (c) screen printed thick film, (d) small bead inserted with coil and needle electrodes, (e) small bead inserted with a single coil (heater and electrode), (f) practical sensor element assembling sensor device, metal cap and filter. 

The versatility and cost-effectiveness of thick-film techniques is demonstrated in consumer applications, as well. Printed thick film (PTF) materials are used in circuitry in games, membrane touch switches, electroluminescent lighting and signage. Thick-film circuitry is used in personal digital products and specialty applications such as those shown in Figure 1.26 and Figure 1.27. 

Wet print thickness=(Emulsion buildup + Screen thickness) X Percentage open area. 

From Table 5.1, the open area of the screen is 41.3% of the overall area. The average wet-print thickness is ... 

There are two basic approaches to measuring print thickness off-contact and contact. Off-contact systems may be used to measure wet, dry, or fired films, whereas contact systems may only be used on dry or fired films. The simplest noncontact method is to focus a high-powered metallurgical microscope with a narrow depth of field on the substrate, mark a reference, and refocus the microscope on the top of the film. The print thickness is the distance the object lens must be moved. This method is somewhat inaccurate as the profile of the print is nonuniform, allowing the thickness to vary considerably across the print. 

The screen has a profound effect on both tiie print thickness and definition. Some characteristics of the screen include ... 

For prints that show uneven print thickness ... 

James, E.J., A practical approach to high resolution printing [thick films]. Proceedings of the SPIE — The International Society for Optical Engineering, Vol. 2649, 1995, p. 319. 

The viscosity of the pastes is typically within the range of 25-200 Pa-sec. The amount and type of organic medium used is determined mainly by the final desired formulation viscosity and print thickness. 

Instead of screen-printing thick-film resistors on DBC substrates, many manufacturers use resistor chips. 

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