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Thick Film

"Thick Film" describes a field of electronics in which specially formulated pastes (or inks) are applied and high-temperature fired onto various substrate materials in a pattern and sequence to produce individual electrical components or complete functional circuits.

These pastes are typically deposited using screen printing methods. The high-temperature firing sinters the printed thick film elements and bonds them to rigid ceramic or other types of substrates.

Overview

Mesh selection

Contact

Some types of circuitry commonly fabricated by screen printing thick film inks include: thick film circuits (automotive, military, aerospace, and medical applications), solar cells, chip resistors and capacitors, low & high temperature co-fired ceramics (LTCC & HTCC) and RFID circuits/antennas.

Introduction

Thick film electronics is appropriately named, because the final thickness of a thick film circuit element will be between 8 to 25 microns - sometimes more ("thin film" electronic elements are a different application process that results in thicknesses around 30 Angstroms).

Thick film technology surfaced in the early 1940's when there was significant interest in developing miniaturized electronic mortar fuses using silver conductive and carbon resistive inks. In the years that followed, the same thick film techniques were applied to consumer products, and eventually the circuits were combined with transistor devices to create what we today call "hybrid circuits"

Hybrid circuit

Significant advances in the thick film inks, substrates, screens and the screen printing process have since generated great improvement in circuit density and miniaturization, and evolved thick film technology into a sophisticated and cost effective, globally accepted means of fabricating highly reliable circuits with vast functionally.

Screen printing is an optimum method for creating thick film circuits that has several advantages over alternate technologies:

Mesh is an excellent transfer substrate for the very viscous/high solid (typically over 80%) thick film inks.

Screen printing can provide a wide range of wet ink deposit thicknesses.

Screen printing is cost efficient and generates very little waste materials.

Screen printing offers good production speeds in comparison to digital technologies (and with greater ink deposit options).

Screen Printing Process

Thick film materials are normally printed using an off-contact, flat bed "thick film screen printer" in a clean room environment. The printers are designed for the critical registration accuracy and precise, repeatable thickness requirements of thick film circuitry.

In high volume applications, the printers are often placed in-line with other equipment designed for sequential processing steps, such as drying and firing.

Thick film inks either conduct, resist or insulate electrical flow. They have a high solid content and are very viscous at rest. The solids are typically precious metals, glass, metallic oxides, and crystalline ceramics. They are formulated to bond to various substrate materials (alumina ceramic, glass, steel with porcelain, crystalline silicon, and unfired ceramic to name a few).

After printing, the ink layers must be processed (dried and fired). At that point additional ink layers are printed as needed (a final circuit design can have as many as 30+ accurately registered print layers).

Screen printing mesh with a high open area and small thread diameter, is preferred for the solid content, particle size, and viscosity of the specialized thick film inks.