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Firing of thick films tutorial

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1. Thick Film Materials and the Firing Process

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 View of a thick-film integrated circuit

 

 

 

A simple thick film passive integrated substrate (or network) is usually fabricated by the following process sequence:

 

At first a conductive layer pattern, usually using Ag-Pd paste, is screen printed, dried and fired. The reason why conductive layers are prepared first is that they are thinner than resistive and dielectric ones, so the steps at the overlapping areas are smaller.

 

Then, usually step by step a few resistive and one or two dielectric/insulator layers are screen printed and dried only.

 

The resistive layers are made of pastes with various sheet resistances according to the requested resistance of the resistors. Their top view shapes are rectangles, near to square form, with an aspect ratio of 0.5 - 5. Top hat resistor shape can also be used, but this shape always requires laser trimming.

 

The dielectric layers are made in two screen printing and drying steps to the same area, in order to avoid leakage current through film faults, using the same paste of 200 or 500 K (dielectric constant). For the insulator layers low K glass paste is used. Please note, that the layers of resistors, capacitor dielectrics and crossover insulators should overlap to the underlying conductive pattern, but there is no overlapping between each other. In this way after all resistive and dielectric layers are screen printed and dried separately, they can be fired in the same step. 

 

Finally the second conductive layer from the same Ag-Pd paste is screen printed, dried and fired, and the network is ready.

 

All these steps are usually followed by laser trimming (adjusting) the resistors, screen printing and firing glass protective or solder resist layer, presoldering the contact pads, lead mounting, encapsulation, testing, and marking. 

1. Thick Film Materials and the Firing Process

pages: previous | 1 2 3 [4]

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