Types and Preparation Methods of Conductive Paste
Overview: Conductive paste, also known as conductive adhesive, is a mixture of precious metal powders, base metal powders, glass powder, and synthetic resin.
Conductive paste, also known as conductive adhesive, is a mixture of precious metal powders, base metal powders, glass powder, and synthetic resin. Solvents can be added to remove materials or graphite. The particle size of metal powder is about 1-2 micrometers, with ultra-fine powder pastes of several nanometers being developed. Conductive paste is applied to the desired areas of a substrate using screen printing or other methods and then fired at 400-1000°C to form conductors. It is mainly used for wiring thick-film integrated circuits, electrodes of ceramic capacitors, and leads of hybrid integrated circuits.
Sintering Type Conductive Paste
Sintering type conductive paste is primarily used in industries like solar cells. After sintering, it is used as an electrode. Cured conductive ink is widely used in printed circuits and electronic packaging. Conductive paste can be classified based on the filler into carbon paste (graphite conductor), metal paste (gold powder, silver powder, copper powder, silver-copper alloy), and modified ceramic paste. Based on curing conditions, it can be divided into thermal curing and UV curing. Precious metal fillers have good conductivity, with carbon paste being the next best. However, gold is too expensive, copper powder has poor oxidation resistance, and silver powder and silver-copper powder have relatively balanced prices and performance. Carbon paste is more wear-resistant than silver paste.
Preparation of Conductive Paste
Conductive paste is prepared by uniformly adding conductive powder into an adhesive, which forms a conductor after curing. It is used for forming electronic circuits, electrodes of electronic components, lead extraction, and forming circuit contacts. Conductive paste can be roughly divided into:
- High-Temperature Sintering Type: Contains glass powder in the adhesive and typically sintered at 450°C-850°C.
- Low-Temperature Sintering Type: Uses synthetic resin adhesive and typically sintered at around 150°C.
- UV Curing Type: Cured by UV irradiation.
Materials Used in Conductive Paste
The sintering time ranges from a few minutes to an hour. Besides the main conductive powders such as silver powder and metal powders like nickel powder, copper powder, and silver-plated copper powder, carbon powder is also used. Synthetic resin adhesives are mainly acrylic, epoxy, and polyester.