Low cost and high safety composite metal conductive paste replaces silver coated copper conductive paste

Compared with other metal fillers, copper powder, as a base metal, has a wide range of sources, low price, similar conductivity to silver, and excellent migration resistance. However, copper has more reactive chemical properties and is easily oxidized in air or high temperature environments to form difficult to conduct copper oxide or cuprous oxide, leading to an increase in electrical resistivity. Therefore, current research on copper electronic pastes mainly focuses on solving oxidation problems.

There are currently four common methods for copper surface modification: one is to coat the copper surface with organic compounds; The second is to perform acid washing treatment on copper; Thirdly, a layer of inert metal is coated on the surface of copper powder; The fourth is organic phosphating. Silver coated copper conductive paste is considered a low-cost and high safety composite materialMetal conductive pasteAlternative solutions have broad application prospects in the fields of flexible printed electronics and photovoltaics.

Ag is a metal material with excellent conductivity, and its price is lower than other precious metals such as Au, Pd, Pt, etc. It has been widely used in production. However, when Ag conductors are used as conductive strips, capacitor electrodes, and termination materials for resistors in thick film hybrid circuits, they can cause electrical migration of Ag, leading to component failure. Electromigration refers to an electrochemical process in which metal ions are deposited from the anode to the cathode under the action of a direct current electric field in a humid and hot environment. Therefore, the functional phase of thick film conductor paste generally does not require pure Ag conductors. Adding cadmium oxide and other substances to silver can to some extent inhibit the migration of silver ions.

Ag Pd conductor pasteIt is currently the most widely used conductor paste in thick film circuits. The Ag Pd conductor slurry prepared by adding a certain amount of Pd to Ag can effectively suppress the migration of silver ions. Ag Pd conductor paste has good compatibility with commonly used resistor paste. When the Pd content in the conductor is high, it can be fired simultaneously with Pd Ag resistors. When the Pd content is low, it can be fired simultaneously with ruthenium based resistors. The resistance of Ag Pd conductor in Ag Pd conductor slurry decreases with increasing silver content, but excessive silver content not only causes Ag migration, but also reduces the solderability. Excessive Pd content can also deteriorate the wettability of the solder. The Pd content in Ag Pd conductors is usually 15-25wt%, with a typical value of 20wt%. Bi2O3 can be added to the Ag Pd conductor to improve its wetting properties on solder and enhance the adhesion strength between the conductor film and the substrate.

The Ag Pt conductor developed to reduce the cost of Ag Pd conductor is made by adding 1-3 wt% Pt to Ag instead of Pd. The Ag Pt conductor has excellent resistance to solder corrosion, but there is a problem of silver ion migration. If Ag Pd Pt conductor is made, it can effectively prevent the migration of silver ions. Ag Pt conductors can also be made into unglazed conductors by adding a certain amount of CuO, CdO, etc. without using glass bonding phase.