The Synthesis Of Low Temperature Silver Paste And The Study Of Its Sintering Properties

Conductive paste is widely used in e lectronic connecting and packaging.Together with the de mand of heat dissipation and high performance for power chip,high integrity circuit and the promotion of lead-free technology,deve loping lower sintering temperature conductive paste with lead-free materia l is a profound research direction.We have developed two parts in this project.In the first part we have synthesized 24 kinds of glass frits,measured its glass formation range and thermal properties,analyzed its network structure changement caused by variation of component.The result shows that,with the increase of Bi₂O₃,the Tg and FWHM are both decrease,that is because the increase of Bi₂O₃ would cause the network of [Bi O₃] and [Bi O6] increase,which bonding energy is weaker than [BO₃] and [BO₄],those fina lly caused glass frits with low Tg and easy to crystallize.However the increase of [BO₃] and [BO₄] would cause glass frits with the properties of high Tg and high thermal stability,the increase of B₂O₃ also widen the infrared absorption in the wave number of vibration.Fina lly we have selected a kind of glass frits with the glass transition temperature is 360 ?,and therma l stability is 187 ? which c omposition is 30Bi₂O₃-55B₂O₃-15 ZnO,using as conductive paste adhesive.this kind of glass frits can be sintered in a lumina ceramic at 430 ? with a very good wetting behavior.The second part is the deve lopment of low sintering temperature paste with high conductivity and adhesion.Compared with the 1 ?m and 10 ?m silver powder as conductive phase in paste,the result shows that paste with 1 ?m silver powder would have lower resistivity,though the existence of glass frits in paste affect its resistivity,it has great contributes on adhesion enha ncement.The thick film only with 7 wt% glass frits and sintered at 550 ? could get 3.2 ??·cm in resistivity and 24.55 MPa in adhesion.In the sintering process,parts of glass frits dispersed in silver film,another parts of glass frits served as adhesion for silver film and ceramic,the SEM dia gram of ceramic surface sheared by tensile test machine shows many bow-like glass frits in the surface of ceramic may increase the contact area for thick film,and increase the shear strength.Additiona lly,the dispersed precipitation of ZnAl₂O₄ and Bi₄B₂O₉ in glass frits at 600 ? would also enhance the strength of glass,which have another contribute to the thick film adhesion for a lumina ceramic.