Electrical property enhancement of electrically conductive adhesives through Ag-coated-Cu surface treatment by terephthalaldehyde and iodine

Abstract

One of the largest obstacles for Ag based electrically conductive adhesives (ECAs), as an alternative for Pb-containing solders in electronic packaging, is that the conductivity of ECAs is lower than that of solders due to the limited physical contact area between/among conductive fillers and the insulated organic lubricant and metal oxide layers on the surface of the conductive fillers. What's more, the high cost of Ag fillers is also restricting the wide use of Ag based ECAs. In this study, Ag-coated-Cu flakes were chosen as a substitute for Ag flakes to reduce the cost. At the same time, the coating of Cu with an Ag layer could protect the Cu-based fillers from oxidation and corrosion. A mixture of weak reducing agents and substituting agents was selected to treat the Ag-coated-Cu flakes to increase the conductivity of the Ag-coated-Cu based ECAs. During the treatment process, the weak reducing agents can reduce the metal oxides on the filler surfaces, enabling more metallic contacts. Meanwhile, the substituting agents can partially remove or replace the long chain fatty acid lubricants on the metal flakes, improving the electron tunneling between/among neighboring flakes. As such, the multiple effects of the reducing agents and substituting agents can improve the conductivity of the ECAs. By using an appropriate amount of terephthalaldehyde and iodine treated Ag-coated-Cu flakes, the resistivity was reduced to as low as 1.28 Â 10 À4 O cm for the ECA with 75 wt% content of treated fillers, which is comparable to that of commercially available Ag-filled ECAs (Â10 À4 O cm). This work suggests that a surface chemical method can enhance the electrical conductivity of metal filler based ECAs.

A Green and Facile Microvia Filling Method via Printing and Sintering of Cu-Ag Core-Shell Nano-Microparticles

“…These results confirm the promising coating quality of the as-synthesized Cu@Ag NPs. Before this study, extensive efforts have been made to prepare Cu@Ag NPs [ 30 , 31 , 32 , 33 ]. However, due to the large potential difference in the Cu-Ag replacement reaction (Δ E = +0.4621 V [ 34 ]), it is difficult to obtain a densely coated silver layer under normal conditions.…”

Electrically conductive epoxy‐based nanocomposite adhesives loaded with silver‐coated copper and silver‐coated reduced graphene oxide nanoparticles

“…For solving these problems, researchers use a mixture of weak reducing and substituting agents. Reducing agents like Terephthalaldehyde (TPTA) can reduce metal oxides (Ag 2 O) on the fillers to Ag particles and its oxidation products, formylbenzoic acid ,or terephthalic acid can remove long chain lubricant on the metal filler . Another way to remove Ag 2 O and surfactant chains on the silver‐coated copper particles is the use of KI and KBr.…”

Synthesis of polypyrrole nanoparticles and their applications in electrically conductive adhesives for improving conductivity

“…Therefore, reductants such as sodium borohydride (NaBH 4 ), Iodine (I 2 ) or terephthalaldehyde have been used to remove Ag 2 O from the surface of Ag akes. 18,19 Besides the surface treatments, the second approach is to add nanomaterials-based conducting materials into ECAs to ll the gap between conductive llers and increase conductive paths. This approach of using nanomaterials as the dopants into ECAs could drastically enhance the electrical conductivity of ECAs.…”