Investigating the curing process of conductive adhesives

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Supervisor:
Dr. Krammer Olivér
Department of Electronics Technology

During the past years isotropic conductive adhesives (ICA) received a lot of attention as they were considered as alternatives of tin-lead and lead-free solders. They offer several advantages over conventional soldering technology such as environmental friendliness, lower curing temperature which allows the application of low temperature resistance components etc. However, there are some limitations of using ICAs as a replacement of conventional soldering technology: the electrical and mechanical properties of ICA joints are worse than the joints made by conventional soldering technology.

The purpose of my work was to investigate the effect of different curing temperatures (120, 150, 175, 210, 230, 250 ºC) on the mechanical and electrical properties of ICA joints. In my work I cured ICA joints in different temperatures and I compared the contact resistances and the shear strength of joints to each other. To investigate the structures of the joints I made pictures with scanning-electron microscope (SEM), and I compared the filler distribution of the joints with the help of an image processing method based on mean intercept length.

The results show that the joints cured in lower temperatures have bigger shear strength and mean intercept length, but it takes much longer time to cure them. In 120 ºC the shear strength was 49.1 N and the mean intercept length was 0,386 µm and the cure took 79 minutes. In 250 ºC the shear strength was 38.0 N, the mean intercept length was 0,332 µm. The lowest contact resistance was reached at the temperature that manufacturer recommended as an optimal curing temperature (175 ºC) ~15 Ω and the cure took 10,5 minutes. In higher curing temperatures (230, 250 ºC) the contact resistance was instable after a quick decrease it began to increase.

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