Investigate the conductivity of ICA joints

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Dr. Illés Balázs György
Department of Electronics Technology

After, when the industry recognized the polluting effects of tin-lead containing solder alloys began to search for alternatives to replace them. Two lines of development occurred: lead-free solders and conductive adhesives. In the begining, the adhesive experiments were unsuccessful and their test ends with failure, so the attention turned to the lead-free solder researching line. Serious changes occured between 2004-2008, when the use of lead containing solders became restricted worldwide. Growing number of studies have been published in the improvement of both electrical and mechanical quality of adhesives. As a result of the experiments and attempts, conductive adhesives technology has reached to a quality level that can meet the requirements and standards standed up by conventional soldering technology, but they are still not perfect as their competitor: lead-free solders.

In my thesis, quality of cured bonded joints at different temperatures were investigated. On 120, 175 and 245 °C managed samples contact resistance was measured by four-wire measuring method, and than prepared for testing their mechanical strength with shear strength test. In order to examine the internal structure of joints, grindings of the samples were subjected to optical inspection.

As the results of experiments, the most stable bondings were cured on 120 ° C for 2 hours and 175 ° C for 20 minutes, (average shear strength: 120°C: 5:07 kg;175°C: 4.57 kg). Contact resistance was 9.7 and 16.2 ohms. Samples, which were cured on 175 ° C for 2 hours and 245 °C for 10 minutes, had the weakest strength of the bonds (the average shear strength: 175°C: 3.93 kg; 245°C: 3.75 kg). Contact Resistance measured on 175°C sample as of 53 ohms, the 245°C degree cured sample had a surprising 3.7 ohms. After optical inspection found that excessive heat may cause irreversible long-term damage in polymer structure, and shrinkage due to this causes extreme amount of delamination.


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