Processing and reliability of fast-flow, snap-cure underfills. I. Processing and moisture sensitivity

This series of articles studies the processing, moisture sensitivity, reliability, and failure mode analysis of a number of commercial fast-flow, snap-cure underfill materials. It includes data on process analysis, processing times, and reliability of the test vehicles in air-to-air thermal cycling (-55°C to 125°C), liquid to liquid thermal shock (-55°C to 125°C), and J Standard 020 Revision A Level 3 Moisture Sensitivity Preconditioning followed by reliability testing. Samples cured using a second reflow pass are compared to baseline samples cured in a standard batch oven based on the underfill manufacturer´s recommended cure schedule. Results from the processing of these new materials have shown a greatly reduced flow time from earlier generation underfill materials as all of these materials had flow times of less than 30 s under 5-mm test die. Through differential scanning calorimetry analysis, it was shown that materials requiring less than 8 min to cure exhibited at least 95% conversion (percentage of material cured) through the modified second side renew profile. Some of these commercial underfills have also passed J Standard 020 Revision A Level 3 Moisture Sensitivity testing. Specifically in this paper, the flip chip processing, underfill processing, moisture preconditioning, and preconditioning failure modes are presented