Study on the hygrothermal aging mechanism of photo-thermal dual-curing solder mask

Photo-thermal dual-curing solder masks with high resolution and excellent mechanical properties are widely used in semiconductor advanced packaging applications. The reliability of electronic products in high temperature and high humidity environments has always been the focus of research in the semiconductor industry. The structural transformation of solder mask as the protection of package substrate lines under high temperature and humidity environment is particularly important. This paper focuses on the hygrothermal aging process and mechanism of photo-thermal dual-curing solder masks. The effects of time, temperature and humidity on the structural and mechanical properties of solder masks during the hygrothermal aging process are thoroughly investigated. After being treated at high temperature and humidity for 168 h, the ester group as cross-linking point in the photo-thermal dual-curing solder mask hydrolyzes to generate carboxyl and hydroxyl group. The crosslink density of the solder mask reduces from 48.42 × 10⁻⁴ mol/ml to 29.27 × 10⁻⁴ mol/ml. Additionally, solder masks are not hydrolysed after being treated at high temperature or humidity for 168 h. Aging of solder masks only occurs when they are treated at high temperature and humidity and when the temperature and humidity reach the threshold values. This study provides a guiding reference for the application of solder masks in the field of advanced packaging.