A novel epoxy encapsulant for CSP (μBGA(R))-new hydrophobic epoxy elastomer

Due to an increasing demand for smaller and higher density packages, Tessera developed μBGA(R) technology as a cost-effective solution for chip-size packaging. Many companies including Intel, 3M, Samsung, Amkor, etc. have licensed the technology since 1995. As a current, leading technology for Chip Scale Packaging (CSP), a μBGA(R) package typically has a compliant layer between the die and the flex interposer to eliminate strain on solder balls by thermal mismatch of the die and printed wire board (PWB). Historically, a silicone-based encapsulant has been the material of choice for this application. However, for hard disk drive and other applications with zero tolerance of siloxane outgassing, a non-silicone encapsulant having excellent reliability performance is highly desired. A novel 3M epoxy encapsulant with excellent hydrophobicity has been developed for an advanced μBGA(R) package platform. The new epoxy encapsulant is designed to meet the requirements of compliancy with good moisture resistance. This new material has demonstrated JEDEC level 1 reliability. During thermal cycling tests, the new encapsulant far surpassed 1000 cycles, both on- and off-board, and survived high temperature aging, as well as 500 hours of pressure cooker testing (PCT). This paper will describe physical properties and reliability performances of the new 3M encapsulant material with emphasis on its hydrophobicity and compliancy. Improvement in reliability trends for μBGA(R) technology will also be reviewed