Advanced Protected Fan-In WLCSP

Abstract

With the advent of bumped die new IC packages evolved: for low IO WLCSP (wafer level chip scale package), for high IO FC (flip chip) CBGA (ceramic ball grid array) and PBGA (plastic ball grid array). For low IO, protected CSP is an emerging and rapidly growing market. In 2020 the market exceeded $2B and is ramping to a forecast $2.5B by 2025.1 Initially WLCSP, also known as FI (fan in), packages were built on the wafer with no active side protection evolving to single sided protection from a package built on the wafer2 which transition to redistribution PSB (passivation stress buffer)3, PSBs were used on FC wafers for high IO BGA packages. These provided acceptable performance initially, however as devices became more complex and reliability requirements increased, these processes no longer provided the required reliability. To attain higher IO capability and better reliability performance evolved to CSP4 (non-WL) which allowed larger area for bump distribution and additional protection to the rest of the exposed die surfaces. Fully protected die CSP (without substrates or leadframes) was initially implemented with processes such as M-series utilizing a FO (fan out) process.5 To obtain higher reliability 6-sided die protection afforded by M-series type processes require die reconstitution, expensive tapes, molding, and other operations generally required in a FO process which can feasibly be eliminated in a WLCSP protected FI process. American Semiconductor's Semiconductor-on-Polymer™ (SoP™) 300mm FleX-TM WLCSP is an advanced packaging process optimized for protected fan-in. FleX-TM produces the thinnest and lowest cost protected FI the industry today. Protected FI process innovations can improve performance in power devices, RF switches, die stacking and thin board applications. This article includes background on the evolution of CSP and the comparison of SOTA (state of the art) FI processes including FleX-TM.