eWLB Package Overview

The eWLB (Embedded Wafer Level Ball Grid Array) package technology was developed in cooperation between 3 companies: Infineon, STMicroelectronics and STATS ChipPAC to solve an interconnect problem that was introduced by the fan-in packaging technology (WLCSP).

The first eWLB package was used in mobile phones in 2009 and since then it gradually became a viable packaging solution for consumer and wireless ASICs.

The Problem With Fan-In Package

Fan-In package (or WLCSP – Wafer Level Chip Scale Package) is essentially a bumped die, and hence, it’s the smallest possible package type available today. WLCSP has great benefits: low price, small size, good electrical performance and more. Some applications require high pin count which means very high number of bumps to be placed under the die. This makes the interconnect and the assembly costly and challenging.

eWLB Market

Today, all the major assembly houses and a few wafer foundries are offering eWLB packaging services. Yole developpement has anticipated the eWLB (Fan-out) market size to increase to USD3.4B in 2026 almost doubling the 2020 market size.

eWLB Package Technology

The main idea behind eWLB is to apply an artificial wafer under the original wafer to create a bigger die area. The artificial wafer is used to connect the die pad to balls (similar functionality to a BGA substrate) – spreading the bumps across a bigger die area allowing more space between the bumps. In eWLB package, the traces are routed outwards (versus inwards in WLCSP).

eWLB Assembly Process

The eWLB assembly process is performed in wafer level. The wafers are first diced, the dies spaced apart and a resin material is flowed over the dies then hardened to form a re-constituted wafer. The distance between the dies determine the final package outline. Multiple routing layers can be used for complex routing of many pads. The redistribution lines are separate by repassivation layers applied in a manner similar to wafer process back-end passivation.