Validation Of High Density Fanout Interposer Through Test Vehicles

Abstract

High density fanout interposer is a promising 2.5D package option based on RDL (redistribution layer) first technology. Test vehicles were designed to validate manufacturing process capability, reliability, design rules and electrical performance. The interposer used various trace width (from 4um to 1.5μm) and length (3~7mm for HBM, 2~5mm for die to die) serpentine & comb structures to detect manufacturing defects and reliability risks. Daisy chains were distributed at high risk regions. Most recent build showed that 1/1um trace width/space can be achieved with optimized process and material.

Differential phase length electrical coupons were designed inside one test vehicle for electrical characterization. The test chips were bonded to the high density fanout interposer with 25um uBump. Underfill was applied and the interposer wafer was molded and ground to target thickness. Singulated units were probed before stress tests.

During fabrication, metal to dielectric material delamination was noticed when large metal plane exists. While low metal density would impact cleaning and plating, balanced and reasonable metal density is found to be critical for high quality manufacturing process.

During stress test, no broken trace was found but shortage risk was identified when larger voltage (> = 1.8V) was applied at bHAST.

Electrical tests were conducted from 1GHz to 30GHz. Cross section of real vehicle indicated that the actual dimension is close to design value.

This study validates high density RDL for 2.5D package through specially designed test vehicles.