Recent Advances and Trends in Fan-Out Wafer/Panel-Level Packaging

The recent advances and trends in fan-out wafer/panel-level packaging (FOW/PLP) are presented in this study. Emphasis is placed on: (A) the package formations such as (a) chip first and die face-up, (b) chip first and die face-down, and (c) chip last or redistribution layer (RDL)-first; (B) the RDL fabrications such as (a) organic RDLs, (b) inorganic RDLs, (c) hybrid RDLs, and (d) laser direct imaging (LDI)/printed circuit board (PCB) Cu platting and etching RDLs; (C) warpage; (D) thermal performance; (E) the temporary wafer versus panel carriers; and (F) the reliability of packages on PCBs subjected to thermal cycling condition. Some opportunities for FOW/PLP will be presented.

High-Temperature Reliability of Direct-Bond-Copper Substrates with Sealed Edges

Recent reports have shown the reliability of direct-bond-copper (DBC) substrates was significantly improved by sealing their edges with polymeric materials. In this work, DBC substrates with and without sealed edges had been prepared. Parylene HT and Nusil R-2188 had been chosen as sealing materials. Parylene HT was applied to the edges of the DBC by chemical vapor deposition (CVD), and Nusil R-2188 by programmable fluid dispensing. The DBC substrates with and without sealed edges were cycled between −55°C to 200°C. The cycled substrates were monitored by optical microscope and scanning electron. DBC substrates whose edges were not sealed were found to fail in approximately 100 cycles. No failure was observed in DBC substrates coated with parylene HT before 300 cycles. Samples whose edges were sealed with Nusil R-2188 exhibited the highest lifetime under the thermal cycling condition of −55°C – 200°C. After 300 cycles, neither detachment of Nusil from DBC surfaces nor failure at Cu/Al2O3 interface was detected. After 900 cycles, 30 μm – 60 μm cracks appeared at the edges of Cu/Al2O3 interface, which are signaling the early stage of substrate failure. Additionally, Nusil was found to be partially detached from DBC surfaces. The improvement in reliability is attributed to the release of thermo-mechanical stress concentrated at the edges of the Cu/Al2O3 interface.

Strength Degradation of Oxide/Oxide and SiC/SiC Ceramic Matrix Composites in CMAS and CMAS/Salt Exposures

CMAS (Calcium-Magnesium-Aluminosilicate) has shown to induce some deleterious effects on yittria-stabilized-zirconia (YSZ) based thermal barrier coatings (TBCs) of hot section components of aeroengines. The effects were shown to be dependent on the types and operating conditions of engines/components. The work presented here explored how CMAS would affect ceramic matrix composites (CMCs) in terms of strength degradation. Four different, gas-turbine grade CMCs were utilized including two types of MI SiC/SiCs and other two types of oxides/oxides (N720/aluminisilicate and N720/alumina). Test specimens in a simple flexure configuration were CMAS-treated at 1200 °C in air under either isothermal or thermal cycling condition. The effects of CMAS were quantified via residual strengths of treated test specimens. Strength degradation with respect to as-received strengths ranged from 10 to 20% depending on the types of CMCs. It was further observed that significant degradation of strength up to 90% occurred in an oxide/oxide CMC when sodium sulfate was added to CMAS.

Visco-Elastic Effect of Underfill Material in Reliability Analysis of Flip-Chip Package

The effect of viscoelasticity of underfill on the reliability analysis of flip-chip package by using FEA has been investigated in this study. The analytical result on thermal warpage of a package is different depending on whether the underfill is assumed to be elastic or viscoelastic. The difference is prominent in materials with low Tg, specifically during the cooling process. The viscoelastic effect of the underfill on the fatigue life of the solder bumps is also appears in materials with low Tg, and the predicted fatigue life of a package is about twice as short if the underfill is assumed to be elastic instead of viscoelastic. Thus, the differences in the assumption regarding the viscoelastic properties of the underfill affect the reliability analysis of the packages under thermal cycling condition using FEA.

Study on Al Alloy Welded Joint Performance Deterioration under Thermal Cycling Condition

This paper investigates the mechanical performance deterioration of aluminum alloy welded joints under thermal cycling condition. The real-time temperature, load and strain of the specimens are monitored during the test. Results show that a long time thermal cycling process can cause a performance decrease in its plasticity and fracture strength.