Silver Nanowire Networks: Ways to Enhance Their Physical Properties and Stability

Silver nanowire (AgNW) networks have been intensively investigated in recent years. Thanks to their attractive physical properties in terms of optical transparency and electrical conductivity, as well as their mechanical performance, AgNW networks are promising transparent electrodes (TE) for several devices, such as solar cells, transparent heaters, touch screens or light-emitting devices. However, morphological instabilities, low adhesion to the substrate, surface roughness and ageing issues may limit their broader use and need to be tackled for a successful performance and long working lifetime. The aim of the present work is to highlight efficient strategies to optimize the physical properties of AgNW networks. In order to situate our work in relation to existing literature, we briefly reported recent studies which investigated physical properties of AgNW networks. First, we investigated the optimization of optical transparency and electrical conductivity by comparing two types of AgNWs with different morphologies, including PVP layer and AgNW dimensions. In addition, their response to thermal treatment was deeply investigated. Then, zinc oxide (ZnO) and tin oxide (SnO2) protective films deposited by Atmospheric Pressure Spatial Atomic Layer Deposition (AP-SALD) were compared for one type of AgNW. We clearly demonstrated that coating AgNW networks with these thin oxide layers is an efficient approach to enhance the morphological stability of AgNWs when subjected to thermal stress. Finally, we discussed the main future challenges linked with AgNW networks optimization processes.

Package Substrate Die Pad Roughening Innovative Solution to Strengthened Die Attach Adhesion

Poor die adhesion to substrate resulting to stray dice issue for the MEMS package was encountered. This die bond failure mechanism has a downstream effect specifically on the mold process. The presence of the stray die resulted to mold compound leakage outside the tool cavity due to planarity not achieved. The mold compound that leaks affected the overall package thickness, thus exposing the wires. Using the Design of Experiment methodology, the team generated different simulations and validations to resolve the stray die problem. Based on the simulation and experiments, it was established that an optimum substrate roughness is necessary to achieve a better adhesion between the Die adhesive and the substrate. This paper presents a systematic study on how the substrate roughness can improve the adhesion of Die Attach film (DAF) to the substrate thereby resolving the Stray Die problem. Results showed that the die adhesion strength on the substrate increases as the substrate surface roughness increased from Ra 0.05 um to Ra 1.5 ~ 2.0 mm. Consequently, the rejection rate of stray dice was eliminated. This new learning will be used to establish a standard on surface roughness for substrate-based material that can be applied to new packages.