Study of 0.6mil silver alloy wire in challenging bonding processes
With competitive price and superior electrical/thermal conductivity and mechanical properties, more and more IC package industries have adopted copper (Cu) and palladium coated copper (PdCu) wires as the alternative to gold (Au) wire in the past decade. However, the high hardness and the excessive ultrasonic energy and bonding motions required during bonding of Cu wire limit its usage in areas such as memory packages and sensitive devices that are prone to damages on the pads and under-layer dielectrics. Silver (Ag) and Ag-alloy wires emerge as other alternatives since they have similar properties like wire hardness, elongation and breaking load at room temperature as Au wire while having a more competitive price. Process capability of ultra-fine (0.6mil) Ag-alloy wire, including free air balls (FAB) and bonding capability on aluminum (Al) die pads were first investigated. Factors affecting the FAB performance were studied and optimum settings were recommended. Comparison of bonding responses between Au, PdCu and Ag-alloy wires on challenging scenarios, such as overhang dies and die-to-die bonding, were also included in the study. Benchmarked Au process, Ag-alloy wire possesses great portability and wide first bond process window. Ag-alloy wire also demonstrates good bonding capability and loop shape control on challenging applications, such as overhang die and long die-to-die applications. However, further optimization of Ag-alloy process is still necessary to overcome its constrains, such as higher hardness and higher energy required during bonding of Ag-alloy wire.
Bonding of Ag-alloy wire in LED packages
The LED lighting market has grown rapidly in recent years. Silver (Ag) and silver-rich alloy wire are drawing more and more attention in the LED industry because of its better thermal and electrical conductivity, much lower price as well as higher reflectance rate. Being considered as a potential alternative to Au wire in LED packages, the bonding capability of Ag-alloy wire on a LED device was evaluated in this study. The performance of Ag-alloy FAB with and without a cover gas was first studied. Using the bonding results of Au wire as the benchmark, investigation of the bonding capability and reliability of the Ag-alloy wire with and without cover gas was also carried out. Generally, Ag-alloy wire delivers better performance when bonding with a cover gas. During bonding of Ag-alloy wire without a cover gas, degradation of FAB repeatability, ball uniformity and bonding strength were observed. However, for low-end LED devices, bonding of Ag-alloy wire without a cover gas is a possible compromise for more cost savings.
A bifunctional Cr/Yb/Tm:Ca3Ga2Ge3O12 phosphor with near-infrared long-lasting phosphorescence and upconversion luminescence.
Currently, upconversion nanocrystals and long-lasting phosphorescent particles have attracted extensive research interest for their possible applications as bioimaging probes. However, there are few reports concerning the achievement of both upconversion luminescence of lanthanide ions and long-lasting phosphorescence of transition metal ions in a sole host so far. Herein, we demonstrate a novel calcium gallium germanium garnet (Ca3Ga2Ge3O12) host where lanthanide ions such as Tm(3+)/Yb(3+) and transition metal ions such as Cr(3+) can be easily incorporated through substituting the Ca(2+) and Ga(3+) respectively. This Cr/Yb/Tm:Ca3Ga2Ge3O12 phosphor exhibits both broadband near-infrared long-lasting phosphorescence of Cr(3+) with an afterglow time of more than 7000 s and near-infrared to near-infrared upconversion luminescence of Tm(3+). Impressively, it is evidenced that the addition of Yb(3+)/Tm(3+) into Cr:Ca3Ga2Ge3O12 not only results in Tm(3+) upconversion luminescence but also greatly increases Cr(3+) afterglow time. Based on excitation/emission, three-dimensional thermoluminescence, and time-resolved luminescence spectra, the related long-lasting phosphorescence and upconversion luminescent mechanisms are systematically discussed as well.