Improving the Reliability of Si Die Attachment with Zn-Sn-Based High-Temperature Pb-Free Solder Using a TiN Diffusion Barrier

The thermal fatigue reliability of Si die-attached joints with Zn-30wt.%Sn, high-temperature, Pb-free solder was investigated, focusing on the interfacial microstructure and joining strength of a Cu/solder/Cu joint during thermal cycling. A sound die attachment on an aluminum nitride (AlN) direct-bonded copper (DBC) substrate was achieved by forming Cu-Zn intermetallic compound (IMC) layers at the interface with the Cu of the substrate. During the thermal cycling test performed between −40°C and 125°C, thermal fatigue cracks were induced by the growth of Cu-Zn IMCs at the interface with the Cu. A␣thin titanium nitride (TiN) film was applied to suppress the formation of Cu-Zn IMCs. Adequate joint formation was accomplished by using an Au/TiN-coated DBC substrate, and only the TiN layer was observed at both interfaces. In conjunction with the TiN diffusion barrier, the Si die-attached joint created with Zn-30wt.%Sn solder exhibited a stable interfacial microstructure during thermal cycling. No microstructural changes, such as IMC formation, grain growth or formation of fatigue cracks, were observed, and the joining strength was maintained even after 2000 cycles.     

Interfacial Reaction and Die Attach Properties of Zn-Sn High-Temperature Solders

Interfacial reaction and die attach properties of Zn-xSn (x = 20 wt.%, 30 wt.%, and 40 wt.%) solders on an aluminum nitride–direct bonded copper substrate were investigated. At the interface with Si die coated with Au/TiN thin layers, the TiN layer did not react with the solder and worked as a good protective layer. At the interface with Cu, CuZn₅, and Cu₅Zn₈ IMC layers were formed, the thicknesses of which can be controlled by joining conditions such as peak temperature and holding time. During multiple reflow treatments at 260°C, the die attach structure was quite stable. The shear strength of the Cu/solder/Cu joint with Zn-Sn solder was about 30 MPa to 34 MPa, which was higher than that of Pb-5Sn solder (26 MPa). The thermal conductivity of Zn-Sn alloys of 100 W/m K to 106 W/m K was sufficiently high and superior to those of Au-20Sn (59 W/m K) and Pb-5Sn (35 W/m K).     

Design and Performance Evaluation of Traffic Grooming Algorithms in WDM Multi-Ring Networks

In this paper, we propose novel traffic grooming algorithms to reduce the cost of the entire system in WDM multi-ring networks. In order to achieve this goal, it is important to construct a virtual topology and groom the traffic in these networks. We consider four kinds of virtual topologies of WDM multi-ring networks according to the way in which traffic is transmitted among rings. Accordingly, we design four kinds of traffic grooming (TG) algorithms depending on the considered virtual topologies: mixed (MTG), partially mixed (PMTG), separate (STG), and independent (ITG) traffic grooming algorithms. Each algorithm consists of a separation, a connection-ring construction, and a grooming procedure. In the separation procedure, all traffic connections are classified into intra and inter-connections. The connection-ring construction procedure makes full connection-rings from traffic connections. The grooming procedure groups connection-rings onto a wavelength in order to reduce the number of SONET add/drop multiplexers (SADMs) and wavelengths and to improve the utilization of network resources. To analyze the performance of each algorithm, a circular multi-ring architecture with uniform traffic is considered. The simulation results show that ITG and PMTG are more efficient in terms of wavelengths. STG and PMTG require a smaller number of SADMs.     

Electrical Resistance and Microstructural Changes of Silver–Epoxy Isotropic Conductive Adhesive Joints Under High Humidity and Heat

In this study, the degradation mechanism of chip resistors mounted with Ag–epoxy isotropic conductive adhesive (ICA) under two different environmental conditions, i.e., humidity exposure (85°C/85% relative humidity) and thermal cycling (TC, –40°C to 125°C), was examined by monitoring the change in electrical resistance and by transmission electron microscopy. The effect of the terminal finishes (Sn/Ni or Au/Ni) of the chip components on joint stability during those two tests was also examined. The electrical resistance of the Sn/Ni-plated chip component joined with Ag–epoxy ICA during both environmental tests increased with exposure time. On the other hand, the electrical resistance of the Au/Ni-plated chip component joined with Ag–epoxy ICA remained unchanged during both tests. In the case of the Sn/Ni-plated chip joint, Sn oxides such as SnO, SnO₂, and Sn-Cl-O were formed inhomogeneously on the surface of the Sn plating during the humidity exposure test. Under the TC test, microcracks were also observed at the Sn/epoxy and the Ag filler/epoxy interfaces. A Ni₃Sn intermetallic compound (IMC) was formed at the interface between Sn and Ni, and the Ni₃Sn₄ IMC was also formed at the Sn surface. In contrast, no oxide was found in the Au/Ni-plated chip joint during the humidity exposure test. Also, no IMC was found in that joint during the TC test. It is suggested that oxides, microcracks, and IMCs cause the electrical degradation of Sn/Ni-plated chip components joined with Ag–epoxy ICA.     

Design and Performance Evaluation of a Separated Control Signaling Protocol for WDM Optical Networks

In WDM optical networks, an efficient control signaling protocol is required to dynamically establish lightpaths. This paper proposes a separated control signaling protocol (SCSP) and compares the performance of SCSP with a conventional integrated control signaling protocol (ICSP). The conventional ICSP makes reservations sequentially from the source to the destination for setting up and tearing down lightpaths. It increases the control overhead and wastes the network resource if it cannot reserve the network resource at an intermediate node. Specifically, if the receiver at the destination is not available after successful reservation at intermediate nodes, it wastes a lot of bandwidth. It causes decreasing chances of reservation for other lightpaths. Instead, SCSP separates bearer control from call control to reduce the waste of network resources. The call control function checks the availability of network resources such as wavelengths and receivers. Bearer control reserves, allocates, and releases network resources. To evaluate the performance of the two protocols, they are mathematically analyzed using a probabilistic model. Simulation results are also provided to compare the proposed protocol with the conventional ICSP in terms of utilization and blocking probability. From the results of simulation and iterative analysis, we can observe that SCSP performs better than ICSP.     

QoS Supporting Algorithms for Optical Internet Based on Optical Burst Switching

In this paper, we propose a protocol architecture and quality of service (QoS) supporting algorithms for optical Internet based on optical burst switching (OBS) technology. Firstly, the function of each layer of the protocol architecture and the formats of control packets are defined in order to adopt GMPLS to the control plane of OBS. Then, the offset time decision (OTD) algorithm to cooperate with the proposed protocol architecture is designed for optical Internet. A new burst loss formula taking into account the effect of offset time is introduced to design the OTD algorithm. This algorithm can decide on the appropriate priority-offset time according to the required QoS by using the reversed equation of the so-called heuristic loss formula (HLF) which is approximated as a proportional equation of our new loss formula. Finally, we propose a CAC algorithm based on the OTD algorithm for the purpose of increasing the availability of wavelength resources and supporting the QoS of established connections in optical Internet. The performance of the proposed algorithms is evaluated in terms of burst loss rate and the number of connections through simulation.