Papers by Keyword: Electroless Nickel-Immersion Gold (ENIG)

Abstract: Flip chip technology has grown by leaps and bounds and is getting even smaller in size. Optimization of process parameters in manufacturing is eminent due to reliability issues. This paper reports the parameters that affect the quality of the bump height in electroless nickel immersion gold (ENIG) and their relationships between each other. A total of four different combinations of parameters have been carried out for this investigation using the design of experiment (DOE) approach. It can be concluded that higher temperature of electroless nickel permits an increase of bump height where as the increment in immersion gold temperature does not nessasarily affect the value of bump height. All four samples recorded a higher value of bump height than the controlled bump height value. This implies reliability of the solder joint and assembly process robustness can be improved with an increase of bump height by increasing the time.

Abstract: The effects of chemical bath time in response to the bump height in electroless nickel immersion gold (ENIG) process was investigated. This paper presents the correlation between electroless process time, immersion gold process time and the bump height. A certain bump height need to be achieved in order to create acceptable solder bumps for reflow process. The study was done using a full factorial design of experiment (DOE). The DOE matrix is made of two levels with two factors. Analysis was done by plotting the main effects plot for each factor. The results suggest that higher process time increases the plating rate where the temperature fixed at 70 °C. Electroless nickel time has more influence to the bump height compared to immersion gold time.

Abstract: This paper reports the factors that affect the bump height in electroless nickel immersion gold (ENIG) and their interrelation between each other. Bump height is a critical issue that needs to be investigated because a certain quality and requirements of bump height needs to be achieved prior to reflow oven soldering process. A total of four controllable process variables, with 16 sets of experiments were studied using a systematically designed design of experiment (DOE). The result suggests that the electroless nickel bath time has the most significant effect on the formation on bump height and consequently provide larger area for conductivity.

Abstract: Neural probe array is used for neural recording and simulation applications. It will be implanted into the motor cortex of a paralytic human to control robotic arm and perform tasks such as grasping an object. The major components are silicon (Si) probes, Si platform, application-specific integrated circuit (ASIC), polyimide flexible cable and wireless IC. In-plane Si probes are inserted into the Si platform to form a three-dimensional (3D) probe array. Wirebonding technique is used to integrate the ASIC and the probe array. Pad finishes play an important role in wire bonding as it would affect the reliability of the electrical connections. As such, the focus of the paper will be on the evaluation and characterization of an electroless nickel immersion gold (ENIG) pad finishing and its bonding parameters for wirebonding application. ENIG pad having a 0.1-µm gold (Au) thickness combined with an additional Au stud and wirebonding temperature of 200 °C are found to have comparable wirebonding capabilities as a 0.3-µm thick Au finishing pad. The wire pull test result and SEM observation between the ENIG and Au finishing pad at different bonding parameters were presented and discussed.

Abstract: The interfacial reaction between eutectic Sn-3.5Ag solder and ENIG substrate during reflow was investigated. During the reflow, the topmost Au layer dissolved into the molten solder, and the reaction layers of Ni3Sn4/Ni-Sn-P/Ni3P formed between Sn-Ag solder and Ni-P plating layer. After the reflow at 255 for 3 min, most of Ni3Sn4 intermetallic compound (IMC) spalled off the substrate. The formation of thick Ni3P and Ni-Sn-P layers was related to the direct reaction between solder and Ni-Sn-P layer by the IMC spalling.

Abstract: The interaction between Cu/Sn-Ag and Sn-Ag/Ni interfacial reactions has been studied during isothermal aging at 150°C for up to 1000h using a Cu/Sn-3.5Ag/ENIG sandwich solder joint. A typical scallop-type Cu-Sn intermetallic compound (IMC) layer formed at the upper Sn-Ag/Cu interface after reflowing. On the other hand, a (Cu,Ni)6Sn5 IMC layer was observed at the Sn-Ag/ENIG interface. The Cu in the (Cu,Ni)6Sn5 IMC layer formed on the Ni side has to be contributed from the dissolution of the opposite Cu metal pad or Cu-Sn IMC layer. When the dissolved Cu arrived at the interface of the Ni pad, the (Cu,Ni)6Sn5 IMC layer formed on the Ni interface, preventing the Ni pad from reacting with the solder. Although a long isothermal aging treatment at 150°C was performed, any Ni was not detected in the Cu-Sn IMC layer formed on the Cu side. Compared to the single Sn-Ag/ENIG solder joint, the formation of the (Cu,Ni)6Sn5 IMC layer of the Cu/Sn-Ag/ENIG sandwich joint retarded effectively the consumption of the Ni from the electroless Ni-P layer.