Flexible Printed Circuit boards (FPC) are used in various electronic devices due to their mechanical characteristics and are indispensable to electronic devices requiring smaller, thinner, and lighter production design, and multifunctionality. Although generally printed wired board has obtained adhesion strength between the insulation material and the conductor by the anchoring effect, fine-pattern productivity is difficult and high-frequency transmission loss due to the skin effect becomes larger. We have developed an innovative double-sided flexible printed circuit manufactured by direct copper plating on a polyimide film treated using a molecular junction agent. The adhesion strength between the copper and polyimide films is 15 N/cm and will degrade slightly after aging at 150°C for 168 h and at 260°C for 5 min. The new FPC has the advantages of thinness, weight, flexibility, fine pattern productivity, and high-frequency transmission properties compared to conventional FPCs. Moreover, this new FPC technology has great advantages in cost and environmental considerations.

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A bonding technique that makes use of silver oxide particles with a reducing agent was developed for a high-temperature environment. The silver oxide particles are reduced using a reducing agent at 150°C, and the sintering of the silver nanoparticles which are produced occurs at this temperature. To investigate the reliability of the bond layer formed by the sintered silver, a power cycling test was performed on the module. The module survived more than 75,000 power cycles in a test with T_jmax = 150°C (ΔT_j = 120 K) while the number of cycles to failure for a soldered (Pb3.5Sn1.5Ag) power device didn’t exceed 25,000 cycles. This result shows that the sintered silver bonding technique could be used to increase the lifetime of the power module by eliminating the solder layer.

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This paper discusses the mechanical properties, thermo-mechanical fatigue (TMF) and isothermal low cycle fatigue (LCF) life evaluation of Sn-0.7Cu-0.3Ag. Sn-0.7Cu-0.3Ag is proposed as a low-cost alternative material because it contains a low proportion of Ag. Static tensile test were conducted to determine the mechanical properties of Sn-0.7Cu-0.3Ag at various temperatures. As solder joints in electronic devices undergo cyclic TMF damage caused by the mismatch of the thermal expansion coefficients of different materials, TMF tests were conducted in in-phase and out-of-phase conditions in the temperature range of 253 K-353 K and isothermal LCF tests were conducted at 253 K and 353 K.
The authors have previously proposed a method of evaluating the TMF and LCF lives of solders based on the energy parameter calculated as multiplication stress and strain in tension including consideration of the mean stress amplitude. In this study, we confirmed an application of the evaluation parameter to the TMF and LCF life of Sn-0.7Cu-0.3Ag.

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Silver plated films have been used as reflective films in LED reflectors because of their outstanding reflection properties for visible light. In this application, the formation of tarnish films on the silver surface is a serious problem. This tarnish is caused by the reaction of the silver films with trace amount of sulfur compounds in the atmosphere and by diffusion of copper from the underlying substrate.
In this paper, we report on the design of a novel multilayer plating system for the copper substrate, consisting of electrodeposition of palladium and nickel films as diffusion barrier layers, silver film as a reflective layer, followed by electrodeposition of ZnO film to prevent sulfuration. Formation of a dense ZnO film (90 nm) on the bright silver film is found to inhibit sulfuration of the silver film. The decrease in the reflectance of the silver film due to the diffusion of copper can be inhibited by the formation of protective palladium (0.1 μm) and nickel (1 μm) layers between the silver film and the copper substrate.

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Zn/Al/Zn and Zn/Al/Cu clad materials were developed for high-temperature die attachment. The clad structure is used in an attempt to improve the wettability of Zn-Al solder by preventing oxidation of the Zn and Al. The materials were produced by clad-rolling Zn, Al and Cu strips, which act as solder following eutectic melting at temperatures above 382°C. The wettability, bondability and reliability of the clad materials were evaluated. The Zn/Al/Cu clad materials could be used in an atmospheric oxygen concentration of 100 ppm. The thermal cycle life of chip-to-substrate joints formed using the Zn/Al/Cu clad materials was four times longer than that formed using Pb-Sn-Ag solder.

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Electroless Ni/Au or electroless Ni/Pd/Au plating is widely used as surface finishing for electronics assembly. Conventional electroless Ni plating films contain small amounts of lead derived from additives in their plating baths. However, it is expected that lead-free electroless nickel plating will be required if stricter environmental regulations are in force. In this study, the reliability of solder joints with lead-free electroless Ni/Au and Ni/Pd/Au plating was investigated. It was found that certain factors, such as Ni corrosion pitting and the behavior of the IMC (thickness, ratio of components and shape), affect the reliability of the lead-free solder joint in complex ways. Moreover, it was confirmed that these factors vary with the amount of additives (bismuth and sulfur) incorporated into these lead-free plating films.

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