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The effect of the activators and surfactants in halogen-free fluxes on the wettability of Sn-0.7Cu-0.05Ni solder on Cu substrate (or under bump metallization, UBM) was investigated in this study. The spreading area of Sn-0.7Cu-0.05Ni solder on Cu substrate was used to estimate the wetting performance of the solder influenced by the activators with different amounts added in halogen-free fluxes. The wetting time (t) and wetting force (Fmax) of Sn-0.7Cu-0.05Ni solder on Cu substrate were used to evaluate the wetting performance of the solder influenced by the surfactants with different amounts added in halogen-free fluxes. The results show that the flux formula with a composition design of “citric acid: glutaric acid: adipic acid = 1: 3: 6” provides the best activity for soldering, and 0.10% surfactant dosage could be the optimal concentration in halogen-free fluxes. Moreover, fluorosurfactant (FC4430) performs much better in improving the wettability of the solder in terms of wetting time and wetting force than both cetrimonium bromide (CTAB) and sodium dodecyl surfactant (SDS) when the dosage is more than 0.10%.

Linear frequency signal (LFM) signal is first used in radar fields due to its remarkable properties, such as wide bandwidth, high energy and high signal-to noise ration. LFM excitation has recently been introduced in medical ultrasonic scanning, and much exciting results were obtained by research staffs. However, there is little study aiming to inspect solid materials utilizing coded excitation. In the present study, LFM signal were distinguished with pulsed compression method even merged noise. LFM signal with large time-bandwidth product can be designed theoretically, but the limited bandwidth of a transducer will lead to energy loss. Several coded signals were used to excite transducer, then the received signals' amplitude and spectrum were analyzed. The results show that the amplitude will decrease when the frequency exceed the transducer's bandwidth. In order to investigate the transmitting law in solid materials, the waveform and spectrum were analyzed after LFM signals penetrating steel materials with different thickness. Through the analysis, it is found that wave at high frequency band attenuates much quickly than wave at low frequency band. The results of investigations of the field structure in a steel plate are provided. The results of measured pressure field distributions before and after compression were compared with the recorded signals using short pulse excitation. The characteristics of waveform and spectrum were analyzed with LFM coded excitation. The SNR of LFM signal at output side will be improved with pulsed compression method. At the same time, the range resolution increase after matched filter. The sound field on the surface of a steel plate was measured using several LFM coded signal excavating. This paper shows the feasibility of inspecting steel material with LFM signals.

The hypo-eutectic Sn-Zn based solder alloys were developed by adding Bi and mixed rare earth (MRE) elements in this study. The melting characteristics of the modified Sn-Zn-Bi-MRE solders were studied by differential scanning calorimetry (DSC), and the wettability of the solders on Cu substrate was evaluated by the spreading test. The microstructural features of the solders and the intermetallic compound (IMC) formation at the solder/Cu interface were characterized by SEM-EDS. Results show that the Sn-5Zn-5Bi solder has the best wettability among the Sn-Zn-Bi series solders. The addition of Bi element decreases the melting temperature evidently, while MRE has almost no influence on the melting temperature but can improve the wettability and refine the microstructure of the solders. During soldering, Cu5Zn8 IMC phase is formed at the solder/Cu interface, addition of MRE can make the IMC layer much thinner.