Novel Ultrasonic Soldering Technique for Lead-Free Solders

Abstract

Sn-Bi alloy is one of the representative low temperature type lead-free solders. However, the bonding properties of the Sn-Bi solder are not good. The reason for such properties is related to Bi microcrystallines that segregate at the interface between the solder and a Cu substrate. We found that ultrasound improves the bonding strength for the Sn-Bi alloy system solders by dispersing and miniaturizing the Bi crystals. To achieve such dispersion, we invented a novel ultrasonic soldering technique. By using this technique, ultrasound can be applied to printed wiring boards (PWB). Besides the improved bonding strength, we found that the temperature of a PWB is increased by the application of ultrasound to the PWB. Sn-58 mass%Bi solder is melted by the vibrational energy of ultrasound without other heating methods. Moreover, the interfacial layer between the Sn-58Bi solder and the Cu land is homogenized by ultrasound. Also, the interfacial layer between the Sn-8Zn-3Bi solder and a Cu land becomes thinner by ultrasound. We believe that these changes in the interfacial structure improve the mechanical properties of the solders. Therefore, ultrasonic soldering technique will improve the usability and reliability of Sn-Bi alloy system solders.

Joint strength of aluminum ultrasonic soldered under liquidus temperature of Sn–Zn hypereutectic solder

“…This process propagates ultrasonic vibrations through substrates directly without using a solder bath (Faridi et al, 2000). Kago et al (2004) conducted this type of ultrasonic soldering for joining Cu substrates. Naka and Hafez (2003) reported that joints of Al 2 O 3 to Cu using Zn-Al filler alloy were successfully obtained.…”

Effect of ultrasonic vibration on interfacial reaction of Ni/Sn/Ni soldered joint

“…Tan et al (2017) brazed Cu with Sn-Ag-Cu solder by applying ultrasound and found that the interfacial IMCs became thin and uniform under the effects of USV. Kago et al (2004) reported that the mechanical properties of a Cu/Sn-Bi solder joint were improved by ultrasound application during the solidification stage, which was attributed to the homogenization and thinning of the interfacial layer. Luque de Castro and Priego-Capote (2007) investigated the effect of ultrasound on crystallization; they found that USV could effectively accelerate mass transfer and increase the driving force for crystallization in a mixture.…”

Sealing of Sapphire Infrared Windows by Ultrasonic Interfacial Deposition Soldering

“…Thus, the cavitation removes the oxide layer on the liquid and solid metals, and promotes wetting and joining at the interfaces. [14][15][16][17][18][19]However, to date, most applications of this technology are joining light metals, especially aluminum. Only a few research on is application to joiningother metallic materials and ceramics has been reported.…”