Bonding mechanism of lead-free solder and glass plate by ultrasonic assisted soldering method

Highlights: • Pb-free solder can be bonded to glass surface by ultrasonic assisted soldering. • TEM observation showed no obvious intermetallic compound layer at the solder/glass interface. • Chemical shifts of O 1s, Zn 2p and Si 2p were observed in XPS spectra after bonding of the lead-free solder to glass. • Zinc in the solder has an important role in the bonding behavior. - Abstract: Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the bonding mechanism of lead (Pb)-free solder to glass by ultrasonic assisted soldering. In addition, the effects of ultrasonication, the elements and the oxygen concentration in the solder on the bonding behavior were also investigated. Ultrasonication during the soldering process led to an improvement of the wettability and accelerated the bonding between the lead-free solder and glass. No intermetallic compound layer was identified around the solder and glass interface from SEM and TEM observations. Chemical shifts of O 1s, Zn 2p and Si 2p were observed at the interface by X-ray photoelectron spectroscopy (XPS) analysis, which is attributed to chemical bonding between the glass and a solder component element. In particular, zinc was identified as an important element to form the bond between the glass and solder. The chemical bonding is accelerated by acoustic cavitation due to the ultrasonication