High-stability reflective bonding pads for GaN-based flip-chip light-emitting diodes packaged by reflow soldering

We provide a detailed insight into the effects of metal bonding pads on the performance of GaN-based flip-chip blue light-emitting diodes. The flip-chip blue light-emitting diodes with four kinds of reflective bonding pads were fabricated and compared. During the chip package process by reflow soldering, different bonding pads exhibited distinct voidage and bonding force with the solder layers on Cu-coated AlN ceramic substrates. Compared with other samples in this work, the packaged chips with Ti/Al/Ti/Pt/Au bonding pads showed the lowest voidage of 15.48% and thermal resistance, resulting in the highest bonding shear force and light output power. Meanwhile, the optical power of these samples with Ti/Al/Ti/Pt/Au bonding pads only exhibited a degradation rate of 1.8% after accelerated ageing at 100 degrees C for more than 1000 h. It is concluded that GaN-based flip-chip light-emitting diodes with such Ti/Al/Ti/Pt/Au bonding pads bear good mechanical stability, excellent thermal performance and long-term reliability.