Comparative study of solder size and volume effect on properties of Sn–3.0Ag–0.5Cu joints during isothermal aging

The effect of solder ball size on the microstructure and mechanical properties of solder joints during aging was investigated. Sn–3.0Ag0.5Cu solder balls with four different diameters (200, 300, 450, and 600 µm) were used as the joint material. Reflow soldering was employed to attach solder balls to the organic solderability preservative finished Cu ball-grid-array substrate. Aging treatment was performed for up to 2000 h at 150 °C to observe the changes in joint properties. Microstructural evaluation of the intermetallic compound (IMC) formed at the solder joints interface showed that Cu6Sn5 was formed at the interface of four different solder joins after reflow soldering, and Cu3Sn was formed between Cu6Sn5 and Cu during initial aging. As aging time increased, the thickness of the IMC formed at the interface increased. The thickness of IMC formed at the initial 200 µm solder joint was the thickest. However, the 600 µm solder joint formed the thickest IMC as the aging time increased. Upon evaluating the IMC grain size, it was observed that the initial coarse IMCs formed as the solder joint size decreased. However, when the aging time was increased, similar grain size formed at all solder joints. The shear strength increased as the solder joint size decreased. In the initial 24 h aging process, the shear strength decreased rapidly for all solder joints and subsequently decreased slightly as the aging time increased. This study confirmed that the microstructure and strength properties of Sn–3.0Ag–0.5Cu solder joints of different sizes changed with the aging time.