Ultrasonic welding technology for thermoplastics has developed quickly in recent years. For aircraft structural applications, this joining technique shows promise over standard epoxy adhesives, resistance welding, or mechanical fastening in terms of scalability and efficiency. However, identification of optimal ultrasonic welding parameters remains a difficult task. Energy directors with either flat or custom-made geometries have been the focus of much recent research, but a clear winner has not yet emerged. In this study, single-lap joints (SLJ) of unidirectional CF/PPS laminates were manufactured by ultrasonic welding, using commercially available PPS mesh inserts as energy directors. The shear strength was evaluated, and the failure surfaces were examined to understand the relationship between welding parameters and resultant strength. Results indicate that coarser mesh size, along with longer welding times, tend to result in higher SLJ shear strength.