AUTOMATED TEST NON-DESTRUCTIVE ANALYSIS OF TO-247 STRUCTURAL DEFECTS The TO-247 is a popular electronic form factor, so doing non-destructive analysis of possible structural defects could come in handy during the design process. TO-247 form factor. by Tom Adams, Enes Ugur A single pulse of ultrasound fired into the polymer encapsulant of a TO-247 device travels through the polymer at a speed around 3,000 m/s. Its mission is to characterize any internal material interfaces that it encounters. It will be partly reflected by any material interface, but most strongly-virtually 100%-by the interface between a solid and an air gap, and less strongly by solid-to-solid interfaces. 24 EVALUATION ENGINEERING APRIL 2020 When a pulse encounters a solid-to-solid interface, a portion of the pulse crosses the interface and travels deeper, where it may be reflected by a second interface. A solid-to-air interface reflects virtually 100% of the pulse, and no ultrasound crosses the interface. The reflected ultrasound returns at its original speed to the receiver housed with the transducer that launched the pulse.