Failure analysis of the winding inductor caused by hot dip coating tin

Aimed at the unstable output phenomenon of one type of power amplifier in the process of using, previous examinations have located the problem in internal inductance coil. To determine the reason of the fault amplifier, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) have been used to analyze the microstructure and composition of abnormal substances in the bend of coil pin. Results show the thermal stress was so large during hot dip coating tin that the boundary area of the root of lead whose insulating layer was removed suffered from damage, leading to the exposure of copper layer. Under the galvanical situation, the reaction between copper(Cu) and sulfur(S) from bonding adhesive produced copper sulfide (CuS), which stacked on the wire, caused high resistance, concentrated heat, a local temperature rise, and further promoted the growth and accumulation of CuS, resulting in wire breakage, or even rupture, causing the inductor even amplifier failure.