Non-contact method for testing for MR shield short circuits

摘要

The present invention provides a test circuit and method for testing for short circuits in an MR head, merged MR head or piggyback MR head without contacting either of the shield layers. This is accomplished by a bridge circuit which employs part of the components of the head. The bridge circuit has four consecutively arranged branches which are interconnected by four consecutively arranged terminals. The first terminal comprises the substrate or one of the write pads and the second and fourth terminals comprise the first and second read pads. A signal generator is connected across the first and third terminals and a detector, such as a differential amplifier, is connected across the read pads. With this arrangement the first branch of the bridge circuit includes a capacitance which is formed by one of the gap layers between one of the shield layers and a first one of the leads and the second branch of the bridge circuit includes a capacitance which is formed by said one of the gap layers between said one of the shield layers and a second one of the leads. The differential amplifier detects any impedance imbalance in the bridge circuit which indicates that coupling between one or more of the shields and one or more of the leads has changed. Most likely the head has a shield short circuit and can be discarded.