Al Wallash

Electromagnetic field induced degradation of magnetic recording heads in a GTEM cell

A gigahertz transverse electromagnetic mode (GTEM) cell was used to apply a controlled RF electric field to magnetic recording assemblies. The resistance and magnetic properties of the giant magnetoresistive (GMR) and tunneling MR (TMR) sensors were measured before and after exposure to the electric field. No degradation in GMR sensor properties was observed for pulsed field strengths up to 40 V/m for the standard assembly configuration. However, severe resistance and magnetic damage was observed when an additional 7 cm long wire was attached to the input of the GMR sensor. It is concluded that it is important to understand and measure the radiated immunity failure level for extremely ESD sensitive devices like magnetic recording assemblies.

ESD SPICE model and measurements for a hard disk drive

A simple lumped RLC model for a hard disk drive is developed and used in SPICE circuit simulations. Simulation results were compared with experimental measurements using a special ldquohybridrdquo disk drive to validate the SPICE model. The voltage on and between the head and disk inside the drive were modeled during an ESD event to the baseplate and/or disk. Experimental measurements and SPICE modeling show that if the disk grounded when there is a large disk-to-base resistance, then head-to-disk electrical breakdown can occur. It is concluded that an electrical model is valuable in developing an understanding of the effects of ESD on a hard disk drive.

Wire bonding tip study for extremely ESD sensitive devices

Ultrasonic bonding tools are used extensively in many industries. This study will examine the mechanism of Ultrasonic wire bonding & the effects of ESD charge removal using a common ceramic material spread into 3 different resistances groups and recording the behavior. Our purpose is to examine the bonding tools ability to control - voltage and characterize their respective dissipation rates for the purpose of determining an optimum process window. Experimentation will show the positive & negative effects of typical tools in use today as mechanical bonding tools. An analysis is shown of the effectiveness of the tip in simulating the dissipating voltage away from a floating GMR head. We will examine their ability to discharge voltage from devices and reduce ESD currents.

Thermal Effects and Self-Heating Time Constant for GMR Recording Heads

An understanding of the temperature of the GMR reader element used in disk drives during operating and non-operating condition is critical to optimize its performance. Self-heating and/or external heat sources will cause an increase in the temperature of the GMR sensor. In this work we concentrate on the self-heating effect due to bias current. Experiments that monitored the resistance change during very short current pulses showed that state-of-the-art GMR sensors have an extremely short time-constant that is less than 2 ns. This work is applicable to the current transients that the GMR head experiences during electrical crosstalk, electrostatic discharge and thermal asperities.Copyright

Transmission line pulse ESD testing of giant magnetoresistive recording heads

The behavior of giant magnetoresistive recording heads during transmission line pulse (TLP) testing is reported for the first time. The design of a simple TLP tester is described and used to produce current pulses with widths from 0.8 to 40 ns. The TLP tester was used with a quasistatic R(H) tester to measure the resistance and magnetic damage to the recording head. It is concluded that an easily built TLP tester is useful for producing high current pulses of varying width for electrostatic discharge testing of recording heads.