Effect of magnetic field and electric field emission from discharge current in gold ball bonding process upon TMR heads

Abstract

Tunnelling Magnetoresistive (TMR) heads in magnetic recording heads can be damaged by an electric
fi eld and degraded by an external magnetic fi eld. This work presents the effects of electric-magnetic fi eld emission
caused by a discharge current on TMR head during making electrical connection in head gimbal assembly (HGA).
A bonding current was acting as an Electromagnetic Radiation (EMR) source being captured by a current probe.
The effects of electric and magnetic fi elds upon TMR heads were carried out by using a fi nite-integral-based
simulator. The electric and magnetic fi eld strength were monitored and compared with the threshold level of
TMR head technology. The simulations show that the radiated magnetic fi eld strength located at TMR heads is
approximately 0.60 Oe while the radiated electric fi eld strength caused by the discharge current is 0.14 GV/m.
The dielectric strength of MgO is approximately 0.95 GV/m; therefore, the radiated electric fi eld is 14.74% of
the breakdown level while the radiated magnetic fi eld is only 0.63% of threshold magnetic fi eld (exchange bias
fi eld) of 100 Oe. In conclusion, during a gold ball bond process, the possibility of TMR heads being damaged
by dielectric breakdown at MgO layer is 23.40% higher than the case of the magnetization reversal at AFM/FM
interface.