Soft ESD phenomena in GMR heads in the HDD manufacturing process

GMR (giant magnetoresistive) heads used for HDD (hard disk drives) are very sensitive to ESD (electrostatic discharge). Some kinds of ESD damages will cause soft magnetic degradations of head performance with a progressive nature. We report examples of head degradations by ESD damages as well as other damages due to head scratches, electro-migration effects and corrosion of GMR stack. It is usually very difficult to distinguish these phenomena explicitly by QST (quasistatic tester) and spinstand measurement test. We show that head scratches can cause damages similar to damages caused by ESD and that re-magnetization has certain potential to correct the damaged magnetic structure caused by such scratches.