Effects of the suspension interconnect on ESD failures of the head stack assemblies

With increasing recording density and shrinking size of giant magnetoresistive (GMR) read/write heads, the GMR sensor is getting more sensitive to electrostatic discharge (ESD) events. In this study, two different types of head stack assembly (Type A and Type B) were studied in terms of ESD sensitivity. Both head stack assemblies (HSA) consist of head gimbal assemblies (HGA), preamplifier, E-block, flexible printed cable (FPC), voice coil motor (VCM) coil, and 20-pin connector for 3.5-in drive. Type A is a conventional HSA consisting of two or four HGAs with long tail suspensions whereas Type B is a head stack consisting of one HGA with FPC interconnect instead of a long tail. ESD events were simulated by zapping 20-pin connector with an ESD gun. A quasi-static tester (QST) was used for amplitude and resistance measurement of GMR heads after each ESD event. The test results showed that the failure voltage of Type B (1.0-1.2 kV) is much lower than Type A (4.0-5.0 kV). Furthermore, failed HSAs showed different failure modes: preamplifier damage for Type A and read sensor damage for Type B. To understand the main reason for low failure voltage for Type B, we investigated ESD sensitivity by modifying Type B with different interconnects, bonding methods, and arm actuator structures. These results indicate that the write-to-read crosstalk of interconnect (from preamplifier to head slider) during ESD events caused low failure voltage for Type B. It was found that the metallic structure surrounding the VCM coil is another cause for the low failure voltage of Type B.