The development of head induced crown control in hard disk drive head gimbal assembly (HGA) line

Abstract

The Fly Height Gap is the most important factor for Hard Disk Drive reliability because it is one of the
key input process variables (KPIVs) for read-write process efficiency in terms of magnetic flux intensity. The
Fly Height Gap is the distance between the slider or head and the magnetic surface of a disk while the Hard
Disk Drive is operating. Many KPIVs have been studied and controlled in the Head Gimbals Assembly (HGA)
process; Pitch-Roll Static Attitude, Slider Alignment and Induced Crown among others. Controlling the
induced crown reduces the process variations from head to head and from hard drive to hard drive so that the
Fly Height Gap and HGA crown variations can be reduced and controlled.
This research examines the potential KPIVs of induced crown, including the control limit of these
variables. The Six Sigma methodology is employed to investigate the induced crown behavior in the HGA
process. All key HGA processes are considered by following toolkits so as to find the potential KPIVs; Cause
and Effect Diagram, Process Mapping, Prioritization. In totally, thirteen variables are considered in the
experiment. The design of the experiment (DOE) methodology is employed to identify and optimize the
potential KPIVs. The fraction factorial design model is employed to screen the potential KPIVs. The results
indicate six variables which have a significant effect on the induced crown. Only three variables; Parameter C,
E and K; are selected for process behavior study using the Full Factorial Design. The results indicate that two
variables (C and E) have a significant effect on the induced crown. The Central Composite Design (CCD)
experiment is employed as the final stage to identify the optimum machine set up points.