Precision Manufacturing Technology

A VCMA is an assembly consisting of two metal plates, two strong permanent magnets, and spacers used between the plates to create a gap for the coil assembly.

VCMA product



A Voice Coil Motor Assembly (VCMA) is a set of strong rare earth magnets bonded to steel yokes. The magnetic field provided by the VCMA interacts with the actuator coil, which is a multiple turn wire electromagnetic structure that is attached at the end of the actuator arm opposite the heads and actuator pivot.

Applying a current to the coil generates an electromagnetic field, which in combination with the VCMA, drives the actuator arm, positioning the heads over the desired location on the disk. Most HDDs use two VCMA plates—one each for the bottom and the top. Single-headed HDDs, where only one side of the disk is used for data storage, can utilize only the bottom magnet assembly.  The vast majority of HDDs operate with two or more heads. The size and spacing of the magnets depends on the HDD form factor, with 3.5” desktop HDDs requiring thicker magnets to handle the larger multi-headed actuator arms. Precision forming of the yoke assembly is a critical assembly step for VCMAs as the dimensions and tolerances of the yoke are responsible for accurate spacing and positioning of the magnets around the coil. Improper tolerances in the VCMA assembly can cause unwanted actuator behavior during operation, thus increasing the noise of the HDD and possible damage to the delicate head and suspension assemblies at the end of the actuator arm. Some designs can be rather complex, with latches, spacers, pins and stoppers built into the VCMA; therefore sophisticated assembly tooling and processes must be implemented to produce precision parts. In addition to precise forming and assembly of the yokes and magnets, the VCMA production must operate at high yield and low cost to maintain the challenging low price levels demanded by the HDD OEMs for this component.

MMI is vertically integrated, and fabricates the magnets for the VCMA in-house, using rare earth metals mined mostly in China.  MMI’s core competency in tooling development for manufacturing of precision metal components provides the company with certain advantages in VCMA fabrication.  Some VCMA designs can be rather complex with pins, spacers, stoppers and actuator latches built into the VCMA.  For these more integrated designs, tooling must by highly customized and advanced to achieve a high degree of automation. One of MMI’s core strengths is in developing and building its own automated assembly and testing tools—particularly advantageous relative to its competition. The ability to drive out cost through internal process and tooling development allows MMI to maintain leadership in this highly competitive branch of the HDD component industry.

Manufacturing a VCMA