Abstract:
A system and method for the prevention of electrostatic discharge (ESD) by a hard drive magnetic head is disclosed. The magnetic head is secured to a head-gimbal assembly (HGA) by anisotropic conductive paste (ACP) to provide an improved electrostatic discharge path.

Description:
BACKGROUND INFORMATION  
         [0001]    The present invention relates to magnetic hard disk drives. More specifically, the present invention relates to a system and method for securement of a hard drive magnetic head to a head-gimbal assembly (HGA) to prevent electrostatic discharge (ESD) by the magnetic head.  
           [0002]    [0002]FIG. 1 provides an illustration of a typical drive arm configuration as used in the art. A magnetic head  108  is utilized to read from and write to a magnetic hard disk. 106 . Voice-coil motors (VCM)  102  are used for controlling a hard drive&#39;s arm  104  motion across the magnetic hard disk  106 .  
           [0003]    [0003]FIG. 2 provides an illustration of a head gimbal assembly (HGA)  204  and slider  202  as used in the art. Typically, a slider  202  (containing a read/write magnetic head; not shown) is utilized for maintaining a prescribed flying height above the disk surface  106  (See FIG. 1). During flight over the disk, electrostatic charge accumulates on a head&#39;s surface. If the charge is not removed, an electrostatic discharge (ESD) may occur, damaging the magnetoresistive (MR) element. Electrically-conductive adhesives are used in the art to bond head to suspension, allowing static charge to be discharged from the head  202  to the suspension (HGA)  204 .  
           [0004]    As the size of slider/head elements reduces to provide for increasing areal density, the energy necessary to cause damage by an ESD reduces, causing the likelihood for ESD to increase and rendering current methods of ESD prevention obsolete. For example, electrostatic current traveling from head to suspension through electrically-conductive adhesive may experience a resistance of greater than 1000 ohms at a one-volt potential, which is too large to meet giant magnetoresistive (GMR) heads&#39; requirements for ESD prevention.  
           [0005]    [0005]FIG. 3 a - b  illustrates a system for securing a head  302  to a suspension  304  (HGA) with an electrically conductive isotropic adhesive  307  as is used in the art. As seen in FIG. 3 a , conductive isotropic adhesives  307 , such as silver paste, contain conductive particles  311  (e.g., silver), which provide a pathway for electrostatic discharge from the head  302  to ground (suspension  304 /HGA).  
           [0006]    As shown in FIG. 3 b , electrostatic (electrical) resistance is large for current passing through a typical isotropic adhesive  316  from head  312  to suspension  314  due to the distribution of conductive particles  320 , 322  within the head  312  and the isotropic adhesive  316 . The head/slider  312  is typically made of Al 2 O 3    319  and TiC  320  (together known as ALTIC). TiC  320  is electrically conductive, but Al 2 O 3    319  is not. Silver epoxy, a typical isotropic conductive adhesive  316 , is made of a binder resin  321  and silver powder  322 . Silver powder  322  is electrically conductive, but binder resin is not. The internal distribution of these electrically conductive subparticles  320 , 322  causes the resistance problem. Although many TiC  320  particles may line up to provide an electrically conductive path toward the suspension  304 , each TiC particle  320  terminating at the head  302 /adhesive  306  interface has a low probability of being in physical contact with a particle of silver powder in the adhesive  306 . Further, between each particle of silver  322  there is a this film of binder resin  321 , which inhibits electrical current flow. Because of the small size of the silver particles  322 , it can take several particles  322  to form an electrostatic discharge path, and thus, for each path there are several points in which the current must cross (highly resistive) binder resin  321 , increasing the overall resistance across the isotropic adhesive.  
           [0007]    It is therefore desirable to decrease head-to-suspension adhesive resistance to prevent electrostatic discharge (ESD) by the magnetic head as well as providing additional benefits.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 provides an illustration of a typical drive arm configuration as used in the art.  
         [0009]    [0009]FIG. 2 provides an illustration of a head gimbal assembly (HGA) and slider as used in the art.  
         [0010]    [0010]FIG. 3 a - b  illustrates a system for securing a head to a suspension with an electrically conductive isotropic adhesive as is used in the art.  
         [0011]    [0011]FIG. 4 a - b  provides an illustration describing the attachment of a magnetic head to a suspension with electrically conductive anisotropic conductive paste (ACP) under principles of the present invention.  
         [0012]    [0012]FIG. 5 a - b  illustrates ACP attachment of magnetic head to suspension with and without a suspension barrier under principles of the present invention.  
         [0013]    [0013]FIG. 6 a - b  illustrates the ‘dual cure’ process for ACP under principles of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0014]    [0014]FIG. 4 a - b  provides an illustration describing the attachment of a magnetic head  402  to a suspension (HGA)  404  with electrically conductive anisotropic conductive paste (ACP)  401  under principles of the present invention. As is shown in FIG. 4 a , in one embodiment a magnetic head  402  is secured to the suspension  404  by Ultraviolet ACP (ACP)  401 . In an embodiment, a suspension barrier  409  is utilized to maintain proper directional orientation while the ACP is curing. The barrier  409  prevents the head  402  from tilting, etc. in relation to the suspension  404  while the adhesive  410  is still soft.  
         [0015]    As is shown in FIG. 4 b , in an embodiment the conductive particles  405  of the ACP  406  are much larger than the silver particles. In one embodiment, the conductive particles  405  are made of a polymer coated in gold. In an alternative embodiment, the particles  405  are made of a metal, such as nickel, etc., coated in gold. In one embodiment, the adhesive material in which the particles are suspended is Acrylate. In an alternative embodiment, the adhesive material is epoxy resin. The conductive particles  405  are large enough for each particle  405  to touch the head  402  and the suspension  404  simultaneously. Thus, the particles  405  must be at least as large in diameter as the depth of the tongue barrier  409 . (See FIG. 4 a ). Because each conductive path through the ACP  406  is just through a single particle  405 , resistance is greatly reduced.  
         [0016]    [0016]FIG. 5 a - b  illustrates ACP attachment of magnetic head  502  to suspension  504  with and without a suspension barrier  504  under principles of the present invention. In an embodiment, ACP  501  with large conductive particles  503  is utilized with a suspension barrier  509 . As stated, in an embodiment the conductive particles  503  are larger than the suspension barrier  509  in depth (to enable particle  503  contact with head  502  and suspension  504  simultaneously).  
         [0017]    As seen in FIG. 5 b , in an alternative embodiment a suspension barrier  509  is not utilized. Because a suspension barrier is 15 to 25 micrometers (um) in depth, without a suspension barrier, the conductive particles  513  can be smaller than this when a barrier is not utilized (reduced bondline gap).  
         [0018]    [0018]FIG. 6 a - b  illustrates the ‘dual cure’ process for ACP  608  under principles of the present invention. As seen in FIG. 6 a , in one embodiment, ultraviolet (UV) light  609  is directed upon the ACP  608  to cure the exposed surface of the ACP material  608 . This is done to provide a preliminary cure, affixing the head  602  to the suspension  604 , to maintain directional orientation of the head  602 . In an alternate embodiment, a (non-conductive) UV adhesive (not shown), such as UV acrylate or UV epoxy, is utilized additionally for pre-tacking (to shorten the fixture time). As seen in FIG. 6 b , in an embodiment the UV process is followed by a thermal cure (via a heater  611 ). In this, the ACP is fully cured, bringing its bond to full strength.  
         [0019]    Although several embodiments are specifically illustrated and described herein, it will be appreciated that modifications and variations of the present invention are covered by the above teachings and within the purview of the appended claims without departing from the spirit and intended scope of the invention.