KR20040039196A - Thermally conductive polymer overmold for a disc drive actuator assembly - Google Patents

Abstract

The thermally conductive and electrically insulating overmolding 120 encapsulates and supports the actuator coil 118 in the disk drive actuator assembly 110. The overmold is made of a base resin mixed with a ceramic filler compound such as boron nitride, alumina, aluminum nitride, magnesium oxide, zinc oxide, silicon carbide, beryllium oxide, chromium oxide or a mixture thereof. The base resin is preferably polysulfene polysulfide. It is also preferred to add glass fibers and / or binders. The overmold reduces the track deviation error in the read / write head 116 supported by the actuator assembly by reducing the popping force caused by sudden expansion and contraction of the actuator coil during operation.

Description

THERMALLY CONDUCTIVE POLYMER OVERMOLD FOR A DISC DRIVE ACTUATOR ASSEMBLY}

Data storage devices of the kind known as "Winchester" disk drives are well known in the industry. Such disk drives magnetically record digital data on circular concentric data tracks on the surface of one or more rigid disks. The disk is generally mounted to rotate about the axis of the spindle motor. In the current generation of disc drives, the disc spins at speeds of up to 10,000 revolutions per minute.

Data is written to and retrieved from the disc by a vertically aligned read / write head assembly or a row of heads that are controllably disposed by the actuator assembly. Each head generally includes an electromagnetic transducer read and write element received on an air bearing slider. The slider operates in cooperative fluid dynamics with a thin layer of air towed along the rotating disk to slide each head in close proximity to the disk surface. In order to maintain a proper sliding relationship between the head and the disc, the head is attached to and supported by the head suspension or bend.

In fact, the actuator assembly used to position the head assumes several forms. Most disc drives that generate current are integrated with a type of actuator called a rotary voice coil actuator. A typical rotary voice coil actuator includes a pivot shaft fixed to a disc drive housing base deck at a position adjacent to the outer edge of the disc. The pivot shaft is mounted such that its central axis is referenced to the plane of rotation of the disk. The actuator bearing housing is mounted to the pivot shaft by the placement of the correct ball bearing assembly. The actuator bearing housing supports the coil contained in the magnetic field of the permanent magnet. The permanent magnet is mounted to the disc drive housing base deck.

The actuator assembly also includes a centrally located E-block. Opposite the coil in the actuator bearing housing there are a plurality of vertically aligned radially extending actuator arms. The actuator arm and coil are connected to the E-block. The bend is mounted on the actuator arm. When a current is applied to the coil, the coil generates a magnetic field that interacts with the magnetic field of the permanent magnet to move the head across the disk surface by pivoting the actuator bearing housing relative to the pivot shaft.

Closed loop servo systems, such as disclosed in US Pat. No. 5,262,907, published November 16, 1993, assigned to the assignee of the present invention, are generally used to maintain head position relative to the data track. Such a servo system obtains head position information from a servo data field written to a track when manufacturing a disc drive, and keeps the selected head on the associated track during the track advance mode operation.

Seek mode operation, which consists of initial acceleration of the head away from the initial track and subsequent deceleration of the head to the destination track, is also controlled by the servo system. This search operation, where the speed of the head is measured repeatedly and compared to the speed profile, is generally controlled by the current applied to the coil, which is generally proportional to the difference between the actual speed and the profile speed as the head moves to the destination track. .

A continuing trend in the industry is to provide disk drives that further enhance data storage and transfer capabilities. This trend leads to efforts to minimize the time required to perform search operations. Typical seek operations include initialization overhead time while the disk drive is servicing its internal operations, seek time while the head moves to the destination track and settles, and specific sectors on the destination track as the disk rotates about the head. Includes latent time the drive waits until it reaches.

Seek time was minimized by applying a large amount of current to the coil during the acceleration and deceleration phases of the seek operation. However, as the current increases, the electrical energy dissipated as heat by the coil also increases, increasing the temperature of the coil. As the coil temperature rises, the resistance of the coil increases and the magnitude of the control current is limited, which adversely affects the seek time. In addition, elevated coil temperatures can cause degradation of adhesives and insulating materials used in the construction of voice coil motors (VCMs).

Actuator overmolds are used in prior art disc drives to support coils and dampen vibrations. The actuator overmold generally consists of a liquid crystal polymer (LCP), thermoplastic or thermoset plastic resin formed on a portion of the actuator assembly. The actuator body, coils and other components are generally assembled, placed inside a mold having a mold cavity, and thermoplastic material is injected into the mold cavity.

The heat generated by the coils causes the coils to heat up and expand, which causes problems during search operations for some models. The heat generated by the coil heats the overmold, but the overmold expands at a different rate than the rate at which the coil expands. Following the seek operation, the coil and overmold also shrink at different rates. As a result of different rates of expansion and contraction, stresses appear between the coil and the overmold. These stresses are suddenly accentuated by "popping" which produces a sudden force internally in the actuator. This force "tracks off" the head, causing data read and write errors.

The stresses caused by different proportions of expansion are further exacerbated by the fact that the amorphous glass / inorganic filled polymer resin exhibits a sudden increase in the coefficient of thermal expansion when the temperature reaches the glass transition temperature. The glass transition temperature indicates the onset of relative movement between polymer chains that accumulate internal strain energy when the polymer is pressed in some way. This change in the coefficient of thermal expansion can be returned to its original state unless the entire polymer is crystallized. Upon cooling of the overmolded material, the temperature is lower than the glass transition temperature so that popping occurs and the stored energy is available.

As such, there is a need for an improved actuator design that overcomes the above and other limitations of the prior art.

This application claims the benefit of US preliminary application 60 / 290,093, filed May 10, 2001.

FIELD OF THE INVENTION The present invention relates generally to disk drive data storage, and more particularly to a new overmold used to support coils of actuators used to move read / write head rows adjacent to a corresponding number of disk write surfaces.

1 is a plan view of a disk drive constructed in accordance with a preferred embodiment of the present invention.

2 is a perspective view of an actuator assembly according to a preferred embodiment of the present invention.

3 is a time-to-temperature coordinate plot of a test for estimating the heat loss characteristics of an overmold in a disk drive with a single disk.

4 is a time versus temperature coordinate diagram of a test for estimating the heat loss characteristics of an overmolded in a disk drive with two disks.

According to a preferred embodiment, a thermally conductive and electrically insulating overmold is provided which encapsulates and supports the actuator coil of the disc drive actuator assembly. The overmold is made of a base resin mixed with a ceramic filler compound of boron nitride, alumina, aluminum nitride, magnesium oxide, zinc oxide, silicon carbide, beryllium oxide, chromium oxide or mixtures thereof. In certain preferred embodiments, the base resin is a liquid crystalline polymer, polyethylene naphthalic acid, polyethylene terephthalic acid, polybutylene terephthalic acid, polyamide, polyphthalamide, polysulfene sulfide, polycarbonate, polyetheretherketone and oxidation Thermoplastics such as polyphenyline. In some embodiments, the overmolded material includes a binder and / or glass fibers.

The overmolded material is electrically insulating and thermally conductive and has a thermal expansion rate that closely matches the thermal expansion rate of the actuator coil so that it is selected to reduce head position error due to popping (sudden force induced by thermal expansion and contraction of the actuator coil). It is desirable to be.

The above and various other features as well as the advantages of the features of the present invention will become apparent from the following detailed description and the accompanying drawings.

1 provides a top view of a disk drive 100 constructed in accordance with a preferred embodiment of the present invention. Base deck 102 and top cover 104 (some cut away) together form a sealed housing of disk drive 100. Spindle motor 106 rotates a plurality of magnetic recording disks 108 at a constant high speed.

Actuator E-block 110 includes a number of rigid actuator arms 112 that extend adjacent the disk surface. A bendable suspension assembly 114 extends from the arm 112 to support the read / write head 116 rows. The actuator 110 is pivotally moved by applying a current to the actuator coil 118 of the voice coil motor (VCM) 119. The coil 118 is encapsulated and attached to the actuator by an overmolded structure (overmolded) 120.

2 shows a perspective view of the actuator overmold 120 in more detail. The overmold 120 includes an inner bobbin portion 122 disposed within the coil 118 and an outer portion 124 surrounding the outside of the coil 118. The inner and outer portions 122, 124 may be separate members as shown, or integrally such that a portion of the overmold 120 extends over the coil 118 to connect the inner and outer portions 122, 124. It may be formed. The outer portion 124 includes limiting surfaces 126, 128 that contact the limit stops 130, 132 (shown in FIG. 1) in the radial range of actuator travel.

The outer portion 124 also includes a latch arm 134 that engages the magnetic latch 136 (shown in FIG. 1) to latch the actuator 110. The detailed configuration of the overmold 120 may vary depending on the needs of a given application, and the embodiments shown in FIGS. 1 and 2 are for illustrative purposes and not limitation.

The overmold 120 is made of an overmold material comprising a base resin mixed with a ceramic filler compound. The base resin is preferably a thermoplastic polymer compound selected from polyphenylene sulfide (PPS), liquid crystal polymer (LCP) compounds or a mixture of mixtures comprising polyethylene naphthalic acid, polyethylene terephthalic acid and polybutylene terephthalic acid. Other polymers that can be used as the base resin include polyamides, polyphthalamides, polycarbonate esters, polyetheretherketones, and polyphenylene oxides.

In a preferred embodiment, the ceramic filler compound is boron nitride. In another preferred embodiment, the ceramic filler compound is alumina (or aluminum oxide). Other ceramic filler compounds may include aluminum nitride, magnesium oxide, zinc oxide, silicon carbide, beryllium oxide and chromium oxide. The ceramic filler compound may also consist of a mixture of selected ones of the ceramic filler compounds described above. Preferably, the ceramic filler compound constitutes up to 25% to 90% of the mass of the overmolded material. Base resins generally comprise from 10% to 75% of the mass of overmolded material.

Coil 118 is subjected to several cycles of heating and cooling caused by different current demands during operation. The coil material, actuator material and overmold material have different compositions. As a result, these different parts have different coefficients of thermal expansion which cause them to expand and contract at different rates. This causes the overmold 120 to have a significant amount of strain energy. This strain energy is released as popping. In order to effectively prevent popping, the overmolded material preferably has a thermal conductivity of at least 0.40 W / m- ° K to prevent popping by eliminating the heat generated by applying a current to the coil 118.

In certain preferred embodiments, the glass fibers are mixed with the base resin and the ceramic filler compound. In another preferred embodiment, the overmolded material comprises a binder and / or a dispersant, referred to herein as a binder. The binder promotes more sufficient wetting of the ceramic filler compound. The binder also helps to reduce the melt viscosity of the overmolded material and improves the adhesion between the base resin and the ceramic filler compound. Binders are well known in the art and include neoalkoxy titanate binders and monoalkoxy titanate binders. The binder generally comprises a mass of about 0.1% to 5% of the overmolded material.

In addition to providing structural support and vibration dampening for the actuator, the overmold conducts heat away from the coil 118. This heat is transferred by air to the air stream circulating through the disk drive housing. This prevents or reduces stress caused by different expansion rates of the coil and overmold, the occurrence of popping, and read and write errors caused by the head leaving the track by popping.

Test result

Several tests have been done to measure heat loss from disk drives having different kinds of overmolded materials. The temperature of the coil was measured as a function of time for 90 seconds. 3 shows the test results for a particular 1-disk disk drive shown for elapsed time x-axis 140 and temperature (degrees Celsius) y-axis 142. For the tests indicated by the temperature curve 144, the base resin of polyphenylene sulfide (PPS) was filled with 20% of the mass of glass. This is a kind of overmolded material known in the prior art which has a thermal conductivity of 0.3 W / m- ° K.

Curve 148 represents a test using an overmolded material (composition "C") in which a ceramic filler compound of PPS base resin (mass 45%) and boron nitride (mass 40%) was mixed with glass fibers (mass 15%). . Curve 146 represents a test using an overmolded material (composition "G") in which a ceramic filler compound of PPS base resin (mass 45%) and boron nitride (mass 35%) was mixed with glass fibers (mass 20%). .

It can be observed from FIG. 3 that the compositions (C and G) tested both provide significantly better results than conventional compositions.

4 shows the test results for a two-disk disk drive using an overmold of the composition. Curve 154 represents the results for the compositions of the prior art, curve 158 represents the results for composition (C), and curve 156 represents the results for composition (G). As before, composition (C) was found to give the best results of those tested. Both compositions (C and G) worked significantly better than the prior art. The tests also show that the use of both compositions (C and G) significantly reduces track deviation errors due to popping.

Thus, a thermally conductive and electrically insulating overmolded 120 or the like is provided to the disk drive 100 or the like. The overmold is made of a base resin mixed with a ceramic filler compound. In certain preferred embodiments, the ceramic filler compound is selected from the group of boron nitride, alumina, aluminum nitride, magnesium oxide, zinc oxide, silicon carbide, beryllium oxide, chromium oxide, or mixtures thereof. In certain preferred embodiments, the base resin is polyethylene naphthalic acid, polyethylene terephthalic acid, polybutylene terephthalic acid, polyamide, polyphthalamide, polyphenene sulfide, polycarbonate, polyetheretherketone and polyphenylene oxide It is selected from the group of compounds containing. In some embodiments, the overmolded comprises a binder. The presence of the thermally conductive material in the overmold helps to eliminate popping because the overmold conducts heat away from the coil with a higher thermal conductivity compared to the overmold without the thermally conductive material.

For the purposes of the appended claims, the term overmold is understood to describe a structure for encapsulating and supporting an actuator coil 118, consistent with the above description. The overmolded has an inner bobbin portion 112, etc. in the coil, and an outer portion 124, etc. extending out of the coil. The term encapsulation is understood to enclose at least two mating sides of the actuator in contact, and does not necessarily touch all sides of the actuator.

For the purposes of the appended claims, it is understood that the above-described functions performed by the "first means" are performed by the overmold 120 formed in accordance with various embodiments of the base resin and ceramic filler compound compositions described above. Prior art compounds such as the prior art compositions of polyphenylene sulfide and glass fibers described with reference to FIGS. 3 and 4 do not perform the functions described above, are explicitly excluded from the scope of the claims and are explicitly excluded from the definition of equivalents.

While the foregoing description has described various features and advantages of the various embodiments of the present invention along with details of the structures and functions of the various embodiments of the present invention, these detailed descriptions are exemplary only, and in detail, in particular within the principles of the present invention. Modifications may be made in some constructions and arrangements to the fullest extent indicated by the broad general meaning of the terms indicated in the appended claims. For example, certain elements may be modified in accordance with the particular application of the overmold without departing from the spirit and scope of the invention.

Further, while the embodiments described herein refer to overmolds for disk drive actuator assemblies, it will be appreciated by those skilled in the art that overmolds may be used in other devices without departing from the spirit and scope of the claimed invention.

Claims (10)

As a disk drive, Rotatable discs; And A read / write head supported adjacent to the disk, an actuator coil for applying current to rotate the actuator assembly, and encapsulated and supported by the actuator coil, formed of a base resin mixed with a ceramic filler compound, and formed into the actuator coil. And an overmold configured to have a coefficient of thermal expansion that minimizes popping of the overmold during heating of the actuator coil due to applying a current. The disk drive of claim 1, wherein the ceramic filler compound is selected from the group of ceramic filler compounds consisting of boron nitride, alumina, aluminum nitride, magnesium oxide, zinc oxide, silicon carbide, beryllium oxide and chromium oxide. The disk drive of claim 1, wherein the ceramic filler compound is present in the overmold at a mass concentration of 25% to 90%. The disk drive of claim 1, further comprising glass mixed with the resin and the ceramic filler compound. The disk drive of claim 1, wherein the base resin is a liquid crystal polymer. The method of claim 1, wherein the base resin is polyethylene naphthalic acid, polyethylene terephthalic acid, polybutylene terephthalic acid, polyamide, polyphthalamide, polyphenylene sulfide, polycarbonate, polyether ether ketone and polyphenyl oxide A disk drive selected from a set of base resins consisting of lean. The disk drive of claim 1, wherein the base resin is present in the overmolded material at a mass concentration of 10% to 75%. The disk drive of claim 1, wherein the overmolded material further comprises a binder. 9. The disk drive of claim 8, wherein said binder is selected from a set of binders consisting of neoalkoxy titanate or monoalkoxy titanate. The disk drive of claim 1, wherein the overmolded material has a thermal conductivity of at least 0.40 W / m- ° K.