Abstract:
A method and an apparatus for retaining magnetic properties of a magnet while undergoing manufacturing processes are presented. Ferrous materials with relatively good magnetic permeability are disposed adjacent to poles of magnet substantially containing magnetic field lines from the magnet within the ferrous materials. When the magnetic field lines are thereby substantially contained, the magnet can be exposed to elevated temperatures without losing magnetization strength. Adhesives, particularly adhesives that cure when exposed to elevated temperatures can be used with magnets configured to contain magnetic field lines without having the magnets lose magnetic strength.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This U.S. patent application claims priority under 35 USC 119(e) to U.S. Provisional Patent Application No. 61/715,817 filed Oct. 18, 2012 entitled “Magnetic Property Retention” by McBroom et al. which is incorporated by reference in its entirety for all purposes. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates generally to magnetic properties of magnets and more particularly to retaining magnetic properties of magnets during processing at elevated temperatures. 
       BACKGROUND 
       [0003]    A portable computing device can include an enclosure configured to contain the various components that make up the device. For example, the enclosure can include a base portion and a lid portion. In some embodiments, one or more magnets can be used to form a magnetic latch to hold the lid portion in a closed position next to the base portion. Affixing the magnets to the lid portion can require an adhesive that can require exposure to elevated temperatures to cure within a predetermined time period. Unfortunately, elevated temperatures can cause magnets to become partially or totally demagnetized. 
         [0004]    Therefore, what is needed is a way to configure magnets to be able to withstand elevated temperatures without losing some or all of their magnetic properties. 
       SUMMARY 
       [0005]    The present application describes various embodiments regarding systems and methods for curing a temperature sensitive adhesive used in a magnet application while preserving magnetic properties. In one embodiment, a method for attaching a magnet to a lid of a personal computing device can include the steps of receiving a magnet and a magnetic shunt, attaching the magnetic shunt to the lid with an adhesive, attaching the magnet to the magnetic shunt with the adhesive, placing a magnetic keeper on the magnet where the magnet fields from the magnet are substantially contained within the magnetic shunt and the magnetic keeper, heating the magnet, the magnetic shunt and the adhesive to a predetermined temperature for a predetermined amount of time and removing the magnetic keeper. 
         [0006]    A method for reducing the curing time of an adhesive used for bonding a magnet with preserving magnetic properties of the magnet can include the steps of receiving the magnet, affixing the magnet to a support structure with an adhesive, attaching a magnetic keeper to each magnetic pole of the magnet, heating the magnet, adhesive, magnetic keepers and support structure to a predetermined temperature and removing at least one magnetic keeper. 
         [0007]    A fixture for curing an adhesive used for bonding a magnet while preserving magnetic properties of the magnet can include a structure configured to receive the magnet and a magnetic shunt, a temperature sensitive adhesive configured to cure at elevated temperatures placed between the magnetic shunt and the structure and placed between the magnetic shunt and the magnet and a magnetic keeper removably attached to the magnet and configured to substantially contain magnetic field lines from the magnet. 
         [0008]    Other apparatuses, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The included drawings are for illustrative purposes and serve only to provide examples of possible structures and arrangements for the disclosed inventive apparatuses and methods for providing portable computing devices. These drawings in no way limit any changes in form and detail that may be made to the invention by one skilled in the art without departing from the spirit and scope of the invention. The embodiments will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
           [0010]      FIG. 1  shows a front facing perspective view of an embodiment of the portable computing device in the form of portable computing device in an open (lid) state. 
           [0011]      FIG. 2  shows portable computing device in a closed (lid) configuration that shows rear cover and logo. 
           [0012]      FIG. 3  shows an external view of bottom case. 
           [0013]      FIG. 4  is a drawing of a magnetization curve for a magnet. 
           [0014]      FIGS. 5A-5C  show possible effects of ferrous materials placed near a magnet. 
           [0015]      FIG. 6  is a simplified diagram of a portion of the rear cover  122  including a magnetic. 
           [0016]      FIG. 7  is a block diagram of a fixture for curing an adhesive in accordance with one embodiment described in the specification. 
           [0017]      FIG. 8  is a flow chart of method steps for reducing a curing time of an adhesive used for attaching a magnet while preserving magnetic properties of the magnet. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Representative applications of apparatuses and methods according to the presently described embodiments are provided in this section. These examples are being provided solely to add context and aid in the understanding of the described embodiments. It will thus be apparent to one skilled in the art that the presently described embodiments can be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order to avoid unnecessarily obscuring the presently described embodiments. Other applications are possible, such that the following examples should not be taken as limiting. 
         [0019]    The following relates to a portable computing device such as a laptop computer, net book computer, tablet computer, etc. The portable computing device can include a multi-part housing having a top case and a bottom case joining at a reveal to form a base portion. The portable computing device can have an upper portion (or lid) that can house a display screen and other related components whereas the base portion can house various processors, drives, ports, battery, keyboard, touchpad and the like. The base portion can be formed of a multipart housing that can include top and bottom outer housing components each of which can be formed in a particular manner at an interface region such that the gap and offset between these outer housing components are not only reduced, but are also more consistent from device to device during the mass production of devices. These general subjects are set forth in greater detail below. 
         [0020]    In a particular embodiment, the lid and base portion can be pivotally connected with each other by way of what can be referred to as a clutch assembly. The clutch assembly can be arranged to pivotally couple the base portion to the lid. The clutch assembly can include at least a cylindrical portion that in turn includes an annular outer region, and a central bore region surrounded by the annular outer region, the central bore suitably arranged to provide support for electrical conductors between the base portion and electrical components in the lid. The clutch assembly can also include a plurality of fastening regions that couple the clutch to the base portion and the lid of the portable computing device with at least one of the fastening regions being integrally formed with the cylindrical portion such that space, size and part count are minimized. 
         [0021]    The lid and the base portion can be formed of a strong and durable yet lightweight material. Such materials can include composite materials and or metals such as aluminum. Aluminum has a number of characteristics that make it a good choice for the multipart housing. For example, aluminum is a good electrical conductor that can provide good electrical ground and it can be easily machined and has well known metallurgical characteristics. The lid can include magnetic assemblies configured to hold the lid in a closed position next to the base portion. The magnets within the lid can be attached with an adhesive. In one embodiment, the adhesive can benefit from exposure to elevated temperatures to enhance the curing of the adhesive. Unfortunately, exposing magnets to elevated temperatures can cause magnets to partially or fully demagnetize. 
         [0022]    Using a magnetic keeper can help preserve magnetic properties of magnets even while they are exposed to elevated temperatures. This and other embodiments are discussed below with reference to  FIGS. 1-8 . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes as the invention extends beyond these limited embodiments 
         [0023]      FIG. 1  shows a front facing perspective view of an embodiment of the portable computing device in the form of portable computing device  100  in an open (lid) state. Portable computing device  100  can include base portion  102  formed of bottom case  104  fastened to top case  106 . Base portion  102  can be pivotally connected to lid portion  108  by way of clutch assembly  110  hidden from view by a cosmetic wall. Base portion  102  can have an overall uniform shape sized to accommodate clutch assembly  110  and inset portion  112  suitable for assisting a user in lifting lid portion  108  by, for example, a finger. Top case  106  can be configured to accommodate various user input devices such as keyboard  114  and touchpad  116 . Keyboard  114  can include a plurality of low profile keycap assemblies each having an associated key pad  118 . In one embodiment, an audio transducer (not shown) can use selected portions of keyboard  114  to output audio signals such as music. In the described embodiment, a microphone can be located at a side portion of top case  106  that can be spaced apart to improve frequency response of an associated audio circuit. 
         [0024]    Each of the plurality of key pads  118  can have a symbol imprinted thereon for identifying the key input associated with the particular key pad. Keyboard  114  can be arranged to receive a discrete input at each keypad using a finger motion referred to as a keystroke. In the described embodiment, the symbols on each key pad can be laser etched thereby creating an extremely clean and durable imprint that will not fade under the constant application of keystrokes over the life of portable computing device  100 . In order to reduce component count, a keycap assembly can be re-provisioned as a power button. For example, key pad  118 - 1  can be used as power button  118 - 1 . In this way, the overall number of components in portable computing device  100  can be commensurably reduced. 
         [0025]    Touch pad  116  can be configured to receive finger gesturing. A finger gesture can include touch events from more than one finger applied in unison. The gesture can also include a single finger touch event such as a swipe or a tap. The gesture can be sensed by a sensing circuit in touch pad  116  and converted to electrical signals that are passed to a processing unit for evaluation. In this way, portable computing device  100  can be at least partially controlled by touch. 
         [0026]    Lid portion  108  can be moved with the aid of clutch assembly  110  from the closed position to remain in the open position and back again. Lid portion  108  can include display  120  and rear cover  122  (shown more clearly in  FIG. 2 ) that can add a cosmetic finish to lid portion  108  and also provide structural support to at least display  120 . In the described embodiment, lid portion  108  can include mask (also referred to as display trim)  124  that surrounds display  120 . Display trim  124  can be formed of an opaque material such as ink deposited on top of or within a protective layer of display  120 . Display trim  124  can enhance the overall appearance of display  120  by hiding operational and structural components as well as focusing attention onto the active area of display  120 . Lid portion  108  can include magnet assemblies  150  positioned behind display  120  (shown here with dotted lines). The magnet assemblies  150  can be used to magnetically latch the lid portion  108  to the base portion  102 . In one embodiment the magnet assemblies  150  can interact with and attract ferrous attractor plates  155  positioned within top case  106  (shown here with dotted lines). 
         [0027]    Display  120  can display visual content such as a graphical user interface, still images such as photos as well as video media items such as movies. Display  120  can display images using any appropriate technology such as a liquid crystal display (LCD), OLED, etc. Portable computing device  100  can also include image capture device  126  located on a transparent portion of display trim  124 . Image capture device  126  can be configured to capture both still and video images. Lid portion  108  can be formed to have uni-body construction that can provide additional strength and resiliency to lid portion  108  which is particularly important due to the stresses caused by repeated opening and closing. In addition to the increase in strength and resiliency, the uni-body construction of lid portion  108  can reduce overall part count by eliminating separate support features. 
         [0028]    Data ports  128 - 132  can be used to transfer data and/or power between an external circuit(s) and portable computing device  100 . Data ports  128 - 132  can include, for example, input slot  128  that can be used to accept a memory card (such as a FLASH memory card), data ports  130  and  132  can take be used to accommodate data connections such as USB, FireWire, Thunderbolt, and so on. In some embodiments, speaker grid  134  can be used to port audio from an associated audio component enclosed within base portion  102 . 
         [0029]      FIG. 2  shows portable computing device  100  in a closed (lid) configuration that shows rear cover  122  and logo  202 . In one embodiment, logo  202  can be illuminated by light from display  120 . It should be noted that in the closed configuration, lid portion  108  and base portion  102  form what appears to be a uniform structure having a continuously varying and coherent shape that enhances both the look and feel of portable computing device  100 . 
         [0030]      FIG. 3  shows an external view of bottom case  104  showing relative positioning of support feet  302 , insert  112 , cosmetic wall  304  that can be used to conceal clutch assembly  110  and fasteners  306  used to secure bottom case  104  and top case  106  together. Support feet  302  can be formed of wear resistant and resilient material such as plastic. Also in view are multi-purpose front side sequentially placed vents  308  and  310  that can be used to provide a flow of outside air that can be used to cool internal components. In the described embodiment, vents  308  and  310  can be placed on an underside of top case  106  in order to hide the vents from view as well as obscure the view of an interior of portable computing device  100  from the outside. Vents  308  and  310  can act as a secondary air intake subordinate to primary air intake vents located at a rear portion of portable computing device  100  (described below). In this way, vents  308  and  310  can help to maintain an adequate supply of cool air in those situations where portions of the rear vents are blocked or otherwise have their air intake restricted. 
         [0031]    Vents  308  and  310  can also be used to output audio signals in the form of sound generated by an audio module (not shown). Vents  308  and  310  can be part of an integrated support system in that vents  308  and  310  can be machined from the outside and cut from the inside during fabrication of top case  106 . As part of the machining of vents  308  and  310 , stiffener ribs can be placed within vent openings  308  and  310  to provide additional structural support for portable computing device  100 . 
         [0032]    Moreover, trusses  318  can be formed between vents  308  and  310  in combination with ribs  316  can add both structural support as well as assist in defining both the cadence and size of vents  308  and  310 . The cadence and size of vents  308  and  310  can be used to control air flow into portable computing device  100  as well as emission of RF energy in the form of EMI from portable computing device  100 . Accordingly, stiffener ribs can separate an area within vents  308  and  310  to produce an aperture sized to prevent passage of RF energy. As well known in the art, the size of an aperture can restrict the emission of RF energy having a wavelength that can be “trapped” by the aperture. In this case, the size of vents  308  and  310  is such that a substantial portion of RF energy emitted by internal components can be trapped within portable computing device  100 . Furthermore, by placing vents  308  and  310  at a downward facing surface of top case  106 , the aesthetics of portable computing device  100  can be enhanced since views of internal components from an external observer are eliminated. 
         [0033]    Bonding magnet assemblies  150  to rear cover  122  can be difficult and can require an adhesive that can cure more quickly at elevated temperatures. Unfortunately, elevated temperatures can have an adverse affect on magnetic properties of magnets. In some cases, magnets can become partially or fully demagnetized after exposure to elevated temperatures.  FIG. 4  is a drawing of a magnetization curve  400  for a magnet. The magnetization curve  400  illustrates different operating points of a magnetic field B and a magnetizing field H for the magnet. B and H fields are typically related by a magnetic permeability μ=B/H. Vector  405  shows an operating point  410  on the magnetization curve  400  that can show a B/H relationship for the magnet when the magnet is “unloaded”. That is, point  410  can describe the B/H relationship for the magnet when there is no nearby ferrous material. Unfortunately, if the operating point is below a knee  415  on magnetization curve  400 , then when the magnetic is heated, the magnet can partially or completely loose magnetization. 
         [0034]    Vector  425  shows a second operating point  430 . A magnet can be configured to operate at operating points closer to the B axis of the magnetization (such as point  430 ) curve  400  by “loading” the magnet by placing ferrous materials near the magnet. In one embodiment, the operating point  430  can be achieved by containing substantial amounts of magnetic field lines from the magnet within the magnet. One advantage to operating the magnet near the B-axis away from knee  415  is that magnet can be made less sensitive to elevated temperatures. That is, the magnet can undergo exposure to elevated temperatures without losing some or all of its related magnetism. 
         [0035]      FIGS. 5A-5C  show possible effects of ferrous materials placed near a magnet  502 . In  FIG. 5A , magnet  502  is unloaded. That is, no ferrous material is placed near magnet  502 . Magnetic field lines  510  are shown travelling from a first magnetic pole to second magnetic pole. In  FIG. 5B  a first ferrous object  504  is placed near a north pole of magnet  502 . The ferrous object  504  can have sufficient magnetic permeability to contain substantially all of the magnetic field lines  510 . In some embodiments, ferrous objects  504  specifically designed to contain or reflect magnetic field lines are referred to as magnetic shunts.  FIG. 5B  shows magnetic field lines  510  skewed toward the south pole of magnet  502  away from ferrous object  504 .  FIG. 5C  shows magnet  502  with the first ferrous object  504  and a second object  506  positioned near each pole of magnet  502 . In such a configuration substantially all magnetic field lines  510  can be constrained closely to magnet  502 . As substantially all magnetic field lines  510  are maintained within magnet  502 , the operating point of magnet  502  can be moved closer to the B-axis as described in  FIG. 4 . For example, a configuration shown in  FIG. 5C  can move the operating point of magnet  502  from point  410  to point  430  on curve  400 . In doing so, the magnet  502  can be made less sensitive to elevated temperatures. 
         [0036]      FIG. 6  is a simplified diagram of a portion of the rear cover  122  including a magnetic assembly  150 . The rear cover  122  can be configured to support magnetic assembly  150 . In one embodiment, magnetic assembly  150  can include magnet  604  and magnetic shunt  602 . Magnetic shunt  602  can cause field lines of magnet  604  to move away from the magnetic shunt  602 . In one embodiment, magnetic shunt  602  and magnet  604  can be affixed to rear cover  122  with an adhesive. That is, magnetic shunt  602  can be attached to the rear cover  122  with an adhesive. Following that, magnet  604  can be attached to magnetic shunt  602  with the adhesive. In one embodiment, the adhesive can include a curing characteristic that enables the adhesive to cure relatively more quickly when the adhesive is brought to an elevated temperature. For example, the adhesive can cure (set up, or harden) to a predetermined amount when heated to approximately 55 degrees Celsius (within a tolerance amount such as +/−1 degree; other embodiments can have other tolerance amounts) for about five minutes. In another embodiment, the adhesive can cure to the same predetermined amount when heated to approximately 85 degrees Celsius for between one and two minutes. For reference, room temperature can between 25 an 30 degrees Celsius. In one embodiment, the adhesive may not be fully cured after exposure to an elevated temperature for a predetermined time period. Rather, the adhesive can be partially cured and but have an increased tack that can enable further handling of the magnet assembly  150  while the adhesive continues to cure at room temperature. 
         [0037]    A magnetic keeper  606  can be applied to magnet  604 . The magnetic keeper can function much as a magnetic shunt as described above. The magnetic keeper  606  can be formed from a ferrous material and can be configured to include sufficient surface area and volume to substantially contain all magnetic field lines from magnet  604 . The magnetic keeper  606  can be formed from a material with relatively good permeability. In one embodiment magnetic keeper  606  can be larger than magnet  604 . In another embodiment, magnetic keeper and (optionally) magnetic shunt  602  can be formed from a high magnetic permeability material such as American Iron and Steel Institute (AISI)  1010  steel or AISI 1005 steel. In such embodiments, magnetic keeper  606  can be relatively smaller than described above. When magnetic keeper  606  is brought adjacent to magnet  604  substantially all magnetic field lines can be contained with magnet  604 , particularly when magnetic shunt  602  is positioned at an opposing end of magnet  604 . In this configuration, the magnets and adhesive can be heated to an elevated temperature for a predetermined amount of time to cure the adhesive to a first amount. In one embodiment, the adhesive may not be fully cured after exposure to the elevated temperature. But rather, the adhesive can be set enough to allow further manufacturing processing while the adhesive continues to cure at room temperature. In one embodiment, magnet  604  can be formed from a rare-earth material such as neodymium. Magnetic keeper  606  can be removed after heating of the magnet  604 . In one embodiment, the temperature of magnets is reduced prior to removing magnetic keeper  606 . 
         [0038]      FIG. 7  is a block diagram of a fixture for curing an adhesive in accordance with one embodiment described in the specification. Rear cover  122  can be configured to support magnet  604  and magnetic shunt  602 . As shown, magnetic shunt  602  can be affixed to rear cover  122  with adhesive  702 . Magnet  604  can be bonded to magnetic shunt  602  with adhesive  702 . In one embodiment, adhesive  702  can cure faster at elevated temperatures especially when compared to room temperature. Magnetic keeper  606  can be placed on magnet  604 , in this example opposed to magnetic shunt  602 . When magnetic keeper  606  is on one side of magnet  604  and magnetic shunt  602  is on another side of magnet  604 , then substantially all of the magnetic field lines can be contained within magnet  604 . Thus, adhesive  702  can receive an elevated temperature without affecting magnetic characteristics of magnet  604 . 
         [0039]      FIG. 8  is a flow chart of method steps  800  for reducing a curing time of an adhesive used for attaching a magnet while preserving magnetic properties of the magnet. The method begins in step  802  where a magnet  604  and a magnetic shunt  602  are received. In step  804 , the magnet  604  and the magnetic shunt  602  are attached to a support structure. For example, the magnetic shunt  602  can be attached to a rear cover  122  with an adhesive  702  followed by the magnet  604  attached to the magnetic shunt  602  with the adhesive  702 . In one embodiment, the adhesive  702  can cure more quickly when heated to an elevated temperature. In step  806 , a magnetic keeper  606  can be temporarily attached to magnet  604 . In step  808 , the magnet assembly (the magnet, the magnetic shunt, the magnetic keeper, the adhesive and the support structure) can be heated to cure the adhesive. In step  810 , the magnetic keeper  606  can be removed from the magnet  604  and the method ends. 
         [0040]    Although the foregoing invention has been described in detail by way of illustration and example for purposes of clarity and understanding, it will be recognized that the above described invention may be embodied in numerous other specific variations and embodiments without departing from the spirit or essential characteristics of the invention. Certain changes and modifications may be practiced, and it is understood that the invention is not to be limited by the foregoing details, but rather is to be defined by the scope of the appended claims.