BACKGROUND

[0001] Electrostatic discharge may occur when making metal -to- metal contact between a charged metal object and a grounded metal object. Many electronic devices are sensitive to electrostatic discharge (ESD). For example, the Electrostatic Discharge Association labels Class 0 devices as those that are sensitive to voltages less than 250 volts. Integrated circuits in the micron and submicron range are known to be sensitive to voltages under 2 volts. Other electronic components have similar sensitivities to very low ESD voltages.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] FIG. 1 illustrates an example system without electrostatic discharge protection;

[0003] FIG. 2 illustrates electrostatic discharge in an example system without electrostatic discharge protection;

[0004] FIG. 3 illustrates an example system of the present disclosure;

[0005] FIG. 4 illustrates an example system of the present disclosure during a process of creating a connection between two conductive objects;

[0006] FIG. 5 illustrates an example system of the present disclosure with a connection formed between two conductive objects;

[0007] FIG. 6 is an example flowchart of a method for creating a connection between two conductive objects, in accordance with the present disclosure; and

[0008] FIG. 7 is an example flowchart of an additional method for creating a connection between two conductive objects, in accordance with the present disclosure.

DETAILED DESCRIPTION

[0009] The present disclosure broadly discloses a method of controlling electrostatic discharge (ESD) between two conductive objects: a charged conductive object and a grounded conductive object (or a conductive object with a different potential as compared to the charged conductive object). In particular, a surface of at least a first of the conductive objects is coated with a static dissipative material that is sufficiently compliant such that the static dissipative material is displaced from the surface of the first conductive object when the surface of the first conductive object is engaged with the surface of the second conductive object, and is restored to the surface of the first conductive object when the surface of the first conductive object is disengaged from the surface of the second conductive object. Thus, initial contact between the charged conductive object and the grounded conductive object is made through the compliant, static dissipative material. The charge is transferred via a low current over a longer duration of time, as compared to direct conductor-to- conductor (e.g., metal-to-metal) contact, thereby preventing undesirable ESD. After the charge is transferred, the two conductors may be further engaged to displace the compliant, static dissipative material and to have direct conductor- to-conductor contact. If it is necessary to separate the two conductive objects, the compliant, static dissipative material restores its position to again cover the surface of the first conductive object (or the surfaces of both the first and second conductive objects, if the compliant, static dissipative material is applied to both surfaces). In this manner, the two conductive objects can safely be reengaged, while being protected from ESD by the compliant, static dissipative material.

[0010] In accordance with the present disclosure, the compliant, static dissipative material may comprise a material that is applied in a fluid form, e.g., via an aerosol spray, brushed on as a liquid, and so forth. In one example, the compliant, static dissipative material cures in a non-evaporative form. For example, the compliant, static dissipative material may include a solvent that is present when applied, but that evaporates to leave a compliant, solid polymer or gel. In one example, the compliant, static dissipative material has a volume resistance (resistivity) in the range of 10 ⁵ to 10 ¹¹ ohm-centimeters (ohm-cm), e.g., 10 ⁶ to 10 ⁹ ohm-cm.

[0011 ] In one example, the compliancy of the static dissipative material refers to the stiffness, viscosity, fluidity, pliability and/or elasticity of the material. In general, the useful ranges of these properties for a static dissipative material of the present disclosure are based upon the particular application and the particular conductive objects to be connected. For instance, where the conductive objects have a large spring force, or at least one of the contact surfaces is sharp, the static dissipative material can be less compliant. If the spring force is low and/or the contact surfaces are large, then the static dissipative material will have to be more compliant. Thus, a compliant, static dissipative material of the present disclosure is one that: (1 ) remains in position when the contact surfaces approach, (2) is displaced by the contact surfaces when brought together by a nominal force, and (3) is restored to position when the contact surfaces are separated. Some examples of compliant, static dissipative materials include a urethane material referred to as Licron Crystal that is available from Techspray® of Amarillo, Texas, and a material referred to as Staticide® that is available from ACL Incorporated of Chicago, Illinois.

However, these products were not intended for use in the manner disclosed herein, i.e., to make electrical connections. In particular, such products were intended to provide a coating over surfaces throughout a clean room

environment, e.g., on table-tops, floors, walls, handles, bumpers, bins, tools, viewports, and the like.

[0012] In general, it is recommended to avoid the use of Class 0 (zero) electronic devices, which are devices that are classified as being sensitive to ESD voltages of less than 250 volts. In some applications, the use of Class 0 devices is unavoidable in order to provide the product functionality required. In such cases, high sensitivity to ESD damage has to be accommodated. One of these applications is linear tape-open (LTO) tape drive products, which depend on magnetoresistive and giant-magnetoresistive-based (GMR) read data heads that can be damaged by electrostatic discharge voltages as low as 5 volts and 1 .5 volts, respectively. Particularly for the more sensitive GMR devices, control of environmental voltages has been proven to be inadequate to protect the devices from damage during the assembly process. Thus, it is desirable to protect these sensitive components from ESD, particularly during the manufacturing process.

[0013] Although a variety of methods are employed to control large-scale and slowly-varying environmental voltages within plus and minus 5 volts (e.g., grounding pads, grounding straps, ionizers, humidity control, and so forth), these methods are not adequate to control rapidly varying (e.g., less than 10 seconds in duration), spatially-localized (e.g., less than 5 centimeter) charges. Therefore, it is necessary to ensure that all ground contacts or connections to a Class 0 device are static-dissipative. For example, any tools held by a grounded operator must have a static dissipative tip (e.g., approximately 10 ⁶ ohm) so that any charge that is transferred from the device to ground is transferred at a slow rate (e.g. a low current), below the damage threshold.

[0014] This principle also applies when installing a Class 0 device. In an LTO drive, for example, the sensitive GMR head is attached to a flex which has to be plugged into a printed circuit board (PCB). The PCB and LTO drive form a large enough structure that they act like a local ground. The flex has metal traces that can carry a charge due to a variety of sources, such as inadequate environmental control of charged sources, unbalanced ionizers, ungrounded operators, induction charging, and so forth. Any charge present on the metal flex traces or GMR head can discharge quickly to the drive and damage the GMR head.

[0015] To aid in understanding the present disclosure, FIG. 1 illustrates an example system 100 without electrostatic discharge protection. As illustrated in FIG. 1 , the system 100 includes a first conductive object 1 10 and a second conductive object 120. In one example, the first conductive object 1 10 and the second conductive object 120 may each comprise a metal object. However, in accordance with the present disclosure, either or both of the first conductive object 1 10 and the second conductive object 120 may comprise a conductive object of any type. In one example, the first conductive object 1 10 carries a positive charge, illustrated by the plus symbols 150. It should be noted that a "charged object" referred to herein may comprise an object that carries a net charge, or may comprise a polarized object with positive and negative charges that are unevenly distributed such as a local area of the object may have a net positive or a net negative charge.

[0016] As illustrated in FIG. 1 , the second conductive object 120 is connected to ground 140. However, it should be understood that in accordance with the present disclosure, the second conductive object 120 may be sufficiently large such that it acts as a local ground, or may have a different potential as compared to the first conductive object 1 10, e.g., sufficiently different such that ESD may occur when the first conductive object 1 10 and the second conductive object 120 touch or are brought proximate to one another (e.g., as indicated by the direction of the arrow 160). In one example, the system 100 may comprise a portion of an LTO drive, where the first conductive object 1 10 may comprise a GMR head, or components thereof, such as a flex, or metal traces of the flex, and the second conductive object 120 may comprise a PCB, or vice versa. Further examples of the present disclosure may be described in connection with an LTO drive. However, it should be understood the present disclosure is not limited to such examples, and is broadly applicable to various connections between conductive objects relating to various components in electronic devices.

[0017] FIG. 2 illustrates electrostatic discharge in a system 100 without electrostatic discharge protection. For example, the system 100 in FIG. 2 may comprise the same system as in FIG. 1 , where the first conductive object 1 10 and the second conductive object 120 have been brought into contact at the respective surfaces 1 15 and 125. Metal-to-metal contact (or conductor-to- conductor contact) results in electrostatic discharge (ESD) 170, e.g., a high current, large charge transfer over a short time. As illustrated in FIG. 2, the positive charge, indicated by the plus symbols 150 is transferred to ground 140. In the case where system 100 may comprise a portion of an LTO tape drive, the ESD 170 may damage the GMR head.

[0018] To help address ESD in LTO tape drive systems and in other applications, one approach is to make contact through a static dissipative surface. For example, a static dissipative surface may be added to surface 1 15 in FIG. 2. When the first conductive object 1 10 and the second conductive object 120 are brought into contact, any accumulated charge may flow to ground via a low current over a longer duration of time as compared to bare metal-to-metal contact, thereby eliminating the likelihood of ESD when making the connection. However, the static dissipative surface remains in the electrical path between the first conductive object 1 10 and the second conductive object 120, and between the first conductive object 1 10 and ground 140. As a result, the connection has an undesirably high resistance. For example, this would be impractical for a GMR head in an LTO tape drive system.

[0019] Another approach is to make an initial contact through a static dissipative pogo-pin connection, but have the pogo-pin move out of the circuit path as metal-to-metal contact is eventually made. Thus, a high-resistance static dissipative contact is made through the pogo-pin. The pogo-pin is then compressed, allowing a low-resistance connection. However, connectors of this type may be expensive and may not work in space-constrained applications. For example, pogo-pins are too large for an LTO connector, which may comprise up to 80 pins or more in a tight area.

[0020] An additional approach involves immersing conductive objects in isopropyl alcohol (IPA) for making a connection. Initial contact is made through IPA coating one or both of the surfaces to be connected. The resistivity of IPA is approximately 10 ⁶ ohm-cm, which is sufficient to avoid ESD when making the connection between a charged conductive object and a grounded conductive object. In one example, a solution using IPA may involve connectors that are sealed and may not allow the IPA to evaporate. In addition, IPA must be reapplied every time a connection is made between the conductive objects. This is inconvenient when a device and its components may be reworked or reconfigured, and leaves the device at risk to ESD at certain times.

[0021 ] In contrast to the foregoing, the present disclosure utilizes a compliant, static dissipative material that provides an efficient solution for ESD mitigation between two conductive objects. The compliant, static dissipative material allows initial connection to be made through itself, while facilitating a direct conductor-to-conductor contact upon the application of a nominal connective force. The compliant, static dissipative material is restored into position when the conductive objects are disconnected or when the connective force is removed. Thus, the use of a compliant, static dissipative material in accordance with the present disclosure may help mitigate ESD, without the drawbacks of a high permanent resistance in the electrical path, the single-use nature of IPA, or the high cost and size of pogo-pin connections.

[0022] To further aid in understanding the present disclosure, FIG. 3 illustrates an example system 200 that utilizes a compliant, static dissipative material 130. In particular, system 200 may comprise a similar system to that illustrated in FIGs. 1 and 2 with respect to the hardware components. Thus, system 200 includes a first conductive object 1 10, second conductive object 120 and ground 140. An area of positive charge is indicated by the plus symbols 150. The first conductive object 1 10 and second conductive object 120 are to be connected as indicated by the direction of the arrow 160. In one example, as illustrated in FIG. 3, either or both of the first conductive object 1 10 and second conductive object 120 may be coated with the compliant, static dissipative material 130. As shown in FIG. 3, all surfaces of each of the first conductive object 1 10 and second conductive object 120 are coated with compliant, static dissipative material 130. However, in accordance with the present disclosure, more or less of each of the first conductive object 1 10 or second conductive object 120 may be coated with the compliant, static dissipative material 130. For instance, in one example only the first conductive object 1 10 may be coated with the compliant, static dissipative material 130, while the second conductive object 120 may be uncoated. Similarly, only surfaces 1 15 and 125 may be coated.

[0023] In one example, the compliant, static dissipative material 130 comprises a mixture with at least one solvent, and at least one polymer or gel. For example, the at least one solvent may comprise any one or more of:

isopropyl alcohol, isopropanol, propanol, butanol, propane, butane,

nitromethane, methanol, diethylene glycol, and the like. In one example, all or a portion of the solvent may evaporate upon application of the compliant, static dissipative material in a liquid or aerosol form. In one example, the at least one polymer comprises a compliant urethane-type polymer. In one example, the at least one polymer comprises a polystyrene sulfonate substituent, such as a polyethylenedioxythiophene polystyrene sulfonate, sometimes referred to as PEDOT:PSS or P:PSS, e.g., a mixture of poly(3,4-ethylenedioxythiophene) and sodium 4-polystyrene sulfonate. In another example, the at least one polymer comprises an alkyl benzoate, e.g., isodecyl benzoate. In one example, the compliant, static dissipative material may comprise Licron Crystal from

Techspray®, or ACL Staticide®. It should be noted that the foregoing examples are provided for illustrative purposes only. Thus, any suitable compliant static dissipative material that applies in a fluid form, cures in a non-evaporative form, has a resistance of between 10 ⁵ to 10 ¹¹ ohm-cm, and is sufficiently compliant (e.g., (1 ) remains in position when the contact surfaces approach, (2) is displaced by the contact surfaces when brought together by a nominal force, and (3) is restored to position when the contact surfaces are separated), may be utilized in accordance with the present disclosure.

[0024] FIG. 4 illustrates the example system 200 of FIG. 3 as contact is made between the first conductive object 1 10 and the second conductive object 120 in the region 165. As shown in FIG. 4, initial contact is made via the compliant, static dissipative material 130. Thus, any accumulated charge (e.g., represented by plus symbols 150) is passed to ground 140 via a low current through the compliant, static dissipative material 130.

[0025] FIG. 5 illustrates the example system 200 of FIG. 4 after sufficient force is applied to bring surfaces 1 15 and 125 of the first conductive object 1 10 and the second conductive object 120 into direct contact. In one example, the compliant, static dissipative material 130 is displaced to allow the direct conductor-to-conductor contact. Thus, a low resistance connection between the first conductive object 1 10 and the second conductive object 120 is created. Any potential for ESD is mitigated by allowing the accumulated charge to be passed via the compliant, static dissipative material 130, while providing a desirable low-resistance path after the initial connection is made. In addition, when first conductive object 1 10 and second conductive object 120 are disengaged, the compliant, static dissipative material 130 restores to the original position(s) as illustrated in FIGs. 3 and 4. Accordingly, first conductive object 1 10 and second conductive object 120 may be safely reconnected, or reengaged, a number of additional times without having to reapply the protective coating of the compliant, static dissipative material 130. [0026] FIG. 6 illustrates a flowchart of a method 600 for mitigating

electrostatic discharge (ESD), in accordance with the present disclosure. In one example, the steps, operations, or functions (e.g., the "blocks") of the method 600 may be performed in connection with the fabrication or assembly of an electronic device.

[0027] At block 605, the method 600 begins and proceeds to block 610.

[0028] At block 610, a surface of a first conductive object is coated with a compliant, static dissipative material. In one example, a surface of a second conductive object may also be coated with the compliant, static dissipative material. For instance, block 610 may comprise coating the surface of the first conductive object with a first portion of the compliant, static dissipative material and coating the surface of the second conductive object with a second portion of the compliant, static dissipative material. In one example, block 610 may result in a similar system to that which is illustrated in FIG. 3. In one example, at least a portion of the first conductive object or the second conductive object may carry a charge that has the potential to result in ESD. In one example, the first conductive object or the second conductive object has a net zero charge, but is polarized such that charge is unevenly distributed throughout the material. In one example, the first conductive object or the second conductive object has a negative potential as compared to the other of the conductive objects such that it can act as a sink for accumulated charge. Alternatively, or in addition, one of the first conductive object or the second conductive object is grounded, or may comprise a local ground. In one example, the first conductive object may comprise a GMR head or trace of a GMR head in a LTO tape drive system, while the second conductive object may comprise a portion of a PCB of such an LTO tape drive system.

[0029] At block 620, the surfaces of the first and second conductive objects are engaged, i.e., brought into conductor-to-conductor contact. In one example, block 620 comprises first forming a connection between the first conductive object and the second conductive object via the compliant, static dissipative material. For instance, the first and second conductive objects may be positioned in a similar manner as system 200 illustrated in FIG. 4. In one example, a high resistance connection is provided by the compliant, static dissipative material to allow the two conductive objects to safely reach the same potential by transferring charge slowly. In addition, in the case where one of the two conductive objects is grounded, any accumulated charge that would otherwise have had the potential to cause ESD may instead safely pass to ground.

[0030] Thereafter, the operations of block 620 may result in a configuration that is the same or similar to that of system 200 illustrated in FIG. 5. Thus, a low resistance electrical connection between the first and second conductive objects is formed. For example, the first and second conductive objects may comprise an electrical path for components of an electronic device to pass data and/or power signals. In one example, block 620 may comprise forming a connection between complementary pins and/or holes of the surfaces of the first and second conductive objects respectively. As mentioned above, in one example, the first conductive object may comprise a GMR head or trace of a GMR head in a LTO tape drive system, while the second conductive object may comprise a portion of a PCB. The connection of a GMR head to the PCB is an operation that is particularly sensitive to ESD, which may result in irreparable damage and the attending cost of replacement in a significant percentage of cases. Thus, the establishment of a connection between the GMR head and the PCB as per blocks 620 is particularly beneficial. Following block 620, the method 600 proceeds to block 695 where the method ends.

[0031 ] FIG. 7 illustrates a flowchart of an additional method 700 for mitigating electrostatic discharge (ESD), in accordance with the present disclosure. In one example, the steps, operations, or functions (e.g., the "blocks") of the method 700 may be performed in connection with the fabrication or assembly of an electronic device.

[0032] At block 705, the method 700 begins and proceeds to block 710. At block 710, a surface a first conductive object is coated with a compliant, static dissipative material. In one example, a surface of a second conductive object may also be coated with the compliant, static dissipative material. For instance, block 710 may comprise coating the surface of the first conductive object with a first portion of the compliant, static dissipative material and coating the surface of the second conductive object with a second portion of the compliant, static dissipative material. In one example, block 710 may result in a system as illustrated in FIG. 3. In one example, at least a portion of the first conductive object or the second conductive object may carry a charge that has the potential to result in ESD. In one example, the first conductive object or the second conductive object has a net zero charge, but is polarized such that charge is unevenly distributed throughout the material. In one example, the first conductive object or the second conductive object has a negative potential as compared to the other of the conductive objects such that it can act as a sink for accumulated charge. Alternatively, or in addition, one of the first conductive object or the second conductive object is grounded, or may comprise a local ground. In one example, block 710 may comprise the same or substantially similar operations to those described above in connection with block 610 of the method 600.

[0033] At block 720, a connection is formed between the first conductive object and the second conductive object via the compliant, static dissipative material. In one example, block 720 causes the first and second conductive objects to be positioned in the same manner as system 200 illustrated in FIG. 4. In one example, a high resistance connection is provided by the compliant, static dissipative material to allow the two conductive objects to safely reach the same potential by transferring charge slowly. In addition, in the case where one of the two conductive objects is grounded, any accumulated charge that would otherwise have had the potential to cause ESD may instead safely pass to ground.

[0034] At block 730, the surfaces of the first and second conductive objects are engaged, i.e., brought into conductor-to-conductor contact. In one example, the operations of block 730 result in a configuration that is the same or similar to that of system 200 illustrated in FIG. 5. Thus, a low resistance electrical connection between the first and second conductive objects is the result of block 730. For example, the first and second conductive objects may comprise an electrical path for components of an electronic device to pass data and/or power signals. In one example, block 730 may comprise forming a connection between complementary pins and/or holes of the surfaces of the first and second conductive objects respectively. As mentioned above, in one example, the first conductive object may comprise a GMR head or trace of a GMR head in a LTO tape drive system, while the second conductive object may comprise a portion of a PCB. The connection of a GMR head to the PCB is an operation that is particularly sensitive to ESD, which may result in irreparable damage and the attending cost of replacement in a significant percentage of cases. Thus, the establishment of a connection between the GMR head and the PCB as per blocks 720 and 730 is particularly beneficial. In one example, blocks 720 and 730 may comprise the same or substantially similar operations to those described above in connection with block 620 of the method 600.

[0035] At block 740, the surfaces of the first and second conductive objects are disengaged. For instance, a force maintaining the conductor-to-conductor contact may be removed, pins may be disconnected, or the like. In one example, the compliant, static dissipative material is restored to the surface of the first conductive object and/or to the surface of the second conductive object (depending upon whether the compliant, static dissipative material is applied to surfaces of one or both of the first and second conductive objects). For instance, the first and second conductive objects may be disconnected to allow a system layout to be reconfigured, one of the first and second conductive surfaces may comprise a component (e.g., a GMR head) that can be

disconnected for use in a different system, one or both of the first and second conductive objects may be removed for cleaning, and so forth.

[0036] At block 750, it is determined whether the surfaces of the first conductive object and the second conductive object are to be reengaged, or reconnected. If it is determined to reengage the surfaces, the method 700 proceeds back to block 720. Once again, a high resistance, low current initial contact is made through the compliant, static dissipative material, with a low resistance path created when the compliant, static dissipative material is displaced. On the other hand, if it is determined that the surfaces of the first conductive object and the second conductive object are not to be reengaged, the method 700 proceeds to block 795 where the method ends.

[0037] It should be noted that although not explicitly specified, one or more blocks, functions, or operations of the method 600 or the method 700 that recite a determining operation, or involve a decision, do not necessarily require that both branches of the determining operation be practiced. In other words, one of the branches of the determining operation can be deemed as an optional step. Moreover, steps, blocks, functions or operations of the above described methods 600 and 700 can be combined, separated, and/or performed in a different order from that described above, without departing from the examples of the present disclosure.

[0038] In this regard, it should also be noted that the methods 600 and 700 are just two representative examples of the present disclosure, and that several variations of the present methods 600 and 700 may be derived in view of the disclosures herein. For example, the method 700 may be modified to omit blocks 740 and 750. In other words, it is not necessary that conductive surfaces be disengaged or reengaged, despite examples of the present disclosure helping provide the ability to safely perform these operations. Thus, these and other modifications are all contemplated within the scope of the present disclosure.

[0039] In addition, it will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made.