Over-torque protection features for mounting an electronic device to a heat dissipation object

A package for securing a PCB to a heatsink includes mounts with over-torque protection features. The PCB is seated in an open end of the package. Each mount includes a threaded opening for securing the package to the heatsink such that the base layer of the PCB is thermally coupled to the heat sink. The over-torque protection features are connected between the threaded opening and a sidewall of the package. The over-torque protection features may be designed to structurally fail and/or deform in response to over-torqueing of the fasteners, thereby inhibiting flexure of the PCB.

BACKGROUND

Electronic devices typically include various components mounted on a PCB (Printed Circuit Board). If any of the components generate significant amounts of heat, then the device may be thermally coupled to a heat dissipation object. For example, the PCB may be bolted or clamped to a heat sink with a thermally conductive paste, gel, or pad placed therebetween to fill potential air gaps between contact surfaces, and provide a thermal transfer path.

Aluminum PCBs are particularly well suited for electronic devices that generate significant heat. Aluminum PCBs have an aluminum base layer, a dielectric layer and a copper circuit layer. The dielectric and copper circuit layers may be similar or identical to the dielectric and copper circuit layers of common FR4 PCBs. However, the aluminum base layer has better thermal transmittance characteristics than FR4. An aluminum PCB with a 1.5 mm thick base layer has a thermal resistance of about 1-2 degrees per watt, whereas an FR4 PCB with a 1.5 mm thick base layer has a thermal resistance of about 20-22 degrees per watt. Consequently, aluminum PCBs may be preferred for electronic devices for which a heat sink is required.

A problem that may be encountered with electronic devices that are fastened to another object is that surface-mounted components may be damaged by flexure of the PCB. For example, an aluminum PCB that is secured to a heat sink with multiple machine screws that exert enough force to assure contact, and thus thermal coupling, between a flat surface of the heat sink and the entire lower surface of the aluminum PCB may flex during installation if torqueing of the fasteners is not accurately controlled. If either the aluminum base layer or the mounting surface of the heat sink is non-planar, then the aluminum base layer may flex if the fasteners are over-tightened. Even if both the aluminum base layer and the mounting surface of the heat sink are planar, foreign matter located between the surfaces being mated may cause the aluminum base layer to flex if the fasteners are over-tightened. Further, the conductive paste, gel, or pad that is intentionally placed between the surfaces being mated may cause the aluminum base layer to flex if the fasteners are over-tightened. In general, the thickness of the material is proportional or inversely proportional to the likelihood that flexing will occur. Many types of electronic components are relatively tolerant to flexing of the aluminum base layer. However, certain types of components such as surface-mounted ceramic capacitors are more susceptible to damage caused by flexing of the aluminum base layer.

SUMMARY

All examples, aspects and features mentioned in this document can be combined in any technically possible way.

In accordance with some aspects of the invention an electronic device comprises: an electronic circuit comprising one or more or a plurality of electronic components mounted to a printed circuit board comprising a thermally conductive substrate layer; and a package against which the printed circuit board is seated, the package comprising at least one sidewall and one or more or a plurality of mounts via which the electronic device is secured to a heat dissipation object, each mount comprising an opening via which the mount is fastenable to the heat dissipation object and an over-torque protection feature connected between the opening and the sidewall.

In some implementations the over-torque protection feature comprises at least one structural member that is a structurally weakest link between the opening and the sidewall. In some implementations the over-torque protection feature comprises at least one rectangular cuboid bar that interconnects a body of the mount with the sidewall. In some implementations the over-torque protection feature comprises first and second rectangular cuboid bars with a void therebetween. In some implementations the rectangular cuboid bars are oriented with longest surfaces in a first axis that is parallel to an axis defined by a length dimension of a first fastener in the threaded opening. In some implementations the opening is disposed in a cylindrical section and the over-torque protection feature comprises first and second rectangular cuboid bars that connect the cylindrical section to a body of the mount. In some implementations the first and second rectangular cuboid bars are offset by 180 degrees relative to the opening. In some implementations the opening is disposed in a wedge section and the over-torque protection feature comprises the wedge and a correspondingly-shaped opening in a body of the mount. In some implementations the wedge has a truncated polyhedron shape. In some implementations the over-torque protection feature comprises a receiver and a removable tab. In some implementations the receiver comprises a spring beam and the removable tab comprises a cross-beam with a projection that contacts the spring beam. In some implementations the mount is fastenable to the heat dissipation object with a machine screw. In some implementations the thermally conductive substrate layer forms an end-wall of the electronic device. In some implementations an air gap is present between the mount and the heat dissipation object. In some implementations structural failure of the over-torque protection feature creates an audible noise. In some implementations the package comprises solderable mounting posts.

In particular embodiments, each mount of the package can be securable to the heat dissipation object by a fastener extending within the opening of the mount along an axis A. Each mount can have a configuration that allows the package to be tightened by the fastener to the heat dissipation object securely under normal assembly conditions, but also providing a readily apparent mechanical indication of over-torque or force applied to the fastener along the axis A when a predetermined threshold torque or force level is reached while tightening the fastener for preventing the fastener from being tightened over or above the predetermined threshold torque or force level. The readily apparent mechanical indication can include visual indications which can also cause or include audible indications. Each mount can be configured to be generally stable during tightening the fastener along axis A until reaching a predetermined threshold torque or force level at which at least a portion of the mount undergoes, experiences or is caused to have a mechanical alteration. The mechanical alteration can be at least one of deformation, deflection, bending, fracture, slippage, damage, breakage, failure and movement.

In accordance with some aspects of the invention, a package for an electronic circuit including one or more or a plurality of electronic components mounted to a printed circuit board including a thermally conductive substrate layer, comprises: at least one sidewall against which the printed circuit board is seated and one or more or a plurality of mounts via which the printed circuit board is secured to a heat dissipation object, each mount comprising an opening via which the mount is fastenable to the heat dissipation object and an over-torque protection feature connected between the opening and the sidewall, the over-torque protection feature comprising at least one structural member that is a structurally weakest link between the opening and the sidewall.

In some implementations the over-torque protection feature comprises first and second rectangular cuboid bars with a void therebetween. In some implementations the opening is disposed in a cylindrical section and the over-torque protection feature comprises first and second rectangular cuboid bars that connect the cylindrical section to a body of the mount. In some implementations the opening is disposed in a wedge section and the over-torque protection feature comprises the wedge and a correspondingly-shaped opening in a body of the mount.

In particular embodiments, each mount of the package can be securable to the heat dissipation object by a fastener extending within the opening of the mount along an axis A. Each mount can have a configuration that allows the package to be tightened by the fastener to the heat dissipation object securely under normal assembly conditions, but also providing a readily apparent mechanical indication of over-torque or force applied to the fastener along the axis A when a predetermined threshold torque or force level is reached while tightening the fastener for preventing the fastener from being tightened over or above the predetermined threshold torque or force level. Each mount can be configured to be generally stable during tightening the fastener along axis A until reaching a predetermined threshold torque or force level at which at least a portion of the mount undergoes, experiences or is caused to have a mechanical alteration. The mechanical alteration can be at least one of deformation, deflection, bending, fracture, slippage, damage, breakage, failure and movement.

The present invention can also provide a housing for mounting a printed circuit board to a surface. The housing can include at least one sidewall for engaging the printed circuit board, and can be formed of a rigid plastic material. One or more mounts can be integrally formed with the at least one sidewall and extend generally perpendicular therefrom in a cantilevered manner. Each mount can have an opening extending therethrough along an axis A that is generally parallel to the at least one sidewall for allowing the mount to be secured to the surface with a fastener. The mount can have a thickness dimension in the direction of axis A and have two spaced apart bars separated by slot extending along said thickness dimension that connect the mount to the at least one sidewall. The two bars can be configured, shaped and sized to fail when a fastener that is being tightened exerts a force along axis A that reaches a predetermined threshold level of torque or force for protecting the printed circuit board from excessive flexing during fastening.

In particular embodiments, the two bars can each be recessed relative to lateral sides of the mount form a stress concentration line on the bars along said thickness dimension parallel to axis A. The predetermined threshold torque level can be about 1.5 to 3 inch pounds (in lbs.).

The present invention can also provide a method of securing an electronic device to a heat dissipation object. An electronic circuit can be provided comprising one or more electronic components mounted to a printed circuit board comprising a thermally conductive substrate layer. The printed circuit board can be seated against a package. The package can comprise at least one sidewall and one or more mounts. The electronic device can be secured to the heat dissipation object. Each mount can comprise an opening via which the mount is fastenable to the heat dissipation object and an over-torque protection feature can connect between the opening and the sidewall for protecting the printed circuit board from excessive flexing during fastening. Particular embodiments of the method can further include certain details described above.

The present invention can also provide a method of securing a package for an electronic circuit to a head dissipation object. The electronic circuit can include a plurality of electronic components mounted to a printed circuit board having a thermally conductive substrate layer. The printed circuit board can be seated against at least one sidewall of the package, and can be secured to the heat dissipation object with one or more mounts. Each mount can comprise an opening via which the mount is fastenable to the heat dissipation object and an over-torque protection feature can connect between the opening and the sidewall. The over-torque protection feature can comprise at least one structural member that is a structurally weakest link between the opening and the sidewall for protecting the printed circuit board from excessive flexing during fastening. Particular embodiments of the method can further include certain details described above.

The present invention can also provide a method of mounting a printed circuit board to a surface with a housing, comprising engaging the printed circuit board with at least one sidewall of the housing. The housing can be formed of rigid plastic material, and one or more mounts can be integrally formed with the at least one sidewall extending generally perpendicularly therefrom in a cantilevered manner. Each mount can have an opening extending therethrough along an axis A that is generally parallel to the at least one sidewall. The mount can have a thickness dimension in the direction of axis A and have two spaced apart bars separated by a slot extending along said thickness dimension that connect the mount to the at least one sidewall. Each mount can be secured to the surface with a fastener extending within the opening along axis A. The two bars can be configured, shaped and sized to fail when a fastener that is being tightened exerts a force along axis A that reaches a predetermined threshold level of torque or force for protecting the printed circuit board from excessive flexing during fastening. Particular embodiments of the method can further include certain details described above.

Although none of the implementations is required to provide any specific advantage, some implementations may provide the advantage of inhibiting damaging stress to flex-sensitive components. Moreover, some implementations may provide that advantage without increasing the thickness of the PCB and thereby adding weight and cost. Further, some implementations secure the PCB to the heat dissipation feature more firmly than weak attachment clips that are designed to easily flex. Such clips may be impractical for implementations in which the electronic device will be subjected to motion and vibration. Further, some implementations are suitable for use with thermal pads and other materials that may be placed between the PCB and the heat dissipation feature. Such materials tend to increase the likelihood of damaging flexure of the PCB in the absence of over-torque protection features such as those described in this disclosure.

DETAILED DESCRIPTION

A description of example embodiments follows.

FIGS. 1 through 4illustrate an implementation of an electronics package with an over-torque protection feature that functions based on designed structural weakness. The over-torque protection feature, of which there may be multiple instances in the same package, helps to avoid excessive flexure of a PCB mounted in the package. The electronics package is secured to a heat dissipation object such as a heat sink with fasteners such as machine screws. The over-torque protection feature is designed to flex and/or structurally fail in response to excessive fastener tightening force, thereby protecting flex-susceptible components mounted on the PCB.

The illustrated electronics package101has four sidewalls, including sidewall102-A to which mount100-A and mount100-B are connected and can form a housing. Mounts100-C and100-D are connected to a parallel sidewall102-B (FIG. 4). The electronics package101is secured to a heat-dissipation object such as a heat sink via the set of four mounts100-A,100-B,100-C,100-D. The mounts may be fewer or greater than four in number. As will be explained in greater detail below, the PCB may be mounted in the electronics package101such that an aluminum base layer forms a bottom wall of the packaged device. Moreover, the aluminum base layer may protrude from the package such that the sidewall edges and mounts do not contact the heat sink. This helps to avoid interference with thermal coupling of the aluminum base layer with the heat sink and presents an air gap between the mounts and the heat sink that facilitate structural failure at the designed fastener over-torque force because the mount is cantilevered from the sidewall rather than supported by the heat sink. The electronics package, including the mounts, may be molded, printed or machined as a single structure.

Instances of the over-torque protection feature are integrated into the mounts that are attached to the sidewalls. Each mount includes a distal end104, which may be semi-cylindrical, and a rectangular cuboid body106. A metallic threaded insert110may be disposed within the body106and distal end104to receive a fastener such as a machine screw for attaching the device to the heat sink. The threaded insert may traverse all or a portion of the thickness dimension T of the mount. The body is connected to one of the sidewalls via two spaced apart structural rectangular cuboid bars, arms, supports or members108(also referred to as rails). For example, mount100-A connects to sidewall102-A via two bars108. The two bars are oriented with the longest surfaces in parallel, proximate to respective outer surfaces of the body106. An empty rectangular cuboid recess, opening, hole, gap or slot112presents a void between the body106, bars108, and the sidewall. The bars108, which are disposed between the threaded insert and the sidewall, present the mechanically weakest portion of the connection between the mount and the sidewall. The machine screw may apply force against the threaded insert110along an axis A that is parallel with the length dimension L of the bars108(The length L of the bars may be equal to the thickness T of the mount) and perpendicular to the width dimension W. Thus, a tension force component may be applied to the bars proportionate with the tightening force applied by the machine screw. Based on the properties of the material from which the bars are formed (e.g. strength and rigidity) and the dimensions of the bars, e.g. length L, thickness T, and width W, the connection between the mount and the sidewall may be designed to stretch and/or structurally fail at the bars in response to a predictable amount of tension force applied via tightening of a machine screw. For example, the bar dimensions and material may be selected such that the amount of force required to cause mechanical failure of the bars is greater than the force required to maintain a secure connection of the electronics package to the heat sink and less than the force that would cause an undesirable or unacceptable amount of flex of an aluminum PCB mounted in the electronics package. Consequently, over-torqueing of a fastener that connects the package to the heat sink will result in damage and/or failure of the bars of the corresponding mount rather than excessively flexing the PCB and causing damage to electronic components mounted thereon, thereby being a mechanical fuse.

It should be noted that the mount does not necessarily shear completely away from the sidewall when the bars fail due to over-torqueing of a fastener. For example, one or both bars may fracture along all or only a portion of their length but remain partially connected to or in contact with the sidewall. Further, the material from which the electronics package is manufactured may be selected such that failure of a bar results in an audible “snap” sound that alerts the installer that the fastener has been over-torqued, thereby prompting installation of a non-failed device or package. In some implementations a rigid material is used, and the bars fail without deformation in response to an over-torqued fastener. In some implementations the bars deform until the mount contacts the heatsink in response to an over-torqued fastener. In some implementations only a subset of the mounts includes an over-torque protection feature.

In one embodiment, the housing of the electronics package101can be generally rectangular or square in shape with a hollow interior (FIGS. 1, 3 and 20), formed by four sidewalls102-A and a top cover wall. The housing can be formed of a rigid plastic material such as 33% glass filled Polyphthalamide (PPA) in which the mounts100-A through100-D are integrally formed with the sidewalls102-A. The housing can be about 1.5 by 1.5 inches square by about 0.7 inches high or thick, with a wall thickness of about 0.05 inches. The mounts can have a height or thickness dimension T of about ¼ inch or about 0.22-0.24 inches, for example about 0.23 inches, and a mount width WMof about 0.28-0.30 inches, such as 0.29 inches (FIG. 2). The two bars108can have a height or length L that is about the same as the height or thickness dimension T of the mounts. The bars108can each have a width W extending outwardly from the sidewall102-A of about 0.05-0.08 inches, such as about 0.07 inches, and can each have a thickness Tbof about 0.03-0.05 inches, such as about 0.04 inches. The outer lateral surfaces of the two bars108can be about 0.22-0.24 inches apart such as 0.23 inches, so as to form an indent, notch or groove108awith the outer lateral surfaces of the mounts and the sidewalls102-A, of about 0.02-0.03 inches. This can create a stress concentration location generally along a line parallel to axis A on the sides of the bars108to act as an over-torque mechanical fuse. The slot112between the bars108, as well as the indents108a, can reduce and weaken the connecting area of the mounts to the sidewall102-A by about a ⅔ connecting area amount to provide a structurally weakened linkage, in comparison to a connecting area if the slot112and indents108awere not formed in the mounts. The axis A can be centrally located within the mounts and can be located a distance d of about 0.15-0.17 inches or about 0.16 inches away from the sidewalls102-A.

Referring toFIG. 20, the package101can be generically shown as a package602having cantilevered mounts618extending from the sidewalls for securing a planar surface of a PCB600to a planar surface of a heatsink604with fasteners620. The PCB600can sit within the shoulder or shelf608of package602, and extend therefrom to form or define a space or air gap614between the mounts618of the package602from the surface of the heatsink604. In one embodiment of package101, the PCB can be about 1.4×1.4 inches by about 0.1 inches thick, and the air gap614between the surface of the heatsink604and the mounts can be about 0.02-0.03 inches. If the surfaces of the PCB600and/or the heatsink604are uneven, or if there is uneven foreign matter or particles therebetween, in the prior art, tightening the two surfaces together in compression typically requires more torque or force than normal, and can cause excessive flexing of the PCB600and damage to components thereon. However, the mounts in the present invention are configured to fail prior to causing excessive flexing. The mounts of package101are separated from the surface of the heatsink604by a large enough air gap614, to be able to deflect or move a sufficient amount towards the heatsink604when subjected to a force F generated by a fastener620along axis A that reaches a predetermined threshold torque or force level while attempting to bring the surfaces of the PCB600and the heatsink604together, to be able to fail along one or both bars108. The width W of the bars108that extends in the cantilevered direction can also be long enough to allow sufficient deflection and failure of the bars108within the air gap614.

By having two bars108being separated by slot112and having indents108a, the connection of the mounts to the sidewalls102-A is weakened, in some embodiments by a ⅔ reduction in connecting area. However, by having a height or length L that is large in the direction parallel to axis A in comparison to the thickness Tbthat is small in the direction perpendicular to axis A, the bars108are configured to have a structural rigidity or stiffness to be stable in the direction of axis A while the fastener620extending along axis A is being tightened for clamping during normal assembly, until the predetermined threshold torque or force to break the bars108is reached. The two bars108are also laterally spaced a sufficient distance away from each other to have lateral or side to side rigidity under normal conditions. Since the force F directed along axis A is generated by gradually tightening the screw, force F can be considered to be a generally static force, in comparison to a dynamic force caused by impacts.

In one embodiment, the threaded insert110in the mounts can be a brass insert, and the fastener620or screw can be an M 2.5 screw (0.1 inch outer diameter). The minimum amount of torque on the fastener620to clamp the PCB to the heatsink can be about 1.8 inch pounds (in lbs), providing a clamp force F per mount along axis A of about 98 pounds (lbs), and a thermal interface pressure generated by four mounts between the surfaces of about 209 psi (lbs/in2). The recommended fastener torque for clamping the surfaces together can be about 2.2 in lbs, providing a clamp force per mount of about 120 lbs, and a thermal interface pressure of about 255 lbs/in2. One or both bars108can be configured to fail if the fastener620while being tightened, reaches a predetermined threshold torque level or amount of about 2.6 in lbs, providing about a predetermined threshold clamp force level of about 142 lbs, and about 302 lbs/in2thermal interface pressure. As a result, one or both of the bars108of one or more mounts can fail if the predetermined threshold torque or force level is reached to prevent unwanted excessive flexure or bending to the PCB600.

In another embodiment, the fastener620can be an M 2 screw (0.08 inch outer diameter) which engages a threaded nut. In some embodiments, the minimum amount of torque on the fastener620to clamp the PCB to the heatsink can be about 1.3 inch lbs, providing a clamp force per mount along axis A of about 68 lbs, and a thermal interface pressure by four mounts of about 145 lbs/in2. The recommended fastener torque can be about 1.6 in lbs, providing a clamp force per mount of about 85 lbs, and a thermal interface pressure of about 181 lbs/in2. One or both bars108can be configured to fail if a fastener620while being tightened reaches a predetermined threshold torque level of about 1.9 in lbs, providing about a predetermined threshold clamp force level of about 102 lbs, and about 217 lbs/in2thermal interface pressure. As a result, one or both of bars108of one or more mounts can fail if the predetermined threshold torque or force level is reached to prevent unwanted excessive flexure to the PCB600. Accordingly, in some embodiments, the bars108forming the mechanical fuse can be configured to fail when a predetermined threshold level of torque of about 1.5 to 3 in lbs is reached.

FIGS. 5 through 9illustrate an alternative implementation of an electronics package with an over-torque protection feature based on designed structural weakness. The illustrated electronics package201includes four mounts200-A,200-B,200-C,200-D and four sidewalls, including sidewall202-A to which mount200-A and mount200-B are connected. Mounts200-C and200-D are connected to a parallel sidewall202-B (FIG. 8). Each mount includes a semi-cylindrical distal end204, a cylindrical section205, and a rectangular cuboid body206that connects to one of the sidewalls, e.g. mount200-A connected to sidewall202-A as shown inFIG. 6. A metallic threaded insert210is fitted into the cylindrical section205, which is connected to the body206via two rectangular cuboid bars208(also referred to as rails). The bars may be co-planar and disposed 180 degrees apart on the cylindrical section205that holds the threaded insert. Although the bars may be oriented in a wide variety of different ways, in the illustrated example two elongated flat surfaces of each bar are parallel to the adjacent sidewall.

The bars208present the mechanically weakest portion of the connection between the mount and the sidewall. The fasteners may apply force along an axis A that is parallel with the bar length dimension L. Based on the properties of the material from which the bars are formed and the dimensions of the bars, the connection between the mount and the sidewall may flex, deform, and/or fail at the bars in response to a predictable amount of force applied via a fastener when the package is mounted to another object. The bar dimensions and material may be selected such that the amount of force required to cause mechanical failure of the bars is greater than the force required to maintain a secure connection of the package to the object and less than the force that would cause an undesirable amount of flex of an aluminum PCB mounted in the package. The predetermined threshold torque or force level chosen can be similar to that described for package101. Consequently, over-torqueing of a fastener that connects the package to the object will result in deformation and/or failure of the bars of the corresponding mount rather than excessively flexing the PCB and causing damage to the components mounted thereon. The cylindrical section does not necessarily shear completely away from the body when a bar fails due to over-torqueing of a fastener. For example, one or both bars may fracture along all or only a portion of their length but remain partially connected to or in contact with the body. The material from which the package is manufactured may be selected such that failure of a bar results in an audible sound that alerts the installer that the fastener has been over-torqued and prompts installation of a non-failed device or package.

FIGS. 10 through 14illustrate another alternative implementation of an electronics package with an over-torque protection feature based on designed structural weakness. The illustrated electronics package301includes four mounts300-A,300-B,300-C,300-D and four sidewalls, including sidewall302-A (FIG. 10) to which mount300-A and mount300-B are connected. Mounts300-C and300-D are connected to a parallel sidewall302-B (FIG. 14). Each mount includes a semi-cylindrical distal end304and a rectangular cuboid body306that connects to one of the sidewalls, e.g. mount300-A connected to sidewall302-A as shown inFIG. 11. A truncated polyhedron-shaped or conical wedge308is fitted into a correspondingly-shaped opening309(FIGS. 13 and 14) that extends through the body206. For example, the wedge may be disposed in the opening with a friction fit or press fit. Further resistance to moving of the wedge308within the opening309may be determined by the angular orientation of the surfaces of the wedge that contact the body306and frictional properties of the materials and contact surfaces. Steeper angles may present less resistance to movement than shallow angles. The wedge308includes a threaded hole310for receiving the fastener.

The connection between the wedge308and the body presents the mechanically weakest portion of the connection between the mount and the sidewall. The fastener may apply force along an axis A that is parallel with the wedge thickness dimension T. Based on the resistance presented between the wedge and the body, the connection between the mount and the sidewall may partially or completely fail at the wedge in response to a predictable amount of force applied via a fastener when the package is mounted to another object. For example, the wedge may be pulled further into or through the opening in response to over-torqueing of the fastener and can cause portions of the mount surrounding the opening309that holds or contains the wedge308to break or fail. The wedge and opening dimensions, geometry and material may be selected such that the amount of force required to cause mechanical failure of the wedge-to-body connection is greater than the force required to maintain a secure connection of the package to the object and less than the force that would cause an undesirable amount of flex of an aluminum PCB mounted in the package. In one embodiment, the sides of the wedge308such as seen inFIG. 13can each be angled relative to axis A by about 5 degrees for creating mechanical advantage or leverage to cause breakage. The predetermined torque or force level chosen can be similar to that described for package101. Consequently, over-torqueing of a fastener that connects the package to the object will result in failure of the mount at the wedge rather than excessively flexing the PCB and causing damage to the components mounted thereon.

FIGS. 15 through 18illustrate an alternative implementation of an electronics package with an over-torque protection feature. The illustrated electronics package401includes four mounts400-A,400-B,400-C,400-D and four sidewalls, including sidewall402-A to which mount400-A and mount400-B are connected. Mounts400-C and400-D are connected to a parallel sidewall. Each mount includes a receiver404and a removable tab406. Each receiver404includes two parallel vertical members408and an interconnecting spring beam410. Distal ends of the spring beam are connected to the vertical members. A gap is presented between the spring beam and the sidewall such that the spring beam is solely supported by the connections to the vertical members at distal ends, and thus flexes in response to force. Each vertical member includes a first portion that is connected to the sidewall and a second portion that is angled relative to the first portion to form a slot into which a removable tab is inserted, seated and retained. More particularly, the receiver only allows the removable tab mounted therein to slide in one dimension, with range of travel limited in one direction by the spring beam. Each removable tab406includes a body412and an insert414. The body includes a threaded insert416for receiving a fastener. The insert includes two parallel vertical bars418that are interconnected by a cross-beam420. The vertical bars extend beyond the body. The cross-beam includes a projection422. A removable tab406is mounted in a receiver404such that the vertical bars418are retained by the vertical members408of the receiver. The tab is inserted into the receiver until the projection422contacts the spring beam410. The spring beam and cross-beam flex in response to excessive fastener tightening force, thereby inhibiting flexure of the PCB from over-torqueing of the fastener. In some implementations the spring beam may fail in response to over-torqueing of the fastener. The flexing or failure of the beams can be selected to occur at a predetermined threshold torque or force level similar to that in package101.

FIG. 19illustrates an implementation of a power card on an aluminum PCB500. The illustrated example is part of a digital drive. An amplifier circuit includes electronic components that are mounted on the PCB500. The electronic components may include transistors502(e.g. and without limitation MOSFETs) and ceramic capacitors504. Some or all the electronic components may be surface-mounted. The transistors502generate significant amounts of heat that must be transferred away from the amplifier circuit to avoid heat-related damage. The ceramic capacitors504are more susceptible to damage from PCB flexure than the other components. Electrical connector pins506are used to electrically interconnect the amplifier circuit with a control circuit. The various packages described above can be used to house the PCB, secure the PCB to a heat dissipation feature, and reduce the likelihood of damage to the ceramic capacitors by inhibiting flexure of the PCB if the fasteners are over-torqued.

FIG. 20illustrates the spatial relationship between a mounted PCB600, electronics package602and heatsink604in greater detail. The package and PCB may include any of the implementations described above. Outer edges606of the PCB are seated against a shelf608formed along edges of each sidewall of the package602. The PCB600, and specifically the aluminum substrate, extends beyond a distal edge612of the sidewall such that the package602does not inhibit contact, and thus thermal coupling, between an outer surface of the PCB600and the heatsink604. An air gap614is presented between the distal edge612and the heatsink604. The mounts618are flush with the distal edges of the sidewall, so the air gap614is also presented between the mounts618and the heatsink604. Consequently, the mounts618are cantilevered from the sidewalls and can be pulled toward the heatsink in response to over-torqueing of the fastener620, thereby triggering the over-torque protection feature.

Referring toFIG. 21, four solderable mounting posts700, one at each corner of a top wall702of the package704, enable the device to be securely mechanically connected to a control circuit. For example, the mounting posts may be soldered into through-holes formed in the control circuit. The mounting posts may be integral to the housing, e.g., partially enclosed by the top wall and/or sidewalls and held in place by a friction fit or inserted during the manufacture of the housing. The mounting posts help to isolate the electrical connector pins506(FIG. 19) from the mechanical stresses to which the housing is subjected, e.g. stresses caused by vibration and inertial forces resulting from changes in velocity and direction. Mechanical stress created by changes in velocity and direction of the heatsink706is transferred from the heatsink to the control circuit via the housing, thereby protecting the integrity of the electrical connection between the digital drive and the control circuit. As shown in the example, fasteners708may be inserted through openings in the heatsink and mated to threaded openings in the mounts. Further, a thermal pad710may be disposed between contact surfaces of the PCB and heatsink.

In the illustrated examples there are two pairs of mounting tabs formed at distal ends of two opposing sidewalls. However, any number of mounting projections could be implemented on any number of sidewalls. Moreover, the openings are not necessarily threaded. For example, the head of the fastener could be seated against the mounting tab and the threaded shank could be inserted into a threaded opening in the heatsink or held in place by a threaded nut.

While example embodiments have been particularly shown and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the embodiments encompassed by the appended claims. It will be understood that a wide variety of modifications and combinations may be made without departing from the scope of the inventive concepts described herein. Features of the various embodiments can be combined together or omitted.