Lid cover spring design

A module package can include a substrate; at least one device component configured to be positioned on the substrate; a module package lid configured to be positioned over the at least one device component and on the substrate, the module package lid exhibiting a plateau portion; and at least one mounting spring configured to be positioned on the module package lid, wherein the at least one mounting spring is configured to be mechanically coupled with a mounting surface and further positionally secure the module package lid and the at least one device component. Each mounting spring can include a middle portion; an end portion having a mounting hole; and a curved section between the middle portion and the end portion, the middle portion arranged to mate with the plateau portion of the module package lid when the end portion are secured to the substrate, the curved section being configured to prevent contact with a first corner portion of the module package lid.

TECHNICAL FIELD

The disclosed technology pertains generally to power modules and more specifically to power module packages.

BACKGROUND OF THE INVENTION

In order for a typical power electronics module to operate at working power levels, it is critical that the module's package be mounted to a temperature-controlled surface that can facilitate the removal of the resulting heat that will be generated. The mounting procedure for this installation generally requires that a package substrate and mounting plate meet flatness requirements, that the materials meet certain physical property requirements, that a sufficient thermal interface material is applied, and that the package be mounted with uniform and appropriate force.

In power electronics packages, it is common for the thermal interfaces to require 80 to 125 pounds-per-square-inch of pressure to ensure optimal performance. In order to achieve this pressure, screws are typically torqued (e.g., rotated by a screwdriver), which applies force at the mounting location. This force results in a pressure across the entire mounting area of the device. Unfortunately, the resultant pressure may not be uniformly applied.

A simple design, such as that illustrated by the prior art radio frequency (RF) power amplifier100ofFIG. 1, can result in an installation where pressure is higher near the mounting holes104A-D than in other locations on the bottom of the package. Further, such systems generally provide no safeguards against over-tightening of the package, which can result in any of a number of negative results such as plastic deformation or strain, for example. Indeed, it is very easy—and common—for a user to over-tighten a screw, thus causing damage.

Thus, there is a need in the art for a module package that can provide a solution to these problems.

SUMMARY OF THE INVENTION

It is, therefore, an object of the invention to create a module package that combines the benefits of mounting module packages by screws, e.g., providing accurate positioning of the package on a heat sink, with the advantages of mounting module packages by clamps, e.g., providing improved mounting pressure on the package.

As used herein, the term package generally refers to an assembly of components, e.g., a multi-chip module or other type of hybrid module, rather than injection-molded discrete devices, for example. An example of such a module is a radio frequency (RF) power module.

In certain implementations, one or more mounting springs may be used in connection with a lid and/or cover for an RF power module to secure the RF power module to a desired location and/or positioning, such as on a water-cooled high-thermal-capacity high-performance heat sink, for example.

It will be appreciated that packages in accordance with the disclosed technology may be modified and/or adapted for use by any of a number of different suitable devices such as electronic components, for example.

The foregoing and other objects, features and advantages of the invention will become more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.

DETAILED DESCRIPTION

Implementations of the disclosed technology generally include the use of one or more lid cover springs in order to achieve the required mounting force for a power electronics package.FIGS. 2A-Eand3A-E illustrate two respective examples of such implementations.

FIG. 2Aillustrates a perspective exploded view of a power amplifier200having two mounting springs202A-B in accordance with the disclosed technology. In the example, the power amplifier includes a substrate208, multiple device components206(e.g., integrated circuits (ICs), connecting components, and electrical pathways), a module package lid204, and the mounting springs202A-B.

In the example, the mounting springs202A-B have alignment holes203A-B, respectively, that can be configured to respectively receive alignment pins205A-B that are integrated with or otherwise attached to the module package lid204. Such arrangement may be used to advantageously ensure that the mounting springs202A-B are situated or otherwise positioned, and remain so, at the desired locations.

FIG. 2Billustrates a perspective partially assembled view of the power amplifier200having mounting springs202A-B in accordance with the disclosed technology. In the example, the substrate208is positioned on a surface or location (not shown) to which the power amplifier is to be mounted, the device components206are positioned on the substrate208, the module package lid204is positioned over the device components206and the substrate208, the mounting springs202A-B are positioned over the module package lid204, and a cover210is positioned over all of the components.

FIG. 2Cillustrates a perspective assembled view of the power amplifier200ofFIGS. 2A-B. In the example, the mounting springs202A-B may be coupled with the surface209by way of screws (not shown) inserted through mounting holes, such as mounting holes207A-B, in corresponding end portions of the mounting springs202A-B, respectively, for example. The end portions of the mounting springs202A-B are arranged to be parallel with an upper surface of substrate208when the respective screws are inserted through mounting holes207A-B and tightened. In this manner, the mounting springs202A-B advantageously provide the benefits of mounting module packages by screws, e.g., maintaining positioning of the package on a heat sink by preventing lateral movement, as well as the advantages of mounting module packages by clamps, e.g., providing improved mounting pressure on the package. Advantageously, over-tightening of the respective screws does not result in plastic deformation of module package lid204, since any overtightening results in attempt to deform the local portion of mounting springs202A-B and/or the respective portion of substrate208.

FIG. 2Dillustrates a first cross-sectional assembled view of the power amplifier200ofFIGS. 2A-Cin accordance with certain implementations of the disclosed technology. In the example, the first mounting spring202A has two curved sections252A and253A that are each between a corresponding end portion and a middle valley portion260A of the first mounting spring202A. Both curved sections252A and253A are configured to avoid contact with curved corner portions251A and254A of the module package lid204when the first mounting spring202A is coupled with the module package lid204. The curved sections252A and253A of the mounting springs202A may also be referred to as stress arches. Valley portion260A of the first mounting spring202A is arranged to be in contact with plateau portion250A of the module package lid204when the first mounting spring202A is coupled with the module package lid204.

FIG. 2Eillustrates a second cross-sectional assembled view of the power amplifier200ofFIGS. 2A-Din accordance with certain implementations of the disclosed technology. In the example, the second mounting spring202B has two curved sections272A and273A (also referred to as stress arches) that are each between a corresponding end portion and a middle valley portion260B of the second mounting spring202B. Both curved sections272A and273A are configured to avoid contact with curved corner portions271A and274A of the module package lid204when the second mounting spring202B is coupled with the module package lid204.

As mounting screws are tightened through mounting holes207A and207B in the corresponding end portions of the mounting springs202A and202B, for example, the force of tightening is first transferred to the respective valley portions260A and260B which mate with the respective plateau sections250A and250B. Curved sections253A and273A of the mounting springs202A and202B may expand, contract, and/or absorb the energy resulting from the tightening, thus ensuring that the curved sections253A and273A of the mounting springs202A and202B do not come into contact with the corresponding curved corner portions251A and271A of the module package lid204. The mounting springs202A and202B thus each translate the force applied by the mounting screws exclusively onto the plateau portions250A and250B of the module package lid204. Once the mounting screws have fully engaged the respective end portions with substrate208, the mounting springs202A and202B has reached their maximum travel, and the maximum force on each of the plateau portions250A and250B is reached because each mounting spring has reached its maximum extension. Indeed, at this point further turning the mounting screw can only de-form the screw hole base of the mounting spring, which is advantageously preferably made of metal which does not easily deform. Further, the curved sections253A and273A of the mounting springs202A and202B are configured to absorb excess force resulting from over-tightening of the mounting screws in the mounting holes207A and208A.

It will be appreciated that certain implementations of the disclosed technology may include only the curved sections252A and253A of mounting spring202A and/or the curved sections272A and273A of mounting spring202B but no corresponding curved portions of the module package lid204. Other implementations may include the curved corner portions251A,254A,271A, and274A of the module package lid204but no curved sections of the mounting springs202A and202B.

FIG. 3Aillustrates a perspective exploded view of another power amplifier300having a mounting spring302in accordance with the disclosed technology. In the example, the power amplifier includes a substrate308, multiple device components306(e.g., integrated circuits (ICs), connecting components, and electrical pathways), a module package lid304, a cover310, and the mounting spring302, which has a middle portion and four leg portions.

FIG. 3Billustrates a perspective assembled view of the power amplifier300ofFIG. 3A. In the example, the mounting spring302may be coupled with the surface309by way of screws (not shown) inserted through mounting holes, such as mounting holes307A and307B, in corresponding end portions of the legs of the mounting spring302, for example. In this manner, the mounting spring302advantageously provides the benefits of mounting module packages by screws, e.g., maintaining positioning of the package on a heat sink by preventing lateral movement, as well as the advantages of mounting module packages by clamps, e.g., providing improved mounting pressure on the module package lid304.

Unlike the mounting springs202A-B ofFIGS. 2A-E, which are separate components, the mounting spring302ofFIGS. 3A-Bis implemented as a single component. Indeed, it will be appreciated that the mounting springs described herein can be designed in virtually any suitable shapes, arrangements, and combinations.

FIG. 3Cillustrates a first cross-sectional assembled view of the power amplifier300ofFIGS. 3A-Bin accordance with certain implementations of the disclosed technology. In the example, the mounting spring302has two first curved sections356A and356B that each generally slope downward from a middle portion360between the two first curved sections356A and356B towards a respective edge of the mounting spring closest thereto. The two first curved sections356A and356B may also be referred to as stress arches and they are both configured to prevent the mounting spring302from engaging with or otherwise coming into contact with two first curved corner portions358A and358B of the module package lid304. The middle portion360is arranged to mate with a plateau portion350of the module package lid304when the end portions of the mounting spring302are coupled with the substrate308. The middle portion360may be a valley coupling the two first curve sections356A and356B.

FIG. 3Dillustrates a second cross-sectional assembled view of the power amplifier300ofFIGS. 3A-Cin accordance with certain implementations of the disclosed technology. In the example, the mounting spring302has two second curved sections352A and353A that each generally slope downward from the middle portion360between the two first curved sections356A and356B towards a respective edge of the mounting spring closest thereto. The two second curved sections352A and353B may also be referred to as stress arches and they are both configured to prevent the mounting spring302from engaging with or otherwise coming into contact with two second curved corner portions351A and354A of the module package lid304when the mounting spring302is coupled with the module package lid304. As noted above, the middle portion360of the mounting spring302is arranged to mate with the plateau portion350of the module package lid304when the end portions of the mounting spring302are coupled with the substrate308.

FIG. 3Eillustrates a third cross-sectional assembled view of the power amplifier300ofFIGS. 3A-Din accordance with certain implementations of the disclosed technology. In the example, the mounting spring302has two third curved sections372A and373A that that each generally slope downward from the middle portion360between the two third curved sections372A and373A towards a respective edge of the mounting spring closest thereto. The two third curved sections372A and373A may also be referred to as stress arches and they are both configured to prevent the mounting spring302from engaging with or otherwise coming into contact with two third curved corner portions371A and374A of the module package lid304when the mounting spring302is coupled with the module package lid304. As noted above, the middle portion360of the mounting spring302is arranged to mate with the plateau portion350of the module package lid304when the end portions of mounting spring302are coupled with substrate308.

As mounting screws are tightened through mounting holes307A and307B in the corresponding end portions of the corresponding legs of the mounting spring302, for example, the force of tightening is first transferred to the middle section360of the mourning spring302that mates with the plateau section350of the module package lid304. Curved sections353A and373A of the mounting spring302may expand, contract, and/or absorb the energy resulting from the tightening, thus ensuring that the curved sections353A and373A of the mounting spring302does not come into contact with the corresponding curved corner portions351A and371A of the module package lid304. The leg portions of the mounting spring302thus each translate the force applied by the mounting screws exclusively onto the plateau portion350of the module package lid304. Once the mounting screws have fully engaged the respective end portions with substrate308, the mounting spring302has reached its maximum travel, and the maximum force on the plateau portion350of the module package lid304is reached because the mounting spring has reached its maximum extension. Indeed, at this point further turning the mounting screw can only de-form the screw hole base of the mounting spring, which is advantageously preferably made of metal which does not easily deform. Further, the curved sections353A and373A of the mounting spring302are configured to absorb excess force resulting from over-tightening of the mounting screws in the mounting holes307A and308A.

While the examples illustrated byFIGS. 2A-Eand3A-E are power amplifiers, the assembly techniques may be adapted for use with virtually any suitable electronic devices/components.

It will be appreciated that the mounting springs disclosed herein may be constructed out of any of a number of suitable materials including, but not limited to, titanium and stainless steel. Stainless steel such as 17-4PH, which is a precipitation-hardened alloy containing approximately 17% chromium, 4% nickel, and 4% copper, may be used to provide an effective compromise between performance and price. Stainless steel alloys, such as 17-4PH, may advantageously have reduced ferromagnetic self-heating in RF applications compared to other suitable materials, such as titanium. In alternative implementations, the mounting springs may be made of a different material such as a graphite composite or other non-metallic material that may have a certain stress strain behavior and wide elastic regions.

Implementations of the disclosed technology generally allow for protective non-linear plateau behavior to occur without reaching the plastic deformation region of the material used for the mounting springs, thus facilitating potential reuse of the mounting springs. Also, by remaining in the elastic region of the material, a compliant stress-strain buffer may be provided as Coefficient of Thermal Expansion (CTE) stresses deform the shape of the module substrate.

During CTE stress cycling, the substrate and other components generally expand and contract in the x, y, and z axes but, when the mounting spring is coupled to the mounting surface, the resultant stress plateau region is maintained in reference to the applied mounting torque but an elastic and linear stress-strain behavior may also be maintained with reference to CTE stresses, e.g., primarily in the z-axis because that is the direction most likely to cause a failure in a ceramic substrate, for example.

Under standard mounting there is routinely delamination of the epoxy-to-lid interface, often severe enough to cause the lid to become completely mechanically detached from the rest of the module assembly. However, because of the compliancy afforded to the entire module by the linear elastic region maintained by the mounting spring in certain embodiments, the overall stress is desirably lowered in the epoxy-to-lid interfaces by limiting major strain behavior to the mounting springs.

FIG. 4is a graphical representation400of the improvement in screw torque versus substrate reaction force in accordance with certain implementations of the disclosed technology. In the example, the graphical representation400shows how reaction force increases in a device that includes the use of mounting springs in accordance with the disclosed technology (e.g., plotting404) as compared to a device that uses simple mounting holes in accordance with conventional techniques (e.g., plotting402). Whereas overtightening in a conventional design results in a continued increase in the substrate reaction force, the increase in the substrate reaction force in embodiments of the disclosed technology eventually begins to subside during overtightening.

The incorporating of mounting springs into the design of an electronics package as described herein advantageously allows for an even distribution of force across the full area of the substrate, which in turn reduces undesirable plastic deformation of the package. Such force-distribution improvement is accomplished herein by moving the mounting force to the top of the package using the mounting springs, which then apply an even compressive force on the package from above.

FIG. 5is a flow diagram illustrating a method500of assembling a radio frequency (RF) power module package in accordance with certain implementations of the disclosed technology. At502, a substrate is mounted on a mounting surface such as a heat sink. In alternative embodiments, the step at502may be performed at a different point during the method500, e.g., after all of the other steps have been performed.

At504, one or more device components, such as integrated circuits (ICs), connecting components, and electrical pathways, for example, are positioned on the substrate. At506, a package lid is positioned over the device component(s) and the substrate.

At508, one or more mounting springs are positioned on the package lid. In certain embodiments, one or more positioning holes in each mounting spring must be aligned with a corresponding positioning pin on the lid to ensure proper horizontal placement of the lid.

In certain embodiments, each mounting spring includes at least one curved section configured to prevent contact with a corresponding corner portion of the module package lid. In other embodiments, the module package lid has curved corner portions configured to prevent contact with the mounting spring(s). In yet other embodiments, each mounting spring includes at least one curved section configured to prevent contact with a corresponding corner portion of the package lid and the package lid has curved corner portions configured to prevent contact with the mounting spring(s).

At510, the mounting spring(s) are secured to the mounting surface, e.g., by way of one or more mounting screws through mounting holes in corresponding plateau portions of the springs. In alternative embodiments, the step at510may be performed at a different point during the method500, e.g., after all of the subsequent steps have been performed.

At512, a package cover is positioned over the mounting spring(s) and package lid. At514, the package cover is secured to the package lid. It will be appreciated that certain implementations may not include either or both of the steps at512and514.

It should be noted that, among the many advantages provided by the method500, one of them is the general ease of performance. That is, the method500does not require a highly-trained assembly technician to perform the steps as virtually anyone able to perform similar tasks can easily perform the method500.

Having described and illustrated the principles of the invention in a preferred embodiment thereof, it should be apparent that the invention can be modified in arrangement and detail without departing from such principles. We claim all modifications and variations coming within the spirit and scope of the following claims.