In
In
While the conventional process flow just described is adequate to form a semiconductor device package, it may offer certain drawbacks. In particular, the partial etching step shown in
Accordingly, there is a need in the art for a process for forming a semiconductor device package which avoids the need for a partial etching step.
Embodiments of the present invention relate to the use of stamping to form features on a lead frame of a semiconductor device package. In one embodiment, portions of the lead frame such as pins are moved out of the horizontal plane of a diepad by stamping. In certain embodiments, a complex cross-sectional profile, such as chamfered, may be imparted to portions of the pins and/or diepad by stamping. The complexity offered by such a stamped cross-sectional profile serves to enhance mechanical interlocking of the lead frame within the plastic molding of the package body. Other techniques such as selective electroplating and/or formation of a brown oxide guard band to limit spreading of adhesive material during die attach, may be employed alone or in combination to facilitate fabrication of a package having such stamped features.
These and other embodiments of the present invention, as well as its features and some potential advantages are described in more detail in conjunction with the text below and attached figures.
FIGS. 2CA-2CC show end views of various complex cross-sectional profiles that may be imparted by stamping according to embodiments of the present invention.
FIG. 8DA shows a simplified cross-sectional view of still another alternative embodiment of a package in accordance with the present invention.
FIGS. 8FA-FB show plan and cross-sectional views, respectively, of an alternative embodiment of a lead frame in accordance with an embodiment of the present invention.
FIGS. 8GA-GB show plan and cross-sectional views, respectively, of an alternative embodiment of a lead frame in accordance with an embodiment of the present invention.
FIGS. 8IA-IB show plan and cross-sectional views, respectively, of an alternative embodiment of a lead frame in accordance with an embodiment of the present invention.
FIGS. 8LA-LB show plan and cross-sectional views, respectively, of an alternative embodiment of a lead frame in accordance with an embodiment of the present invention.
Embodiments of the present invention relate to the formation of semiconductor device packages utilizing stamping. In one embodiment, portions of the lead frame such as pins are moved out of the horizontal plane of a diepad by stamping. In certain embodiments, the pins of a package may be imbued with a chamfered or other complex cross-sectional profile by a stamping process. Other techniques, employed alone or in combination, may facilitate fabrication of a package by stamping.
In
In
Also defined during the punching step of
Specifically,
Another lead frame feature shown in
According to certain embodiments, the stamping process may raise the pin portions 208a to a height Z above the surface of the diepad 204, where Z corresponds approximately to an expected thickness of a die supported on the diepad, and a conducting adhesive material between the die and the diepad.
Still another feature which may be imparted to a lead frame during the stamping of
In the particular embodiment of FIGS. 2CA-CB, the middle pin portion 208b exhibits a chamfered profile, with sides positioned at an angle relative to the vertical disposition of the sides of the other portions of the pin. In this embodiment, the complex cross-sectional profiles imparted to the lead frame by stamping according to embodiments of the present invention, enhances mechanical interlocking of the pins within the plastic body of the package. In addition, the stamped cross-sections allow the pins to offer a larger surface area to the surrounding molding material, thereby further enhancing mechanical interlocking between lead frame and package body. Moreover, the complex stamped cross-sectional profiles may allow the pins to better relieve physical stress during the subsequent singulation step, thus avoiding damage at the interface between the pin and the plastic package body.
While FIG. 2CA shows the complex cross-sectional profile as being a chamfer, this is not required by the present invention. In other embodiments, the cross-sectional profile imparted by stamping could be hour-glass shaped, T-shaped, H-shaped, angled or curved concave or convex, or saw tooth shaped, as shown in FIG. 2CC.
The various features formed by stamping in
Specifically, electroplated material 222 may be formed on the die attach portion 204b of the diepad 204 that is expected to receive the die. Where the die to be supported by the diepad has an electrical contact on its lower surface (such as the drain of a MOSFET), the electroplated material 222 will likely contain silver (Ag).
Another location of electroplated material is at an end of the elevated portion 208a of the pin 208 proximate to the diepad 204. As discussed in detail below, these electroplated regions are expected to receive the electrically conducting bond wire, bond ribbon, or bond clip from the top surface of the supported die.
The composition of the electroplated material 222 may be dictated by the composition of the bond wire/ribbon/clip with which the electroplated material will be in contact. The following TABLE provides a listing of electroplated materials under different conditions.
During the package singulation process shown in
The package singulation process in
While the particular embodiment shown above depicts fabrication of a package housing a single die, the present invention is not limited to such a package. Alternative embodiments in accordance with the present invention could be used to form packages housing two, three, or even larger numbers of die.
In a second step 304 of process 300, holes are punched completely through to remove material from the metal role and thereby define the pattern of the diepad and pins.
In a third step 306, the patterned metal roll is subjected to one or more stamping processes to create features on the pin and diepad portions of the package. As discussed in detail above, examples of such features include indentations on the underside of the diepad, pin portions exhibiting a chamfered cross-sectional profile, and raised pin portions.
In a fourth step 308, portions of the lead frame may optionally be electroplated with an appropriate metal. Examples of such electroplated regions include the die attach area, and the raised portions of the pins that are expected to receive an end of a bond structure such as a wire, ribbon, or clip having its other end in contact with the die.
In a fifth step 310, the stamped lead frame is exposed to an oxidizing ambient. A result of this exposure to the oxidizing ambient is the formation of brown oxide on all exposed portions of the lead frame surface. As discussed previously, this oxidation may desirably lead to the formation of an oxide guard band circumscribing the die attach area.
In a sixth step 312, brown oxide on the bottom surface of the pins and diepad may be removed. In certain embodiments, this oxide removal may be accomplished by physically lapping the bottom of the lead frame. In other embodiments, this oxide removal may be accomplished by exposure to a chemical etching environment.
The oxide removal step may occur immediately following the oxidation step, as indicated in
In a seventh step 314, the die is attached to the die attach area. In certain embodiments, this die attach step may include prior application of an electrically conducting adhesive material to the die attach area of the diepad. Alternative embodiments may utilize a die having its back side already coated with the electrically conducting adhesive material.
In an eighth step 316, the appropriate bonding structure(s) are attached between the surface of the die and the appropriate pin, which may be electroplated. As discussed above, the bond structure may be a conducting clip, wire, or ribbon.
In a ninth step 318, the die, bond structure, and portions of the pins and diepad are encapsulated within a plastic molding material to form the body of the package. During this step, the diepad and pins remain fixed to the surrounding metal matrix of the original metal roll.
In a tenth step 320, the individual package is singulated from the surrounding metal matrix by punching through the metal. During this singulation process, a chamfered or other complex cross-sectional profile imparted to the pins by stamping, may enhance mechanical interlocking of the pins within the package body, and allow the pins to relieve physical stress resulting from the shearing of the metal.
In additional steps (not shown), the package may be attached to an underlying PC board utilizing solder. The previous removal of brown oxide by lapping may facilitate the performance of this step.
The process described above represents only one particular embodiment of the present invention. Other embodiments may omit certain steps, include additional steps, or perform the steps in a specific order other than that indicated.
For example, the selective electroplating step is not required, and according to certain embodiments the bonding structure may be in contact with the bare metal of the roll rather than an electroplated feature. Moreover, the use of a bonding clip is not required by the present invention and certain embodiments could employ only bonding ribbons or wires to establish electrical connection with contact(s) on the top of the die.
Embodiments in accordance with the present invention offer a number of possible advantages over conventional package fabrication processes. In particular, by avoiding the need for complex and difficult-to-achieve steps of forming raised/recessed features on the lead frame by marking and partial etching, embodiments in accordance with the present invention offer cost savings.
Comparison of
However, various other aspects of processes according to embodiments of the present invention may serve to offset any smaller size of the diepad and die. For example, the formation of the brown oxide guard band circumscribing the die attach area, effectively constrains the flow of the electrically conducting adhesive material during the die attach process. This in turn allows reduction in the peripheral area of the diepad that must be allocated to avoid the flowed material from undesirably affecting regions outside the die attach area.
Moreover, certain embodiments involve the use of clips instead of bond wires. Such use of a bond clip may allow for a reduced resistance electrical connection between the die contacts and the surrounding pins. This may in turn permit the use of a smaller die having performance comparable to a larger one.
Similarly, the use of selective electroplating may also offer a reduced resistance electrical connection between the die contacts and the surrounding pins. Again, this offers the possibility of a smaller die exhibiting performance comparable to a larger die.
The above figures present an exemplary embodiment only, and the present invention is not limited by this particular embodiment. For example, while the above figures show a diepad having indented features formed by stamping, this is not required by the present invention. According to other embodiments, a diepad could have raised features formed by stamping, such as raised features on a periphery of the diepad.
Moreover, while the specific embodiment shown above includes pin portions proximate to the diepad that are elevated by stamping, the present invention is not limited to this approach. In accordance with alternative embodiments, portions of the pins distal from the diepad could be inclined downward by stamping, thereby offering an embodiment wherein the bottom of the diepad is not exposed following encapsulation of the package body.
In addition, while the above figures describe an embodiment of a package configured to house a single die, this is not required by the present invention. Alternative embodiments of packages according to the present invention can be configured to house two or more die.
For example,
The lead frame 403 of the particular embodiment of
Specifically, the stamped end frame 403 of package 420 comprises three diepads 404, 407, and 409, respectively supporting first MOSFET die 412, second MOSFET die 455, and integrated circuit (IC) die 460. Diepad 404 is the largest of the three, having an elongated die attach area 404a configured to support MOSFET die 412.
The pins of the package offer contact with three discrete portions of the first MOSFET die 412. Specifically, ganged pin nos. 21-27 are in low resistance communication with the source contact located on the top surface of the die 412, through clips 450. Pins 16, 20, and 28-31 are integral with the diepad 404, and hence offer a low resistance electrical communication with the drain of the MOSFET through a contact in the bottom surface of the die. The gate of the MOSFET is in electrical communication with a contact of the integrated circuit (IC) die 409 through bond wire 452.
Similarly, the pins of the package 420 offer contact with three discrete portions of the second MOSFET die 455. Specifically, ganged pin nos. 34-36 are in low resistance communication with the source contact located on the top surface of the die 455, through bonding clips 450. Pins 1-2, 4, and 33 are integral with the diepad 407, and hence offer a low resistance electrical communication with the drain of the MOSFET through a contact in the bottom surface of the die. The gate of the MOSFET is in electrical communication with pin 3 through bond wire 452.
Unlike the MOSFET die just described, the IC die 460 features a large number of contacts on its top surface. These various contacts are in electrical communication with the following pin nos.: 5, 7-9, 11-13, 15, and 17-18.
IC die 460 may or may not have an electrical contact in its lower surface. If it does, pins 6, 10, and 14 integral with the diepad 409 provide for low electrical resistance communication with that underside contact.
The multi-die embodiment of the QFN package 420 of
Another feature of the multi-die embodiment of the QFN package 420 of
Yet another feature of the multi-die embodiment of the QFN package 420 of
As previously indicated, the multi-die embodiment of the QFN package 420 includes an IC die which may or may not have an electrical contact on its back side. Such an IC die would not be expected to generate as much heat as other dies such as MOSFETs. Accordingly, an epoxy die attach film may be used to adhere the IC die to the diepad. Such an epoxy film may be formed as a solid, and would not be expected to flow or spread during the die attach step. Accordingly, for embodiments of the present invention where a package is fabricated housing only an IC die, formation of a brown oxide guard band followed by lapping, may not be necessary.
While the embodiments described above illustrate the use of stamping to impart a chamfered cross-sectional profile to pin portions, this particular cross-sectional profile is not required by embodiments of the present invention. According to alternative embodiments, stamping could imbue pins with other cross-sectional profiles and remain with the scope of the invention. Examples of such other cross-sectional profiles include but are not limited to hourglass shaped, angled or curved concave, angled or curved convex, or saw tooth.
During conventional package fabrication processes, the diepad may be secured to the surrounding metal of the roll utilizing tie-bar structures. These conventional tie-bar structures stabilize the diepad during die attach, and encapsulation steps, and are then severed during the package singulation.
One advantage of embodiments in accordance with the present invention, is the dispensing of the need for a tie-bar structure. Specifically, the embodiment of
The absence of tie-bars offer a number of advantages. One advantage is having more area in the corners of a package to place more pins. Another advantage is that there is no exposed part of tie bars on a surface of a package.
While the embodiment of
The embodiment of
Types of features other than those explicitly described above, can be formed on a lead frame by coining according to alternative embodiments of the present invention. For example,
The embodiment of
In addition, the holes 602 serve to isolate and preserve rim/runway area 606 (from the die to the edge of the die-pad) for down bonding. In particular the presence of the holes serves to contain unwanted bleeding or overflow of die attach material during the die attach step. For example, in one embodiment where the diepad has an overall width of 5.1 mm, the hole may have a width of 0.2 mm, and may be separated from the diepad edge by a distance of 0.2 mm forming the down bond runway.
Lead frames according to embodiments of the present invention may combine multiple features that are formed by coining. For example, the lead frame shown in
As a further example of a lead frame having multiple coined features,
Specifically, the lead frame 700 of the embodiments of
The following disclosure describes drawings that may include callouts that are the same as other callouts in the previous drawings. In such situations the callouts refer to drawings in
Package 200 comprises MOSFET die 202 having a top surface featuring gate pad 204 and source pad 206. The bottom surface of MOSFET die 202 features a drain contact 208.
Drain contact 208 is in electrical communication with an underlying first metal layer 224, through electrically and thermally conducting adhesive material 220. One example of such an electrically and thermally conducting material is solder. In certain embodiments, the first metal layer can be provided pre-bumped with solder balls or pre-formed with a solderable contact surface.
Integral projections of the first metal layer 224 extend outside of the plastic package body to provide leads for electrical contact with the MOSFET drain. The underside portion of the first metal layer that is exposed by the package body, may serve as a heat sink.
Package 200 includes a second metal layer 226 overlying the die. A first portion of 228 of the second metal layer is in electrical communication with gate pad 204 through a solder connection 230. A second portion 232 of the second metal layer is in electrical communication with source pad 206 through multiple solder connections 234. Portions 228 and 232 of the upper metal layer 226 are in turn routed to extend out of the plastic package body to serve as leads for connection to the gate and source. This routing may involve changing the vertical height of the metal portions 228 and 232 to match the height of the first metal layer. In particular embodiments, the shape of the second metal layer can be formed by bending. In other embodiments, the second metal layer can be provided in a pre-formed shape.
The package design of
Embodiments of the present invention may also offer advantageous electrical performance. For example, the reduced inductance of metal layers relative to bond wires offers reduced inductance, and may allow faster switching speeds. The use of metal layers in place of narrow bond wires may also advantageously offer a reduced resistance contact to the die housed by the package.
Another possible advantage offered by the embodiment of the package shown in
Moreover, the upper metal layer is also in substantial thermal contact with large areas of the die through the solder connections, and in particular the source pad present on the upper surface of the die. This large area of contact further enhances the flow of heat from the die out of the package to the surrounding environment through the leads. And, in certain embodiments, a portion of the upper metal layer is exposed on the outside of the package, thereby serving as a heat sink to the surrounding environment.
While the specific embodiment of
And while the specific embodiment of
Moreover,
Following encapsulation of the die within the plastic package body, the package of
FIG. 8DA shows a simplified cross-sectional view of yet another embodiment of a package in accordance with the present invention. This embodiment shows a reverse-gull wing shaped lead projecting upward toward the heat sink disposed on the top of the package.
FIGS. 8E-8EA show simplified plan and cross-sectional views, respectively, of another embodiment of a package in accordance with the present invention. The package of FIGS. 8E-8EA includes projecting leads located on only one side of the package. A first projecting lead is formed from a portion of the lower metal layer that is positioned at mid-thickness of the package and in contact with a source pad on the die through solder contacts. A second projecting lead is also formed from a portion of the lower metal layer that is in contact with a gate pad on the die through a solder contact. A third projecting lead is formed from a portion of the upper metal layer which is in contact with the drain pad of the die, and which is bent downward before ultimately exiting the package body at the mid-thickness height. As shown in
The embodiments described so far relate to packages housing MOSFET devices having three (gate, source, drain) terminals. However, the present invention is not limited to housing a die of this type. Alternative embodiments of packages in accordance with the present invention can be configured to house die having fewer or more terminals.
For example, FIGS. 8FA-B show plan and cross-sectional views along line 8F-8F′, of a lead frame for a planar two-terminal device (such as a diode) in accordance with an embodiment of the present invention. The lead frame includes a lower metal layer in thermal communication only with a back of the die. The two portions of the upper metal layer are in electrical communication with respective contacts on the upper side of the die.
Similarly, FIGS. 8GA-B show plan and cross-sectional views along line 8G-8G′, of a lead frame for a vertical two-terminal device (such as a diode) in accordance with an embodiment of the present invention. The lead frame includes a lower metal layer in electrical communication with a contact on the back side of the die, and an upper metal layer in electrical communication with a contact on the front side of the die.
While the embodiments of packages and lead frames just described are designed for a single die, this is not required by the present invention. Alternative embodiments in accordance with the present invention could be configured to house multiple die.
For example, FIGS. 8IA-B show simplified plan and cross-sectional views along line 8I-I′, of an embodiment of a lead frame in accordance with the present invention, which is configured to house two dual die. In this particular embodiment, the two die share the same terminal for a common backside contact, and have separate terminals and contacts on their front sides.
While the embodiment of
Similarly, FIGS. 8LA-B show simplified plan and cross-sectional views for a lead frame having multiple source terminals for each of two MOSFET die having drains isolated from each other. The portions of the lead frame in contact with these drains are secured together by a tie-bar structure that is severed (for example by punching) after the molding step.
Similarly,
While the embodiments described so far relate to lead frames and packages configured to house the same type of die, this is also not required by the present invention. Alternative embodiments could be configured to house different die types, for example MOSFETs and integrated circuits (ICs).
For example,
The upper metal layer 302 of the lead frame defines the leads in contact with various pads on the upper surface of the housed die. For example, die 304 represents an IC die having many contacts on its upper surface. Accordingly, the upper metal layer 302 of the lead frame comprises a plurality of leads (nos. 5-17) extending over these pads, with intervening solder contacts 312 providing the necessary electrical and thermal communication with the die.
Moreover, the leads of the upper metal layer 302 of the lead frame are not limited to contacting an IC die of a particular size. Thus, as shown in
By contrast, die 306 and 308 are MOSFETs having only a gate pad and a larger source pad on each of their top surfaces. Accordingly, the upper metal layer includes only two separate portions for each MOSFET die, which extend over the respective gate/source pads and is in thermal and electrical communication with each through an intervening solder contact(s) 312. Specifically, upper metal portion 330 is in contact with the gate pad of MOSFET die 306 (lead no. 4), and larger upper metal portion 332 is in contact with the source pad of die 306 (lead nos. 33-36).
Although not required, in this particular embodiment the larger upper metal portion 332 comprises a grid-like structure defining a pattern of apertures 333. These apertures reduce the thermal strain in the larger metal portion that results from shrinking and expansion in response to the changing thermal environment inside the package.
While the apertures of the embodiment of
Similarly, larger portion 340 of the upper metal layer allows thermal and electrical contact with the source pad MOSFET die 308 (lead nos. 21-27). In the particular embodiment of
The upper metal layer 302 features solitary leads (nos. 18-20 and 32) and ganged leads (nos. 1-3 and 28-31). As described particularly below, leads 1-3, 28-31, and 32 and are in electrical communication with the drain pads on the underside of the MOSFET die, through the lower metal layer.
As indicated in the cross-sectional view of
The configuration of the lower metal layer 348 shown in
In particular embodiments requiring connection between two or more die, the connect is provided by having two (or multiple) ball contact locations on an appropriately patterned and continuous pin. Pin 17 in
Portion 352 of the lower metal layer is in electrical and thermal communication with the drain pad on the underside of MOSFET die 306. Regions 352A jog upward to meet the ganged pins 1-3 and solitary pin 32 of the upper metal layer, thereby providing contact with the drain of MOSFET die 306. These upward jogs in the lower metal layer also serve to provide mechanical interlocking of that layer in the encapsulant of the plastic package body. The underside of lower metal portion 352 is also exposed by the underside of the package to provide a heat sink.
Portion 354 of the lower metal layer is in electrical and thermal communication with the drain pad on the underside of MOSFET die 308. Portions 354a jog upward to meet the ganged pins 28-31 and pin 18 of the upper metal layer, thereby providing contact with the drain of MOSFET die 308. These upward jogs in the lower metal layer also serve to provide mechanical interlocking of that layer in the encapsulant of the plastic package body. The underside of lower metal portion 354 is also exposed by the underside of the package to provide a heat sink.
In the particular embodiment of the package of
The embodiment of the lead frame just described, offers certain advantages. One advantage is ready adaptability to house different configurations of die and die sizes. For example, while the MOSFET die are shown occupying the majority of the area available on the grid-like lower metal portions, this is not required. The embodiment of a lead frame shown in
Portions of the metal layers of a lead frame projecting as pin(s) from the body of the package in accordance with embodiments of the present invention, can function internal to the package to perform a signal routing function between two or more separate die mounted on the same horizontal plane according to application needs. For example,
While the embodiments shown so far depict a package and lead frame configured to house multiple die located with signal routing in the same horizontal plane, this is not required by the present invention. Alternative embodiments of packages and lead frames in accordance with the present invention may feature multiple die oriented in a vertical stack or other orientations.
For example,
Apart from the stacked die configuration, a couple of aspects of the embodiment of
Second, embodiments in accordance with the present invention are not limited to the use of two or any number of multiple metal layers, or to incorporating only two die. Rather, embodiments of the present invention can utilize multiple metal layers sandwiching any number of desired die.
As described above in connection with
For example,
Embodiments in accordance with the present invention are not limited to housing particular types of die. However, certain types of die such as power devices are particularly suited for packaging according the present invention. For purposes of the instant application, the term “power device” is understood to refer to semiconductor devices used as switches or rectifiers in power electronic circuits. These include but are not limited to discrete devices such as diodes, power MOSFETs, insulated gate bipolar transistors (IGBTs), and Power Integrated Circuits used in the analog or digital control of the discrete devices.
In combination, the power devices are commonly employed to provide power management functions such as power supply, battery charging control systems. Power discrete devices having a planar or vertical structure, can handle power from a few milliwatts to tens of kilowatts. For the packages described above, a typical power device may operate at between about 500 W and 5 mW. In the off state, reverse breakdown can occur at voltages from about a few volts up to about 2000 volts. The operating current for power devices can range from a few milli-Amperes, to several hundred Amperes.
The leads 1405 are coupled with the die 1415 through the diepad 1410. The diepad 1410 can include any features, characteristics, or proprieties discussed throughout this disclosure in regard to other diepads (e.g., diepad 204). Moreover, the connection between the die 1415, the die pad 1410, and/or the leads 1405 can be made using any techniques know in the art. For example, connection to the die pad 1410 can include a connecting layer that may, for example, include a plurality of solder balls, solderable bumps, and/or solderable pillars. The heat sink 1420 can be coupled with the die 1415 using any number of techniques. For example, the heat sink 1420 can be coupled with the die 1415 using thermally conductive glue and/or solder 1425.
The components of device 1400 can have dimensions that vary. For example, the leads 1405 can vary in length. Also, the die 1415, the diepad 1410, and/or the heat sink 1420 can include widths.
Heat sink 1420 can comprise a complex shape. This complex shape, for example, can include one or more notches, like notch 1426. The complex shape of and/or notches in heat sink 1420 can provide added features for plastic encapsulation to provide traction for the encapsulant. Encapsulation can be a plastic material that encapsulates the die, diepad, all or a portion of the leads, and all or a portion of the heat sink.
The leads 1405 can have a first portion that is coupled with the die 1415 and a second portion that extend beyond the body of the die 1415. The portions of the leads 1405 that extend beyond the body of the die 1415 can be substantially parallel with one another. For example, these leads are parallel within standard manufacturing tolerances.
Moreover, leads 1405 do not require clips or plate connections. Instead, each lead is an unitary structure that extends from the die 1415 to the portion of the lead that connects with external circuitry. No additional fingers or leads are connected with leads 1405.
At block 1615 the heat sink can be attached with the die. The heat sink can be attached to the opposite side of the die as the finger frame or leads as shown in
While the above is a full description of the specific embodiments, various modifications, alternative constructions and equivalents may be used. Therefore, the above description and illustrations should not be taken as limiting the scope of the present invention which is defined by the appended claims.
This application is a continuation-in-part of U.S. patent application Ser. No. 12/186,342, filed Aug. 5, 2008, by Tsui et al., which claims priority to U.S. Provisional Patent Application No. 61/053,561, filed May 15, 2008, both of which are incorporated by reference in their entirety herein for all purposes. This application is also a continuation-in-part of U.S. patent application Ser. No. 12/903,626, filed Oct. 13, 2010, by Tsui et al., which is a division of U.S. patent application Ser. No. 12/191,527, filed Aug. 14, 2008, which issued as U.S. Pat. No. 7,838,339 on Nov. 23, 2010, which claims priority to U.S. Provisional Application No. 61/042,602 filed Apr. 4, 2008, all of which are incorporated by reference in their entirety herein for all purposes.
Number | Date | Country | |
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61053561 | May 2008 | US | |
61042602 | Apr 2008 | US |
Number | Date | Country | |
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Parent | 12903626 | Oct 2010 | US |
Child | 13348298 | US | |
Parent | 12186342 | Aug 2008 | US |
Child | 12903626 | US |