High-density flip-chip package for wireless transceiver

Abstract

An RF flip chip is provided in which a local bump region adjacent to a die corner includes a balun having a centrally located bump. The centrally located bump can be floating with respect to signals within the balun. The local bump region includes a crack stop region at the die corner in which bumps are excluded. The local bump region also includes at least one output bump for the balun.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of U.S. Non-Provisional Patent Application No. 16 / 875,972, filed May 15, 2020, which is incorporated herein by reference in its entirety as if fully set forth below and for all applicable purposes. Technical Field

[0003] The present application relates to integrated circuit packaging, and more particularly, to high-density flip-chip packaging for wireless transmitters and receivers. Background Art

[0004] Compared to purely digital devices, radio frequency (RF) systems for wireless applications typically require multiple passive components for filtering and matching purposes. These passive components are difficult to integrate onto a single semiconductor die with other transceiver components. Similarly, the various active components in a wireless transceiver, such as power amplifiers, are often produced using semiconductor technology that requires different semiconductor technology than more digitally based components such as modems. Transceivers for wireless devices such as cellular phones will therefore have multiple different semiconductor dies and passive components. It is beneficial to integrate these various discrete dies and passive components into an RF system-in-package (SiP). For example, RF SiPs offer many advantages, such as improved power efficiency, simplified design, and reduced noise. Despite these advantages, the design goal of increasing density must overcome many challenges. Summary of the Invention

[0005] According to a first aspect of the present disclosure, there is provided an RF flip chip die, comprising: a crack stop region, the crack stop region including a corner of the die; a local bump region, the local bump region adjacent to the crack stop region, the local bump region comprising; a first balun formed by a coil arranged around a central region; and a die interconnect located within the central region.

[0006] According to a second aspect of the present disclosure, a method for transmitting RF signaling is provided, comprising: driving a differential RF signal into a first coil of a balun, the balun located within a local bump region adjacent to a corner region for an RF flip-chip die, the first coil being formed around a central balun region including floating copper pillars for the local bump region; and generating a single-ended RF signal in a second coil of the balun in response to the driving of the differential RF signal.

[0007] According to a third aspect of the present disclosure, an RF flip chip is provided, comprising: a semiconductor substrate having a corner region surrounding a corner of the semiconductor substrate; a plurality of metal layers adjacent to the corner region, the plurality of metal layers being configured to form a first balun having a coil; a first copper pillar; and an uppermost dielectric layer having a portion located between a central region of the coil and the first copper pillar.

[0008] According to a fourth aspect of the present disclosure, there is provided a method for transmitting RF signaling, the method comprising: driving a single-ended RF signal in a first coil of a balun located within a local bump region adjacent to a corner region for an RF flip-chip die, the first coil being formed around a central balun region including a floating copper pillar for the local bump region; and generating a differential RF signal in a second coil of the balun in response to the driving of the single-ended RF signal.

[0009] These and other advantageous features will be better understood from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 The figure shows a conventional RF flip chip in which the local bump area has evenly distributed bumps.

[0011] Figure 2 An RF system including an RF flip chip with a localized bump area according to one aspect of the present disclosure is illustrated.

[0012] Figure 3 Illustrated is mounting an RF flip chip having localized bump areas onto a carrier substrate according to one aspect of the present disclosure.

[0013] Figure 4A is a simplified perspective view of a balun for a localized bump area according to one aspect of the present disclosure.

[0014] Figure 4B yes Figure 4A A plan view of a balun.

[0015] Figure 5 is a plan view of a local bump region according to one aspect of the present disclosure.

[0016] Figure 6 A method of transmitting RF signaling using a balun in a local bump area according to one aspect of the present disclosure.

[0017] Figure 7 Several example electronic systems are shown, each incorporating an RF flip chip according to an aspect of the present disclosure.

[0018] The embodiments of the present disclosure and their advantages are best understood by referring to the following detailed description.It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures. DETAILED DESCRIPTION

[0019] Several methods can be used to integrate a die into an RF integrated circuit package such as a SiP, such as wire bonding and flip-chip technology. Flip-chip mounting of a die is particularly attractive due to the increased interconnect density it provides compared to wire bonding. In both types of packages, the die has an active surface where active devices such as transistors are formed. This active surface faces away from the underlying substrate, such as the package carrier in wire bonding applications. However, in flip-chip packaging, the active surface of the die faces the package carrier. Therefore, the "flip" in flip-chip packaging comes from the fact that the die is "flipped" upside down compared to its orientation in traditional wire bonding applications.

[0020] The interconnects between the flip-chip die and the underlying substrate can be formed using solder balls. To further increase density, metal pillars (e.g., copper pillars) can be used to form these interconnects. In the following description, the term "bump" will be understood to refer to general flip-chip interconnects, regardless of whether the interconnect is a solder ball or a metal pillar. However, please note that solder bumps have an inherent spherical shape that limits bump density. In contrast, metal pillars such as copper pillars can be spaced apart to significantly increase bump density. Therefore, the following discussion will focus on embodiments in which the bumps are copper pillars without loss of generality. However, even if copper pillars are used to form bumps, there are still many obstacles that hinder further improvement in density. For example, traditionally, dies are formed from a semiconductor wafer that contains a layout for many other dies. To separate the wafer into individual dies, the wafer is segmented in the Cartesian x and y directions so that each die is rectangular. The rectangular shape of the die generates mechanical stress at the die corners. Therefore, crack stop regions are provided at each die corner to limit this mechanical stress. No bumps are allowed within the crack stop regions. However, on the remaining active surface of the die, the bump density must meet a minimum threshold density to properly secure the die to the underlying substrate. In addition, there is also a minimum spacing distance between each bump. For example, in a square area of ​​the die including the die corners and their crack arrest areas (denoted herein as the local bump area), the two factors of minimum bump density and minimum bump spacing lead to density issues. The definition of the local bump area depends on the semiconductor manufacturing requirements, but it will be assumed in this article that if the minimum bump spacing is defined by the pitch p, then in some semiconductor process technologies, the width and length of the local bump area is 3*p. The minimum bump spacing or pitch p can be defined as the minimum spacing from the center of a bump to the center of an adjacent bump. In one semiconductor process node, p is equal to 130μm. However, it will be understood that the pitch p and the width and length of the local bump area will vary depending on the semiconductor process node or technology.

[0021] The crack arrest area can form a right triangle, where the vertices of the right angle are the corners of the die. If the bumps are evenly distributed over the 3*p length and width of the local bump area, then such a local bump area will have six bumps. Figure 1 This can be better understood by referring to the example die 100 shown in FIG. The die 100 has four corners and, therefore, four crack stop regions 105 and four associated local bump regions 110, each with six bumps 115. Additional bumps may be added if the bump distribution is not homogeneous. Regardless of the number of bumps 115, including them in each local bump region 110 has traditionally limited the types of components that can be integrated into the active surface (not shown) of the die below each local bump region 110.

[0022] In general, a local bump area can be defined by a rectangular area of ​​the die that includes the die corners and has a length and width greater than the bump pitch p. Since the base and length of the crack stop area are the bump pitch p, the resulting rectangular area of ​​the die will include the crack stop area. The local bump area can be further defined as including the remaining portion of the rectangular area when the crack stop area is excluded. Therefore, the local bump area can be the die area adjacent to the crack stop area. Since the local bump area is adjacent to the crack stop area including the die corners, the local bump area can also be designated as the corner area of ​​the die in this article. In some embodiments, the local bump area can have a shape other than a rectangle or a rectangle with the corners removed.

[0023] The local bump area 110 and the example die 110 are not necessarily Figure 1 The die 100 is drawn to scale. The die 100 may be sized and / or shaped such that the local bump regions 110 are spaced farther apart than shown. Additionally, the die 100 may have an aspect ratio and / or shape different from that shown.

[0024] One type of component commonly used in RF front-end applications is a balun (balanced-to-unbalanced transformer). For example, die 100 may be a transceiver die that includes various RF components such as mixers and / or filters. Such transceivers may use differential signaling, for example because it advantageously eliminates common-mode interference. However, antennas commonly used in cellular phone applications, such as patch antennas, may not be suitable for driving with differential RF signals, or routing differential signals to such components may not be beneficial. In these configurations, a single-ended RF signal can be used to drive the antenna. Similarly, the power amplifier used to amplify the RF signal before it drives the antenna is also typically single-ended. Because power amplifiers used in wireless applications often use semiconductor processes unsuitable for those used to build transceivers, the transceiver and power amplifier may be located on separate dies. The balun converts the differential RF signal into a single-ended RF signal, allowing the transceiver die to drive the resulting single-ended RF signal to the power amplifier die. The resulting die can be integrated into an RF front-end system-in-package, or it can remain as a discrete device or be packaged into a module coupled via a circuit board.

[0025] Figure 2 An example RF front-end system 200 is shown in FIG. A transceiver die 205 includes an RF driver or amplifier 210 that drives a differential RF signal through a first coil 245 in a balun 215. In response to the differential signaling, a second coil 250 in the balun 215 generates a single-ended RF signal that is driven from the transceiver die 205 onto bumps 235. The other end of the second coil 250 is grounded.

[0026] Power amplifier die 230 receives a single-ended RF signal on bumps 240. Alternatively, die 230 can be wire-bonded. In a SiP embodiment for system 200, both die 205 and 230 can be flip-chip mounted into a carrier (not shown). Alternatively, die 205 and 230 can be packaged separately so that their integration into system 200 would be through a circuit board. Power amplifier 220 in die 230 amplifies the single-ended RF signal to drive antenna 225 through another bump 255.

[0027] Note that the balun 215 can alternatively function during a receive mode of operation. For example, the die 230 can include a low noise amplifier (not shown) that amplifies the RF signal received from the antenna 225. The resulting amplified receive RF signal drives the second coil 250 in the balun 215 to produce a differential receive RF signal at the first coil 245.

[0028] The balun 215 is a passive component that may not be integrated into the active surface of the die. Instead, the balun 215 may be formed in a metal layer adjacent to the active surface of the transceiver die 205. Some example metal layers in the flip chip die 300 are Figure 3 3. The die 300 is shown in FIG. 3. The die 300 has an active surface 305 in which various active components such as transistors are integrated. The active surface 305 is separated from the various metal layers by corresponding dielectric layers. For clarity of illustration, only the first metal layer M1 and the second metal layer M2 are shown, but it will be appreciated that more multiple metal layers are typically provided. As is known in the semiconductor art, metal layers such as metal layers M1 and M2 are patterned to form various conductors for signals of the die 300 as well as to provide power and ground. In addition, the metal layers may be patterned to form passive components such as the balun 215 ( Figure 2 ) inductive coil in. After the metal layer is patterned as desired, the pillar 310 can be deposited, for example, by electroplating. The pillar 310 is attached to the final or outermost dielectric layer by an under bump metallization (UBM) region 315. See again Figure 1 Since no UBM is formed in the crack stop regions 105, each crack stop region 105 can also be designated as a UBM-free region. The die 300 is then mounted on a substrate 320 by fusing the substrate 320 to the pillars 310. The substrate 320 will have similar metal layers for distributing signals, power, and ground. In a SiP embodiment, the substrate 320 can be a carrier that also supports the power amplifier die 230. Alternatively, in an embodiment where the transceiver die 205 and the power amplifier die 230 are packaged separately, the substrate 320 can be a circuit board.

[0029] The patterned metal layer forming the balun 400 is formed in Figure 4A is shown in a perspective view of . In this simplified view, the metal layer 405 is patterned into an open-ended loop to form a first coil 410. Similarly, the metal layer 415 is patterned into another open-ended loop to form a second coil 420. In general, each coil can be distributed over more than one metal layer, with multiple loops in each metal layer. Furthermore, while the first coil 410 is illustrated as being above the second coil 420, in alternative embodiments, the order may be reversed or the coils may be interleaved. It will therefore be appreciated that the balun 400 is shown in simplified form for clarity of illustration. In the balun 400, the second coil 420 includes two input ports 425 for receiving differential RF signals. The first coil 410 includes an output port 430 for a single-ended RF signal and also includes an output port for grounding. As Figure 4B As shown in plan view, each coil surrounds a central region 435 .

[0030] See again Figure 1 Baluns, such as balun 215 or balun 400, are typically excluded from LBR 110. The required bump density would cause signals to interfere with the operation of such baluns. For this reason, the die space beneath each LBR 110 is traditionally used to integrate other components, such as input / output (I / O) switches and attenuators, electrostatic discharge (ESD) protection circuitry, and digital block transceiver control circuitry. However, the use of such traditional components does not fully occupy the die space area beneath each LBR 110. For example, the typical utilization rate for LBR die space is approximately 55%. In order to significantly improve the die space usage (and therefore increase density) for LBR 110, an LBR layout is provided that includes at least one balun.

[0031] See again Figure 2 , note that it is beneficial for the associated active circuitry of the balun 215, such as the RF amplifier 210, to be located on the active die surface directly below the balun 215. Generally speaking, the RF differential signal driven into the balun 215 by the RF amplifier 210 will be relatively strong and will therefore tend to couple strongly to other signals in the transceiver die 205, which is undesirable. However, by keeping the associated circuitry in the immediate vicinity of the balun 215, this coupling will be reduced. Now turning to Figure 5, shows an example LBR 500 in which the balun 505 is substantially contained within the LBR 500. The location of the balun 505 within the LBR 500 enables the transceiver die 205 to locate associated circuitry such as the RF amplifier 215 within the LBR 500 to significantly improve density. For example, the utilization factor for the transceiver die 205 in the LBR 500 can be increased to 80% or even 90% or higher. Thus, the density is significantly improved compared to the conventional 55% utilization factor. In this embodiment, the balun 505 is completely contained within the LBR 500. However, in alternative embodiments, portions of the balun 505 may be outside the LBR 500. To maintain the desired bump density, the posts 510 are located in the central region 435 ( Figure 4B ) in. See again Figure 4A Balun 505 can have multiple stacked metal layer loops so that the first and second coils can be magnetically coupled to each other. Post 510 can be located substantially at the center of these loops. To reduce any coupling to the differential and single-ended RF signals processed by balun 505, post 510 is floating relative to these RF signals. As used herein, a post is considered floating relative to a signal if there are no conductive traces or leads in the metal layer for signals connected to the post via vias. In some embodiments, post 510 can be grounded or floating. In this regard, if a post is defined as floating without reference to any signal, then such post is not conductively connected to any signal node, nor is it conductively connected to any DC node such as ground or a power supply node. Although post 510 can be floating, it is noted that the metal layer beneath post 510 can be patterned in a "dummy" manner accordingly. In other words, even if no signal is routed to post 510, the metal layer is patterned to support post 510, for example, to provide greater structural integrity.

[0032] The transceiver die 205 ( Figure 2) can operate on several frequency bands. The RF signal generated for each frequency band is processed by a corresponding balun. For example, the transceiver die 205 may need a low-band balun, a mid-band balun, a high-band balun, and so on. Each balun is configured to operate within its corresponding frequency range. For example, the low-band balun will be configured for a relatively low-frequency RF carrier signal. Similarly, the mid-band balun will be configured for an intermediate-frequency RF carrier signal having a frequency higher than the relatively low-frequency RF carrier signal. Note, however, that the intermediate band may partially overlap with the low band. In general, the transceiver die 205 can have any number of such frequency bands and corresponding baluns, and their outputs can be routed to components (such as corresponding power amplifiers) configured to further process the signals in the corresponding frequency bands. Although the post 510 is floating with respect to any RF signal, in a multi-band embodiment, the balun 505 may be a low-band (LB) balun 505 to further reduce interaction of the post 510 with the RF signal in the LB balun 505 .

[0033] LBR 500 also includes a portion of another balun, such as mid-band (MB) balun 535. It should be understood that such partial inclusion of another balun is optional. Generally speaking, it is beneficial to locate the balun near the periphery of the transceiver die 205 because it will propagate to the power amplifier die 230 ( Figure 2 ) are relatively powerful. To reduce the power loss of such signals, the routing distance between the balun output bumps (such as bumps 235) and the power amplifier die bumps 240 should be reduced, which may result in the balun being positioned along the perimeter of the transceiver die 205. In some embodiments, the carrier frequency for the mid-band balun 535 can be approximately 3 GHz. Similarly, in some embodiments, the carrier frequency for the low-band balun 505 can be approximately 1 GHz.

[0034] Referring again to LBR 500, the positioning of the output posts, similar to bumps 235, will now be discussed. Regarding this positioning, it should be noted that operation within any given frequency band can be further divided into sub-bands or for operation using different signaling protocols. For example, MB balun 535 can switch between operation in a first sub-band and a second sub-band. Transceiver die 205 can therefore include a band switch (not shown) having a first configuration in which MB balun 535 is driven by a first IF sub-band differential RF signal to produce a first IF sub-band (MB1) single-ended RF signal at output MB1 post 530. Similarly, a second configuration can exist in which MB balun 535 is driven by a second IF sub-band differential RF signal to produce a second IF sub-band (MB2) single-ended RF signal at output MB2 post 525. Posts 530 and 525 are located near the perimeter of LBR 500 and also near the perimeter of the corresponding transceiver die 205. As is known in the semiconductor art, the perimeter of the transceiver die 205 is associated with a seal ring formed in a corresponding metal layer. Figure 5 5. The LBR 500 is shown as dashed line 515. Because output MB1 pillar 530 and output MB2 pillar 525 are adjacent to the die perimeter, these pillars are adjacent to the seal ring on one side of the crack stop region 105 (and therefore on one side of the vertex or corner of the transceiver die 205). The edge of the LB balun 505 is also adjacent to the seal ring on the other side of the crack stop region (and therefore on the other side of the same die corner). Because the LB balun 505 is adjacent to the die perimeter on one side of the die corner in the LBR 500, while output MB1 pillar 530 and output MB2 pillar 325 are adjacent to the die perimeter on the other side of the die corner in the LBR 500, there is space in the LBR 500 for only one output pillar of the LB balun 505 to be adjacent to the die perimeter. As previously discussed, there may be a minimum separation distance p between the pillars in the LBR 500. As used herein, a bump is considered adjacent to the die perimeter in LBR 500 if such bump is located within a distance p from the die perimeter or from the inside edge of the crack stop region 105. Given this proximity, in some manufacturing and / or design processes, no other bumps may be positioned between a bump adjacent to the die perimeter and the die perimeter.

[0035] LB balun 505 is similar to MB balun 535 in that LB balun 505 has a first low-band sub-band (output LB1) post 545 and a second low-band sub-band (output LB2) post 550. As noted above, there is room for only one such output bump at the die perimeter in LBR 500. In one embodiment, adjacent to the die perimeter is output LB2 post 550, although in alternative embodiments it could be output LB1 post 545. Note that even if the posts are only partially contained within LBR 500, as is the case with output LB1 post 545 and output LB2 post 550, the posts can still be considered to be within LBR 500. Output LB1 post 545 is located along the interior perimeter of LBR 500 and is separated from output LB2 post 550 by approximately the minimum separation distance P. Also located near the inner corners of LBR 500, along the same inner perimeter of LBR 500, are ground (GND) posts 540 that can serve as ground posts for MB balun 535. Balun GND posts 555, located between MB balun 535 and LB balun 505 in LBR 500, serve as ground posts for LB balun 505. Finally, there is ample space between LB balun 505 and crack stop region 105 for seal ring posts 520, which cover the seal ring and can serve as a ground post or floating connection. While the previous discussion relates to the integration of balun 505 into LBR 500, note that balun 505 can be replaced by a single coil forming a discrete inductor. The resulting single coil would thus have a central area that can advantageously be occupied by a bump, similar to that discussed with respect to post 510.

[0036] See again Figure 1Recall that an LBR with a length and width of 3 times the bump pitch p may require a minimum of six bumps to meet the required minimum bump density. If LBR 500 has the same minimum bump density of six bumps, it will be appreciated that the LBR can be rearranged in a variety of ways while still meeting the minimum bump density. For example, if mid-band balun 535 is removed from LBR 500, posts 530 and 525 can instead be used as output ports for LB balun 505. Therefore, posts 545 and 550 can be removed in such an embodiment or used for different purposes. Generally speaking, it is beneficial for the output posts of a balun to be adjacent to the balun to reduce the possibility of coupling with other signals. Note that LB balun 505 has a lower edge adjacent to the die perimeter, leaving no space for any posts between this lower edge and the die perimeter. For such a balun, the output posts can therefore be located on either side of the balun to reduce the routing distance between the balun and the output posts. In LB balun 505, output posts 545 and 550 are on the left side of balun 505, but in alternative embodiments, they can be relocated to the right side. In contrast, replacing ground post 555 with an output post would be less advantageous because post 555 is relatively removed from the die perimeter. Thus, according to the concepts disclosed herein, there are many ways to arrange posts within an LBR, including a balun containing posts. For example, in alternative embodiments, LBR 500 can have six posts, seven posts, or more than eight posts.

[0037] Now about Figure 6 The flowchart shown in discusses a method for transmitting RF signaling. The method includes act 600: driving a differential RF signal into a first coil of a balun, the balun located within a local bump region adjacent to a corner region of an RF flip-chip die, the first coil formed around a central balun region including floating copper pillars for the local bump region. An example of act 600 is driving an LB balun 505 with a differential RF signal. The method also includes act 605: generating a single-ended RF signal in a second coil of the balun in response to the driving of the differential RF signal. Generating the single-ended RF signal in one of the output pillars of the LB balun 505 is an example of act 605.

[0038] The method for receiving an RF signal would be similar. For example, such a method may include the act of driving a single-ended RF signal in a first coil of a balun. The balun is located within a localized bump region adjacent to a corner region for an RF flip-chip die, with the first coil formed around a central balun region including floating copper pillars for the localized bump region. Driving the received RF signal into LB balun 505 is an example of such an act. Furthermore, the method for receiving an RF signal may include the act of generating a differential RF signal in a second coil of the balun in response to the driving of the single-ended RF signal. Generating the received RF differential signal in LB balun 505 is an example of such an act.

[0039] The RF flip chip disclosed herein may be advantageously incorporated into any suitable mobile device or electronic system. Figure 7 As shown in FIG, a cellular phone 700, a laptop computer 705, and a tablet PC 710 can all include RF flip chips according to the present disclosure. Other exemplary electronic systems such as communication devices or personal computers can also be configured with RF flip chips constructed according to the present disclosure.

[0040] It should be understood that many modifications, substitutions, and changes may be made to the materials, devices, configurations, and methods of use of the devices of the present disclosure without departing from the scope of the present disclosure. In view of this, the scope of the present disclosure should not be limited to the scope of the specific embodiments illustrated and described herein, as they are intended only as some examples thereof, but should be fully commensurate with the scope of the claims hereinafter appended and their functional equivalents.

Claims

1. A radio frequency (RF) flip chip bare die, comprising: a crack stop region, the crack stop region including a corner of the die; as well as a local bump region, the local bump region being adjacent to the crack arrest region, the local bump region comprising: a first balun formed by coils arranged around a central region; as well as A die interconnect is located within the central region.

2. The RF flip chip die of claim 1 , wherein the die interconnects are solder balls.

3. The RF flip chip die of claim 1 , wherein the die interconnects are metal pillars. The RF flip chip die of claim 3 , wherein the metal pillars are copper pillars. 5 . The RF flip chip die of claim 4 , the local bump area further comprising a portion of a second balun. 6 . The RF flip-chip die of claim 5 , wherein the copper pillar is configured to float relative to an RF signal carried by the first balun. The RF flip chip die of claim 5 , wherein the copper pillar is grounded.

8. The RF flip chip die of claim 6 , wherein the first balun is configured to process a low-band differential carrier RF signal and the second balun is configured to process a mid-band differential carrier RF signal, the mid-band differential carrier RF signal having a higher frequency than the low-band differential carrier RF signal.

9. The RF flip chip die of claim 6 , wherein an edge of the first balun is within a minimum bump separation distance from a perimeter of the die on a first side of the crack stop region, and wherein the local bump region includes a first output post for the second balun adjacent to the perimeter of the die on a second side of the crack stop region.

10. The RF flip chip die of claim 9, wherein the local bump area includes a first output post for the first balun adjacent an inner perimeter of the local bump area.

11. The RF flip chip die of claim 10, wherein the local bump area further comprises: a second output post for said first balun; as well as A second output post for the second balun. 12 . The RF flip chip die of claim 9 , further comprising a seal ring post located in a portion of the local bump area between the crack stop region and the first balun.

13. The RF flip chip die of claim 6, wherein the RF flip chip die is bonded to a substrate for an RF system-in-package through the copper pillars, the RF system-in-package further comprising a power amplifier configured to amplify the single-ended RF signal from the first balun.

14. The RF flip chip die of claim 1, wherein the RF flip chip die is integrated within a cellular phone.

15. The RF flip chip die of claim 6, wherein the width and height of the local bump area are three times the minimum bump spacing distance.

16. A method for sending radio frequency (RF) signaling, comprising: driving a differential RF signal into a first coil of a balun located within a local bump area for an RF flip-chip die, the first coil being formed around a central balun area including a floating copper pillar for the local bump area; and A single-ended RF signal is generated in a second coil of the balun in response to the driving of the differential RF signal.

17. The method according to claim 16, further comprising: amplifying the single-ended RF signal in a power amplifier to produce an amplified single-ended RF signal; as well as An antenna is driven with the amplified single-ended RF signal.

18. The method of claim 17, wherein amplifying the single-ended RF signal in the power amplifier comprises amplifying the single-ended RF signal in an RF system-in-package.

19. A radio frequency (RF) bare chip, comprising: a semiconductor substrate having a crack stop region including a corner of the die and having a corner region adjacent to the crack stop region; a plurality of metal layers adjacent to the corner region, the plurality of metal layers configured to form a first balun having a coil; a first leg, the first leg being within a central region of the coil; as well as An uppermost dielectric layer has a portion located between a central region of the coil and the first leg.

20. The RF die of claim 19, further comprising under-bump metallization between the first pillar and the uppermost dielectric layer.

21. The RF die of claim 19, wherein the first pillar is a first copper pillar.

22. The RF die of claim 21, wherein the first copper pillar is configured to float relative to an RF signal of the first balun.

23. The RF die of claim 21, wherein the first copper pillar is a ground node for the first balun.

24. The RF die of claim 21, wherein the corner region comprises an additional seven copper pillars.

25. A method for sending radio frequency (RF) signaling, comprising: driving a single-ended RF signal in a first coil of a balun located in a local bump area for an RF flip-chip die, the first coil being formed around a central balun area including a floating copper pillar for the local bump area; and A differential RF signal is generated in a second coil of the balun in response to the driving of the single-ended RF signal.

26. The method according to claim 25, further comprising: receiving an RF signal at an antenna; as well as The received RF signal is amplified to generate the single-ended RF signal.

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