Air cavity packaging structure for W wave band

Abstract

The invention discloses an air cavity packaging structure for a W wave band. The packaging structure comprises a chip, a packaging substrate and a plastic packaging shell. The packaging substrate comprises four metal layers used for transmitting signals, four metal layers used as reference ground and a substrate dielectric layer. The metal ground of the substrate is hollowed out below the position of the substrate used for transmitting signals, and the distance between the transmission structure on the top layer of the substrate and the metal ground right below the transmission structure is increased, so that the quality factor of a signal transmission path is improved, and the signal transmission loss is reduced. The chip is arranged on the top layer of the substrate, the chip output Pad is connected with the top metal layer for signal transmission through a bonding structure, and the chip back ground is connected with the top metal layer of the reference ground through a connecting piece; the plastic packaging shell is arranged on the packaging substrate, and the chip is packaged in the plastic shell. Compared with a traditional packaging scheme, the substrate cavity packaging structure is selected, the signal transmission loss can be reduced, the production consistency is improved, and the production cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of packaging technology, and more specifically to a W-band air cavity packaging structure. Background Technology

[0002] W-band (75-110 GHz) radio frequency chips, especially power amplifiers, have important applications in radar, communication, and imaging systems. These chips place extremely stringent requirements on packaging performance: First, they must have extremely low signal transmission loss, as conductor loss, dielectric loss, and reflection loss introduced by discontinuous structures increase dramatically with frequency; second, they need excellent and reliable thermal management capabilities to dissipate the high heat generated during chip operation; and finally, while meeting high performance requirements, they must also achieve miniaturization, high production consistency, and controllable cost.

[0003] Currently, packaging technologies suitable for high-frequency bands mainly include: ceramic packaging, which has advantages such as good high-frequency performance, high hermeticity, and good thermal conductivity, but is expensive and has poor compatibility with mainstream PCB processes; wafer-level packaging, which can achieve ultra-high integration and extremely small size, but requires extremely high process precision and usually has limited heat dissipation capacity; and traditional plastic packaging technology, which, although low in cost and suitable for mass production, introduces significant dielectric loss and parasitic effects in the W-band, making it difficult to meet high-performance requirements.

[0004] Air cavity packaging, as a compromise, effectively reduces dielectric loss in signal transmission by creating an air dielectric region within the package. However, in W-band applications, existing air cavity packaging still faces two significant challenges: first, signal transmission loss needs further reduction; second, the packaging structure is extremely sensitive to the back-end matching network, leading to significant performance fluctuations between different batches or different package units, making it difficult to guarantee production consistency. Furthermore, achieving effective heat dissipation in high-frequency plastic encapsulation structures is also an engineering problem that needs to be solved.

[0005] Therefore, there is an urgent need for a new W-band packaging structure that can further optimize signal integrity, reduce sensitivity to matching, and enhance heat dissipation through structural innovation while maintaining the low-loss advantage of the air cavity, and is compatible with low-cost, high-consistency mass production processes. Summary of the Invention

[0006] The purpose of this invention is to propose an air cavity packaging structure for W-band, which reduces signal transmission loss while taking into account performance, cost and reliability, and overcomes the problems of high loss, poor production consistency due to sensitivity to matching networks, and limited heat dissipation capacity of existing W-band packaging structures.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A W-band air cavity packaging structure includes: a chip, a packaging substrate, and a plastic encapsulation shell;

[0009] The packaging substrate includes a dielectric layer, and a radio frequency signal transmission layer group and a ground signal transmission layer group disposed within the dielectric layer and physically separated from each other.

[0010] The radio frequency signal transmission layer group includes a top-level signal metal layer, a second-top-level signal metal layer, a second-bottom-level signal metal layer, and a bottom-level signal metal layer arranged from top to bottom.

[0011] The ground signal transmission layer group includes a top ground metal layer, a second top ground metal layer, a second bottom ground metal layer and a bottom ground metal layer arranged from top to bottom;

[0012] In the vertical projection area corresponding to the radio frequency signal transmission layer group, the ground metal layer of the ground signal transmission layer group is hollowed out to increase the effective distance between the signal transmission line and the reference ground plane.

[0013] The chip is disposed on and fixed on the top metal layer;

[0014] The signal output terminal of the chip is electrically connected to the top signal metal layer through a bonding structure.

[0015] The top signal metal layer, the second-top signal metal layer, the second-bottom signal metal layer and the bottom signal metal layer of the radio frequency signal transmission layer group are vertically interconnected through the first set of vias, and the bottom signal metal layer is used to connect to external circuits.

[0016] The ground signal transmission layer group is vertically interconnected between its various metal layers via a second set of dense vias.

[0017] The plastic encapsulation shell is disposed on the packaging substrate and seals the chip therein.

[0018] Furthermore: the chip is a GaAs power amplifier chip that operates in the W-band, and the bonding structure is a gold wire bonding structure.

[0019] Furthermore, the chip is fixed to the top metal layer using gold-tin alloy solder as a connector.

[0020] Furthermore, the top-level signal metal layer comprises three sequentially connected functional parts: a stub for bonding and positioning, a connecting line, and a connecting part. These three parts, through their own shapes and coupling relationship with the side ground metal layer, together form an impedance matching network.

[0021] Furthermore: the first set of vias includes vias connecting the top signal metal layer and the bottom signal metal layer, vias connecting the top signal metal layer and the next-lowest signal metal layer, and vias connecting the next-lowest signal metal layer and the bottom signal metal layer.

[0022] Furthermore, all metal layers in the packaging substrate are made of pure copper.

[0023] Furthermore, the dielectric layer of the packaging substrate is made of PP material (GHPL-970LF) with low expansion and low shrinkage rates, which can effectively reduce the warpage of semiconductor packaging and has irreplaceable advantages in electrical connection and heat conduction.

[0024] Furthermore, the encapsulation shell in the package is made of EMC (epoxy molding compound), which has the functions of protecting the chip from the influence of the external environment, resisting external solvents, moisture, and impact, and ensuring electrical insulation between the chip and the external environment.

[0025] Compared to other existing technologies, this invention completely separates the signal transmission portion of the substrate from the ground signal transmission portion, artificially increasing the distance between the reference ground plane below the RF signal and the signal transmission plane. This improves the Q value of the circuit, reduces circuit losses, and simultaneously reduces the sensitivity of the package matching network, effectively improving chip consistency. Circuit matching is achieved by setting the shape of the top metal layer used for RF signal transmission and surface coupling with the side ground in the substrate. Positioning points are set at the nodes connecting the bonding structure in the top signal metal layer to ensure consistency during subsequent bonding with the chip. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of this invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below:

[0027] Figure 1 This is a side view of the W-band encapsulation structure in an embodiment of the present invention;

[0028] Figure 2 This is a top view of the W-band encapsulation structure in an embodiment of the present invention;

[0029] Figure 3 This is a bottom view of the W-band packaging structure in an embodiment of the present invention.

[0030] Figure 4 This is a cross-sectional view of the W-band encapsulation structure in an embodiment of the present invention;

[0031] Figure 5 This is a schematic diagram of the matching network structure in an embodiment of the present invention;

[0032] Figure 6The figure shows the simulation results of the packaging structure loss in the embodiment of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] refer to Figure 1 This invention proposes a packaging structure for a W-band air cavity, comprising: a chip 1, a packaging substrate 2, and a plastic housing 3.

[0035] The packaging substrate 2 includes: a radio frequency signal transmission layer group 21, a ground signal transmission layer group 22, and a substrate dielectric layer 23. The radio frequency signal transmission layer group 21 and the ground signal transmission layer group 22 are physically separated from each other and there is no direct electrical connection between them.

[0036] The radio frequency signal transmission layer group 21 includes: a top signal metal layer 211, a second-top signal metal layer 212, a second-bottom signal metal layer 213, and a bottom signal metal layer 214. The radio frequency signal transmission layer group 21 is connected and conductive through a first set of vias 6.

[0037] The ground signal transmission layer group 22 includes: a top ground metal layer 221, a second-top ground metal layer 222, a second-bottom ground metal layer 223, and a bottom ground metal layer 224. The ground signal transmission layer group 22 is connected and conductive through a second set of densely packed vias 5, which constitute the main heat dissipation channels of the chip 1.

[0038] The chip 1 is placed on the packaging substrate 2, specifically above the top metal layer 221 via a connector (such as gold-tin alloy solder).

[0039] The ground metal layer 22 is hollowed out in the region corresponding to the radio frequency signal transmission path, forming an opening of size X1 (see...). Figure 2 This design increases the effective distance between the signal transmission line (especially the bottom signal metal layer 214) and the reference ground plane below, thereby improving the quality factor (Q value) of the signal transmission path, which is a key measure to reduce transmission loss in the W-band.

[0040] The plastic housing 3 is disposed on the packaging substrate 2, and the chip 1 is located inside the plastic housing 3.

[0041] refer to Figure 2The top-layer signal metal layer 211 includes: a spur 211-1 with bonding positioning points (equivalent to a capacitor), a connecting line 211-2 (equivalent to an inductor), and a connecting portion 211-3 (equivalent to a capacitor) connected to the via 6. These three parts, through their specific shapes and coupling with the side ground metal, together integrate a matching network inside the package substrate.

[0042] The size of the opening X1 in the middle of the ground signal transmission layer group 22 is determined by the size of the chip 1.

[0043] Combination Figure 4 and Figure 5 The transmission and matching path of the radio frequency signal is as follows: The signal is generated from the output Pad of chip 1, transmitted to the branch 211-1 of the top signal metal layer 211 through the gold wire bonding wire 4, then passes through the connecting wire 211-2 and the connecting part 211-3 in sequence, and then is vertically transmitted to the bottom signal metal layer 214 through the first set of through holes 6, and finally output to the external PCB. Figure 5 The physical layout structure of the matching network on the top signal metal layer of the package substrate is shown.

[0044] The capacitance of the support 211-1 is adjusted by adjusting the distance X2 between the support 211-1 and the side ground, and the line width w2 coupled to the side ground. The equivalent inductance of the connecting line 211-2 is determined by the line width and length of the metal wire. The capacitance of the connecting part 211-3 is adjusted by adjusting the distance X3 between the connecting part 211-3 and the side ground, and the line width w3 coupled to the side ground. The first group of through holes 6 themselves have equivalent inductance characteristics, and their inductance is determined by their number, diameter, depth, and other geometric parameters.

[0045] Example:

[0046] For details, please refer to Figure 1-5 In one embodiment, the present invention provides a W-band air cavity packaging structure, including a chip 1, a packaging substrate 2, and a plastic housing 3.

[0047] The chip 1 and the packaging substrate 2 are encapsulated together in a plastic housing 3.

[0048] The packaging substrate 2 includes a radio frequency signal transmission layer group 21, a ground signal transmission layer group 22, and a substrate dielectric layer 23.

[0049] Specifically, the substrate dielectric layer 23 used in the embodiment is a PP material (GHPL-970LF) substrate with low dielectric constant Dk=3.4 and low tangent angle loss Df=0.003, which has excellent welding heat resistance, high rigidity and low expansion rate.

[0050] All metal layers of the packaging substrate are made of copper, and each metal layer is 20 μm thick.

[0051] The size of the opening X1 of the ground signal transmission layer group 22 is determined by the chip size; in this embodiment, the opening is 940um.

[0052] In this embodiment, chip 1 is a power amplifier chip for the W-band fabricated using GaAs technology.

[0053] The chip 1 is fixed to the top ground metal layer 221, which serves as the ground in the packaging substrate 2, by a connector, which is typically made of gold-tin alloy solder.

[0054] The chip 1 and the packaging substrate 2 transmit signals through a bonding structure 4.

[0055] The bonding structure 4 is connected at one end to the output Pad of the chip and at the other end to the support 211-1 of the packaging substrate. Two positioning points are set on the support 211-1 to facilitate the bonding position without affecting the matching effect, and to ensure that the equivalent inductance of the gold wire bonding wire remains consistent during mass production.

[0056] After the radio frequency signal enters the stub 211-1, it passes through the connecting line 211-2 (which can be equivalent to an inductor) and then enters the connecting part 211-3. After that, it enters the bottom signal metal layer 214 in the packaging substrate 2 through the through hole 6.

[0057] The width w2 of the support 211-1 and the distance X2 between it and the side reference ground are determined by the required capacitance value. The positioning point is placed on the other side, which is a certain distance from the reference ground, and will not affect the equivalent capacitance value.

[0058] In the embodiment, the width w2 of the branch 211-1 is 680um, and the distance X2 between it and the side reference ground is 70um.

[0059] The connecting line 211-2 described in the embodiment is a metal connecting line with a width of 40um and a length of 120um.

[0060] The width w3 of the connecting part 211-3 and the distance X3 between it and the side reference ground are determined by the required capacitance value. In this embodiment, w3 is 250um and X3 is 90um.

[0061] The radio frequency signal transmission layer group 21 of the substrate is connected through the first group of through holes 6; the ground signal transmission layer group 22 is connected through the second group of through holes 5.

[0062] The configuration of the first group of vias 6 includes: two vias connecting the top signal metal layer 211 and the bottom signal metal layer 214, two vias connecting the top signal metal layer 211 and the second bottom signal metal layer 213, and one via connecting the second bottom signal metal layer 213 and the bottom signal metal layer 214.

[0063] The second group of vias 5 is a way to connect the layers of the ground signal transmission layer group 22. It consists of multiple vias from the top metal layer to the bottom metal layer, which can provide good heat dissipation for the chip.

[0064] according to Figure 6 Simulation results show that the RF signal is output from the chip, passes through the bonding structure, and is output after passing through the packaging substrate. Within the required frequency band in this embodiment, the overall circuit loss is within 0.8dB, which meets the packaging design requirements.

[0065] The encapsulation shell 3 is made of EMC (epoxy molding compound), which has the functions of protecting the chip from the influence of the external environment, resisting external solvents, moisture and impact, and ensuring the chip is insulated from the external environment.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A W-band air cavity encapsulation structure, characterized in that: include: Chip (1), packaging substrate (2) and plastic encapsulation shell (3); The packaging substrate (2) includes a dielectric layer (23), and a radio frequency signal transmission layer group (21) and a ground signal transmission layer group (22) disposed within the dielectric layer (23) and physically separated from each other. The radio frequency signal transmission layer group (21) includes a top-level signal metal layer (211), a second-top-level signal metal layer (212), a second-bottom-level signal metal layer (213), and a bottom-level signal metal layer (214) arranged from top to bottom. The ground signal transmission layer group (22) includes a top ground metal layer (221), a second top ground metal layer (222), a second bottom ground metal layer (223), and a bottom ground metal layer (224) arranged from top to bottom. In the vertical projection area corresponding to the radio frequency signal transmission layer group (21), the metal of the ground signal transmission layer group (22) is hollowed out to increase the effective distance between the signal transmission line and the reference ground plane; The chip (1) is disposed on and fixed on the top metal layer (221); The signal output terminal of the chip (1) is electrically connected to the top signal metal layer (211) through a bonding structure (4); The top signal metal layer (211), the second-top signal metal layer (212), the second-bottom signal metal layer (213), and the bottom signal metal layer (214) of the radio frequency signal transmission layer group (21) are vertically interconnected through the first set of vias (6), and the bottom signal metal layer (214) is used to connect to external circuits. The ground signal transmission layer group (22) is vertically interconnected between the ground metal layers through a second set of dense vias (5); The plastic encapsulation shell (3) is disposed on the packaging substrate (2) and seals the chip (1) therein.

2. The air cavity encapsulation structure for W-band according to claim 1, characterized in that: The chip (1) is a GaAs power amplifier chip that operates in the W band, and the bonding structure (4) is a gold wire bonding wire.

3. The air cavity encapsulation structure for W-band according to claim 1, characterized in that: The chip (1) is fixed to the top metal layer (221) by means of gold-tin alloy solder as a connector.

4. The air cavity encapsulation structure for W-band according to claim 1, characterized in that: The top-level signal metal layer (211) comprises three functional parts connected in sequence: a stub (211-1) for bonding positioning, a connecting line (211-2), and a connecting part (211-3). These three parts together form an impedance matching network through their own shape and coupling relationship with the side ground metal layer.

5. A W-band air cavity encapsulation structure according to claim 1, characterized in that: The first set of vias (6) includes a via connecting the top signal metal layer (211) and the bottom signal metal layer (214), a via connecting the top signal metal layer (211) and the second bottom signal metal layer (213), and a via connecting the second bottom signal metal layer (213) and the bottom signal metal layer (214).

6. A W-band air cavity encapsulation structure according to claim 1, characterized in that: All metal layers in the packaging substrate (2) are made of pure copper.

7. A W-band air cavity encapsulation structure according to claim 1, characterized in that: The dielectric layer (23) of the encapsulation substrate (2) is made of PP material with low expansion rate and low shrinkage rate.

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