Packaged electronic device, multilevel lead frame coupler and method of fabricating packaged electronic device

Abstract

This invention discloses a packaged electronic device (100) comprising a multilayer lead frame (110) having first and second trace layers (111, 112), a first pass layer (114) between the first and second trace layers (111, 112), a conductive feed structure (140), and a conductive reflector wall (150). The first trace layer (111) includes a conductive coupler antenna (120) extending in a plane orthogonal to one of the first and second directions (X, Y), a conductive first ground structure (121), and a portion of the conductive coupler antenna (120) extending outward along a third direction (Z) orthogonal to one of the first and second directions (X, Y). The conductive reflector wall (150) has an opening (160) and extends around a portion of the conductive coupler antenna (120) along the third direction (Z) between the first and second trace layers (111, 112). The conductive feed structure (140) is coupled to the conductive coupler antenna (120) and extends along the first direction (X) through the opening (160) of the conductive reflector wall (150).

Description

[Previous Technology]

[0001] In the microwave to millimeter-wave (mm-wave) region, molecular spectroscopy is used to construct microwave or millimeter-wave atomic or molecular clocks and other systems requiring accurate timing signals with wavelengths λ in the mm range. The mm-wave spectrum lies between microwaves and infrared waves and has frequencies between approximately 30 GHz and approximately 300 GHz. A millimeter-wave atomic clock can be implemented using a dipole gas in a physical unit coupled to a transceiver (or a separate transmitter and receiver). The atomic clock uses mm-wave radiation induced by an RF transceiver to excite the gas within a physical or gaseous unit, and the system detects rotational quantum transitions of dipole molecules for a reference. Specific gas molecules (e.g., water or H2O) have defined quantum rotational transitions, and these molecules absorb energy at a very repeatable frequency when transitioning between rotational states. For example, water absorbs energy based on quantum rotational transitions at approximately 183 GHz, and other physical units (e.g., carbonyl sulfide or OCS) have peak absorption at approximately 121 GHz. An antenna can be used to couple a chip-scale gas cell to a transceiver circuitry system to, for example, transmit a 121 GHz signal from a mm-wave transceiver to the antenna and transmit the same signal from a substrate package to a silicon solid cell to implement an atomic clock based on cost-effective and high-efficiency transitions. The signal interrogates the gas in the solid cell to lock onto a quantum rotation molecular transition for atomic clock applications. High efficiency is achieved when the antenna structure provides a coupler-reflector at λ / 4, but this requires a thick antenna or coupler substrate. In some applications, package size constraints limit the overall size of the packaged antenna solution, and it is desirable to provide a mm-wave package in a very thin package substrate. [Summary of the Invention]

[0002] In one embodiment, a packaged electronic device includes a physical unit, a transceiver, and a multilayer lead frame. The multilayer lead frame has first and second trace levels, a pass level between the first and second trace levels, a conductive feed structure, and a conductive reflector wall. The first trace level has a conductive coupler antenna extending in a plane orthogonal to one of the first and second directions, and a conductive ground structure. A portion of the conductive coupler antenna opens into a conductive layer of the physical unit along a third direction orthogonal to one of the first and second directions. The conductive reflector wall has an opening and extends around a portion of the conductive coupler antenna along the third direction between the first and second trace levels. The conductive feed structure is coupled to the conductive coupler antenna and extends along the first direction through the opening in the conductive reflector wall.

[0003] In another embodiment, a multilayer leadframe includes first and second trace layers, a pathway layer between the first and second trace layers, a conductive feed structure, and a conductive reflector wall. The first trace layer has a first patterned conductive feature, and the second trace layer has a second patterned conductive feature. The pathway layer includes conductive pathways that interconnect the respective first and second patterned conductive features. The first trace layer includes a conductive coupler antenna extending along a first side in a plane orthogonal to one of the first and second directions, and a conductive ground structure. A portion of the conductive coupler antenna faces outward along a third direction orthogonal to one of the first and second directions. The conductive reflector wall has an opening and extends along the third direction between the first and second trace layers. The conductive reflector wall extends around a portion of the conductive coupler antenna. The conductive feed structure is coupled to the conductive coupler antenna and extends along the first direction through the opening in the conductive reflector wall.

[0004] In another embodiment, a method of manufacturing a packaged electronic device includes: forming a first trace layer of a multilayer lead frame; forming a pass layer on the first trace layer; and forming a second trace layer on the pass layer. The first trace layer has first patterned conductive features and an insulating portion between the first patterned conductive features. The first patterned conductive features include a conductive coupler antenna extending in a plane of a first direction and an orthogonal second direction, and a conductive ground structure. The conductive coupler antenna has a portion extending outward from a first side of the multilayer lead frame along a third direction. The pass layer has conductive passes and another insulating portion between the conductive passes. The second trace layer has second patterned conductive features and another insulating portion between the second patterned conductive features. The method includes forming a conductive feed structure coupled to the conductive coupler antenna and extending along the first direction. The method includes forming a conductive reflector wall having an opening. The conductive reflector wall extends along the third direction between the first trace level and the second trace level, the conductive reflector wall extends around a portion of the conductive coupler antenna, and the conductive feed structure extends along the first direction through the opening in the conductive reflector wall.

Implementation Method

[0017] In the drawings, the same element symbols refer to all identical elements, and various features are not necessarily drawn to scale. Furthermore, the term "coupling" includes indirect or direct electrical or mechanical connections or combinations thereof. For example, if a first device is coupled to or with a second device, the connection may be via a direct electrical connection or via an indirect electrical connection through one or more intervening devices and connections. The following describes one or more operating characteristics of various circuits, systems, and / or components in the context of functionality, where functionality arises in some cases from the configuration and / or interconnection of various structures when the circuit system is energized and operated.

[0018] Figures 1 and 1A to 1C illustrate a mm-wave clock packaged electronic device 100. Figure 1 is a perspective view of the packaged electronic device 100, Figure 1A shows a partial cross-sectional side view taken along line 1A-1A in Figure 1, Figure 1B shows another partial cross-sectional side view taken along line 1B-1B in Figure 1, and Figure 1C is a partial cross-sectional top view taken along line 1C-1C in Figures 1, 1A, and 1B. A portion of the packaged electronic device 100 is enclosed by a package structure 101, which may be a molded plastic material or a metal shield. The example packaged electronic device 100 has a generally rectangular shape. For ease of illustration and discussion, the example packaged electronic device 100 is shown in a three-dimensional space defined by mutually orthogonal directions or axes (including a first direction (labeled X), an orthogonal second direction (labeled Y), and a third direction orthogonal to one of the first and second directions (labeled Z)). In the illustrated location, the top of the packaged electronic device 100 is spaced apart from one of its bottom sides along a third direction. In this example, the packaged electronic device 100 has a rectangular outline, wherein the opposing lateral sides are spaced apart from each other along a first direction X and the front and rear sides are spaced apart from each other along a second direction Y. The positioning of the device in a three-dimensional coordinate system can be changed without affecting the structural relationships of the components and features.

[0019] The packaged electronic device 100 includes a physical unit 102 (e.g., FIG. 1A and FIG. 1B) having a cavity 103 and a conductive layer 104 along a bottom side 105 of the physical unit 102. The conductive layer 104 has an opening 106 (e.g., a window) along the bottom and a glass layer 107, as shown in FIG. 1A and FIG. 1B. In one example, the physical unit 102 includes a semiconductor material (which may be or include silicon) and a cavity 103 formed therein. The physical unit 102 includes one or more metallization layers or levels, which(e.g.) include the conductive layer 104 and its opening 106. The packaged electronic device 100 also includes a transceiver 108 having a bottom side 109.

[0020] The packaged electronic device 100 includes a multilayer leadframe 110, which may be a wireable leadframe. The multilayer leadframe 110 provides an integrated antenna that couples a signal from a transmitter output of transceiver 108 to a first port of physical cell 102 and couples a second port of physical cell 102 to the receiver circuitry of transceiver 108. The packaged electronic device 100 is configured to operate as a rotational transition-based atomic clock that utilizes the quantum-defined rotational dynamics of a dipole molecular vapor in cavity 103 of physical cell 102. The quantum rotational dynamics of the cavity gas occur at frequencies in the mm wavelength range (e.g., 10 GHz to 1000 GHz) without the need for optical components such as lasers, photodetectors, and lenses. In one example, transceiver 108 is a low-cost mm-wave CMOS transceiver configured to interrogate physical cell 102 over a bandwidth covering the corresponding quantum state transition. At the transition frequency, a detectable minimum absorption value is used to determine an absolute frequency reference.

[0021] In one example, the multilayer leadframe 110 is a five-level structure, comprising a first trace level 111 (e.g., a first metal layer M1), a second trace level 112 (e.g., a second metal layer M2), a third trace level 113 (e.g., a third metal layer M3), a first pass level 114 (e.g., V1), and a second pass level 115 (e.g., V2). Figure 10 below shows another example using a three-level leadframe structure. In one example, the patterned conductive features of the trace level and the conductive paths of the pass level may contain copper or other conductive metals. The multilayer leadframe 110 in Figures 1 to 1C has a first (e.g., top) side 116 and a pair of opposing second (e.g., bottom) sides 117. The respective bottom sides 105 and 109 of the physical unit 102 and the transceiver 108 are mounted to the first side 116 of the multilayer leadframe 110.

[0022] In one example, the packaged electronic device 100 includes conductive leads (not shown) exposed on the bottom and one or more lateral sides. In practice, the leads are soldered to corresponding conductive pads on a host PCB (not shown) to mechanically mount the packaged electronic device 100 and form an electrical connection between the circuitry of the PCB and one or more circuits or components of the packaged electronic device 100. In another embodiment, the packaged electronic device includes one or more conductive leads exposed in the interior of the bottom side, such as in a grid array type (e.g., LGA or BGA) package. The multilayer leadframe 110 further includes one or more layers of an insulator, such as multiple layers of ANZEN multilayer film (ABF), for example, a 2 μm to 5 μm silicon dioxide layer with epoxy resin.

[0023] The physical unit 102 and transceiver 108 are configured to operate according to a signal wavelength λ, which can be varied by a controller or processor (not shown) of the transceiver 108. The multilayer leadframe 110 has a leadframe thickness 118 along the third direction Z that is less than 4 times the signal wavelength λ. In one example, the leadframe thickness 118 along the third direction Z is less than 250 μm, such as about 170 μm to about 230 μm. As previously discussed, the efficient operation of the atomic clock is enhanced when the coupling structure ensures a coupled reflector of λ / 4. However, the package size requirement for mm wavelengths will necessitate the use of a high coupler structure with a top and bottom ground configuration. In this regard, the distance λ / 4 of an OCS physical unit gas will require a coupler thickness of more than 625 µm due to the non-zero thickness of the upper and lower conductor layers and will require a thickness of more than 408 µm for an H2O physical unit gas. Example 5 multilayer leadframe 110 includes a reflector wall structure to provide sufficient atomic clock operating efficiency, while achieving a significantly reduced coupler thickness 118 and allowing operation at mm-wave frequencies, such as 183 GHz or approximately 183 GHz for an H2O solid unit gas and 121 GHz for an OCS solid unit gas.

[0024] The multilayer lead frame 110 has conductive upper and lower ground planes spaced apart by a distance 119, the distance 119 corresponding to the thickness of a conductive reflector wall structure further described below. The first trace level 111 has a first patterned conductive feature comprising a conductive coupler antenna 120 (e.g., a patch antenna) and a conductive first ground structure 121. The conductive coupler antenna 120 and the conductive first ground structure 121 extend along a respective portion of a first side 116 in a plane (e.g., an XY plane) in a first and a second direction. The conductive coupler antenna 120 has a portion of an opening 106 in the conductive layer 104 facing the solid element 102 along a third direction Z. The second trace level 112 has a second patterned conductive feature 122.

[0025] The third trace layer 113 has a third patterned conductive feature 123, for example, providing a single conductive layer of a second ground plane. A first path layer 114 extends between the first trace layer 111 and the second trace layer 112. The first path layer 114 includes a conductive first path 124 interconnecting each of the first and second patterned conductive features 121 and 122. The second path layer 115 includes a second conductive path 125 and extends between the second trace layer 112 and the third trace layer 113. The third trace layer 113 includes a second conductive ground structure 123 extending in a second plane of a first direction X and a second direction Y. The second conductive ground structure 123 extends along a second side 117. The first conductive ground structure 121 and the second conductive ground structure 123 are parallel to each other. The second conductive path 125 interconnects each of the second and third patterned conductive features 122 and 123. In one embodiment, the first trace layer 111 includes one or more insulating (e.g., dielectric) portions 131, the second trace layer 112 includes one or more insulating portions 132, the first pass layer 114 includes one or more insulating portions 134, and the second first pass layer 115 includes one or more insulating portions 135.

[0026] Example: The second conductive feature in the second trace level 112 of the multilayer leadframe 110 includes a conductive feed structure 140 (e.g., a coupler antenna). In one example, the conductive feed structure 140 has a strip of feed conductor embedded in a dielectric, wherein a generally continuous ground plane lies above and below the conductive feed. In this example, the conductive feed structure 140 includes a passage 124 (e.g., Figures 1A and 1C) in the first passage level 114 contacting the conductive coupler antenna 120 of the first trace level 111, and a laterally extending conductive feature 122 extending laterally from the passage 124 and below the transceiver 108 along a first direction X (e.g., to the left in Figure 1B). The conductive feed structure 140 is configured to couple a signal at a port of the physical unit 102 from the conductive coupler antenna 120 to the transceiver 108. The conductive feed structure 140 is coupled to the conductive coupler antenna 120 of the first trace layer 111 via a path 124 in the first path layer 114. In one embodiment, the other end of the conductive feed structure 140 is coupled to a terminal of the transceiver 108. This coupling provides signal transmission from a first port of the physical unit 102 to the receiver circuitry (not shown) in the transceiver 108. The other port of the physical unit 102 is coupled to the transmitter circuitry (not shown) of the transceiver 108.

[0027] The multilayer lead frame 110 includes a conductive reflector wall 150 that facilitates use of a thin multilayer lead frame 110 in which a thickness 118 is less than λ / 4. In this example, the conductive reflector wall 150 is formed by conductive features of the pass layers 114 and 115 and the second trace layer 112. The conductive reflector wall 150 provides a conductive connection between the conductive first ground structure 121 in the first trace layer 111 and the second conductive ground structure 123 in the third trace layer 113. The conductive reflector wall 150 forms a wall defining an interior having a width 151 in the X direction. The conductive reflector wall 150 and the two respective sides of the conductive coupler antenna 120 are spaced apart by a gap distance 152 along the first direction X.

[0028] As previously described, the conductive reflector wall 150 extends between the upper and lower ground planes and has a reflector wall thickness 119 in a third direction Z. The sum of the gap distance 152 and the reflector wall thickness 119 is greater than the lead frame thickness 118. In one embodiment, the sum of the gap distance 152 and the reflector wall thickness 119 is equal to λ / 4 (e.g., within a manufacturing tolerance such as 5%). This example provides efficient operation for signal transmission via antenna coupling while allowing the total Z-direction thickness 118 to be less than λ / 4. The conductive reflector wall 150 has an opening 160 having a lateral (e.g., Y-direction) width 162, as shown in Figures 1 and 1C. The conductive reflector wall 150 extends in a third direction Z between the first trace level 111 and the second trace level 112, and the conductive reflector wall 150 extends around a portion of the conductive coupler antenna 120. The conductive feed structure 140 extends along a first direction X through an opening 160 in the conductive reflector wall 150, as shown in the perspective and top views of Figures 1 and 1C. In the illustrated example, the conductive reflector wall 150 extends along a third direction Z in the pathway layer 114, the second trace layer 112, and the second pathway layer 115, defining a continuous conductive (e.g., copper) structure within the first trace layer 111 and the third trace layer 113, wherein only a single gap is provided by the opening 160.

[0029] Since the reflector wall thickness 119 is less than the total coupler thickness 118, the Z-direction distance 119 is less than λ / 4 of an OCS or H2O solid unit gas. However, the conductive reflector wall structure provides lateral spacing by means of gap distances 119 and 152 to accommodate the reduced thicknesses 118 and 119, while still providing sufficient reflection distance within one of the reflector wall structures.

[0030] The antenna packaging solution provided by the multilayer leadframe 110 incorporates a lateral reflector and reduces the thickness of the packaged electronics 100, while also reducing electromagnetic (EM) leakage and crosstalk. In one embodiment, the conductive reflector wall 150 reduces the lateral propagation of EM signals through the package substrate and through the glass layer 107, a major source of leakage and crosstalk. Furthermore, the use of the conductive reflector wall 150 facilitates high-frequency antennas in very thin substrates in a simple and low-cost packaging solution using standard materials and providing one of the ultra-thin product profiles required in numerous system applications for various applications such as 5G, RADAR, IoT, and other high-frequency applications requiring antennas.

[0031] In one embodiment, the physical cell 102 is a 28x9 mm² wafer-level physical cell comprising a glass layer 107 and a silicon structure forming the top and sidewalls of the defining cavity 103. The cavity 103 uses an alloy of gold and indium (AuIn) for trapping low-pressure OCS gas. In this example, the multilayer lead frame 110 is a multilayer package substrate having a lateral reflector provided by reflector wall 150 to implement an integrated antenna coupling structure in a very thin substrate, wherein the thickness 118 is limited only by the design rules of the manufacturing technology and not by the operating signal wavelength λ. In this embodiment, the first trace layer 111 has a thickness of approximately 35 μm ± 10 μm along the third (Z) axis in a first trace layer with a maximum etchback of 5 μm; the second trace layer 112 has a third axis thickness of 35 μm ± 10 μm; the third trace layer 113 has a third axis thickness of 30 μm ± 10 μm; the first pass layer 114 has a third axis thickness of 35 μm; and the second pass layer 115 has a third axis thickness of 30 µm and a nominal etchback of 5 µm ± 5 µm. In one example, the bottom side 117 of the multilayer leadframe 110 includes a surface mount technology (SMT) short axis thickness of 30 μm ± 15 μm along the third axis. In this embodiment, the thickness 118 of the multilayer leadframe 110 prior to the packaging molding process is approximately 200 μm ± 30 μm. The dimensions of these examples may vary depending on a specific process tolerance limit (e.g., + / - 1%). As shown in Figures 1A and 1C, a conductive (e.g., copper) reflector wall 150 extends between the top and bottom ground planes and provides a lateral reflector for signals from the conductive coupler antenna 120.

[0032] Other designs implement an antenna in the top layer and a reflector at a distance of λ / 4 from the ground of the bottom layer, but require a total thickness greater than λ / 4, for example, greater than 400 μm to 500 μm, depending on the dielectric constant of the dielectric and the operating frequency. As discussed above, certain application design specifications do not allow for such a large coupler substrate thickness; for example, the maximum permissible thickness is 200 μm. A conductive reflector wall 150 with appropriate spacing distances 119 and 152 surrounding the conductive coupler antenna 120 operates as an effective lateral reflector and thus promotes signal coupling efficiency much smaller than λ / 4 of the package thickness 118.

[0033] Referring now to Figures 2 through 9, Figure 2 illustrates a method 200 for manufacturing a packaged electronic device, and Figures 3 through 9 illustrate partial cross-sectional side views of a packaged electronic device 100 manufactured according to method 200. Method 200 includes manufacturing a multilayer leadframe 110 at 202. In one embodiment, the leadframe 110 is manufactured one layer at a time, starting with the manufacture of an initial core layer, followed by the manufacture of additional layers, such as one or more quinoa multilayer film (ABF) layers, using copper or other conductive metals and insulating materials. Leadframe manufacturing 202 is described below as starting at 203 from a first trace layer 111 and continuing to sequentially form a first pass layer 114, a second trace layer 112, a second pass layer 115, and then a third trace layer 113. In other embodiments, a different sequence may be used, for example, starting from an inner layer and manufacturing additional layers on both sides of an initial (e.g., core) layer. In a particular implementation, a particular trace level includes patterned conductive features and steps with different thicknesses (e.g., stepped copper features or traces of the first trace level 111), which can be formed by a mask-back etch process.

[0034] At 203, a patterned first trace layer and an insulating portion (e.g., also labeled M1 in FIG. 4) of the first trace layer 111 are formed. FIG. 3 illustrates an example of the first trace layer 111 undergoing a single-level process 300. Process 300 forms a first patterned conductive feature of a conductive coupler antenna 120 and a conductive first ground structure 121 extending along a respective portion of a first side 116 in a plane (e.g., an XY plane) in one of the first and second directions, and an associated insulating portion 131 between the first patterned conductive features. As discussed above, the patterning of the first conductive feature provides an X-direction width 151 and a gap distance 152 along the first direction X between the lateral side of the conductive coupler antenna 120 and the lateral inner edge of the conductive first ground structure 121. The conductive coupler antenna 120 formed at 202 has a portion facing outward from the first side 116 (e.g., downward in FIG. 3).

[0035] In one embodiment, the single-layer process 300 uses a quinone multilayer insulating layer bonded to an insulating structure 131 with patterned conductive features via vacuum lamination, followed by thermal pre-curing and the formation of the desired laser path and smearing removal in the ABF laminate. After depositing a copper seed layer as needed, a thin copper layer is plated on the ABF layer, and a photoresist layer is formed and patterned on the deposited copper to facilitate the formation of a stepped or flat copper structure in the fabricated first trace layer 111. Subsequently, further copper deposition is performed, for example, using copper electroplating, and then the patterned photoresist layer is removed. The thin copper is then etched as needed, followed by, for example, full curing at 180°C to 200°C.

[0036] In one example, a similar process is used to subsequently manufacture the remaining layers 112 to 115 of the multilayer leadframe 110 in leadframe fabrication 202. Similar processing steps can be used to form other multilayer leadframes, such as the three-layer example in Figure 10 below.

[0037] Method 200 continues at 204, wherein a patterned first path layer and an insulating portion of one of the first path layers 114 are formed on the completion side of the first trace layer 111. Figure 4 shows an example of the first path layer 114 (e.g., also labeled V1 in Figure 4) undergoing a single-level process 400, which forms a first conductive path 124 of the conductive reflector wall 150 and a conductive path 124 of the conductive feed structure 140, as well as another insulating portion 134 between the first patterned conductive paths 124.

[0038] A patterned second trace layer and an insulating portion are formed in the second trace layer 112 at 205. Figure 5 shows an example of the second trace layer 112 undergoing a single-level process 500, which forms a second patterned conductive feature 122 of the conductive reflector wall 150, a lateral extension of the conductive feed structure 140, and an associated insulating portion 132 between the second patterned conductive features.

[0039] At 206, a patterned second path layer and an insulating portion of the second path layer 115 are formed on the completed side of the second trace layer 112. Figure 6 shows an example where the second path layer 115 undergoes another single-level process 600, which forms one or more second conductive paths 125 and associated insulating portions 135 of the conductive reflector wall 150.

[0040] At 208, a patterned third trace layer and an insulating portion of the third trace layer 113 are formed. Figure 7 shows an example where the third trace layer 113 undergoes a single-level process 700, which forms the third patterned conductive feature of the second conductive grounding structure 123 as, for example, a single flat copper layer.

[0041] Process 202 provides forming a portion of a conductive feed structure 140 in one of a first trace layer 111 and a first pass layer 114, wherein the conductive feed structure 140 is coupled to a conductive coupler antenna 120 and extends along a first direction X. In a five-layer example, process 202 includes forming another portion of the conductive feed structure 140 in a second trace layer 112 of a multilayer lead frame 110. Process 202 also provides forming a conductive reflector wall 150 having an opening 160, wherein in the illustrated example, the conductive reflector wall 150 includes a stack of one of several conductive first passes 124, several conductive structures 122, and several conductive second passes 125 extending along a third direction Z between the first trace layer 111 and the third trace layer 113. Furthermore, the conductive reflector wall 150 extends around a portion of the conductive coupler antenna 120 (e.g., as shown in Figures 1 and 1C above), and the conductive feed structure 140 extends along a first direction X through an opening 160 in the conductive reflector wall 150.

[0042] In another embodiment, the conductive feed structure 140 is configured as part of the first trace level 111 in 203 of FIG2, and processes 206 and 208 may be omitted, for example, to manufacture the three-level leadframe structure discussed below in conjunction with FIG10. In another embodiment, further processing is included to form further trace and / or pathway levels after 208 in method 200.

[0043] After fabricating the multilayer leadframe 110 at 202, method 200 then mounts (e.g., solders) one or more electronic components or subassemblies to an associated first conductive feature of the first trace level 111 at 210 in FIG. 1. In one example, this includes mounting physical unit 102 and transceiver 108 to a first side 116 of the multilayer leadframe 110. FIG. 8 shows the electronic device 100 undergoing a component attachment procedure 800, which provides solder paste to a selected area (e.g., a conductive landing pad, not shown) on or along the top side 116 of the multilayer leadframe 110, followed by an automated pick-and-place operation to place physical unit 102 and transceiver 108 onto the associated conductive landing pad. The solder paste is then thermally reflowed at 210 to form a solder connection between the component terminals and the top side of the conductive landing pad.

[0044] At 212 (e.g.) via a molding process 900 shown in FIG9, a package structure 101 is formed to surround the physical unit 102 and the transceiver 108. In one embodiment, at 212, a molding compound is used to mold the upper portion of the electronic device 100 to form the package structure 101. The illustrated method 200 also includes performing selective package separation (e.g., orthogonal package sawing operation) at 214 to separate the individual finished electronic devices from a starting panel lead frame structure, and method 200 ends at 216 with final device testing.

[0045] Figures 10 and 10A through 10C illustrate another mm-wave clock packaged electronic device 1000 with a multi-layer leadframe coupler. This example uses a three-layer leadframe, which facilitates further size reduction by incorporating a conductive reflector wall. Figure 10 shows a perspective view of the packaged electronic device 1000, Figure 10A is a partial cross-sectional side view taken along lines 10A-20A in Figure 10, Figure 10B is a partial cross-sectional side view taken along lines 10B-10B in Figure 10, and Figure 10C is a perspective view of a portion of the packaged electronic device in Figures 10, 10A, and 10B.

[0046] A portion of the packaged electronic device 1000 is enclosed by a package structure 1001, which may be a molded plastic material. The packaged electronic device 1000 has a generally rectangular shape and is shown in three-dimensional X, Y, Z space. The packaged electronic device 1000 includes a physical unit 1002 (e.g., Figures 10A and 10B) having a cavity 1003 and a conductive layer 1004 along a bottom side 1005 of the physical unit 1002. The conductive layer 1004 has an opening 1006 (e.g., a window) along the bottom and a glass layer 1007, as shown in Figures 10A and 10B. In one example, the physical unit 1002 includes a semiconductor material (which may be or include silicon) and a cavity 1003 formed therein. The physical unit 1002 includes one or more metallization layers or levels, which(e.g.) include the conductive layer 1004 and its opening 1006. The packaged electronic device 1000 has a transceiver 1008 including a bottom side 1009.

[0047] The packaged electronic device 1000 includes a three-level multilayer leadframe 1010, which may be a wireable leadframe. The multilayer leadframe 1010 provides an integrated antenna that couples a signal from the transmitter output of transceiver 1008 to a first port of physical cell 1002 and couples a second port of physical cell 1002 to the receiver circuitry of transceiver 1008. The packaged electronic device 1000 is configured to operate as a rotational transition-based atomic clock that utilizes the quantum-defined rotational dynamics of a dipole molecular vapor in cavity 1003 of physical cell 1002. The rotational dynamics of the cavity gas occur at frequencies within the mm wavelength range (e.g., 10 GHz to 1000 GHz) without the need for optical components such as lasers, photodetectors, and lenses. In one example, transceiver 1008 is a low-cost mm-wave CMOS transceiver configured to interrogate physical cell 1002 over a bandwidth covering the corresponding quantum state transition. At the transition frequency, a detectable minimum absorption value is used to determine an absolute frequency reference.

[0048] The multilayer leadframe 1010 in Figures 10 to 10C comprises a three-level structure including a first trace level 1011 (e.g., a first metal layer M1), a second trace level 1012 (e.g., a second metal layer M2), and a first path level 1014 (e.g., V1). In one embodiment, the patterned conductive features of the trace level and the conductive paths of the path level may include copper or other conductive metals. The multilayer leadframe 1010 in Figures 10 to 10C has a first (e.g., top) side 1016 and a pair of opposing second (e.g., bottom) sides 1017. The respective bottom sides 1005 and 1009 of the physical unit 1002 and the transceiver 1008 are mounted to the first side 1016 of the multilayer leadframe 1010.

[0049] The packaged electronic device 1000 includes conductive leads (not shown) that can be soldered to corresponding conductive pads on a host PCB (not shown) for mechanical mounting of the packaged electronic device 1000 and to form an electrical connection between the circuitry of the PCB and one or more circuits or components of the packaged electronic device 1000. In another embodiment, the packaged electronic device includes one or more conductive leads exposed in the bottom-side interior, such as in a grid array type (e.g., LGA or BGA) package. The multilayer leadframe 1010 further includes an insulator in one or more of its layers, such as multiple layers of ANZEN multilayer film (ABF), for example, a 2 μm to 5 μm silicon dioxide layer with epoxy resin.

[0050] The physical unit 1002 and transceiver 1008 are configured to operate at a signal wavelength λ, which can be varied by a controller or processor (not shown) of the transceiver 1008. The multilayer leadframe 1010 has a leadframe thickness 1018 along the third direction Z that is less than 4 / 4 of the signal wavelength λ. In one example, the leadframe thickness 1018 along the third direction Z is less than 250 μm, such as about 170 μm to about 230 μm. The example three-level multilayer leadframe 1010 includes a conductive reflector wall structure to provide sufficient atomic clock operating efficiency while achieving a significant reduction in coupler thickness 1018 and allowing operation at mm-wave frequencies, such as approximately 183 GHz for an H2O physical unit gas and 121 GHz for an OCS physical unit gas.

[0051] The multilayer leadframe 1010 has conductive upper and lower ground planes spaced apart by a distance 1019. A first trace level 1011 has a first patterned conductive feature, comprising a conductive coupler antenna 1020 (e.g., a patch antenna), a conductive first ground structure 1021, and a conductive feed structure 1040. In one example, the conductive feed structure 1040 is a coplanar waveguide (CPW) configuration. The conductive coupler antenna 1020, the conductive first ground structure 1021, and the conductive feed structure 1040 extend in an XY plane along a respective portion of a first side 1016. The conductive coupler antenna 1020 has a portion of an opening 1006 in the conductive layer 1004 of the solid element 1002 along a third third direction Z-axis. A second trace level 1012 has a second patterned conductive feature 1022, which forms a conductive second ground structure 1022 providing a second ground plane extending along a second side 1017. A first path layer 1014 extends between a first trace layer 1011 and a second trace layer 1012. The first path layer 1014 includes a conductive first path 1024 that interconnects the respective first and second patterned conductive features to form a conductive reflector wall 1050. A second conductive ground structure 1022 extends along a second side 1017 of the multilayer lead frame 1010. The first conductive ground structure 1021 and the second conductive ground structure 1022 are parallel to each other. In one embodiment, the first trace layer 1011 includes one or more insulating (e.g., dielectric) portions 1031, and the first path layer 1014 includes one or more insulating portions 1034.

[0052] The conductive feed structure 1040 is spaced apart from the conductive ground structure 1021 in the first trace layer 1011. The conductive feed structure 1040 is configured to couple a signal at one port of the physical unit 1002 from the conductive coupler antenna 1020 to the transceiver 1008. This coupling provides signal transmission from a first port of the physical unit 1002 to the receiver circuitry (not shown) in the transceiver 1008. The other port of the physical unit 1002 is coupled to the transmitter circuitry (not shown) of the transceiver 1008.

[0053] In this example, the conductive reflector wall 1050 is formed by one or more conductive paths 124 of vial layers 114 and facilitates the use of a thin multilayer lead frame 1010 in which the thickness 1018 is less than λ / 4. The conductive reflector wall 1050 provides a conductive connection between the conductive first ground structure 1021 in the first trace layer 1011 and the second conductive ground structure 1022 in the second trace layer 1012. The conductive reflector wall 1050 forms a wall defining an interior having an X-direction width 1051 (e.g., FIG. 10 and FIG. 10C), and the conductive reflector wall 1050 is spaced apart from the two respective sides of the conductive coupler antenna 1020 along the first direction X by a gap distance 1052. The sum of the gap distance 1052 and the reflector wall thickness 1019 is greater than the lead frame thickness 1018. In one embodiment, the sum of the gap distance 1052 and the reflector wall thickness 1019 is equal to λ / 4 (e.g., within a manufacturing tolerance such as 5%). This coupler design facilitates efficient signal transmission through antenna coupling while allowing the total Z-direction thickness 1018 to be less than λ / 4.

[0054] The conductive reflector wall 1050 has an opening 1060 with a lateral (e.g., Y-direction) width 1062, as shown in Figures 10 and 10C. The conductive reflector wall 1050 extends in a third direction Z in the first trace layer 1011 and the pass layer 1014. The conductive reflector wall 1050 extends in a third direction Z between the first trace layer 1011 and the second trace layer 1012 and extends laterally around a portion of the conductive coupler antenna 1020. The conductive feed structure 1040 extends in a first direction X through the opening 1060 of the conductive reflector wall 1050, as shown in the perspective and top views of Figures 10 and 10C. In the illustrated example, the conductive reflector wall 1050 extends in a third direction Z in the pass layer 1014 between the first trace layer 1011 and the second trace layer 1012 to define an interior continuous conductive (e.g., copper) structure, wherein a gap is provided by the opening 1060. In this example, the Z-direction distance 1019 is less than λ / 4 of an OCS or H2O solid unit gas, and the conductive reflector wall 1050 provides lateral spacing through gaps 1019 and 1052 to accommodate the reduced thickness 1018, while still providing sufficient reflection distance within the conductive reflector wall 150. Furthermore, the three-tiered design of the example in Figure 10 provides the aforementioned advantages associated with the device 100 of Figure 1, while allowing for a further reduction in lead frame thickness 118 and providing additional cost benefits.

[0055] In one embodiment, the physical cell 1002 is a 28x9 mm² wafer-level physical cell comprising a glass layer 1007 and a silicon structure forming the top and sidewalls of a defining cavity 1003. The cavity 1003 uses an alloy of gold and indium (AuIn) for trapping low-pressure OCS gas. In this example, the multilayer leadframe 1010 is a multilayer package substrate having a lateral reflector provided by reflector wall 1050 to implement an integrated antenna coupling structure in a very thin substrate, wherein the thickness 1018 is limited only by the design rules of the manufacturing technology and not by the operating signal wavelength λ. In one embodiment, the distance between the upper and lower ground planes (e.g., the thickness of the via layer 114 along the third direction Z) can be substantially less than λ / 4, especially when the sum of distances 1019 and 1052 is approximately equal to λ / 4 (e.g., within manufacturing tolerances (e.g., 1%)). In one example, the operating frequency is approximately 121.6 GHz, the dielectric constant of insulator materials 1031 and 1034 is 3.1, λ is 1.43 mm, λ / 4 = 358 μm, the vertical distance 1019 is 135 μm, and the gap distance 1052 is 230 µm and 365 µm. In one example, the first trace layer 1011 has a thickness of approximately 40 µm ± 10 µm along the third (Z) axis in a first trace layer with a maximum etch of 5 µm, and the second trace layer 1012 has a thickness of 40 µm ± 10 µm along the third axis.

[0056] In another example, the leadframe has two trace levels interleaved with two path levels, wherein the patch antenna is in the first trace level, the conductive feed structure is in the first path level, and the ground plane is in the second path level. The first path level has a third-axis thickness of 40 µm ± 10 µm and a nominal etchback of 5 µm ± 5 µm, and also has a third-axis thickness of 65 µm. The second trace level has a third-axis thickness of 40 µm ± 10 µm, a third-axis thickness of 65 µm, and a nominal etchback of 5 µm ± 5 µm. In one example, the leadframe includes a short-axis level with a SMT short-axis third-axis thickness of 30 µm ± 15 µm. In this embodiment, the thickness of the multilayer leadframe prior to the packaging molding process is approximately 200 µm ± 25 µm. The dimensions of these instances may vary depending on a specific process tolerance limit (e.g., + / -1%).

[0057] Figure 11 shows one of the analog S-parameter signals in the packaged electronic device 100 of Figures 1 to 1C, a signal diagram 1100, which includes an S11 curve 1111, an S12 curve 1112, and an S22 curve 1122 of the HFSS analog signal of the first and second ports of the physical unit 102. The -2.2 dB signal 1112 (S12) shows good insertion loss at a frequency of interest (e.g., about 121.6 GHz), and curve 1111 (S11) shows good return loss in the desired frequency band around 121 GHz.

[0058] Figure 12 shows one of the analog S-parameter signals in the packaged electronic device 1000 of Figures 10 to 10C, a signal diagram 1200, which includes an S11 curve 1211 and an S12 curve 1212 that have similar good performance results at the frequency of interest (e.g., about 121.6 GHz).

[0059] The described example provides an improved package configuration for an atomic clock device, wherein the physical units 102, 1002 are interrogated by a mm-wave patch antenna implemented in a low-cost multilayer leadframe 110, 1010, the low-cost multilayer leadframe 110, 1010 containing a package substrate with a thickness of less than λ / 4. The described solution can be implemented in various packaged antenna packaging solutions including 5G, RADAR, automotive, IoT and more applications. A shallow mm-wave reflector with optimal antenna performance is produced by using vertical package plating (a wall between the top and bottom grounds) at an appropriate distance from the patch antenna. The same vertical package plating with conductive reflector walls 150, 1050 provides a lateral reflector (e.g., a lateral wall) to reduce mm-wave signal leakage propagation in the glass layers 107, 1007 of the physical unit 102 and the package itself to mitigate or avoid crosstalk problems.

[0060] Within the scope of the patent application, the described example may be modified and other implementation schemes may be feasible. [Simplified Explanation of the Diagram]

[0005] Figure 1 is a perspective view of a mm-wave clock packaged electronic device having a multilayer lead frame coupler.

[0006] Figure 1A is a partial cross-sectional side view taken along line 1A-1A in Figure 1.

[0007] Figure 1B is a partial cross-sectional side view taken along line 1B-1B in Figure 1.

[0008] Figure 1C is a top view of a section taken along line 1C-1C in Figures 1, 1A and 1B.

[0009] Figure 2 is a flowchart of one method for manufacturing a packaged electronic device.

[0010] Figures 3 to 9 are partial cross-sectional side views of the packaged electronic devices of Figures 1 to 1C manufactured according to the method of Figure 2.

[0011] Figure 10 is a perspective view of another mm-wave clock packaged electronic device having a multilayer lead frame coupler.

[0012] Figure 10A is a partial cross-sectional side view taken along line 10A-10A in Figure 10.

[0013] Figure 10B is a partial cross-sectional side view taken along line 10B-10B in Figure 10.

[0014] Figure 10C is a perspective view of a portion of the packaged electronic device shown in Figures 10, 10A and 10B.

[0015] Figure 11 is a signal diagram of one of the analog S-parameter signals in the packaged electronic device of Figures 1 to 1C.

[0016] Figure 12 is a signal diagram of one of the analog S-parameter signals in the packaged electronic devices shown in Figures 10 to 10C.

Claims

1. A packaged electronic device comprising: A physical unit having a cavity and a conductive layer along one side of the physical unit, the conductive layer having an opening; a transceiver having one side; and a multilayer lead frame having a first side, an opposite second side, a first trace level, a second trace level, a pass level, a conductive feed structure, and a conductive reflector wall; the first trace level includes a conductive coupler antenna extending along the first side in a plane of a first direction and a second direction, the first direction being orthogonal to the second direction, the conductive coupler antenna having a portion facing the opening of the conductive layer of the physical unit along a third direction, the third direction being orthogonal to the first direction and the second direction; The conductive reflector wall has an opening and extends along the third direction between the first trace level and the second trace level. The conductive reflector wall extends around a portion of the conductive coupler antenna. The conductive feed structure is coupled to the conductive coupler antenna and the transceiver and extends along the first direction through the opening of the conductive reflector wall.

2. The packaged electronic device of claim 1, wherein the conductive feed structure extends along the first direction through the opening in the second trace layer of the conductive reflector wall.

3. The packaged electronic device as described in claim 2, wherein: The pathway layer extends between the first trace layer and the second trace layer; the multilayer lead frame further includes a third trace layer and a second pathway layer, the second pathway layer extending between the second trace layer and the third trace layer; and the conductive reflector wall extends along the third direction between the first trace layer and the third trace layer in the pathway layer, the second trace layer and the second pathway layer.

4. The packaged electronic device as described in claim 3, wherein: The third trace level includes a second conductive grounding structure extending in a second plane of either the first direction or the second direction; and the conductive grounding structure and the second conductive grounding structure are parallel to each other.

5. The packaged electronic device as claimed in claim 4, wherein the second conductive grounding structure extends along the second side.

6. The packaged electronic device as claimed in claim 1, wherein: The conductive feed structure extends along the first direction through the opening in the first trace layer of the conductive reflector wall; and the conductive reflector wall extends along the third direction in the first trace layer and the passage layer.

7. The packaged electronic device as claimed in claim 6, wherein the conductive feed structure is spaced apart from the conductive ground structure in the first trace level.

8. The packaged electronic device of claim 7, further comprising a second conductive grounding structure extending along the second side in the second trace level.

9. The packaged electronic device as claimed in claim 1, wherein: The physical unit and the transceiver are configured to operate according to a signal wavelength; and the multilayer lead frame has a lead frame thickness along the third direction that is less than the signal wavelength divided by 4.

10. The packaged electronic device as claimed in claim 9, wherein: The conductive reflector wall is spaced apart from the conductive coupler antenna by a gap distance along the first direction; the conductive reflector wall has a reflector wall thickness along the third direction; and the sum of the gap distance and the reflector wall thickness is greater than the lead frame thickness.

11. The packaged electronic device as claimed in claim 10, wherein the sum of the gap distance and the reflector wall thickness is equal to the signal wavelength divided by 4.

12. The packaged electronic device as claimed in claim 1, wherein: The physical unit and the transceiver are configured to operate according to a signal wavelength; the conductive reflector wall is spaced apart from the conductive coupler antenna by a gap distance along the first direction; the conductive reflector wall has a reflector wall thickness along the third direction; and the sum of the gap distance and the reflector wall thickness is equal to the signal wavelength divided by 4.

13. A multilayer lead frame, comprising: The first and second sides are opposite each other; A first trace level, which has a first patterned conductive feature; A second trace level, which has a second patterned conductive feature; A pathway layer between the first trace layer and the second trace layer, the pathway layer including conductive pathways interconnecting the respective first and second patterned conductive features; a conductive feed structure; and a conductive reflector wall; the first trace layer includes a conductive coupler antenna extending along a first side in a plane of a first direction and a second direction, the first direction being orthogonal to the second direction, the conductive coupler antenna having a portion extending outward from the first side along a third direction, the third direction being orthogonal to the first direction and the second direction; the conductive reflector wall having an opening, the conductive reflector wall extending along the third direction between the first trace layer and the second trace layer, the conductive reflector wall extending around a portion of the conductive coupler antenna; and the conductive feed structure coupled to the conductive coupler antenna, the conductive feed structure extending along the first direction through the opening of the conductive reflector wall.

14. The multilayer lead frame of claim 13, wherein the conductive feed structure extends along the first direction through the opening in the second trace layer of the conductive reflector wall.

15. As in request item 13, a multi-layered leadframe, wherein: The conductive feed structure extends along the first direction through the opening in the first trace layer of the conductive reflector wall; and the conductive reflector wall extends along the third direction in the first trace layer and the passage layer.

16. The multilayer leadframe of claim 13, wherein the multilayer leadframe has a leadframe thickness of less than 250 μm along the third direction.

17. As in request item 13, a multi-layered leadframe, wherein: The conductive reflector wall is spaced apart from the conductive coupler antenna by a gap distance along the first direction; the conductive reflector wall has a reflector wall thickness along the third direction; and the sum of the gap distance and the reflector wall thickness is greater than the thickness of one of the multilayer lead frames.

18. A method for manufacturing a packaged electronic device, the method comprising: A first trace layer of a multilayer lead frame is formed, the first trace layer having first patterned conductive features and an insulating portion between the first patterned conductive features, the first patterned conductive features including a conductive coupler antenna and a conductive ground structure extending in a plane of a first direction and a second direction, the first direction being orthogonal to the second direction, the conductive coupler antenna having a portion extending outward from a first side of the multilayer lead frame along a third direction, the third direction being orthogonal to the first direction and the second direction; a pass layer of the multilayer lead frame is formed on the first trace layer, the pass layer having conductive passes and another insulating portion between the conductive passes; a second trace layer of the multilayer lead frame is formed on the pass layer, the second trace layer having second patterned conductive features and another insulating portion between the second patterned conductive features; A conductive feed structure is formed in one of the first trace layer and the pass layer of the multilayer lead frame. The conductive feed structure is coupled to the conductive coupler antenna and extends along the first direction. A conductive reflector wall with an opening is formed. The conductive reflector wall extends along the third direction between the first trace layer and the second trace layer. The conductive reflector wall extends around a portion of the conductive coupler antenna, and the conductive feed structure extends along the first direction through the opening of the conductive reflector wall.

19. The method of claim 18, further comprising: A physical unit and a transceiver are mounted to the first side of the multilayer lead frame; And to form an encapsulation structure that encloses the physical unit and the transceiver.

20. The method of claim 18, comprising forming the conductive feed structure in the pass layer of the multilayer lead frame.

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