Multilayer flexible array interconnect structure for ultrasonic transducers and method for fabricating same

Abstract

Systems and methods for multilayer flex array interconnect structures for ultrasound transducers, as well as methods for their fabrication, are disclosed. The systems and methods described herein provide consistent and controllable alignment between odd and even flex layers. Furthermore, ground layers are added between signal layers to simplify the configuration while improving crosstalk performance. In some implementations, vias are introduced at the interfaces of electromechanical array elements (e.g., lead zirconate titanate (PZT) elements) to increase the surface area of ​​conductive material, thereby improving the quality of electrical and physical contact. Furthermore, unused and discarded board area is strategically utilized to provide machining alignment and verification aids, allowing for (i) confirmation of alignment between the flex circuit and processing equipment, and (ii) adjustment of the flex circuit position relative to the processing equipment to prevent the flex circuit from being processed to an unusable state.

Description

[Technical Field]

[0001] Ultrasound scanners (e.g., probes) are extremely sensitive devices. Fabrication of ultrasound transducer arrays is crucial to the scanner's performance and is challenging due to a variety of factors, including very small element dimensions, tight tolerance limits, a large number of connections, environmental durability requirements, and high performance expectations. Physical limitations of the manufacturing process limit the desired design parameters. [Background technology]

[0002] One partial solution to transducer construction, described in U.S. Patent No. 6,043,590 (1997) entitled "Composite Transducer with Connective," shows a method for embedding a flex circuit into a backing block, forming a durable interconnect structure for lead zirconate titanate (PZT) crystals. Another approach, described in U.S. Patent No. 7,804,970 (2005) entitled "Array Interconnect for Improving Directivity," further enhanced array performance by using two flex circuits, split into odd and even elements. This odd / even approach reduces crosstalk between adjacent elements, thereby widening the acceptance angle of the element pattern and improving beamforming quality. Summary of the Invention [Problem to be solved by the invention]

[0003] One challenge with this odd / even array configuration is ensuring a good connection between the flex circuit trace terminations (contact surface area defined by the width and thickness of the copper traces) and the plated PZT crystals. As new transducer performance advances, element pitches and geometries become smaller, making manufacturing much more difficult. As a result, transducer yields decrease due to circuit breaks and shorts associated with the embedded flex array configuration.

[0004] In addition to the small contact surface area of ​​copper trace terminations, the physical alignment between odd and even flex circuits also challenges the limits of trace width and spacing as odd and even flex circuits approach the pitch of the array. [Means for solving the problem]

[0005] Systems and methods for multilayer flex array interconnect structures for ultrasound transducers, as well as methods for their manufacture, are disclosed. The systems and methods described herein provide more consistent and controllable alignment of the array interconnect structure between odd and even flex layers. Furthermore, ground layers are added between signal layers, simplifying array configuration while improving crosstalk performance. In some implementations, vias are introduced at the interfaces of electromechanical array elements (e.g., PZT elements) to increase the surface area of ​​conductive material, thereby improving the quality of electrical and physical contact. Additionally, unused and discarded board area is strategically utilized to provide machining alignment and verification aids, allowing for (i) confirmation of alignment between the flex circuit and processing equipment, and (ii) adjustment of the flex circuit position relative to processing equipment to prevent unusable processing of the flex circuit (e.g., over-cutting).

[0006] In several aspects, a flex array interconnect structure for an ultrasonic circuit is disclosed. The flex array interconnect structure includes a first signal layer, a second signal layer, and one or more ground layers. The first signal layer includes a first plurality of conductive traces configured to be electrically and physically connected to interfaces of electromechanical array elements of an ultrasonic transducer. The second signal layer includes a second plurality of conductive traces configured to be electrically and physically connected to interfaces of the electromechanical array elements of the ultrasonic transducer. One or more ground layers are disposed between the first and second signal layers to reduce crosstalk between the first and second signal layers.

[0007] In some embodiments, the flex array interconnect structure further includes at least two external ground layers, with the first and second signal layers positioned between the at least two external ground layers. In some implementations, each of the first and second signal layers is between one or more internal ground layers and one of the at least two external ground layers. In some embodiments, the flex array interconnect structure further includes a plurality of vias filled and plated with a conductive material, where a first via of the plurality of vias connects a first conductive trace of the plurality of first conductive traces of the first signal layer to a third layer of the flex array interconnect structure, the first via providing the first conductive trace with an enlarged surface area relative to a cross-section of the first conductive trace at a machined interface of the ultrasonic circuit for connection to an interface of an electromechanical array element of an ultrasonic transducer. In some implementations, the third layer corresponds to one of the internal ground layers, and the first via is not grounded. In another implementation, the third layer corresponds to an external ground layer, the first via is ungrounded, and the first signal layer is disposed between the external ground layer and one or more internal ground layers. In some embodiments, a second via of the plurality of vias connects a second conductive trace of the second plurality of conductive traces of the second signal layer to a fourth layer of the flex array interconnect structure, and the second via provides the second conductive trace with an enlarged surface area relative to its cross-section at the machined interface of the ultrasonic circuit for connection to an interface of the electromechanical array element of the ultrasonic transducer. In some implementations, the one or more internal ground layers include first and second internal ground layers, the third layer corresponds to the first internal ground layer and the first via is ungrounded, and the fourth layer corresponds to the second internal ground layer and the second via is ungrounded. In some embodiments, the third layer corresponds to the first external ground layer, and the first via is ungrounded, and the first signal layer is disposed between the first external ground layer and one or more internal ground layers; the fourth layer corresponds to the second external ground layer, and the second via is ungrounded, and the second signal layer is disposed between the second external ground layer and one or more internal ground layers.

[0008] In some embodiments, another flex array interconnect structure for an ultrasonic circuit is disclosed. The flex array interconnect structure includes multiple layers and multiple vias. The multiple layers include at least a first layer and a second layer, where the first layer has a first plurality of conductive traces and the second layer has a second plurality of conductive traces. The multiple vias are filled and plated with a conductive material. One of the multiple vias connects a trace of the first plurality of traces on the first layer to a third layer of the multiple layers. The via provides an enlarged surface area for the trace in the flex array interconnect structure relative to the cross-section of the trace for connection to an electromechanical array element of an ultrasonic transducer. In some embodiments, a second via of the multiple vias connects a second trace of the second layer's plurality of traces to a fourth layer of the multiple layers, and the second via provides an enlarged surface area for the second trace at a processing interface of the ultrasonic circuit relative to the cross-section of the second trace for connection to an interface of the electromechanical array element of the ultrasonic transducer. In some implementations, the second layer is disposed between the first layer and the third layer, such that a first via extends through the second layer from the first layer to the third layer, and the third layer is disposed between the second layer and the fourth layer, such that a second via extends through the first layer from the second layer to the fourth layer. In some embodiments, the ultrasonic circuit includes first and second external ground layers disposed on opposite sides of the ultrasonic circuit, such that the first and second layers are both between the first and second external ground layers. In some implementations, the first and second vias extend from the first external ground layer to the second external ground layer through the first and second layers, respectively, where the first and second vias are not grounded.

[0009] In some embodiments, another flex array interconnect structure for ultrasonic circuits is disclosed. The flex array interconnect structure includes a first layer and a second layer. The first layer includes a first plurality of conductive traces with a first set of machining alignment aids. The second layer is stacked on the first layer and includes a second plurality of conductive traces with a second set of machining alignment aids. The first and second sets of machining alignment aids provide a measurable indication of machining depth during the machining process. In some embodiments, the measurable indication is measurable based on at least one of capacitance, resistance, or impedance. The measurable indication can be both visual and measurable based on one or more physical dimensions. In some embodiments, the machining alignment aids provide a measurable indication of machining diameter error of the machining process. In some implementations, the first set of machining alignment aids includes a connection between two traces of the first plurality of traces. The connection electrically connects the two traces until the connection is removed by a processing step, at which time the connection electrically isolates the two traces from each other and provides an indication of processing depth. In some embodiments, the flex array interconnect structure includes one or more ground layers between the first and second layers to reduce crosstalk between the first plurality of conductive traces on the first layer and the second plurality of conductive traces on the second layer.

[0010] In several embodiments, a method is disclosed. The method includes casting from epoxy a backing block having an embedded flex circuit, the embedded flex circuit including one or more machined alignment aids connected to signal traces thereof. The method includes machining the backing block to a proper geometry to expose the signal traces on the flex circuit for contacting the electromechanical array. The method further includes monitoring the machining of the embedded flex circuit of the backing block during machining based on the one or more machined alignment aids. The method further includes verifying alignment of the backing block with a processing device based on monitoring with the one or more machined alignment aids of the embedded flex circuit. The method also includes bonding the electromechanical array to the backing block to form a bonding module after machining the backing block to the proper geometry. The method further includes placing the bonding module on a dicing saw and cutting the bonding module with the dicing saw, cutting each element of the bonding module to a depth that isolates each element and its corresponding electrical connection.

[0011] The accompanying drawings illustrate embodiments and are therefore exemplary implementations and should not be considered as limiting the scope of the claims. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 illustrates an example environment of an ultrasound system having an ultrasound scanner, according to one or more implementations. [Figure 2] FIG. 2 illustrates an exemplary implementation of the ultrasound scanner of FIG. 1. [Figure 3] 1A and 1B illustrate cross sections of exemplary array configurations and interconnect structures for high sensitivity transducers of an ultrasound scanner. [Figure 4A] FIG. 1 is a diagram illustrating a single flex circuit implementation. [Figure 4B] FIG. 1 is a diagram illustrating a dual flex circuit implementation. [Figure 5] FIG. 1 illustrates an example implementation of a dual flex circuit with a ground plane. [Figure 6] FIG. 1 illustrates an example implementation of a multi-layer flex circuit with an internal ground plane. [Figure 7] FIG. 1 illustrates an example implementation of a multi-layer flex circuit with internal and external ground planes. [Figure 8] 1A-1C illustrate an example implementation of a multilayer flex circuit with an internal ground plane and plated and filled microvias at the machined interface. [Figure 9] 1A-1C illustrate an example implementation of a multilayer flex circuit with internal and external ground planes and plated and filled microvias at the machined interfaces. [Figure 10] 1A-1C illustrate an example implementation of a multilayer flex circuit with an internal ground plane and plated and filled microvias below the machined interface. [Figure 11] 1A-1C illustrate an example implementation of a multilayer flex circuit with inner and outer ground planes and plated and filled microvias below the machined interface. [Figure 12] 1A-1C illustrate an example implementation of a multilayer flex circuit with inner and outer ground planes and plated and filled through-hole vias at the machined interfaces. DETAILED DESCRIPTION OF THE INVENTION

[0013] Systems and methods for multilayer flex array interconnect structures for ultrasonic transducers, as well as methods for their manufacture, are disclosed. The systems and methods described herein provide more consistent and controllable alignment between odd and even flex layers. For example, during the casting process of the transducer's backing block, the flex circuit structure was constrained by methods other than mechanical fastening. Furthermore, reducing the number of flex circuits used in the ultrasonic transducer allows for a simplified array configuration, while adding ground layers between signal layers to improve crosstalk performance. In some implementations, vias are introduced at interfaces (e.g., PZT interfaces) of the electromechanical array. The presence and location of these vias increases the surface area of ​​the conductive material, thereby improving the quality of the electrical and physical connections.

[0014] Additionally, machining alignment and verification aids are provided by strategically utilizing unused and discarded board area. These machining alignment and verification aids (i) verify the alignment of the flex circuit with the processing equipment during the machining process, and (ii) allow for adjustment of the flex circuit position relative to the processing equipment to prevent the flex circuit from being machined into an unusable state (e.g., cutting the flex circuit's copper traces out of alignment for electrical connection with the plated PZT crystals). The machining alignment and verification aids include markers on the board portion to be cut to provide indication of the alignment of the flex circuit with the processing equipment as well as the depth of the cut. (ultrasound system)

[0015] 1 illustrates an exemplary environment for an ultrasound system 100 having an ultrasound scanner, according to one or more implementations. Generally, the ultrasound system 100 includes an ultrasound device 102 that generates data based on high-frequency sound waves reflecting off body structures. The ultrasound device 102 includes various components, including a scanner 104, one or more processors 106, a display device 108, and a memory 110.

[0016] A user 112 (e.g., a nurse, ultrasound technician, operator, sonographer, etc.) aims the scanner 104 at a patient 114 to non-invasively scan internal structures (organs, tissues, etc.) of the patient 114 for examination, diagnosis, or other therapeutic purposes. In some implementations, the scanner 104 includes an ultrasound transducer array and electronic circuitry communicatively coupled to the ultrasound transducers for transmitting ultrasound signals into the patient's anatomy and receiving ultrasound signals reflected from the patient's anatomy. In some implementations, the scanner 104 is an ultrasound scanner, also referred to as an ultrasound probe.

[0017] The display device 108 is coupled to the processor 106 and processes the reflected ultrasound signals to generate ultrasound data. The display device 108 is configured to generate and display an ultrasound image (e.g., ultrasound image 116) of the anatomical structure based on the ultrasound data generated by the processor 106 from the reflected ultrasound signals detected by the scanner 104. In some embodiments, the ultrasound data includes the ultrasound image 116 or data representative of the ultrasound image 116.

[0018] 2 illustrates an implementation 200 of the ultrasound scanner 104 of FIG. 1. The scanner 104 (e.g., an ultrasound scanner) includes a housing 202 extending between a distal end 204 and a proximal end 206. The housing 202 includes a central axis 208 (e.g., longitudinal axis) that intersects the distal end 204 and the proximal end 206. The scanner 104 is electrically connected to an ultrasound imaging system (e.g., ultrasound machine 102) via a cable 210 connected to the proximal end 206 of the scanner 104 by a strain-free element 212. In some implementations, the scanner 104 is wirelessly connected to the ultrasound imaging system and communicates with the ultrasound imaging system via one or more wireless transmitters, receivers, or transceivers over a wireless connection or a network (e.g., Bluetooth, Wi-Fi, etc.).

[0019] A transducer assembly 214 having one or more transducer elements is electrically connected to system electronics 216 of the ultrasound device 102. During operation, the transducer assembly 214 transmits ultrasonic energy from one or more transducer elements toward a subject and receives ultrasonic echoes from the subject. The ultrasonic echoes are converted by the transducer elements into electrical signals and electrically transmitted to the system electronics 216 within the ultrasound device 102 for processing and generation of one or more ultrasound images.

[0020] Acquiring ultrasound data from a subject using a transducer assembly (e.g., transducer assembly 214) generally involves generating an ultrasound signal, transmitting the ultrasound signal into the subject, and receiving the ultrasound signal reflected from the subject. A wide range of ultrasound frequencies can be used to acquire ultrasound data, such as, for example, low-frequency ultrasound (e.g., less than 15 megahertz (MHz)) and / or high-frequency ultrasound (e.g., 15 megahertz (MHz) or greater). The particular frequency range to use can be readily determined based on various factors, including, for example, the depth of the image, the desired resolution, etc.

[0021] In some implementations, the system electronics 216 includes one or more processors (e.g., processor 106 of FIG. 1 ), integrated circuits, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), and power supplies to support the functionality of the ultrasound device 102. In some implementations, the ultrasound device 102 also includes an ultrasound control system having one or more processors. At least one processor, FPGA, or ASIC causes the transducer of the scanner 104 to transmit electrical signals to emit sound waves and receives electrical pulses from the scanner 104 generated from the returning echoes. The one or more processors, FPGAs, or ASICs process raw data related to the received electrical pulses to generate an image that is transmitted to the ultrasound imaging subsystem 220 for display via the display device 108 (e.g., image 116 of FIG. 1 ). In this manner, the display device 108 displays an ultrasound image from the ultrasound data processed by the processor of the ultrasound control subsystem 218.

[0022] In some implementations, the ultrasound device 102 includes one or more user input devices (e.g., a keyboard, cursor control device, microphone, camera, etc.) that allow data to be entered and measurements to be acquired from the display device 108 of the ultrasound device 102. The ultrasound device 102 may also include disk storage (e.g., a computer-readable storage medium such as read-only memory (ROM), flash memory, dynamic random access memory (DRAM), NOR memory, static random access memory (SRAM), NAND memory, etc.) for storing acquired ultrasound images. Additionally, the ultrasound device 102 may also include a printer that prints images from the displayed data. Such user input devices, disk storage, and printer are not shown in FIG. 2 so as not to obscure the technology described herein.

[0023] 3 is a cross-sectional view 300 illustrating an exemplary array configuration and interconnect structure for a high sensitivity transducer of an ultrasound scanner. Cross-section 300 represents a cross-section of the distal end 204 of the ultrasound scanner 104 of FIG.

[0024] In the illustrated example, an ultrasonic scanner (e.g., ultrasonic scanner 104 of FIG. 2) includes a piezoelectric ceramic element (e.g., piezoelectric material 302) transducer sandwiched between a backing material 304 and a set of matching layers 306 (e.g., matching layers 306-1, 306-2, 306-3). On the side of matching layer 306 opposite piezoelectric material 302 is an acoustic lens (e.g., lens 308) that has an outer surface 310 that faces outward (away from proximal end portion 206 as shown in FIG. 2). Outer surface 310 of lens 308 is convex (e.g., curved toward the set of matching layers 306).

[0025] The piezoelectric material 302 includes a crystal with electrodes (e.g., electrodes 312), formed, for example, by plating a thin film of gold or silver on the crystal surface. The piezoelectric material 302 can be made of any suitable material, one example being lead zirconate titanate (PZT). Other examples include quartz, barium titanate, and polyvinylidene fluoride (PVDF). The electrodes 312 can include a first electrode between the piezoelectric material 302 and a set of matching layers 306 and a second electrode between the piezoelectric material 302 and the backing material 304. In the illustrated example, the first electrode is adjacent to the front side of the piezoelectric material 302 (e.g., facing the lens 308), and the second electrode is adjacent to the back side of the piezoelectric material 302 (e.g., facing the backing material 304). The set of matching layers 306 provides an acoustic impedance gradient for the acoustic energy generated by the piezoelectric material 302, allowing it to pass smoothly through the patient's body tissue and also allowing the reflected acoustic waves (return echoes) to return smoothly to the piezoelectric material 302 for detection.

[0026] In some implementations, the backing material 304 has a U-shaped cross-section with a recessed area for receiving the piezoelectric material 302. In this manner, the backing material 304 provides structural support to the sides (sides intersecting the x-axis and / or y-axis) of the piezoelectric material 302 as well as the back side (side away from the lens 308). Thus, a portion of the backing material is between the piezoelectric material 302 and the housing 202 (e.g., in the x- and y-directions). The backing material 304 can be made of a variety of materials. Some examples include tungsten, iron, magnesium, and aluminum. In some implementations, the backing material 304 is a composite support material, such as tungsten particles bonded to an epoxy. The backing material 304 is configured to prevent rearwardly radiated acoustic waves from reflecting off the piezoelectric material 302 and ringing and being detected.

[0027] The ultrasound scanner 104 also includes an electrical connection 314 to a power source that provides alternating current to the second electrode 302. Additionally, a ground electrode 316 provides an electrical connection to ground 318 and serves as a terminal on the back side of the piezoelectric material 302.

[0028] The embodiment shown in Figure 3 is one example of a transducer array structure and interconnect structure for the ultrasonic scanner 104. The techniques disclosed herein may also be implemented using other types of ultrasonic transducers, including array structures and interconnect structures with other configurations. For example, the techniques disclosed herein may be applied to piezoelectric micromachined ultrasonic transducers (PMUTs), capacitive micromachined ultrasonic transducers (CMUTs), or any other suitable electromechanical array, sensor, or transducer that uses electrical connections from one structure to another.

[0029] Figures 4A through 12 show examples of flex circuits used in ultrasonic transducers. Typically, when constructing an ultrasonic array module, a backing block is cast with epoxy that encapsulates the flex circuit. Once the backing block is constructed, it is machined to the correct geometry for connection to the PZT array, exposing signal traces on the flex circuit for connection to the PZTs. The PZTs are then bonded to the backing block. This bonded module is then placed on a dicing saw, and each "element" is cut to a depth that isolates each element and its electrical connections. In each of Figures 4A through 12, each circuit is shown in a front view (xy plane), a corresponding right side view (yz plane), and a top view (xz plane).

[0030] In historical implementations of single and dual flex circuits, shown in Figures 4A and 4B, respectively, special tooling was required to ensure alignment of the flex circuit while it was cast in epoxy, followed by machining and dicing. If not properly secured, odd and even traces could overlap, potentially causing shorts or open circuits during dicing. However, using multi-layer flex (with three or more layers), as shown in Figures 5 through 12, allows the odd and even signal layers, respectively, to be aligned to tighter tolerances, thereby reducing the complexity of tooling alignment.

[0031] As previously mentioned, Figure 4A shows an implementation 400 of a single flex circuit 402. For simplicity, the single flex circuit 402 is shown showing the conductive (e.g., copper) traces 404 before (406) and after (408) dicing. Each trace 404 is adjacent to an insulating layer 410 on each side of the trace 404 (in the z-axis), with the trace 404 between two adjacent insulating layers 410. Figure 4B shows an implementation 450 of a dual flex circuit 452. The dual flex circuit 452 is shown showing the conductive traces 404 before (454) and after (456) dicing.

[0032] By using a dual flex circuit 452 (FIG. 4B) and increasing the signal trace spacing on the flex circuit, the "inter-element" crosstalk introduced from adjacent traces on the flex circuit is reduced compared to a single flex circuit 402 (FIG. 4A). This improvement results in an improved element pattern, resulting in a higher performance transducer. If a dual flex circuit were implemented as an odd / even flex circuit without spacing between them, the crosstalk would increase and could reach the level of a single flex circuit. Adding a ground plane to the flex circuit can alleviate this issue, allowing greater freedom in designing and fastening the array blocks. This ground plane can be implemented in a dual flex design (FIG. 5) or a multi-layer flex with multiple odd and even traces (e.g., FIGS. 6-9).

[0033] 5 shows an example implementation 500 of a dual flex circuit 502 with a ground plane 504. For simplicity, the dual flex circuit 502 is shown showing the traces 404 before dicing (506) and after dicing (508).

[0034] 6 illustrates an example implementation of a multilayer flex circuit 602 having an internal ground plane 604 (e.g., an internal ground layer). In embodiments, the internal ground layer may include two ground layers. For simplicity, the multilayer flex circuit 602 is shown with traces 404 before dicing (606) and after dicing (608).

[0035] FIG. 7 illustrates an example implementation 700 of a multilayer flex circuit 702 having an internal ground plane 604 and an external ground plane 704, respectively. For simplicity, the multilayer flex circuit 702 is shown with the traces 404 before dicing (706) and after dicing (708). The external ground planes 704 (e.g., external ground layers) are positioned such that the traces 404 are between at least two external ground planes 704. The internal ground planes 604 are positioned between the traces 404. In the illustrated embodiment, each trace layer is stacked between two ground planes (e.g., the internal ground plane 604 and the external ground plane 704). For example, the internal ground planes 604 and the external ground plane 704 are adjacent to opposite sides of the traces 404, with a first insulating layer 410 separating the traces 404 from the internal ground plane 604 and a second insulating layer 410 separating the traces 404 from the external ground plane 704.

[0036] FIG. 8 illustrates an implementation 800 of a multilayer flex circuit 802 having an internal ground plane 604 and plated and filled microvias 804 at a machined interface 806. The vias 804 can connect traces 404 on a first layer of the multilayer circuit 802 to a second layer of the multilayer circuit 802. The second layer can accommodate a ground layer, such as the internal ground plane 604 or the external ground plane 704, without connecting the traces 404 to ground. Another via 804 can connect traces 404 on a third layer of the multilayer circuit 802 to a fourth layer of the multilayer circuit 802. The third layer can accommodate a ground layer, such as the internal ground plane 604 or the external ground plane 704, but the vias 804 are not grounded (e.g., do not connect the traces 404 to ground). For simplicity, the multilayer flex circuit 802 is shown with the traces 404 before (808) and after (810) dicing. In the illustrated embodiment, the vias 804 include annular ring vias 812, which are also plated and filled. By comparing the multilayer flex circuit 802 before dicing (808) and after dicing (810), it can be seen that cutting the multilayer flex circuit to a depth (e.g., cut depth 814) exposes the traces 404 and increases the surface area of ​​conductive material, thereby improving the quality of the electrical and physical connections to the traces 404. While the embodiments shown in Figures 9-12 show similar cut depths, this is for illustrative purposes only and is not intended to be limiting.

[0037] 9 shows an example implementation 900 of a multilayer flex circuit 902 having inner and outer ground planes 604 and 704, respectively, and having plated and filled microvias 804 at a processing interface 806. For simplicity, the multilayer flex circuit 902 is shown with traces 404 before (904) and after (906) dicing.

[0038] 10 shows an example implementation 1000 of a multilayer flex circuit 1002 with an internal ground plane 604 and microvias 804 plated and filled below the machined interface 806. For simplicity, the multilayer flex circuit 1002 is shown with traces 404 before (1004) and after (1006) dicing.

[0039] 11 shows an example implementation 1100 of a multilayer flex circuit 1102 having inner and outer ground planes 604 and 704, respectively, and plated and filled microvias 804 below the processing interface 806. For simplicity, the multilayer flex circuit 1102 is shown with traces 404 before (1104) and after (1106) dicing.

[0040] 12 shows an example implementation 1200 of a multilayer flex circuit 1202 having inner and outer ground planes 604 and 704, respectively, and plated and filled through-hole vias 1204 at the machined interface. For simplicity, the multilayer flex circuit 1202 is shown with traces 404 before (1206) and after (1208) dicing.

[0041] A common failure point during transducer manufacturing is poor electrical contact between the array block flex and the PZT matching layer stack. In many array block designs, the contact surface area is a function of the trace width (~100 μm) and copper thickness (~10 μm or approximately 1000 μm). 2 ). When multi-layer flex is used, there is an opportunity to add a filled via (e.g., via 804) in an adjacent layer or in a layer located directly opposite an adjacent insulating layer. If this via is at the PZT interface (as shown in Figures 8 and 9, where via 804 is at the machining interface 806), the filled via after machining can increase the signal surface area by approximately six times (100 μm x (10 μm (copper) + 25 μm (Kapton) + 10 μm (copper) + 19 μm (plating)) = 6400 μm 2). If the cut depth is too deep and cuts to the bottom of the via annular ring 812 at that via location, it is possible to move the via below the cut depth (as shown in Figures 10 and 11). In this case, the exposed surface area is increased by approximately four times (100 μm x (10 μm (copper) + 10 μm (copper) + 19 μm (plating)) = 3900 μm 2 ) is increased by a factor of 10. An additional tradeoff between crosstalk and contact surface area can be made by extending the vias through to short adjacent traces. In this case, the traces are separated by dicing, leaving the entire width of the flex exposed copper and available for electrical connection (see Figure 12).

[0042] Alignment of the flex circuit within the backing block is key to high yield during machining. Since much of the flex circuit is discarded during the machining process, that material can be used to measure alignment accuracy using visual or electrical tools. Some or all of the layers can be used to create features using resistance, capacitance, inductance, or optical measurements. For example, consider FIG. 13, which shows an example of a multi-layer flex circuit 1300 embedded in a backing block. The example shown is of the flex circuit 1300 before machining and dicing.

[0043] Dashed line 1302 represents the nominal machining plane of exemplary flex circuit 1300. During machining, material above dashed line 1302 is removed (e.g., the portion including flex circuit 1300 is machined (e.g., milled) away in the direction of arrow 1304). The portion of flex circuit 1300 below dashed line 1302 remains (e.g., the portion of dashed line 1302 opposite arrow 1304 remains). As shown, flex circuit 1300 includes various exemplary features that can be used to provide indications of machining precision (e.g., depth, alignment, etc.).

[0044] For example, first trace 1306 includes or connects to a larger width portion 1308 that tapers or narrows in width in the direction of arrow 1304 toward dashed line 1302. Second trace 1310 includes or connects to a smaller width portion that widens (e.g., tapers or narrows in width) in the direction of arrow 1304 toward dashed line 1302. By monitoring the two portions (e.g., 1308 and 1312) of traces 1306 and 1310, respectively, during the machining process, an operator can determine the machining depth. For example, as part is removed, the width of larger width portion 1308 decreases and the width of smaller width portion 1312 increases.

[0045] The portions 1308 and 1312 are visually observable, allowing changes in one or more physical dimensions (e.g., length, width) to be monitored as the flex circuit is cut. For example, if the two portions 1308 and 1312 are not identical in size, measuring them can estimate the current cut from a nominal value (e.g., the nominal depth is at dashed line 1302). In some implementations, if the outer trace (e.g., trace 1306) is larger than the inner trace (e.g., trace 1310), the cut diameter is too large. If the outer trace (e.g., trace 1306) is smaller than the inner trace (e.g., trace 1310), the cut diameter is too small. As the flex circuit 1300 is cut, at some point within the allowable depth range of dashed line 1302, the widths of the two portions 1308 and 1312 will be substantially the same as each other, providing a visual indication that the proper depth for that portion has been reached. Furthermore, the operator will know that he has removed too much material if the width of the first trace 1306 becomes smaller than the width of the second trace 1310. A close-up of section 1314 is shown in FIG.

[0046] FIG. 14 shows a close-up view 1400 of section 1314 of FIG. 13. As the part is cut in the direction of arrow 1304, the width (x-direction) of, for example, second trace 1310 can be measured and monitored. Second trace 1310 can have a predetermined length (y-direction dimension) at the desired width, which provides a tolerance for the processing process. The length (e.g., length 1402) can be any suitable length, such as a length in the range of 0.001 mils to 0.005 mils. For example, if length 1402 is 0.002 mils, then the tolerance for both traces 1306 and 1310 (shown in FIG. 13) to have the same dimension (e.g., width) is + / - 0.001 mils from center.

[0047] Returning to FIG. 13 , another feature implemented on the flex circuit to provide alignment aids includes the connecting traces forming the sacrificial circuit. For example, traces 1316 and 1318 are connected at section 1320. A pad (not shown) can be connected to the outer trace (trace 1316) and a digital multimeter (DMM) can be used to verify the connection between the pad and the first pin on the connector. This connection verification is for dicing purposes and becomes a significant issue if the operator is unable to determine whether they diced deep enough to remove the area of ​​curvature (e.g., area 1322 of section 1320 remaining from the cut in the direction of arrow 1304) between the wider section of trace 1316 (e.g., section 1324) and the narrower section of trace 1316 (e.g., section 1326). To quickly verify the absence of a connection using conventional techniques, the operator would pull the part from the dicing saw, perform a capacitance test, and if there is a short, return the part to the dicing saw. When the part is returned to the dicing saw, it must be realigned, but with conventional methods, parts are rarely aligned accurately. However, the above implementation using connecting section 1320 allows the operator to cut, check, and re-cut the part without removing it from the saw. Such functionality therefore eliminates the need for part realignment, reducing or eliminating the problem of misalignment during re-cutting.

[0048] Furthermore, when flex circuit 1300 is cut at section 1320 (e.g., cut in the direction of arrow 1304 to separate traces 1316 and 1318), and traces 1316 and 1318 are separated and measured to confirm separation, the cut provides an indication that the remaining traces have been similarly separated. Thus, section 1320 allows for real-time monitoring without removing the part from the dicing machine, thereby preventing potential errors from reloading the part into the cutting machine and making additional cuts.

[0049] The described features are on opposite sides (front and back) of the flex circuit. Careful monitoring that these features are uniform (same) on both sides of the flex circuit provides additional assistance during the processing process. In embodiments, any suitable electrical property can be measured, such as capacitance, impedance, resistance, etc., that changes as portions of the part are removed during the processing process.

[0050] Figure 15 shows an example of a flex circuit 1500 with additional features that provide machining alignment aids. Additional features can be located at three locations (e.g., left, center, and right) on the surface of the array. For example, as the part is being machined, balance between machining and diameter can be verified. This allows the operator to account for any unevenness and tolerances in the diameter.

[0051] In one example, a printed circuit board (PCB) may have lights (e.g., light emitting diodes (LEDs)) electrically connected to one or more traces on the PCB. Some of the traces (e.g., traces 1502, 1504, 1506, 1508) may be connected to each other by small connections (e.g., connections 1510, 1512, 1514). Each connection between the traces acts like a switch for one or more lights on the PCB. As the part is machined in the direction of arrow 1516, one or more connections 1510, 1512, 1514 are removed, affecting the electrical connection to the lights on the PCB. Dashed line 1518 represents an example of a machined surface 1520 as the part is machined in the direction of arrow 1516.

[0052] In an example where connections 1510, 1512, 1514 are located at the same depth and each trace 1502, 1504, 1506, 1508 is electrically connected to a different light, if all lights connected to traces 1502, 1504, 1506, 1508 are turned off, the lights turning off simultaneously indicates an even cut.

[0053] If the lights go out at different times, it indicates that the block is not machined evenly. At least one connection 1510, 1512, 1514 may be at a different depth than the other smaller connections 1510, 1512, 1514. In some implementations, connections 1510, 1512, 1514 are located at different depths from each other. Also, the connections are placed at the same depth that the part is normally machined. Therefore, if an operator expects to machine a part so that only the last connection (e.g., connection 1514) is still connected, but the other two connections (e.g., connections 1510 and 1512) are still connected, this indicates a radius machining issue at those two connections.

[0054] FIG. 16 shows an implementation 1600 of a multilayer flex circuit 1602 having multiple machined alignment aids. FIG. 17 shows another view 1700 of the multilayer flex circuit 1602 of FIG. 16. FIG. 16 shows the front side 1604 (orthogonal to the z-axis) of the multilayer flex circuit 1602. FIG. 17 shows the back side 1606 (orthogonal to the z-axis) of the multilayer circuit 1602, opposite the front side. The illustrated circuit 1602 is shown after machining. Portions of the machined alignment aids used during the machining process can be seen on opposite sides (orthogonal to the z-axis) of the illustrated circuit 1602, such as the front side 1604 and back side 1606, respectively. For example, adjacent traces 1608 and 1610, which have widths that vary inversely from one another below the top surface (machining surface), have equal widths (similar to traces 1306 and 1310 in FIG. 13). Such a combination of features indicates that a desired depth has been achieved during machining. Also, the corresponding traces 1612 and 1614 on the back side of circuit 1602 have matching widths, indicating that the machined surface was cut evenly.

[0055] Additionally, some traces (e.g., traces 1616, 1618, 1620) have filled vias 1622 partially machined to form larger connection areas 1624 than the connection areas formed by the ends of the traces. For example, the connection area 1624 formed by the filled vias 1622 is larger than the connection area 1626 of the trace 1614. In the illustrated example, the vias 1622 extend through all layers of the flex circuit 1602, but corresponding traces on the opposite side (e.g., traces 1702, 1704, 1706 on the back side 1606 in FIG. 17 ) are interleaved (e.g., odd and even traces) with respect to the traces 1616, 1618, 1620 on the front side. In this manner, the vias 1622 do not interconnect with traces on the opposite side of the flex circuit. (Exemplary Method)

[0056] FIG. 18 illustrates a method 1800 for manufacturing a flex circuit according to an example implementation disclosed herein. While method 1800 is illustrated as a set of blocks specifying operations to be performed, the order or combination of operations performed is not necessarily limited to the order or combination of operations indicated by the respective blocks. Furthermore, any of one or more of the operations may be repeated, combined, rearranged, or concatenated to provide a wide range of additional and / or alternative methods. In some of the following discussion, reference may be made to the example system 100 of FIG. 1 and / or items or processes detailed in FIGS. 2-17. However, such references are for illustrative purposes only. The technology is not limited to execution by one item or multiple items operating on a single device.

[0057] At 1802, a backing block is cast with epoxy encapsulating the flex circuit. The encapsulated flex circuit includes one or more machined alignment aids connected to the signal traces. The machined alignment aids may be part of the signal traces, such as portions 1308, 1312, sections 1320, 1324, connections 1510, 1512, 1514, etc., as described with respect to Figures 13-17.

[0058] At 1804, the backing block is machined to the appropriate shape to expose signal traces on the flex circuit for connection to the lead zirconate titanate (PZT) array. In some embodiments, a milling machine is used to remove a portion of the backing block. For example, a portion of the component illustrated in FIGS. 13 and 14 is removed in the direction of arrow 1304 to a target depth represented by dashed line 1302. In another example, a portion of the component illustrated in FIG. 15 is removed in the direction of arrow 1516 to a target depth represented by dashed line 1518.

[0059] During machining of the backing block, the machining status is monitored at 1806 based on one or more machining alignment aids of the embedded flex circuit of the backing block. In the example of FIG. 13, as the part is cut away, the width of large width portion 1308 decreases and the width of small width portion 1312 increases. The change in the physical dimensions of portions 1308 and 1312 can be visually and physically observed and measured to provide an estimate of the current cut depth relative to a nominal depth (e.g., target depth). Other examples of machining alignment aids used for process monitoring are described in connection with FIGS. 13-17.

[0060] At 1808, based on the monitoring, alignment of the backing block and processing equipment is verified based on one or more machining alignment aids of the embedded flex circuit. For example, if a first trace (e.g., trace 1306) is substantially the same dimension as a second adjacent trace (e.g., trace 1310) at the processing interface, the processing step has reached the correct depth. If the first trace is smaller than the second trace, the processing diameter is too small. If the first trace is larger than the second trace, the processing diameter is too large. Other examples are described in Figures 13-17.

[0061] After the backing block is machined to the proper shape, it is bonded to the PZT array to form the bonded module at 1810. The backing block can be bonded to the PZT array using any suitable bonding technique.

[0062] The bonding module is attached to a dicing saw at 1812. The bonding module is attached and aligned to the dicing saw, and cut to a depth that separates each device and its electrical connections.

[0063] At 1814, the junction module is cut with a dicing saw to a depth that separates each element of the junction module and its corresponding electrical connections. Examples of circuits before and after dicing are shown and described comparatively with respect to Figures 4A-12.

[0064] While the examples described herein use flexible circuits, the disclosed techniques can also be implemented using rigid PCBs. Additionally, while the examples described herein use PZT ultrasonic transducers, the techniques can be implemented using any suitable electromechanical array, sensor, or transducer that uses electrical connections from one structure to another.

[0065] Some examples are given below.

[0066] In a first embodiment, a flex array interconnect structure for an ultrasound circuit includes a first signal layer, a second signal layer, and one or more ground layers. The first signal layer includes a first plurality of conductive traces configured to be electrically and physically connected to interfaces of electromechanical array elements of an ultrasound transducer. The second signal layer includes a second plurality of conductive traces configured to be electrically and physically connected to interfaces of the electromechanical array elements of the ultrasound transducer. One or more ground layers are disposed between the first and second signal layers to reduce crosstalk between the first and second signal layers.

[0067] In addition to the first embodiment, in some aspects, the flex array interconnect structure further includes at least two outer ground layers, and the first and second signal layers are arranged between the at least two outer ground layers. In some implementations, each of the first and second signal layers is between one or more inner ground layers and one of the at least two outer ground layers.

[0068] In addition to the first embodiment, in some aspects, the flex array interconnect structure includes a plurality of vias filled and plated with a conductive material, where a first via of the plurality of vias connects a first conductive trace of a first plurality of conductive traces of a first signal layer to a third layer of the flex array interconnect structure, and the first via provides the first conductive trace with an enlarged surface area relative to its cross-section at the machined interface of the ultrasonic circuit for connection to an interface of an electromechanical array element of an ultrasonic transducer. In some implementations, the third layer corresponds to one of the internal ground layers, and the first via is ungrounded. In other implementations, the third layer corresponds to an external ground layer, the first via is ungrounded, and the first signal layer is disposed between the external ground layer and one or more internal ground layers. In some aspects, a second via of the plurality of vias connects a second conductive trace of the second plurality of conductive traces of the second signal layer to a fourth layer of the flex array interconnect structure, the second via providing the second conductive trace with an enlarged surface area relative to a cross-section of the second conductive trace at the machined interface of the ultrasonic circuit for connection to an interface of the electromechanical array element of the ultrasonic transducer. In some implementations, the one or more internal ground layers include first and second internal ground layers, the third layer corresponds to the first internal ground layer and the first via is ungrounded, and the fourth layer corresponds to the second internal ground layer and the second via is ungrounded. In some embodiments, the third layer corresponds to the first external ground layer, and the first via is ungrounded, and the first signal layer is disposed between the first external ground layer and one or more internal ground layers; the fourth layer corresponds to the second external ground layer, and the second via is ungrounded, and the second signal layer is disposed between the second external ground layer and one or more internal ground layers.

[0069] Further to the first embodiment, in some aspects, the first plurality of conductive traces comprises a first set of machining alignment aids, a second signal layer is stacked to the first signal layer, and the second plurality of conductive traces comprises a second set of machining alignment aids, and the first and second sets of machining alignment aids provide a measurable indication of machining depth during the machining process.

[0070] In a second embodiment, the ultrasonic circuit includes a plurality of layers and a plurality of vias. The plurality of layers includes at least a first layer and a second layer, the first layer having a first plurality of conductive traces and the second layer having a second plurality of conductive traces. The plurality of vias are filled and plated with a conductive material. One of the plurality of vias connects a trace of the first plurality of traces of the first layer to a third layer of the plurality of layers. The via provides the trace with an enlarged surface area relative to the cross-section of the trace at the processing interface of the flex array interconnect structure for connection to the electromechanical array elements of the ultrasonic transducer.

[0071] Further to the second embodiment, in some aspects, a second via of the plurality of vias connects a second trace of the plurality of traces of the second layer to a fourth layer of the plurality of layers, the second via providing the second trace with an enlarged surface area relative to a cross-section of the second trace at the processing interface of the ultrasonic circuit for connection to an interface of the electromechanical array element of the ultrasonic transducer. In some implementations, the second layer is disposed between the first layer and the third layer, such that the first via extends through the second layer from the first layer to the third layer, and the third layer is disposed between the second layer and the fourth layer, such that the second via extends through the first layer from the second layer to the fourth layer.

[0072] In addition to the second embodiment, in some aspects, the ultrasonic circuit includes first and second external ground layers disposed on opposite sides of the ultrasonic circuit, with the first and second layers both being between the first and second external ground layers. In some implementations, a first via and a second via extend through the first and second layers, respectively, from the first external ground layer to the second external ground layer, where the first and second vias are not grounded.

[0073] In a third embodiment, a flex array interconnect structure for ultrasonic circuits includes a first layer and a second layer. The first layer includes a first plurality of conductive traces with a first set of machined alignment aids. The second layer is stacked on the first layer and has a second plurality of conductive traces with a second set of machined alignment aids. The first and second sets of machined alignment aids provide a measurable indication of machining depth during the machining process.

[0074] Further to the third embodiment, in some embodiments, the measurable indicator is measurable based on at least one of capacitance, resistance, or impedance. The measurable indicator may be visible and measurable based on one or more physical dimensions. In some embodiments, the machining alignment aid provides a measurable indicator of machining diameter error of the machining process.

[0075] Further to the third example, in some implementations, the first set of machining alignment aids includes a connection between two traces of the first plurality of traces, which electrically connects the two traces until the connection is removed by the machining process, and which electrically isolates the two traces from each other when the connection is removed, thereby providing an indication of machining depth. In some aspects, the flex array interconnect structure includes one or more ground layers between the first and second layers to reduce crosstalk between the first plurality of conductive traces of the first layer and the second plurality of conductive traces of the second layer.

[0076] In a fourth embodiment, the method includes casting a backing block with an embedded flex circuit with epoxy, the embedded flex circuit including one or more machining alignment aids connected to signal traces. The method includes machining the backing block to a proper geometry to expose signal traces on the flex circuit that contact the electromechanical array. The method further includes monitoring the machining of the embedded flex circuit of the backing block during machining based on the one or more machining alignment aids. The method further includes verifying alignment of the backing block with a processing device based on monitoring by the one or more machining alignment aids of the embedded flex circuit. The method also includes bonding the electromechanical array to the backing block after machining the backing block to the proper geometry to form a bonding module. The method further includes placing the bonding module on a dicing saw and cutting the bonded module with the dicing saw to a depth that separates each element of the bonding module and its corresponding electrical connection. (Conclusion) Advantageously, embodiments of the multilayer flexible array interconnect structure for ultrasound transducers and methods of fabrication described herein can provide more consistent and more controllable alignment between odd and even flex layers, improve crosstalk between signal layers, and simplify the construction of flex circuits. Additionally, the techniques of the present disclosure can increase the surface area of ​​conductive traces and / or reduce the amount of scrap material.

Claims

1. 1. A flex array interconnect structure for an ultrasonic circuit, comprising: a first signal layer having a first plurality of conductive traces configured to be electrically and physically connected to interfaces of the electromechanical array elements of the ultrasound transducer; a second signal layer having a second plurality of conductive traces configured to be electrically and physically connected to the interfaces of the electromechanical array elements of the ultrasound transducer; one or more internal ground layers disposed between the first and second signal layers to reduce crosstalk between the first and second signal layers; 1. A flex array interconnect structure comprising:

2. 10. The flex array interconnect structure of claim 1, further comprising at least two outer ground layers disposed such that the first and second signal layers are between the at least two outer ground layers.

3. 3. The flex array interconnect structure of claim 2, wherein each of the first and second signal layers is between the one or more inner ground layers and one of the at least two outer ground layers.

4. further comprising a plurality of vias filled and plated with a conductive material; a first via of the plurality of vias connecting a first conductive trace of the first plurality of conductive traces of the first signal layer to a third layer of the flex array interconnect structure; the first vias provide the first conductive traces with an enlarged surface area relative to a cross section of the first conductive trace at a machined interface of the ultrasonic circuit for connection to an interface of the electromechanical array element of the ultrasonic transducer; 10. The flex array interconnect structure of claim 1.

5. 5. The flex array interconnect structure of claim 4, wherein the third layer corresponds to one of the internal ground layers and the first via is not grounded.

6. 5. The flex array interconnect structure of claim 4, wherein the third layer corresponds to an outer ground layer, the first via is not grounded, and the first signal layer is disposed between the outer ground layer and the one or more inner ground layers.

7. a second via of the plurality of vias connecting a second conductive trace of the second plurality of conductive traces of the second signal layer to a fourth layer of the flex array interconnect structure; 5. The flex array interconnect structure of claim 4, wherein a second via provides an enlarged surface area to a second conductive trace relative to a cross section of the second conductive trace at the machined interface of the ultrasonic circuit for connection to an interface of an electromechanical array element of an ultrasonic transducer.

8. the one or more internal ground layers include a first internal ground layer and a second internal ground layer; the third layer corresponds to the first internal ground layer, and the first via is not grounded; 8. The flex array interconnect structure of claim 7, wherein the fourth layer corresponds to the second internal ground layer, and the second via is not grounded.

9. the third layer corresponds to a first external ground layer, and the first via is not grounded; the first signal layer is disposed between the first outer ground layer and the one or more inner ground layers; the fourth layer corresponds to a second external ground layer, and the second via is not grounded; 8. The flex array interconnect structure of claim 7, wherein the second signal layer is disposed between the second outer ground layer and the one or more inner ground layers.

10. the first plurality of conductive traces comprising a first set of machined alignment aids; the second signal layer is stacked on the first signal layer; the second plurality of conductive traces comprising a second set of machined alignment aids; 10. The flex array interconnect structure of claim 1, wherein the first and second sets of machining alignment aids provide a measurable indication of machining depth during the machining process.

11. 1. An ultrasonic circuit comprising: a plurality of layers including at least a first layer and a second layer, the first layer having a first plurality of conductive traces and the second layer having a second plurality of conductive traces; a plurality of vias filled and plated with a conductive material, a first via of the plurality of vias connecting a first trace of the first plurality of traces of the first layer to a third layer of the plurality of layers, the first via providing an enlarged surface area for the first trace at a machined interface of the ultrasonic circuit relative to a cross section of the first trace for connection to an interface of an electromechanical array element of an ultrasonic transducer; an ultrasonic circuit.

12. 12. The ultrasonic circuit of claim 11, wherein a second via of the plurality of vias connects a second trace of the plurality of traces of the second layer to a fourth layer of the plurality of layers, and the second via provides the second trace with an enlarged surface area compared to a cross-section of the second trace at a processing interface of the ultrasonic circuit for connection to an interface of the electromechanical array element of the ultrasonic transducer.

13. the second layer is disposed between the first layer and the third layer such that the first via extends from the first layer to the third layer through the second layer; 13. The ultrasonic circuit of claim 12, wherein the third layer is disposed between the second layer and the fourth layer such that the second via extends from the second layer through the first layer to the fourth layer.

14. 12. The ultrasonic circuit of claim 11, further comprising a first external ground layer and a second external ground layer disposed on opposite sides of the ultrasonic circuit, the first layer and the second layer both being between the first external ground layer and the second external ground layer.

15. 15. The ultrasonic circuit of claim 14, wherein the first via and the second via extend through the first layer and the second layer, respectively, from the first external ground layer to the second external ground layer, wherein the first and second vias are not grounded.

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