Connection for multi-dimensional matrix transducers

Abstract

For a transducer having a chip-on-array arrangement, the de-matching layer extends beyond the footprint of the array, allowing connection of ground planes without sidewall metallization. The flexible circuit material is tiled, so that thermal deformation is reduced, the cost is reduced, and the process yield is improved. In a given transducer, the de-matching layer extension and the tiled flex circuit may be used together or separately.

Description

Background Art

[0001] This embodiment relates to interconnecting transducer arrays with electronics. Typical ultrasound imaging systems have a limited number of channels (e.g., 64 to 256 channels), determined by the number of cables used to communicate with the ultrasound transducers. Because two-dimensional (2D) matrix ultrasound transducers can have many more elements than the system's channels (e.g., exceeding tens of thousands of acoustic elements), a microbeamforming application-specific integrated circuit (ASIC) placed as close as possible to the acoustic elements directly operates the acoustic elements. In a chip-on-array (COA), one or more ASICs placed beneath the cut acoustic elements directly drive the acoustic elements individually or in small groups for various beamforming functions. To connect the ASICs, less-than-ideal low-temperature connections are used to avoid issues caused by applying heat to the laminated stack of acoustic elements. For flexible circuits, routing all element signals can be costly and suffer from poor process yields. To connect the ground trace from the PZT layer to the ASIC, PZT sidewall metallization is used. This metallization results in a limited thickness connection, which increases undesirable resistance and is prone to breakage. Summary of the Invention

[0002] By way of introduction, the preferred embodiments described below include methods, systems, and components for transducers with COAs. The dematching layer extends beyond the array footprint, allowing for ground plane connection without sidewall metallization. The flexible circuit material is laid flat, reducing thermal deformation, lowering costs, and improving process yield. Within a given transducer, the dematching layer extension and the laid-flat flexible circuit can be used together or separately.

[0003] In a first aspect, a multidimensional transducer array system is provided. An acoustic array has transducer elements arranged in a grid in two dimensions in a first region. A dematching layer is adjacent to the acoustic array. The dematching layer has a second region that is larger than the first region, such that at least a first portion extends beyond the footprint of the acoustic array. The dematching layer is conductive. A ground return layer is adjacent to the acoustic array on a side opposite the dematching layer. The ground return layer extends into the dematching layer. A flexible circuit material layer is adjacent to the dematching layer. The flexible circuit material is divided into a plurality of tiles. An integrated circuit chip is connected to the flexible circuit material layer. A ground path extends from the integrated circuit chip, through the flexible circuit material layer, and through the dematching layer to the ground return layer.

[0004] In one embodiment, the transducer element is electrically connected to the integrated circuit chip through the slit portion of the dematching layer and the via hole in the flexible circuit material layer. In another embodiment, the integrated circuit chip is an application-specific integrated circuit flip chip mounted to the flexible circuit material layer.

[0005] As another embodiment, the transducer elements are separated by slits and each comprises a matching layer, a piezoelectric layer, a slit portion of the dematching layer, and a signal electrode. The ground return layer has no slits and is adjacent to the matching layer.

[0006] According to one embodiment, the ground return layer is a metal sheet that is bent at the edge of the acoustic array to connect to the first portion of the dematching layer that extends beyond the footprint of the acoustic array. In one example, the dematching layer has the first and second portions that extend beyond the footprint of the acoustic array. The metal sheet connects to both the first and second portions of the dematching layer. Alternatively, the ground return layer is a polymer layer (e.g., polyester film) coated with a thin metal (e.g., a metal sheet in a laminate or supported by other materials).

[0007] In one embodiment, the dematching layer is tungsten carbide.

[0008] In other embodiments, the flexible circuit material is divided into multiple pieces, as separate sheets in the same plane, or as sheets with slits formed therein.

[0009] In a second aspect, a transducer array system is provided. Transducer elements are disposed in an array. A ground layer is disposed above the transducer elements of the array. An integrated circuit chip is electrically connected to the transducer elements. A dematching layer is disposed between the array and the integrated circuit chip. The dematching layer is electrically conductive and has a portion not covered by the array. The ground layer extends from above the transducer elements of the array to the portion of the dematching layer not covered by the array.

[0010] According to one embodiment, the dematching layer is tungsten carbide.

[0011] As another embodiment, the array has a first area in a plane parallel to the acoustic surface, and the dematching layer has a second area parallel to the plane, and the second area is larger than the first area by an area of the portion.

[0012] In another embodiment, the ground layer is a metal sheet that is bent at the edge of the array to connect to the dematching layer.

[0013] In another embodiment, a sheet of flexible circuit material is between the dematching layer and the integrated circuit chip.The sheet is divided into two or more tiles such that different tiles are electrically connected to different ones of the transducer elements.

[0014] In a third aspect, a method for forming an acoustic transducer is provided. A patch of flexible circuit material is bonded to a dematching layer. A semiconductor chip is attached to the flexible circuit material. The attachment is achieved using applied heat. An array of transducer elements is stacked on the dematching layer.

[0015] In one embodiment, separate sheets of flexible circuit material in the same plane are bonded to different portions of the dematching layer.

[0016] According to one embodiment, a sheet of flexible circuit material is bonded to the dematching layer. The sheet has gaps forming the tiles.

[0017] In another embodiment, the semiconductor chip is attached to the flexible circuit material after the patch of flexible circuit material is bonded to the dematching layer. The applying heat is from solder reflow or anisotropic conductive film thermocompression bonding.

[0018] As yet another embodiment, the array is stacked on the dematching layer, wherein the dematching layer has a larger surface area on a first surface than an area of a largest surface of the array, such that the dematching layer extends beyond the array. A ground plane is laid over the array and connected to the dematching layer outside the footprint of the largest surface of the array.

[0019] The present invention is defined by the appended claims, and nothing in this section should be construed as limiting those claims. Other aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments and may be claimed hereafter independently or in combination. Different embodiments may or may not achieve different objectives or advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The components and drawings are not necessarily drawn to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the different views.

[0021] Figure 1 is a cross-sectional view of one embodiment of a multi-dimensional transducer array system; Figure 2 is a top view of one embodiment of an array on an extended dematching layer; Figure 3 and Figure 4 is a bottom view illustrating an example of a lay-flat flexible circuit material; Figure 5 is a flow chart of one embodiment of a method for forming an acoustic transducer using an extended dematching layer and / or tiled flexible circuit material; and Figure 6-11 Pictured Figure 5 The various stages of formation of the method. DETAILED DESCRIPTION

[0022] The 2D matrix ultrasound transducer offers various improvements to COA technology. A simpler ground return path is provided in the 2D matrix transducer. The dematching layer has an expanded footprint relative to the transducer element array, allowing the ground plane to be connected to the dematching layer instead of using metallized sidewalls. To enable high-temperature ASIC attachment with improved reliability and cost-effective integration of flex circuits, tiled flex circuit material is used. This provides improved process yield and design freedom.

[0023] Various matrix transducers, such as transthoracic ultrasound (TTE) transducers, transesophageal ultrasound (TEE) transducers, catheter transducers, or other ultrasound transducers using COAs with minimal parasitics, can be matched using tiling or spreading.

[0024] Figure 1 is a cross-sectional view of one embodiment of a transducer array system. The cross-section is in the depth-height dimension, where the depth is vertical in the figure and the height is horizontal in the figure.

[0025] The system is used in an ultrasound transducer probe, such as a handheld probe for scanning from outside a patient or an endocavity (e.g., TEE or TTE) or catheter-based probe for scanning from within a patient. The system includes a one-dimensional or multi-dimensional transducer array, such as a matrix array having elements 135 distributed in both azimuth and elevation. Multi-dimensional transducer array systems are also available.

[0026] The array system includes matching layers 100, 120, a ground layer 150, an array layer (e.g., a piezoelectric layer 130), a dematching layer 140, a flexible circuit material layer 160, a chip 170 (e.g., an application-specific integrated circuit), and an acoustic backing 180. Additional, different, or fewer layers may be included, for example, excluding the acoustic backing 180, the chip 170, and / or the second matching layer 100. In one example, a lens and / or housing is positioned around the transducer system or adjacent to the second acoustic matching layer 100. In other examples, the flexible circuit material layer 160 is provided without the dematching layer 140, or vice versa.

[0027] The array system and the corresponding probe use Figure 5 method or another method.

[0028] Matching layers 100 and 120 are layers of material with a quarter-wave thickness. Multiple layers with gradually varying acoustic impedances can be used, but in other embodiments, only one matching layer is provided. Second matching layer 100 provides a transition in acoustic impedance between the patient, lens, or other material and first matching layer 120. Similarly, first matching layer 120 provides an acoustic impedance transition from second matching layer 100 to piezoelectric or other transducer array layer 130. In one example, second matching layer 100 is polyurethane or another material with or without fillers. First matching layer 120 is graphite or another conductive material. Graphite can be impregnated with copper or other metals to enhance conductivity.

[0029] The array layer is shown as a PZT layer 130, but may include a first matching layer 120 and / or a dematching layer 140. The PZT layer 130 is a thick plate or slab of PZT material. Solid PZT can be used. Single crystal or polycrystalline PZT material can be used. In other embodiments, a composite material of a piezoelectric and epoxy or another polymer is used. A microelectromechanical (capacitive film) element 135 may be used in place of PZT. This article uses a piezoelectric example, so the array layer will be referred to as the PZT layer 130.

[0030] The multi-dimensional transducer array 132 is an array of PZT elements 135. Slits 190 separate the elements 135 of the PZT layer 130. Slits 190 also separate the first acoustic matching layer 120 and the dematching layer 140. In other embodiments, the slits 190 separate the second matching layer 100. In still other embodiments, the slits 190 do not extend through the dematching layer 140 and / or the first acoustic matching layer 120. When viewed from the acoustic surface of the transducer, the slits 190 can be arranged in a grid pattern, for example, forming separate elements 135 in elevation and azimuth. The array layer includes elements 135 that convert between acoustic energy and electrical energy, for example, an array of transducer elements 135 formed of PZT material. The transducer elements 135 of the array layer are arranged in a grid pattern in one or two dimensions.

[0031] The array can be flat, concave, or convex. In one embodiment, elements 135 are distributed in two dimensions. Elements 135 are distributed along any of a variety of spacings, such as every 150, 250, 400, or 500 microns, at full sampling intervals along two dimensions (e.g., azimuth and elevation). This provides for full or sparse sampling of the placement of elements 135.

[0032] Each transducer element 135 of the array includes at least two electrodes. A conductive ground return layer 150 provides one of the electrodes. The other electrode is separated from the PZT layer 130 by a slit 190, such as an electrode deposited on a segmented portion of the conductive monomers of the PZT layer 130 or the dematching layer 140. The elements 135 convert between electrical and acoustic energy. The ground layer 150 defines a 0 volt or ground signal. Electrical energy generated by or supplied to the PZT is supplied to the electrode opposite the ground layer 150. This signal electrode is separate for each element 135, providing a separate conductive path from the PZT layer 130 and through the dematching layer 140 to the flexible circuit material layer 160. Because the slits 190 extend through the dematching layer 140, different, separate portions of the dematching layer 140 form part of the conductive path for the signal.

[0033] Because the entire ground layer 150 covers the elements 135 of the PZT layer 130, the slits 190 may be filled with air or another gas. By wrapping the stack with the ground layer 150 and the dematching layer 140 (or the flexible circuit material layer 160), a gas-filled slit 190 can be used, which has better sensitivity than epoxy or another filler. In an alternative embodiment, the slits 190 are filled with epoxy or another filler.

[0034] The array of PZT layer 130 has a certain footprint in azimuth and elevation. The largest surface of PZT layer 130 lies in a plane normal to the transmit and receive directions, such as the plane defining the acoustic face of the array. Elements 135 are distributed in this plane parallel to the acoustic face, creating an area that defines the footprint of the array. Curved or convex surfaces can be used to distribute the elements in azimuth and elevation.

[0035] The dematching layer 140 is a layer of material with a thickness of 1 / 4, 1 / 8, 1 / 16, or another wavelength. Any material can be used, such as tungsten carbide (WC) or graphite. The dematching layer 140 provides a clamped boundary condition, resulting in better sensitivity and wider bandwidth of the ultrasonic transducer. The dematching layer 140 is located between the array (PZT layer 130) and the integrated circuit chip (170).

[0036] The dematching layer 140 is conductive. The material of this layer itself can be conductive and / or have fillers or composite materials added to provide conductivity. The dematching layer 140 serves to form a common ground connection for the 2D matrix transducer. To drive the PZT elements 135, a ground return path is established by connecting the top electrodes (ground layer 150) of all the individual segmented acoustic elements 135 to the electrical ground of the ultrasound system. Ground layer 150 is connected to the system ground. In an alternative embodiment, a metallized coating is used on the sidewalls of the array's outermost acoustic elements 135. This metallized coating can result in high resistance in the ground path and is prone to fracture at sharp corners of the piezoelectric layer 130, thus requiring expensive beveling at the corners of the fragile piezoelectric ceramic layer 130.

[0037] In one embodiment, the dematching layer 140 is used for ground connection.The acoustic dematching layer 140 extends beyond the active acoustic area. Figure 2 An example is shown. The PZT layer 130 has a footprint that defines the area of the acoustic face of the array. This area is defined by the distribution of the transducer elements 135. The dematching layer 140 is sized to extend beyond the footprint of the array. Figure 2 The dematching layer 140 is shown extending beyond the area of the array of PZT layer 130 on two sides, but only one, three, or all four sides of the dematching layer 140 may extend beyond the array 130 when viewed from above or below (i.e., normal to the largest surface of the array and / or dematching layer 140).

[0038] The dematching layer 140 has an area that is greater than the area of the array such that at least one portion 200, 210 extends beyond the footprint of the acoustic array. The area of the dematching layer 140 parallel to the plane of the array, the acoustic face, or the average plane through the array is greater than the area of the array by the area of the portion 200, 210.

[0039] The portions 200, 210 that extend beyond the array or PZT layer 130 form pads for ground connections. The components or portions 200, 210 of the dematching layer 140 that are not covered by the array of the PZT layer 130 can be used to connect to the ground layer 150. By extending beyond the active acoustic area, the ground return layer 150 can terminate on, adjacent to, or against the dematching layer 140. The dematching layer 140 itself is conductive and is connected to the electrical ground of the flexible circuit material layer 160, completing a conductive ground path from the top of the cut array to the flexible circuit material layer 160 without any sidewall metallization on the acoustic elements 135.

[0040] The ground layer 150 is a metal foil or sheet. For example, a copper sheet or other conductive material is used. Alternatively, the ground return layer is a polymer layer (e.g., polyester film) coated with a thin metal.

[0041] The ground layer 150 is distributed on the PZT layer and / or one or both matching layers 100, 120. Figure 1 As shown in FIG, the ground layer 150 covers the first matching layer 120 and is covered by the second matching layer 100. Slits 190 are formed to separate the transducer elements 135, and then the ground layer 150 without the slits is laid over the separated transducer elements 135. The ground layer 150 is adjacent to the acoustic array on a side opposite the dematching layer 140 (e.g., positioned against the elements 135 and / or conductively connected to the PZT layer 130).

[0042] The ground plane 150 is a ground return path and is therefore connected to the chip 170 or ultrasound system ground. To facilitate this connection, the ground plane 150 extends to the dematching layer 140. The ground plane 150 extends from above the array's transducer elements 135 to the portions 200 and 210 of the dematching layer 140 not covered by the array. The ground plane 150 can have some flexibility. By extending the conductive dematching layer 140 beyond the footprint of the PZT layer 130 and the corresponding array of transducer elements 135, the ground plane 150 can bend at the edge of the array to extend down to, contact, or rest over a portion of the dematching layer 140. At least a portion of the ground plane 150 extends to and terminates at the extended dematching layer 140. This extension allows the ground plane 150 to contact the dematching layer with less severe bending. A thicker ground plane layer 150 than the metallized surface can be used. The metal sheet bends without breaking or tearing at the edge of the acoustic array to connect to portions 200 and / or 210.

[0043] In one embodiment, the metal sheet of the ground plane 150 extends from the entire perimeter (e.g., all four edges of a square or rectangular array) to the dematching layer 150, with a portion extending beyond the footprint on all (e.g., four) sides. The ground plane 150 has no slits 190. This allows the array to be sealed so that air is trapped in the slits. Figure 1 In the example of FIG, ground layer 150 extends from two parallel edges on opposite sides of the array of elements 135 and rests on portions 200, 210. Ground layer 150 is connected to dematching layer 140 on less than all sides (e.g., only on two sides).

[0044] The ground return layer 150 is connected to the dematching layer 140. Various bonding materials can be used to terminate the ground return layer 150 on the dematching layer 140. For example, epoxy, silver paste, or anisotropic conductive paste (ACP) can be used. The matching layers 100, 120, the PZT layer 130, the dematching layer 140, and / or the flexible circuit material layer 160 can be bonded using the same or different bonding materials.

[0045] Flexible circuit material layer 160 is a sheet of flexible material on and / or in which traces and / or vias may be formed (e.g., deposited and / or etched). For example, a sheet of polyimide may be used. This sheet is positioned between dematching layer 140 and chip 170. Passive and / or active electronic devices may be attached.

[0046] The flexible circuit material layer 160 includes a plurality of vias. One via is provided for each transducer element 135, although additional or fewer vias may be provided. Similarly, one or more vias are provided for a ground return path (e.g., electrically connected to portions 200, 210 of the dematching layer 140 to which the ground layer 150 is connected). These vias are formed in the flexible circuit material layer 160, for example, by etching, deposition, drilling, or molding. A conductor, such as copper, is lined along or fills the vias to create a conductive path through the thickness of the flexible circuit material layer 160. These vias (with or without traces) provide a conductive path from one side of the flexible circuit material layer 160 to the other, allowing electrical connection from the signal electrodes of the elements 135 to the chip 170.

[0047] A single layer of flexible circuit material is used. In other embodiments, more than one layer of flexible circuit material 160 is provided. For example, a stack of two, three, or more layers of flexible circuit material may be provided. The internal routing of traces and / or routing on different layers of flexible circuit material may allow for a redistribution or change in spacing between the pitch of the array of components 135 and the pitch of the connection pads of chip 170.

[0048] A flexible circuit material layer 160 is connected to the acoustic stack to form an acoustic module. A rough contact is provided from the separate portions of the dematching layer 140 of the element 135 to traces, vias, or other conductors on and / or in the flexible circuit material layer 160. Signal electrodes (e.g., metallized electrodes on PZT or separate portions of the conductive dematching layer 140) are connected to separate pads and traces of the flexible circuit material layer 160. Physical connection is achieved by bonding, thereby providing a bonding material layer while still providing the flexible circuit material layer 160 adjacent to the dematching layer 140. The bonding material may be epoxy, Ag paste, or ACP. The flexible circuit material layer 160 is bonded to the acoustic stack or array, for example, to secure the flexible circuit material 160 to the dematching layer 140.

[0049] Flexible circuit material layer 160 is adjacent to chip 170. One or more chips 170 are connected to flexible circuit material layer 160. Soldering, ACF, or other chip-to-flex circuit connections can be used. For example, solder bumps or balls are provided for soldering pads of chip 170 adjacent to pads on flexible circuit material layer 160. Heat is used to create electrical joints 175, for example, to cause solder to flow.

[0050] Given the rigidity of the adjacent dematching layer 140 opposite the chip 170, and to provide greater resistance to deformation caused by the heat used to attach the adjacent chip 170, the flexible circuit material layer 150 is tiled. The flexible circuit material is divided into multiple (e.g., two, three, four, or more) tiles. In the case of a large number (e.g., hundreds or thousands) of transducer elements 135, the flexible circuit material layer 160 connecting the chip 170 to the acoustic elements 135 is large and complex, with higher circuit routing and an increasing number of vias, while the features on the flex circuit are small (the vias on the flex circuit are small and the lines / traces are thin). With COA technology, using a single, large flex circuit to achieve a larger aperture 2D matrix transducer is uneconomical. Alternatively, tiling is not used. Instead, a single sheet or stack of sheets is used that extends the entire array reach.

[0051] refer to Figure 3 and Figure 4 , the flexible circuit material layer 160 is divided into two or more tiles 162 such that different tiles 162 are electrically connected to different ones of the transducer elements 135. The divided tiles 162 are connected to different groups of elements 135 (indicated by circles), thereby forming four tiles 162 in the same plane or distributed along azimuth and / or elevation angles.

[0052] Figure 3 An embodiment using tiling is shown. Four separate sheets 164 of flexible circuit material form a flexible circuit material layer 160. Each separate sheet 164 is a separate tile 162 of the flexible circuit material layer 160. The separate sheets 164 are arranged in the same plane. Multiple small-sized flex circuits are tiled on the dematching layer 140, replacing a single large flex circuit. With smaller flex circuit sizes, flex manufacturing process yield and cost can be improved. Compared to a single large flex circuit, the small and tiled flex circuits can further reduce the thermal deformation mismatch between the dematching layer 140 and the flexible circuit material layer 160, thereby enabling high-temperature processes for attaching chips 170, such as reflow soldering and ACF thermocompression bonding, which are preferred ASIC interconnects due to their excellent reliability. One or more chips 170 are mounted on each tile 162.

[0053] Figure 4 Another method for laying out a layer of flexible circuit material 160 is shown. The sheet or layer of flexible circuit material 160 is divided into a plurality of tiles 162 as sheets having gaps 400 formed therein. The small gaps 400 are introduced into the flexible circuit material layer 160 and these gaps 400 minimize thermal deformation mismatch (if any) between the flexible circuit material layer 160 and the dematching layer 140 during high temperature processes for die attach, such as reflow soldering and ACF thermocompression bonding. Figure 4Two slits 400 are shown forming a "+" pattern. Other patterns of slits 400 may be used, such as one slit in azimuth or elevation. Slits 400 may be of any thickness, such as less than the pitch of elements 135 (e.g., 1 / 2 or 1 / 4). Slits 400 extend less than the entire length or width of flexible circuit material layer 160. Alternatively, slits 400 extend along the entire width or length, thereby forming separate sheets 164. Other tilings may also be used. Slits 400 may be formed completely through the thickness of the sheet. Slits 400 extending less than the entire thickness of flexible circuit material layer 160 may be used.

[0054] One or more integrated circuit chips 170 are connected to the flexible circuit material layer 160. The integrated circuit chip 170 is an integrated circuit, such as Figure 1 , analog circuits, digital circuits, switches, multiplexers, controllers, processors, digital signal processors, field programmable gate arrays, or other active electrical components now known or later developed. Integrated circuit chip 170 may be in the form of a chip that is an integrated circuit.

[0055] Active electrical components are semiconductors, such as transistor devices. The term "active" is used to describe the type of device, not its operation. Transistor-based or switch-based devices are active, while resistors, capacitors, or inductors are passive devices. Active electrical devices are one or more integrated circuits, such as ASICs.

[0056] Semiconductor or active electronic devices include transmit and / or receive circuitry for ultrasound scanning using the acoustic array of element 135. For example, multiple transmit circuits may be provided as a semiconductor chip, multiple receive circuits may be provided as a semiconductor chip, and a controller may be provided as a semiconductor chip. The transmit components may be separate from the receive components or may be integrated with the receive components. The transmit components may include a high-voltage pulser, a filter, a memory, a delay, a phase rotator, a multiplier, a combination thereof, or other transmit beamformer components now known or later developed. The receive components may include a filter, an amplifier, a delay, an adder, a combination thereof, or other receive beamformer components now known or later developed. Because the receive beamformer components may operate at a lower voltage than the transmit components, the receive and transmit components may be separate devices (e.g., separate chips or integrated circuits), but a combined device for transmit and receive operations may be provided. Integrated circuit chip 170 includes all or part of the transmit beamformer, pulser, receive beamformer, amplifier, phase rotator, delay, adder, and / or other active electronic components used for ultrasound scanning.

[0057] The semiconductor chip includes input / output (I / O) pads. The semiconductor chip includes I / O conductors exposed on the largest surface. In alternative embodiments, the pads are located away from the chip edge and distributed across the largest surface via wire bonding or flexible circuit routing. The I / O pads are conductors formed on chip 170. Cu pillars, electrodes, traces, vias, or other conductive structures can be used for the I / O pads.

[0058] Flexible circuit material layer 160 is bonded to chip 170, for example, using flip-chip mounting. Epoxy or other bonding material secures flexible circuit material layer 160 to integrated circuit chip 170 at joints 175. The bonding material can also form electrical connections between the chip's input / output pads and pads or vias on flexible circuit material layer 160. For example, anisotropic conductive film (ACF) or solder can be used. In one embodiment, Cu stud bump joints (e.g., a Sn-Ag-Cu composition) with solder caps are used. Chip 170 is placed face-down on flexible circuit material layer 160. Joints 175 are formed to the pads (caps of the Cu stud bump joints) by high-temperature reflow to melt the solder caps (e.g., temperatures >250°C). Other connections for physical and / or electrical connection can be used, such as roughened contacts with epoxy bonding.

[0059] Figure 1 An embodiment is shown in which two or more tiled chips 170 are connected to the flexible circuit material layer 160, but connected to different tiles 162 due to gaps 400. In one embodiment, a single chip 170 is used and therefore connected to all tiles 162, or to a single flexible circuit sheet if tiling is not used. A larger number of acoustic elements 135 and corresponding apertures result in a larger chip 170 to process the acoustic signals. Larger chips 170 are more expensive because they are more likely to have defects during semiconductor processing. To reduce the size of the chip 170, two or more chips 170 are tiled in the same or different tiling pattern (footprint, shape, and / or orientation) as the tiles 162 of the flexible circuit material layer 160.

[0060] The I / O of chip 170 is electrically connected to the transducer elements 135. The transducer elements 135 are electrically connected to the integrated circuit chip 170 through slit portions of the dematching layer 140 and vias in the flexible circuit material layer 160. An electrically independent path is provided from the one or more integrated circuit chips 170 to each element 135. A ground return path is connected from the one or more integrated circuit chips 170, through the flexible circuit material layer 160, and through the dematching layer 140 to the ground return layer 150.

[0061] Figure 9is a flow chart of one embodiment of a method for forming an acoustic transducer. The ground path is connected through an extended dimension dematching layer and / or a flat layer of flexible circuit material.

[0062] This method forms Figure 1 The array system or another array system is implemented as a manufacturing method for the array system and / or probe. A technician or robot uses, for example, a guidepost or frame to stack and align the probes. An oven, iron, induction welder, press, and / or wave bath are used to bond or interconnect the probes. A frame, housing, fixture, or holder is used to form and position the probes in the probe housing.

[0063] Additional, different, or fewer actions may be used. For example, action 500 incorporates the flex circuit without tiling. As another example, action 540 is not performed. In another example, actions are provided for adding matching layers, lenses, or other probe components. In yet another example, testing of components, portions, subassemblies, and / or entire assemblies is provided. These actions may be performed in the order shown or in other orders.

[0064] In act 500, a patch of flexible circuit material is bonded to the dematching layer 140. For example, separate pieces of flexible circuit material are bonded to different portions of the dematching layer 140 in the same plane (see Figure 3 As another example, a sheet of flexible circuit material having slots 400 forming tiles 162 is bonded to the dematching layer 140 (see Figure 4 ). Figure 6 An example of a dematching layer 140 is shown bonded to a layer of flexible circuit material 160. The dematching layer 140 will bond to the piezoelectric layer 130, thus also acting as a bonding layer for subsequent attachment.

[0065] In one embodiment, the dematching layer 140 is electrically connected to the flexible circuit material layer 160 using one or more of a variety of bonding materials, such as epoxy, Ag paste, solder, anisotropic conductive film (AFC), or anisotropic conductive paste (ACP). ACF / ACP is a composite film / paste consisting of a base resin (epoxy or acrylic) and conductive spheres / beads (polymer core plated with Ni / Au) dispersed within the base resin. These materials are placed between the dematching layer 140 and the pads of the flexible circuit material layer 160. During thermocompression bonding, the conductive spheres within the ACF / ACP are trapped between the pads, providing a current path. The flexible circuit material layer 160 provides a vertical electrical connection between the integrated circuit chip 170 mounted beneath the flexible circuit material layer 160 in act 510 and the acoustic element 135 later formed in act 520, as well as signal routing from the transducer toward the ultrasound system.

[0066] In act 510, one or more semiconductor chips 170 are attached to the flexible circuit material layer 160 opposite the dematching layer 140. This attachment uses the application of heat to provide a physical and electrical connection. After the patch 162 of flexible circuit material is bonded to the dematching layer 140, the semiconductor chips 170 are attached to the flexible circuit material. Figure 7 An example is shown.

[0067] This attachment utilizes any die attach method, such as reflow soldering or ACF thermocompression bonding. This attachment utilizes thermoformed joint 175. Because dematching layer 140 is inherently very rigid (elastic modulus > 530 GPa), it provides dimensional stability to flexible circuit material layer 160 for various die attach processes. Compared to the elastic modulus and thermal expansion coefficient of flexible circuit material layer 160 (20 GPa and 18 ppm / °C), the higher elastic modulus and lower thermal expansion coefficient of dematching layer 140 (5-6 ppm / °C) suppress thermal expansion of the flexible circuit material during various high-temperature processes (e.g., soldering or ACF bonding), thereby reducing the thermal deformation mismatch between integrated circuit die 170 and flexible circuit material layer 160. This also helps maintain a flat chip-flex circuit assembly without any undesirable bending or warping. Additionally, this configuration can reduce stress induced at the solder joint 175 due to thermal deformation mismatch between the integrated circuit chip 170 and the flexible circuit material during cooling after reflow soldering at a temperature of ˜250° C., thereby improving joint reliability.

[0068] In act 520, the array of transducer elements 135 is stacked on the dematching layer 140. The stack may have the layer before cutting, or may have the array already cut. The stack before cutting is further described below.

[0069] In act 510, an integrated circuit chip is attached (see Figure 7 ), various acoustic layers (eg, the PZT layer 130 and the first acoustic matching layer 120) are laminated on the dematching layer 140, as shown in FIG. Figure 8 As shown in .

[0070] The array layer is stacked on the dematching layer. The dematching layer has a larger surface area on the first surface than the area of the largest surface of the array. This results in the dematching layer extending beyond the array, as shown in FIG. Figure 1 and Figure 8 As shown in .

[0071] After lamination or bonding, the elements 135 are formed. The matching layer 120, PZT layer 130, and dematching layer 140 are cut to form slits 190. Any cutting pattern can be used, such as a cross or parallel cutting pattern. The cutting creates an array of elements 190 that are separated from each other. Figure 9 An example is shown.

[0072] In act 530, a ground plane layer 150 is laid down on the array. The ground plane layer 150 is a sheet or foil that is laminated over the elements 135 of the array and onto the dematching layer 140. Extensions of the dematching layer 140 are used as pads for electrical and physical connection to the ground plane layer 150.

[0073] A ground plane layer 150 is conductive and is attached to the cut array to provide a ground return path in the transducer. Figure 10 An example is shown. The dematching layer 140 is longer than the piezoelectric layer 130 and the first acoustic matching layer 120. One end of the conductive ground plane layer 150 terminates on the dematching layer 140 extending beyond the piezoelectric layer 130 and the first acoustic matching layer 120.

[0074] In act 540, the ground plane 150 is connected to the dematching layer 140 outside of the largest surface footprint of the array. Various bonding materials can be used to terminate the ground return layer 150 on the dematching layer 140, such as epoxy, silver paste, and ACP.

[0075] The laid ground plane 150 may also be bonded to the array, for example, using epoxy. Alternatively, a loose fit or press fit may be provided. The piezoelectric layer 130 and the first acoustic matching layer 120 are active acoustic apertures for generating ultrasonic waves in the transducer's transmit mode and receiving reflected ultrasonic waves in the receive mode.

[0076] like Figure 11 As shown in FIG, the second acoustic matching layer 100 may be stacked or laid on the ground layer 150. The second acoustic matching layer 100 is bonded or press-fitted to the ground layer 150.

[0077] The various bonding or attachments occur sequentially. The PZT layer 130 and first matching layer 120 can be bonded together and to the dematching layer 140 in one bonding step (ie, simultaneously). Lenses can be added to the stack.

[0078] Regardless of how the grammatical term is used, the term includes individuals with male, female, or other identities.

[0079] Although the present invention has been described above with reference to various embodiments, it will be appreciated that many changes and modifications may be made without departing from the scope of the invention. Therefore, the foregoing detailed description is intended to be illustrative rather than restrictive, and it is to be understood that the appended claims, including all equivalents, are intended to define the spirit and scope of the invention.

Claims

1. A multi-dimensional transducer array system, comprising: an acoustic array having transducer elements distributed in a grid in two dimensions in a first region; a dematching layer adjacent to the acoustic array, the dematching layer having a second area larger than the first area such that at least a first portion extends beyond a footprint of the acoustic array, the dematching layer being electrically conductive; a ground return layer adjacent to the acoustic array on a side opposite the dematching layer, the ground return layer extending to the dematching layer; a layer of flexible circuit material adjacent to the dematching layer, the flexible circuit material being divided into a plurality of tiles; as well as An integrated circuit chip is connected to the flexible circuit material layer, wherein a ground path is connected from the integrated circuit chip, through the flexible circuit material layer, and through the dematching layer to the ground return layer.

2. The multi-dimensional transducer array system according to claim 1, wherein: The transducer elements are electrically connected to the integrated circuit chip through the slit portions of the dematching layer and the vias in the flexible circuit material layer, respectively.

3. The multi-dimensional transducer array system according to claim 1, wherein: The integrated circuit chip comprises an application specific integrated circuit flip chip mounted to the layer of flexible circuit material.

4. The multi-dimensional transducer array system according to claim 1, wherein: The transducer elements are separated by slits and each include a matching layer, a piezoelectric layer, a slit portion of the dematching layer, and a signal electrode, and wherein the ground return layer is not slit and is adjacent to the matching layer.

5. The multi-dimensional transducer array system according to claim 1, wherein: The ground return layer includes a metal sheet that is bent at an edge of the acoustic array to connect with the first portion of the dematching layer that extends beyond a footprint of the acoustic array.

6. The multi-dimensional transducer array system according to claim 5, wherein: The dematching layer has first and second portions extending beyond a footprint of the acoustic array, and wherein the metal sheet is connected to both the first and second portions of the dematching layer.

7. The multi-dimensional transducer array system according to claim 1, wherein: The dematching layer includes tungsten carbide.

8. The multi-dimensional transducer array system according to claim 1, wherein: The layer of flexible circuit material is divided into multiple tiles that are separate sheets in the same plane.

9. The multi-dimensional transducer array system according to claim 1, wherein: The flexible circuit material layer is divided into a plurality of pieces as sheets having slits formed therein.

10. A transducer array system comprising: transducer elements in an array; a ground layer distributed over the transducer elements of the array; an integrated circuit chip electrically connected to the transducer element; as well as a dematching layer between the array and the integrated circuit chip, the dematching layer being conductive and having a portion not covered by the array; The ground layer extends from above the transducer elements of the array to a portion of the dematching layer not covered by the array.

11. The transducer array system according to claim 10, wherein: The dematching layer includes tungsten carbide.

12. The transducer array system according to claim 10, wherein: The array has a first area in a plane parallel to the acoustic surface, and the dematching layer has a second area parallel to the plane, the second area being larger than the first area by the area of the fraction.

13. The transducer array system according to claim 10, wherein: The ground layer includes a metal sheet that is bent at an edge of the array to connect to the dematching layer.

14. The transducer array system of claim 10, further comprising a sheet of flexible circuit material between the dematching layer and the integrated circuit chip, the sheet being divided into two or more tiles such that different tiles are electrically connected to different ones of the transducer elements.

15. A method for forming an acoustic transducer, the method comprising: bonding the piece of flexible circuit material to the dematching layer; attaching a semiconductor chip to the flexible circuit material, the attachment being achieved using the application of heat; as well as An array of transducer elements is stacked on the dematching layer.

16. The method according to claim 15, wherein Bonding tiles includes bonding separate sheets of the flexible circuit material in the same plane to different portions of the dematching layer.

17. The method according to claim 15, wherein: Bonding the tile includes bonding a sheet of the flexible circuit material to the dematching layer, the sheet having a gap forming the tile.

18. The method according to claim 15, wherein Attaching includes attaching the semiconductor chip to the flexible circuit material after the patch of flexible circuit material is bonded to the dematching layer, and wherein applying heat includes reflow soldering or anisotropic conductive film thermocompression bonding.

19. The method according to claim 15, wherein Stacking includes stacking the array on the dematching layer, wherein the dematching layer has a larger surface area on a first surface than an area of a largest surface of the array, such that the dematching layer extends beyond the array, and further includes laying a ground plane on the array and connecting the ground plane to the dematching layer outside the footprint of the largest surface of the array.

Images