PATENT DOCUMENT

Publication Number: US-9681570-B2
Application Number: US-201414487869-A
Country: US
Kind Code: B2

Title: Welded high-density low-profile interconnect system

Abstract:
An electronic device may have printed circuits to which electrical components are mounted. The printed circuits may have metal traces that form signal lines and contact pads. Vias or other conductive structures may be used in interconnecting the signal lines to the contact pads. The contact pads may have elongated shapes or other shapes and may be formed in arrays on the printed circuits. Laser welds or other electrical connections may be used to join contact pads on a first printed circuit to respective contact pads on a second printed circuit. The laser welds may form part of a rectangular region of welds or may form part of a non-rectangular region of welds such as a region with a curved edge. Alignment marks may be used in aligning the contact pads.

Claims:
What is claimed is: 
     
       1. An apparatus, comprising:
 a first printed circuit having a first metal trace and a first elongated contact; 
 a second printed circuit having a second metal trace and a second elongated contact, wherein the first printed circuit extends along a first axis, the second printed circuit extends along a second axis that is oriented at a non-zero angle with respect to the first axis, the first elongated contact extends in parallel with the first axis and an edge of the first printed circuit, and the second elongated contact extends in parallel with the second axis and an edge of the second printed circuit; and 
 a laser weld that couples the first metal trace to the second metal trace, wherein the first and second contacts partially overlap and are welded together with the laser weld. 
 
     
     
       2. The apparatus defined in  claim 1  wherein the first metal trace has a first signal line and wherein the second metal trace has a second signal line. 
     
     
       3. The apparatus defined in  claim 1  wherein the first and second axes are orthogonal to each other. 
     
     
       4. The apparatus defined in  claim 1  wherein the first and second axes are oriented at an angle of 45° with respect to each other. 
     
     
       5. The apparatus defined in  claim 2  wherein the first elongated contact is one of a first array of elongated contacts on the first printed circuit, wherein the second elongated contact is one of a second array of elongated contacts on the second printed circuit, and wherein the laser weld is one of an array of laser welds each of which couples a respective elongated contact in the first array of elongated contacts to a respective elongated contact in the second array of elongated contacts. 
     
     
       6. The apparatus defined in  claim 5  wherein the array of laser welds has a rectangular outline. 
     
     
       7. The apparatus defined in  claim 5  wherein the array of laser welds has a non-rectangular outline. 
     
     
       8. The apparatus defined in  claim 7  further comprising:
 an electronic device housing in which the first and second printed circuits are located; and 
 a structure in the electronic device housing, wherein the first and second printed circuits and the array of laser welds have shapes that accommodates the structure. 
 
     
     
       9. The apparatus defined in  claim 8  wherein at least one of the first and second printed circuits has a curved edge that runs around the structure. 
     
     
       10. The apparatus defined in  claim 5  further comprising:
 a first array of vias coupled to each of the elongated contacts in the first array of elongated contacts; and 
 a second array of vias coupled to each of the elongated contacts in the second array of elongated contacts. 
 
     
     
       11. An apparatus, comprising:
 a first flexible printed circuit comprising metal traces forming a first set of contact pads, wherein the first flexible printed circuit has a first curved edge; 
 a second flexible printed circuit comprising metal traces forming a second set of contact pads, wherein the second flexible printed circuit has a second curved edge; 
 an electronic device component, wherein the first curved edge and the second curved edge accommodate the electronic device component, the second flexible printed circuit overlaps a non-rectangular region of the first flexible printed circuit, and the first curved edge defines an edge of the non-rectangular region; and 
 welds that respectively join each of the contact pads in the first set of contact pads to a corresponding one of the contact pads in the second set of contact pads, wherein the electronic device component is formed adjacent to the first curved edge of the first flexible printed circuit and the second curved edge of the second flexible printed circuit, the first flexible printed circuit extends along a first longitudinal axis, and the second flexible printed circuit extends along a second longitudinal axis that is oriented at a non-zero angle with respect to the first longitudinal axis. 
 
     
     
       12. The apparatus defined in  claim 11  wherein the welds are laser welds. 
     
     
       13. The apparatus defined in  claim 12  further comprising an electrical component soldered to the first flexible printed circuit. 
     
     
       14. The apparatus defined in  claim 11  wherein the first and second flexible printed circuits have respective first and second alignment marks. 
     
     
       15. The apparatus defined in  claim 11 , wherein the electronic device component comprises a component selected from the group consisting of: a speaker, a support structure, an integrated circuit, an electronic device housing structure, a microphone, a sensor, a status indicator, a vibrator, and a light-emitting component.

Description:
BACKGROUND 
     This relates generally to electronic devices, and, more particularly, to interconnecting printed circuits in electronic devices. 
     Electronic devices include electronic components such as integrated circuits, sensors, and other circuitry. Electronic components may be mounted on printed circuit boards. Printed circuits may also be used to form signal cables. 
     Plastic connectors with interlocking met pins can be soldered to printed circuit substrates. To interconnect the signal paths on one printed circuit to the signal paths on another printed circuit, mating connectors on the two printed circuits can be plugged into each other so that the pins of the connectors form electrical connections. Connectors such as these can be time consuming to design and test, sometimes consume more volume than desired, and do not always provide as much electromagnetic shielding as desired. Cowlings may be used to ensure that connectors do not become detached from one another during as drop event or other stress on a device, but the use of cowlings may consume valuable space within an electronic device. Connector footprints tend to be rectangular, but reliance on rectangular connectors can make it difficult or impossible to efficiently accommodate non-rectangular printed circuit connection regions. 
     It would therefore be desirable to be able to provide improved ways in which to interconnect printed circuits in an electronic device. 
     SUMMARY 
     An electronic device may have printed circuits to which electrical components are mounted. The printed circuits may have metal traces that form signal lines and contact pads. The printed circuits may contain vias such as through vias and blind vias. Vias or other conductive structures may be used in interconnecting the signal lines and the contact pads. 
     The signal lines on overlapping printed circuits can be joined by forming welds between mating contact pads. No connectors are needed, so the weld-based interconnection region may exhibit a low profile. Welds May be used to form robust permanent connections. 
     The contact pads may have elongated shapes or other shapes to facilitate alignment operations. Contacts may be formed in arrays on the printed circuits. Laser welding or other techniques may be used in joining contact pads on a first printed circuit with respective contact pads on a second printed circuit. The laser welds may form part of a rectangular region of welds or may form part of a non-rectangular region of welds such as a region with a curved edge that accommodates a structure within an electronic device. Alignment marks may be used in aligning arrays of mating contacts on overlapping printed circuits. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative electronic device in accordance with an embodiment. 
         FIG. 2  is a cross-sectional side view of an illustrative electronic device in accordance with an embodiment. 
         FIG. 3  is a diagram of illustrative equipment that may be used in forming interconnections between printed circuits in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of an illustrative pair of printed circuits being aligned, and interconnected using machine vision equipment and laser welding equipment in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an illustrative via structure that may be used to facilitate welding of contact pads in first and second printed circuits in accordance with an embodiment. 
         FIG. 6  is a cross-sectional side view of an illustrative printed circuit having a through via and a blind via in accordance with an embodiment. 
         FIG. 7  is a top view of a pair of printed circuits being interconnected using an array of overlapping elongated contact pads in accordance with an embodiment. 
         FIG. 8  is a top view of a pair of printed circuits of the type that may be interconnected using welded connections following a reflow process in which components are soldered to the printed circuits in accordance with an embodiment. 
         FIG. 9  is a cross-sectional side view of an illustrative electrical connection between printed circuit contacts in which a layer of solder is used to facilitate formation of the connection in accordance with an embodiment. 
         FIG. 10  is a top view of printed circuits being interconnected using multiple regions of selectively welded interconnections in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electrical components in an electronic device may be interconnected using signal paths in printed circuits. Printed circuits may be joined with each other using selectively formed connections such as welded connections. The selectively formed connections may be formed at the intersections between signal lines on one printed circuit and signal lines on another printed circuit. 
     An illustrative electronic device of the type that may include printed circuits that are interconnected using selectively formed connections is shown in  FIG. 1 . Electronic device  10  may be a computing device such as a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, a device embedded in eyeglasses or other equipment worn on a user&#39;s head, or other wearable or miniature device, a television, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, equipment that implements the functionality of two or more of these devices, or other electronic equipment. 
     As shown in  FIG. 1 , electronic device  10  may have control circuitry  16 . Control circuitry  16  may include storage and processing circuitry for supporting the operation of device  10 . The storage and processing circuitry may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in control circuitry  16  may be used to control the operation of device  10 . The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors and other wireless communications circuits, power management units, audio chips, application specific integrated circuits, etc. 
     Input-output circuitry in device  10  such as input-output devices  18  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output devices  18  may include buttons, joysticks, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors such as touch sensors, proximity sensors, ambient light sensors, compasses, gyroscopes, accelerometers, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device  10  by supplying commands through input-output devices  18  and may receive status information and other output from device  10  using the output resources of input-output devices  18 . 
     Input-output devices  18  may include one or more displays. Device  10  may, for example, include a touch screen display that includes a touch sensor for gathering touch input from a user or a display that is insensitive to touch. A touch sensor for a display in device  10  may be based on an array of capacitive touch sensor electrodes, acoustic touch sensor structures, resistive touch components, force-based touch sensor structures, a light-based touch sensor, or other suitable touch sensor arrangements. 
     Power the device  10  may be provided by an external source of power and/or an internal battery. The components for device  10  such as circuitry  16  and devices  18  and other structures in device  10  may be implemented using integrated circuits, discrete components (e.g., resistors, capacitors, and inductors), microelectromechanical systems (MEMS) devices, portions of housing structures, packaged parts, and other devices and structures. 
     Control circuitry  16  may be used to run software on device  10  such as operating system code and applications. During operation of device  10 , the software running on control circuitry  16  may display images for a user on one or more displays and may use other internal components such as input-output devices  18 . Device  10  may use communications circuits to send and receive wireless and wired data. For example, device  10  may use light-emitting components to transmit data and may use light-receiving components to receive transmitted light signals. Device  10  may also use light-emitting components, light-receiving components, audio components, capacitive sensors, microelectromechanical systems devices, and other components as sensors and output devices. Device  10  may use wireless circuits in circuitry  16  (e.g., a baseband processor and associated radio-frequency transceiver circuitry) to transmit and receive wireless signals. For example, device  10  may transmit and receive cellular telephone signals and/or wireless local area network signals or other wireless data. 
     A cross-sectional side view of an illustrative electronic device is shown in  FIG. 2 . As shown in  FIG. 2 , device  10  may have a housing such as housing  12 . Housing  12 , which may sometimes be referred to as an enclosure or case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of any two or more of these materials. Housing  12  may be formed using a unibody configuration in which some or all of housing  12  is machined or molded as a single structure or may be formed using multiple structures (e.g., an internal frame structure, one or more structures that form exterior housing surfaces, etc.). Device  10  may have inner housing structures that provide additional structural support to device  10  and/or that serve as mounting platforms for printed circuits and other structures. Structural internal housing members may sometimes be referred to as housing structures and may be considered to form part of housing  12 . 
     Device  10  may have a display such as display  14 . Display  14  may be a touch screen display that incorporates a layer of conductive capacitive touch sensor electrodes or other touch sensor components (e.g., resistive touch sensor components, acoustic touch sensor components, force-based touch sensor components, light-based touch sensor components, etc.) or may be a display that is not touch-sensitive. Capacitive touch screen electrodes may be formed from an array of indium tin oxide pads or other transparent conductive structures. 
     Display  14  of device  10  may be formed from a display module such as display module  22  mounted under a cover layer such as display cover layer  20  (as an example). Display  14  (display module  22 ) may be a liquid crystal display, an organic light-emitting diode display, a plasma display, an electrophoretic display, a display that is insensitive to touch, a touch sensitive display that incorporates and array of capacitive touch sensor electrodes or other touch sensor structures, or may be any other type of suitable display. Display cover layer  20  may be planar or curved and may be formed from clear glass, a transparent plastic member a transparent crystalline member such as a sapphire layer, clear ceramics, other transparent materials, or combinations of these structures. 
     Electrical components  26  may be mounted within the interior of housing  12 . Components  26  may be mounted to printed circuits such as printed circuit  24  within the interior of housing  12 . Printed circuit  24  may be a rigid printed circuit board (e.g., a printed circuit board formed from fiberglass-filled epoxy or other rigid printed circuit board material) or may be a flexible printed circuit (e.g., a printed circuit formed from a sheet of polyimide or other flexible polymer layer). Patterned metal traces within primed circuit board  24  may be used to form signal paths between components  26 . If desired, components such as connectors may be mounted to printed circuit  24 . As shown in  FIG. 2 , for example, a cable such as flexible printed circuit cable  28  may couple display module  22  to connector  30 . Connector  30  may couple cable  28  to traces within printed circuit  24 . When coupled as shown in  FIG. 2 , signals associated with operation of display  14  may pass to display module  22  from signal lines in printed circuit  24  through cable  28  and connector  30 . 
     The use of connectors such as connector  30  can be minimize or even eliminated using connections such as welded connections between overlapping signal traces on respective printed circuits. Illustrative equipment of the type that may be used in forming welded interconnections between printed circuits is shown in  FIG. 3 . As shown in  FIG. 3 , printed circuits and components  40  (e.g., printed circuits  24  and components  26 ) may be processed using inspection equipment  42 , patterning tools  44 , lamination tools  46 , soldering and welding equipment  48 , and other equipment. 
     Patterning tools  44  may be used in forming desired patterns of signal lines in printed circuits  24 . Metal traces for printed circuit signal paths may be patterned using photolithography, by evaporating metal through a shadow mask, by stamping a desired metal pattern into a layer of metal foil, or using other suitable patterning techniques. Patterning tools  44  may include cutting tools, etching tools, deposition equipment, equipment for machining metal and other structures, drilling equipment, and other suitable equipment. 
     Inspection equipment  42  may include manually controlled and/or automated equipment for inspecting the structures associated with components and primed circuit structures  40  before assembly and during manufacturing operations. Equipment  42  may include optical inspection equipment, visible light inspection equipment, infrared light inspection equipment, X-ray inspection equipment, equipment that uses microscopes and other optical equipment to gather images of structures  40 , and equipment that digitizes images so that digitized image data may be used in automatically aligns structuring and otherwise processing structures  40 . Equipment  42  may include machine vision equipment that digitally captures images of structures  40  using optical camera equipment, X-ray camera equipment, or other image sensor. Information gathered on structures  40  using a machine vision system or other inspection equipment may be used by the other equipment of  FIG. 3  in processing components and printed circuit structures  40 . For example, machine vision data from equipment  42  may be used to align metal traces on first and second printed circuit boards with each other and may be used to position a laser welding beam at a desired location relative to the metal traces. 
     Lamination tools  46  may be used to attach printed circuit layers together. For example, lamination tools  46  may be used to attach metal interconnect layers and dielectric layers in a stack that forms a printed circuit (e.g., printed circuit  24 ). Adhesive may optionally be used in attaching layers together. Tools  46  may attach metal layers to dielectric substrate layers such as layers of polyimide, other polymers, fiberglass-filled epoxy for rigid printed circuit board substrates, etc. Metal traces may be formed on printed circuit board substrates by depositing blanket metal layers and patterning the deposited layers using patterning tools  44  or may be patterned prior to attachment to a printed circuit hoard structure using lamination tools  46 . 
     Soldering, and welding equipment  48  may be used to attach components to printed circuits in structures  40 . For example, soldering equipment such as a reflow oven or hot bar may be used to heat solder paste on a printed circuit sufficiently to melt the solder and thereby attach an electrical component to that printed circuit. Soldering equipment (e.g., a hot bar) may also be used in forming solder connections between interconnect lines in respective overlapping printed circuits. With one suitable arrangement, which may sometimes be described herein as an example, laser welding equipment or other welding equipment is used to selectively weld metal traces together from different printed circuits. 
     A first printed circuit and a second printed circuit may, for example, be provided with respective metal trace segments. These metal trace segments may overlap in an array pattern. Laser welding may be used to weld together some of the metal trace segments from the first printed circuit and some of the metal trace segments from the second printed circuit. The pattern of laser welds that is formed in this way can serve as a connector that joins the signal lines on the first printed circuit to the signal lines on the second printed circuit. 
     The welds may consume less vertical space (i.e., less height) than a plastic connector that is soldered to the printed circuits, allowing the welded printed circuit area to serve as a low-profile connector. The density of the welds (i.e., the weld-to-weld pitch) may be 10-100 microns, more than 20 microns, less than 30 microns, less than 15 microns, or other suitable density. If desired for example, the welded printed circuits may form a high density connector. The shape of the printed circuits that are being coupled and the corresponding shape of the Welded area can have curved edges or other shapes that help the printed circuit avoid internal device components while efficiently using area mailable within device  10  to provide suitable printed-circuit-to-printed-circuit connections. 
     A cross-sectional side view of an illustrative pair of printed circuits that are being interconnected in this way is shown in  FIG. 4 . As shown in  FIG. 4 , printed circuits  24 A and  24 B may overlap sufficiently to allow circuit-to-circuit connections such as connection  66  to be formed. Printed circuit  24 A has metal traces  62  in dielectric substrate  74 A. Printed circuit  24 B has metal traces  64  in dielectric substrate  74 B. Dielectric substrates  74 A and  74 B may be rigid and/or flexible substrates formed from layers of flexible polyimide or other flexible printed circuit polymer substrate material rigid printed circuit board material, or other insulating substrate material. Metal traces  62  and  64  may be formed in one or more layers within printed circuits  24 A and  24 B (i.e., printed circuits  24 A and/or  24 B may be single layer printed circuits or multilayer printed circuits). 
     Each connection  66  may be a welded connection or other conductive connection that shorts a trace in printed circuit  24 A such as trace  62  to a trace in printed circuit  24 B such a trace  64 . There may be any suitable number of connections between the traces of printed circuits  24 A and  24 B (e.g., one or more, two or more, ten or more 100 or more, less than 500, less than 200, 10-100, etc.). A single connection such as connection  66  is shown in  FIG. 4  to avoid over-complicating the drawings. 
     Connections such as connection  66  may be formed by welding. As an example, connections such as connection  66  may be formed by laser welding using equipment  48 . Equipment  48  may include a laser such as laser  52 . Laser  52  may produce a laser beam such as laser beam  60  that is focused onto printed circuits  24 A and  24 B to weld together overlapping traces such as traces  62  and  64 , thereby forming welded connection  66 . Laser beam  60  may be an infrared light beam, a visible light beam, or other laser beam. A computer-controlled positioner such as positioner  4  may be used to adjust the position of laser beam  60  (e.g., by moving the position of laser  52 , by adjusting mirror positions, etc.) so that beam  60  is directed onto the locations in printed circuits  24 A and  24 B where contact pads are overlapping. If desired computer-controlled positioners such as positioners  56  may be used to move printed circuits  24 A and/or  24 B relative to laser  52  in addition to or instead of moving laser  52  and beam  60  relative to printed circuits  24 A and  24 B. 
     Before welding traces  62  and  64  to each other, printed circuits  24 A and  24 B should be aligned with each other, so that appropriate portions of traces  62  and  64  (i.e., contact pad portions) overlap as desired. Computer-controlled positioners  56  may be used to perform alignment operations. To assist in performing alignment operations, machine vision equipment such as inspection equipment  42  may be used to observe the relative positions of printed circuits  24 A and  24 B. Printed circuits  24 A and  24 B may have alignment marks such as alignment mark  68  in printed circuit  24 A and alignment mark  70  in printed circuit  24 B. Alignment marks  68  and  70  may be formed from metal traces or other suitable structures in printed circuits  24 A and  24 B. Alignment marks  68  and  70  may have the shape of crosses, circles, nested squares, segmented squares or crosses, lines, dots, or other suitable shapes. In the example of  FIG. 4 , alignment mark  68  has an opening such as opening  72  within which alignment mark  70  is visible when marks  68  and  70  are in alignment with each other. 
     The locations of alignment marks  68  and  70  may be observed using visual light cameras, infrared light cameras, x-ray cameras, or other inspection equipment  42 . To facilitate visual alignment of marks  68  and  70  to each other, it may be desirable to form some or all of printed circuits  24 A and or  24 B from a transparent or semi-transparent substrate material (e.g., clear or amber polyimide). For example, upper layer  24 A may be formed from a material that is transparent in the visible spectrum so that a visible-light camera in system  42  can observe the position of lower-layer alignment mark  70  through the substrate material of upper layer  24 A. 
     In some applications it may be desirable to form printed circuits in device  10  from a visually opaque material. In this type of scenario, the relative positions of alignment marks  68  and  70  may be observed using x-ray inspection equipment or an infrared image sensor that is able to penetrate the visibly opaque material. For example, the visibly opaque material may be formed from an infrared-transparent material (e.g., ink on a substitute, an additive in a polymer substrate, or other materials that are transparent at infrared wavelengths and opaque at visible wavelengths). Printed circuits  24 A and/or  24 B may also be treated with a coating or other material following printed circuit alignment and formation of welded connections. For example, a visually opaque material may be applied to printed circuits  24 A and/or  24 B following alignment of marks  68  and  70  and if desired following formation of welded connections  66 . 
     There may one or more different types of alignment marks on printed circuits  24 A and  24 B. For example, a single set of alignment marks may be used for coarse and fine alignment operations. As another example, a single set of coarse alignment marks may be formed so that time alignment operations are performed exclusively by observing the overlap and alignment of traces  62  and  64  with respect to each other. More alignment marks (e.g., coarse, medium, and fine alignment marks) may also be used. In some situations, coarse and fine alignment operations can be performed using only signal lines  62  and  64  or other alignment mark schemes may be used. 
     An advantage of using alignment marks  68  and  70  for coarse alignment is that the use of alignment marks may facilitate automatic alignment operations using machine vision equipment (e.g., camera(s) in equipment t) and computer-controlled positioners such as positioners  56 . Fine alignment operations such as operations involved in establishing final alignment between overlapping contact portions of traces  62  and  64  may be performed using an automated approach and/or manual alignment. For example, fine alignment may be performed by capturing images using system  42  and adjusting the positions of printed circuits  24  and  24 B accordingly. Laser beam  60  may likewise be aligned using computer-controlled positioner  54  to adjust laser  52  in equipment  48 . If desired, some or all of these operations may also be performed under the manual control of a technician (e.g., a technician controlling positioners  56  and/or  54 ). 
     During laser welding, the metal of overlapping portions of traces  62  and  64  is welded together and forms an electrical connection between traces  62  and  64  (i.e., laser welds such as welds  66  are formed). The pattern of welds that is established may follow a predetermined pattern (e.g., a two-dimensional matrix of N rows and M columns or a pattern of connections with other shapes) or may be selected dynamically to accommodate last-mute design changes, detected defects in printed circuits  24 A and/or  24 B, or other factors that might influence the desired placement of welds  66  on printed circuits  24 A and  24 B. The shape of the region of welds that is formed may be rectangular or may be non-rectangular. 
     As shown in  FIG. 5 , vias such as via  76  may be formed in printed circuit  24 A. Via  76  may be formed by plating metal traces  62  onto the inner surfaces of through hole  78  in printed circuit substrate  74 A. Because though hole  78  passes through substrate  74 A, vias such as via  76  may sometimes be referred to as through hole vias or through vias. As shown in  FIG. 5 , the presence of opening  78  in via  76  of printed circuit  24 A may help laser beam  60  to penetrate through to traces  64  on lower printed circuit  24 B during welding. 
     If desired, printed circuits  24  and/or  24 B may contain structures such as through vias and blind vias for interconnecting metal traces on different printed circuit layers. An illustrative configuration for printed circuit  24  in which both a through via and a blind via are present is shown in  FIG. 6 . As shown in the example of  FIG. 6 , printed circuit  24  may be formed form multiple layers of metal traces  84  on the upper and lower surfaces of one or more different dielectric layers  74 . Printed circuit  24  may contain one or more through vias such as through via  80 . Each through via may have an opening such as opening  82  that passes through one or more dielectric layers  74 . The interior of opening  82  may be coated with metal traces  84  to form a conductive path between respective layers of printed circuit  24 . Printed circuit  24  may also contain one or more blind vias such as blind via  86  having printed circuit substrate openings such as opening  88  that do not pass through all substrate layers  74  but rather pass through a subset of layers  74 . Metal traces  84  may coat the interior surface of each blind via opening  88  to form conductive paths between respective metal layers in printed circuit  24 . In the example of  FIG. 6 , via  86  interconnects metal traces  84  on the lowermost layer of printed circuit  24  with metal traces  84  in an embedded layer within printed circuit  24 . In general vias such as blind vias and through vias may be used to join metal traces on any suitable layers within a printed circuit. 
     Printed circuit  24  of  FIG. 6  (e.g., a printed circuit such as printed circuit  24 A or printed circuit  24 B) may have different numbers of layers in different areas. In the configuration of  FIG. 6 , for example, region  92  has three metal layers and two interposed layers of dielectric  74 . Whereas region  92  has two metal layers and a single interposed layer of dielectric  74 . Configurations for printed circuit  24  that have different numbers of layers in different areas or that have the same number of layers throughout printed circuit  24  may also be used. The configuration of  FIG. 6  is merely illustrative. 
     When it is desired to form welded interconnections between printed circuit  24 A and printed circuit  24 B, printed circuits  24 A and  24 B may be aligned so that portions of traces  62  such as contact pads in traces  62  in printed circuit  24 A overlap respective portions of traces  64  such as contact pads in traces  64  in printed circuit  24 B. The overlapping portions of the metal traces in printed circuits  24 A and  24 B (i.e., the overlapping contacts) may have any suitable shapes (e.g., crosses, perpendicular lines, square pads, circular pads, grid-shapes, shapes with curved edges, non-rectangular shapes with straight edges, shapes with combinations of curved and straight edges, etc.). An at of overlapping traces may be formed that has rows and columns of overlapping contact regions or overlapping traces may have other suitable layouts. 
     An illustrative interconnection pattern that may be used for joining traces  62  and  64  is shown in the top view of printed circuits  24 A and  24 B of  FIG. 7 . In the illustrative configuration of  FIG. 7 , two printed circuits are being interconnected by laser welds  66 . In particular, traces  62  on printed circuit substrate  74 A of printed circuit  24 A are being welded to traces  64  on printed circuit substrate  74 B of printed circuit  24 B using an array of laser welds  66 . 
     Printed circuits  24 A and  24 B overlap each other in to rectangular region containing a three-by-two array of contacts (contact pads) extending across lateral dimensions X and Y. Traces  62  on printed circuit  24 A include portions that form signal lines  62 - 1  that run along dimension Y. Traces  62  also include portions that form elongated contacts  62 - 3  that run along dimension Y. Lines  62 - 1  may be formed on the upper surface of substrate  74 A (or may be embedded within the substrate) and contacts  62 - 3  may be formed on the opposing lower surface of substrate  74 A. Traces  62  may include vias  62 - 2  that extend through substrate  74 A and electrically short lines  62 - 1  to respective contacts  64 - 3 . Contacts  64 - 3  may also include vias such as via  76  of  FIG. 5 . Traces  64  on printed circuit  24 B include portions that form signal lines  64 - 1  that run along dimension X. Traces  64  also include portions that form elongated contacts  64 - 3  that run along dimension X. Lines  64 - 1  may be formed on the lower surface of substrate  74 B (or may be embedded within substrate  74 B) and contacts  64 - 3  may be formed on the opposing upper surface of substrate  74 A immediately adjacent to corresponding contacts  62 - 3  in traces  62 . Traces  64  may include vias  64 - 2  that extend through substrate  74 B and electrically short lines  64 - 1  to respective contacts  64 - 3 . Vias may also be used in forming contacts  64 - 3  (see. e.g., via  76  of  FIG. 3 ). 
     The elongated shapes of contacts  62 - 3  on printed circuit  24 A and mating contacts  64 - 3  on printed circuit  24 B helps ensure that contacts  62 - 3  will overlap contacts  64 - 3  so that satisfactory laser welds  66  may be formed by laser  52  during welding, even in the event that there is slight misalignment between printed circuits  24 A and  24 B. Other overlapping contact pad shapes may be used for contact pads  62 - 3  and  64 - 3  if desired (e.g., shapes were one or both contacts are circular, are square have cross-shapes, have diamond shapes, etc.). When elongated contact patterns are used for the contacts of printed circuits  24 A and  24 B, the elongated contacts may cross perpendicularly to each other (as shown in the example of  FIG. 7 ), may cross at a  45  angle with respect to each other, or may cross at other suitable angles. 
     Following coarse alignment with alignment marks  68  and  70  ( FIG. 4 ), each contact  62 - 3  in printed, circuit  24 A will overlap a respective contact  64 - 3  in printed, circuit  24 B. System  42  may then be used to identify the locations of each overlapping region between these contacts. Using positioner  54 , laser  52  may be moved so that beam  60  is successively aligned with each overlap region in the arrays of contacts. A weld  66  may be formed at each overlap between a contact in printed circuit  24 A and a corresponding contact in printed circuit  24 B, so that all desired interconnections are formed between printed circuit lines  62 - 1  and printed circuit lines  64 - 1 . During welding, only some of the potential welds  66  may be formed or all welds  66  may be formed (i.e., a weld may be formed wherever one of contacts  62 - 3  overlaps one of contacts  64 - 3 ). Welding decisions can be made based on real time information gathered using inspection system  42 , based on last minute changes to the design and layout of the structures for printed circuits  24 A and  24 B, etc. The resulting connections that are formed between printed circuits  24 A and  24 B may have limited height in direction Z and may be permanent. 
     As shown in  FIG. 8 , electrical components  26  may be soldered to traces  62  and  64  using contacts  80 . On printed circuit  24 A, contacts  80  may be formed from portions of traces  62 . On printed circuit  24 B, contacts  80  may be formed from portions of traces  64 . Components  26  may be soldered to printed circuits  24 A and  24 B using solder before or after forming laser welded connections  66 . As an example components  26  may be soldered to printed circuits  24 A and  24 B before using laser welding to form connections  66 . A robotic assembly tool or other equipment may place components  26  and solder paste on printed circuits  24 A and  24 B. Components  26  and printed circuits  24 A and  24 B may then be heated in a solder reflow oven or solder joints for mounting components  26  to printed circuits  24 A and  24 B may be formed using other soldering techniques (e.g., using hot bar soldering, using laser-based soldering, etc). After a desired number of components  26  have been mourned to printed circuits  24 A and  24 B, printed circuits  24 A and  24 B may be interconnected using laser welds  66 . 
     If desired, the contact structures that are used in forming connections between printed circuits  24 A and  24 B may include solder. As shown in  FIG. 9 , fir example, one or more solder layers such as solder layer  100  may be interposed between respective pads such as contact  62 - 3  and contact  64 - 3 . Solder layer  100  may be melted when laser beam  60  is applied to weld and/or solder contacts  62 - 3  and  64 - 3  together. Hot bar heating and other heating techniques may be used instead of laser welding and for in addition to laser welding to join contacts  62 - 3  and  64 - 3 . The metal of traces  62  and  64  may be copper one or more other metals, or other suitable materials that are compatible with welding processes and other processes for forming electrical connections. 
     As shown in the illustrative top view of  FIG. 10 , printed circuits in device  10  may be joined using potentially complex patterns of welds  66  including non-rectangular weld patterns. There are two weld arrays in the example of  FIG. 10  and each weld in these arrays is associated with an overlapping pair of contacts one of which is formed on a printed circuit and one of which is formed on an overlapping aligned second printed circuit. 
     As shown in  FIG. 10 , printed circuit  24 A may, for example, be connected to printed circuit  24 B- 1  using laser welds  66 - 1  and may be connected to printed circuit  24 B- 2  using laser welds  66 - 2 . Welds  66 - 1  may be formed within a rectangular weld region in which printed circuit protrusion  24 A-P of printed circuit  24 A overlaps printed circuit  24 B- 1 . Welds  66 - 2  may be formed within a non-rectangular weld region such as region  102 . 
     Lines  62 - 1  and contacts  62 - 3  on printed circuit  24 A may run along dimension Y in area  102 . Lines  64 - 1  and contacts  64 - 3  on printed circuit  24 B in area  102  may run diagonally (i.e., at an angle of 45° to dimension Y). In region  66 - 1 , the contact pads of printed circuit  24 A and printed circuit  24 B- 1  may be orthogonal to each other (as an example). 
     Printed circuits in device  10  may have shapes that are configured to avoid obstacles such as obstacles  104  and  106  (e.g., speakers, support structures, integrated circuits on other printed circuits, housing structures, microphones, sensors, status indicators, vibrators, light-emitting components, and other components  26 ). For example, printed circuits  24 A and  24 B- 2  may have curved edges such a curved edge  108  and the region of welds  66  formed between printed circuits  24 A and  24 B- 2  may have a corresponding curved edge. The curved edges and other edges of printed circuits  24 A and  24 B- 2  and weld region  102  may run along the edge of obstacles  104  and  106  to accommodate obstacles  104  and  106  while maximizing area for forming the array of welds  66 . Because weld area  102  need not have a rectangular outline (i.e., because welds  66 - 2  may be spread out over the overlapping portions between printed circuits  24 A and  24 B in a shape other than a rectangular shape such as a shape with curved edges and/or non-perpendicular edges), it is possible to use overlapping printed circuit area efficiently. If desired, laser welded connections between contacts may be used in forming ground plane connections, rows of lateral shielding to shield signal line traces in a printed circuit, or other electrical connection structures in printed circuits. 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20140916
Publication Date: 20170613
Grant Date: 20170613
Priority Date: 20140916
Inventors: LEGGETT WILLIAM F.
RAFF JOHN
Assignee: APPLE INC
CPC Classifications: [{"code": "H05K2201/10128", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/368", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2203/107", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/09918", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K7/1427", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K3/363", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/361", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/189", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/361", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K2201/09918", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K7/1427", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K3/368", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K3/363", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/361", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2203/107", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/189", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F1/1658", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2201/10128", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F1/1658", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2201/09918", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/363", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2203/107", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/10128", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/189", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/368", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 55456247