# Patent

## Title
Low-profile circuit board assembly

## Abstract

Devices and methods for constructing low-profile, minimal-thickness electronic devices using existing production techniques are disclosed in this application. An electronic component and interposer form a sub-assembly. The sub-assembly is placed in an aperture in a circuit board with the interposer providing interconnections between the electronic component and the circuit board. Such placement conceals the thickness of the integrated circuit within the thickness of the circuit board, reducing overall thickness.

## Background
BACKGROUND
Mobile users increasingly demand devices having smaller and smaller form factors (that is, an overall size of the device). The advent of surface mount technology (“SMT”) has resulted in thinner devices, such as cellular phones, portable media players, table computers, netbooks, laptops, electronic book readers, and so forth. SMT places surface mount devices (“SMDs”) on the surface of a circuit board. These surface mount devices may include integrated circuits, discrete components, and so forth. However, traditional SMT results in a device which is at least as thick as the height of the circuit board plus the height of the SMD.



BRIEF DESCRIPTION OF THE DRAWINGS
The detailed description is set forth with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The use of the same reference numbers in different figures indicates similar or identical items.
FIGS. 1A-1C depict cross-sectional views of joining a component, such as an integrated circuit (“IC”), and an interposer to form a “T” sub-assembly which is then placed in an aperture in a backplane and joined to the component, resulting in a low-profile assembly.
FIG. 2 depicts a cross-sectional view and an enlargement of a pathway between the component and the backplane provided by the interposer.
FIG. 3 is a plan view of a component and the backplane joined by the interposer.
FIGS. 4A-4B depict cross-sectional views of a backplane comprising an aperture with a ledge configured to receive a portion of the interposer of the “T” sub-assembly, thus allowing the “T” sub-assembly to be at least partially recessed within the backplane.
FIGS. 5A and 5B are cross-sectional views of joining a “T” sub-assembly with a second interposer to form an “H” sub-assembly.
FIG. 6 is a cross sectional view of a “C” sub-assembly comprising an IC and an extended interposer.
FIG. 7 is a cross-sectional view of a component comprising an integrated interposer within a “T” package.
FIG. 8 illustrates an example process that includes forming a “T” sub-assembly, cutting an aperture in a backplane, placing the “T” sub-assembly within the aperture, and joining the “T” sub-assembly to the backplane.
FIG. 9 is a flow diagram of an example process of building a low-profile assembly, such as the assemblies described in FIGS. 1-8.



DETAILED DESCRIPTION
This disclosure is directed, in part, to low-profile assemblies comprising a backplane and a component, as well as a method for constructing such low-profile assemblies. These low-profile assemblies may be used in electronic devices, such as laptops, electronic book readers, portable media players, smartphones, and so forth. By using low-profile assemblies, thinner devices may be made. This application uses the term “electronic” for convenience, and not by way of limitation. For example, the devices and methods used here may apply to devices which are electronic, optical, optoelectronic, spintronic, and so forth. Also the term “low-profile” as used in this application indicates an assembly which has an overall thickness “Z” less than a sum of a thickness of the circuit board “B” plus a thickness of a component “C.” Stated another way, Z<(C+B).
Furthermore, the devices and methods discussed herein are compatible with existing component packaging and assembly techniques. Thus, existing packaging technologies such as land grid array (“LGA”) and ball grid array (“BGA”) as well as assembly techniques such as automated pick-and-place may be used with some implementations described herein.
The discussion begins with a section entitled “Illustrative Arrangements,” which describes several non-limiting examples of the claimed devices. Among these examples are a “T” sub-assembly, a recessed “T” sub-assembly, a “H” sub-assembly, a “C” sub-assembly, and a “T” package. A section entitled “Illustrative Processes” follows, and describes example flow diagrams of one implementation of the process for assembling the devices. Finally, a brief conclusion ends the discussion.
This brief introduction, including section titles and corresponding summaries, is provided for the reader's convenience and is not intended to limit the scope of the claims, nor the proceeding sections. Furthermore, the techniques described in detail below may be implemented in a number of ways and in a number of contexts. Example implementations and context are provided and described below in more detail. However, it is to be appreciated that the following implementations and context are but some of many.
Illustrative Arrangements
“T” Sub-Assembly
FIG. 1A depicts a component 102 having a height “C.” Components include capacitors, resistors, inductors, diodes, memristors, transistors, semiconductor devices, integrated circuits (“ICs”) optical devices, power converters, optoelectronic devices, and so forth. These components may be analog, digital, or combination devices.
The component 102 may be joined with an interposer 104, along a direction indicated by an arrow. An interposer 104 comprises one or more pathways suitable for coupling the component 102 to a backplane. In some implementations, these pathways may be electrical, optical, electromagnetic, fluidic, or mechanical. For example, in an electronic device, the interposer 104 may comprise pathways such as electrically conductive material suitable for conveying an electric current between the component 102 and the backplane. Likewise, an interposer 104 for an optical device may comprise an optical pathway either in free space or via a waveguide, optical pipe, and so forth, to convey photons between the component and backplane. The interposer 104 may also comprise fluidic channels allowing coupling of fluidic channels on the component to fluidic channels on the backplane. In other implementations, the interposer may comprise a mechanical joint or other mechanical connection between the component and the backplane.
The interposer 104 may have interconnects suitable for joining to the component 102 and the backplane 114, and as described above may provide pathways. FIG. 1 further illustrates interposer-to-component interconnects 106, as well as interposer-to-backplane interconnects 108. These interconnects may be joined via soldering, eutectic bonding, affixing with adhesive, mating an interference fit, filling a gap with a polymer, inserting an elastomeric material, proximity, and so forth. Once the component 102 and the interposer 104 have been joined at least in part by the interposer/component interconnects 106, they form a “T” sub-assembly 110.
FIG. 1B shows the “T” sub-assembly 110 being inserted into an aperture 112 in the backplane 114 along the direction indicated by an arrow. The backplane 114 has a height “B,” and may comprise a printed circuit board, a larger assembly of other components, a rigid material, a semi-rigid material, a flexible material, and so forth. The “T” sub-assembly 110 is inserted into the aperture 112 whereupon the interposer/backplane interconnect(s) 106 may join the “T” sub-assembly 110 to the backplane 114. For example, where the joining is accomplished by soldering, heat may be applied to solder the “T” sub-assembly 110 to the backplane. Joining may comprise establishing one or more pathways. These pathways may be electrically conductive, may provide an optical path, establish an electromagnetic waveguide, provide a fluidic channel or a mechanical joint.
FIG. 1C shows the “T” sub-assembly 110 joined with the backplane 114 to form the assembly 116. The overall height “Z” of the interposer 104 and the backplane 114 is also shown. As depicted, the height “Z” is less than the sum of the height “C” of the component 102 and the height “B” of the backplane 114. Stated another way, Z<(C+B). As a result, assembly 116 has a lower-profile compared to assemblies formed via traditional SMT where the component is mounted atop the backplane and has a height of C+B. While a bottom of the component 102 is shown flush with the bottom of the backplane 114, in some implementations the component 102 may extend below the backplane 114.
As illustrated, an edge gap 118 may exist between an edge of the component 102 and the backplane 114. In some implementations, this gap may be filled with an adhesive, epoxy, polymer, elastomeric material, and so forth. Filling this edge gap 118 may improve longevity of the assembly by minimizing mechanical strain on the interposer 104 and on the interposer/component interconnects 106 and interposer/backplane interconnects 108. Where the filler is conductive, other benefits may accrue, such as the providing of an electrical ground between the component and the backplane 114.
In another implementation, the interposer/component interconnect 106 may be joined using a different material or process then that used in the interposer/backplane interconnect 108. For example, the interposer/component interconnect 106 may use a high temperature solder, while the interposer/backplane interconnect 108 may use a lower temperature solder. Thus, during joining the “T” sub-assembly 110 may be soldered to the backplane 114 without melting the interposer/component interconnect 106 solder.
In another implementation, a “T” sub-assembly 110 may not be used. For example, the component 102 may be placed within the backplane 114, an interposer 102 placed, and the interposer 102 may be joined to the component 102 and the backplane 114 at about the same time.
FIG. 2 depicts a cross-sectional view 200 of assembly 116 and an enlargement of an electrical pathway between the component 102 and the backplane 114 as provided by the interposer 104. A conductive path 202, such as a metal trace, on the interposer 104 provides a path for electric current, as shown by a double-headed arrow, to flow between a conductive path 202 on the component 102 and a conductive path 202 on the backplane 114. Thus, the interposer 104 couples the component 102 and the backplane 114.
FIG. 3 is a plan view 300 of a component 102 and the backplane 114 joined by the interposer 104 which provides a plurality of conductive pathways 202. In this view, the conductive paths 202 are shown bridging the interposer/component interconnects 106 and the interposer/backplane interconnects 108. Also shown is the edge gap 118 extending around the perimeter of the component 102.
Recessed “T” Sub-Assembly
In some instances, the already slim low-profile assembly described above with respect to FIGS. 1-3 may be further reduced. FIGS. 4A-4B depict cross-sectional views 400 of a backplane 114 comprising a ledge 402 extending along at least a portion of the perimeter of aperture 112 and configured to receive a portion of the interposer of the “T” sub-assembly 110. This ledge 402 allows clearance for the upper portion of the “T” sub-assembly 110 to be at least partially recessed within the backplane 114. In FIG. 4A “T” sub-assembly 110 is placed along the direction indicated by an arrow into the aperture 112 in the backplane 114 having the ledge 402. At shown in FIG. 4B, once the “T” sub-assembly 110 is joined to the backplane 114, a recessed “T” assembly 402 results. The overall height “R” of this recessed “T” assembly 402 is less than the overall height “Z” as described above. Stated another way, R<z<(C+B). In other implementations, the “T” sub-assembly 110 may not be fully recessed, and thus extend above the surface of the backplane.
“H” Sub-Assembly
In some instances, it may be useful to provide additional pathways between the component 102 and the backplane 114. For example, a high density integrated circuit may be packaged such that contacts are on both a top and a bottom. FIGS. 5A and 5B depict cross-sectional views 500 of joining a “T” sub-assembly 110 with a second interposer 502 to form an “H” sub-assembly 504. This “H” sub-assembly has a height of “H.”
To further reduce the profile, in some implementations one or both interposers 104 and 502 may be recessed as described above with respect to FIGS. 4A-4B. For example, a first interposer 104 in the “T” sub-assembly 110 may be recessed within the backplane 114 as shown in FIG. 4B.
“C” Sub-Assembly
In some implementations, the height “C” of component 102 may be such that a planar interposer such as interposer 104 is not able to establish a pathway between the component 102 and the backplane 114. In these instances, a “C” sub-assembly as shown in FIG. 6 may be used. FIG. 6 is a cross sectional view 600 of a “C” sub-assembly 602. “C” sub-assembly 602 comprises a component 102 having a top which extends beyond the height “B” of the backplane which is joined to an extended interposer 604. The extended interposer 604 is configured to provide a pathway between component 102 and backplane 114.
“T” Package
Component packaging may be modified to include an interposer in some instances. FIG. 7 is a cross-sectional view 700 of a “T” package 702 for a component 102. The component 102 may have one or more protrusions 704. The protrusions 704 may be disposed to extend at least in part beyond an edge of the aperture 112 in which the component 102 resides. Protrusions 704 may also be configured to provide a coupling between the component 102 and the backplane 114. These protrusions 704 may be affixed to the component, or may be integral to the component.
Illustrative Processes
FIG. 8 illustrates an example process 800 for assembling a low-profile assembly. Operation 802 joins a component 102, such as an integrated circuit, to an interposer to form a “T” subassembly 110. As described above, joining may comprise soldering, adhering, interfacing mechanically, and so forth.
Operation 804 cuts an aperture 112 in a backplane 114. A variety of mechanisms exist for placing apertures in a backplane, including cutting, routing, punching, ablating, vaporizing, and so forth. In another implementation, the backplane 114 may be formed with the aperture 112. However placed or formed, the aperture may pass through the entire thickness of the backplane 114.
Operation 806 places the “T” sub-assembly 110 into the aperture 112 in the backplane 114. Placement may occur manually or using a pick-and-place device or other automated equipment. While the figures in this application depict the “T” sub-assembly 110 being inserted from a top of the backplane 114, it is understood that the “T” sub-assembly 110 may be inserted from a bottom of the backplane 114 as well.
Operation 808 joins the “T” sub-assembly 110 and the backplane 114 to form an assembly 116. As described above, joining may comprise soldering, adhering, interfacing mechanically, and so forth. In some implementations, the edge gap 118 between the component 102 and the backplane 114 may be at least partially filled.
FIG. 9 shows an illustrative process 900 of assembling a low-profile device. The process 900 is illustrated as a collection of blocks in a logical flow graph, which represent a sequence of operations that can be implemented in hardware, software, or a combination thereof. In the context of software, the blocks represent computer-executable instructions that, when executed by one or more processors, perform the recited operations. Generally, computer-executable instructions include routines, programs, objects, components, data structures, and the like that perform particular functions or implement particular abstract data types. The order in which the operations are described is not intended to be construed as a limitation, and any number of the described blocks can be combined in any order and/or in parallel to implement the process. For discussion purposes, the process will be described in the context of the examples of FIGS. 1-8, but may be utilize other devices.
Block 902 joins a component and an interposer to form a sub-assembly. Joining may comprise soldering, adhering, interfacing mechanically, and so forth. Block 904 places the sub-assembly into a corresponding aperture in a backplane. The corresponding aperture completely passes through the backplane (although it need not) and is sized to accept the component. Block 906 joins the sub-assembly to the backplane. As above, joining may comprise soldering, adhering, interfacing mechanically, and so forth. Block 908 fills at least a portion of the edge gap between the component and the backplane.
Moreover, the acts and methods described may be implemented by a computer, processor or other computing device based on instructions stored on memory, the memory comprising one or more computer-readable storage media (CRSM).
The CRSM may be any available physical media accessible by a computing device to implement the instructions stored thereon. CRSM may include, but is not limited to, random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other solid-state memory technology, compact disk read-only memory (CD-ROM), digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by a computing device.
CONCLUSION
As shown above, very low profile assemblies are possible, leading to lower profile devices. Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features, dimensions, or acts described. Rather, the specific features, dimensions, and acts are disclosed as illustrative forms of implementing the claims. Moreover, any of the features of any of the devices described herein may be implemented in a variety of materials or similar configurations.

## Claims

1. A device comprising:
a circuit board comprising a ledge and an aperture contiguous with the ledge, the aperture extending through the circuit board and containing at least a portion of a surface mount component, wherein the surface mount component and the circuit board are coupled such that an edge gap exists between the surface mount component and the circuit board and the edge gap is filled with a conductive filler providing an electrical ground between the surface mount component and the circuit board; and
an interposer coupling the surface mount component having at least a portion contained within the aperture to the circuit board, the interposer having interposer-to-component interconnects to join the interposer to the surface mount component and interposer-to-backplane interconnects to join the interposer to the circuit board, wherein the interposer-to-component interconnects and interposer-to-backplane interconnects are located on a same side of the interposer.

2. The device of claim 1, wherein the surface mount component comprises one or more of the following:
a capacitor;
a resistor;
an inductor;
a diode;
a memristor;
a transistor;
a semiconductor device;
an integrated circuit;
an optical device;
a power converter; and
an optoelectronic device.

3. The device of claim 1, wherein the component is packaged as a land grid array or a ball grid array.

4. The device of claim 1, wherein the coupling of the surface mount component having at least a portion contained within the aperture of the circuit board by the interposer provides a pathway between the component and the circuit board.

5. The device of claim 4, wherein the interposer further comprises one or more of the following:
a capacitor;
a resistor;
an inductor;
a diode;
a semiconductor device; and
an integrated circuit.

6. The device of claim 4, wherein the pathway comprises one or more of the following:
an electrical conductor;
an optical path;
an electromagnetic waveguide;
a fluidic channel; and
a mechanical joint.

7. A device comprising:
a backplane having an aperture and a ledge, the ledge extending along at least a portion of a perimeter of the aperture within the backplane; and
a main body comprising an electronic component, an interposer, and a protrusion to provide a coupling between the electronic component and the backplane, the main body fitting at least partially within the aperture in the backplane and on the ledge such that the main body is at least partially recessed within the backplane, the main body being coupled to the backplane to form an edge gap between the main body and the backplane and the edge gap being filled with a conductive filler providing an electrical ground between the main body and the backplane.

8. The device of claim 7, wherein the aperture passes through the backplane.

9. The device of claim 7, wherein the ledge receives the protrusion and the electronic component at least partially within the backplane.

10. The device of claim 7, wherein the protrusion extends at least in part beyond an edge of the aperture.

11. The device of claim 7, wherein the protrusion is integral to the interposer.

12. The device of claim 7, wherein the electronic component is affixed to the protrusion.

13. The device of claim 7, wherein the protrusion is an extension to establish a pathway between the electronic component and the backplane where a planar interposer is not able to establish the pathway.

14. The device of claim 1, wherein the interposer has an extension to establish a pathway between the surface mount component and the circuit board where a planar interposer is not able to establish the pathway.

15. A device comprising:
a component;
a circuit board comprising an aperture and a ledge, the ledge extending along at least a portion of a perimeter of the aperture within the circuit board, the component and the circuit board being coupled such that an edge gap exists between the component and the circuit board, and the edge gap being filled with a conductive filler providing an electrical ground between the component and the circuit board; and
an interposer to establish a pathway to join the component to the circuit board when at least a portion of the component is contained within the aperture, wherein the ledge receives the interposer such that the interposer is at least partially recessed within the circuit board.

16. The device of claim 15, wherein the component extends below the circuit board.

17. The device of claim 15, wherein the component is flush with the bottom of the circuit board or extends below the circuit board.

18. The device of claim 15, in which the interposer has an extension to establish the pathway between the component and the circuit board.

19. The device of claim 15, in which the component is packaged as a land grid array or a ball grid array.

20. The device of claim 15, wherein the ledge receives the interposer such that the interposer is completely recessed within the circuit board.