# Patent

## Title
Package substrate dynamic pressure structure

## Abstract

Devices and methods for their formation, including electronic assemblies having a shape memory material structure, are described. In one embodiment, a device includes a package substrate and an electronic component coupled to the package substrate. The device also includes a shape memory material structure coupled to the package substrate. In one aspect of certain embodiments, the shape memory material structure is formed from a material selected to have a martensite to austenite transition temperature in the range of 50-300 degrees Celsius. In another aspect of certain embodiments, the shape memory material structure is positioned to extend around a periphery of the electronic component. Other embodiments are described and claimed.

## Background
This application is a continuation of U.S. patent application Ser. No. 13/424,202, filed Mar. 19, 2012, which is a divisional of U.S. patent application Ser. No. 11/771,990 filed Jun. 29, 2007, issued as U.S. Pat. No. 8,143,721. The above patent applications and patent are hereby incorporated by reference in their entirety.


RELATED ART
Integrated circuits may be formed on semiconductor wafers made from materials such as silicon. The semiconductor wafers are processed to form various electronic devices. The wafers are diced into semiconductor chips (a chip is also known as a die), which may then be attached to a package substrate using a variety of known methods. In one known method for attaching a chip or die to a package substrate, the die may have solder bump contacts which are electrically coupled to the integrated circuit. The solder bump contacts extend onto the contact pads of a package substrate, and are typically attached in a thermal reflow process. Electronic signals may be provided through the solder bump contacts to and from the integrated circuit on the die.
The material of package substrate typically does not provide an exact match with the material of the die with respect to the coefficient of thermal expansion. Thermal expansion mismatch can lead to stresses developing in the electronic assembly during processing procedures, in particular, during heating and cooling operations such as solder reflow. Such stresses may cause warpage in the package substrate. As electronic devices and package substrates become more thin, warpage will continue to be a problem.
Package substrate warpage problems may be addressed using a number of approaches. For example, a thicker substrate may be used. The thicker substrate is more rigid due to its thickness and thus less likely to undergo substantial warpage. Another approach is to use a heat spreader coupled to the die and the substrate. The heat spreader also makes the assembly more rigid and less prone to warpage. Still another approach is to use a stiffener coupled to the package substrate. The stiffener may take the form of a metal ring coupled to the package substrate. The metal ring adds mass to the assembly and makes it more rigid and less prone to warpage. All of these methods add substantial mass and thickness to the package substrate assembly.



BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments are described by way of example, with reference to the accompanying drawings, which are not drawn to scale, wherein:
FIG. 1 illustrates a shape memory material structure on a package substrate, in accordance with certain embodiments;
FIGS. 2(A)-2(C) illustrate processing operations for coupling a shape memory material structure to a package substrate, in accordance with certain embodiments;
FIG. 3 illustrates a top view of a shape memory material structure on a package substrate, in accordance with certain embodiments;
FIG. 4 illustrates a top view of a shape memory material structure on a package substrate, in accordance with certain embodiments;
FIGS. 5(A)-5(C) illustrate processing operations for coupling a shape memory material structure to a substrate and the resultant assembly after heating, in accordance with certain embodiments;
FIG. 6 illustrates a flow chart of certain operations for forming an assembly, in accordance with certain embodiments; and
FIG. 7 illustrates an electronic system arrangement in which certain embodiments may find application.



DETAILED DESCRIPTION
Certain embodiments relate to electronic assemblies. Embodiments include both devices and methods for forming electronic assemblies.
FIG. 1 illustrates an electronic assembly in accordance with certain embodiments. The electronic assembly includes a package substrate 10 having a shape memory material structure 12 and an electronic component such as a die 14 positioned thereon. The package substrate may be a single layer or multilayer, and may be formed from any suitable material, including, but not limited to, ceramics, polymers, and composite structures. One example of a suitable package substrate material is an epoxy resin. As illustrated in the embodiment of FIG. 1, the die 14 may be positioned on a central region of the package substrate 10. The shape memory material structure 12 may encircle the die 14 and be positioned on an outer portion of the package substrate 10.
One example of a shape memory material composition includes an alloy including nickel-titanium and is sold under the trade name NITINOL. Shape memory materials, such as certain alloys, have the unique property of regaining their original shape through a phase transformation below the melting point. In the case of most alloys, the original shape is set at a high temperature while in the austenite crystal phase. Upon cooling, the crystal phase changes to martensite. Any changes to the shape of the material will be reset to the original shape during the crystal structure transformation from martensite to austenite. This transformation imparts a force on the material. For example, a shape memory material that has experienced a strain in the martensitic phase, upon heating, may undergo a phase change to a more ordered austenitic crystal phase. This phase change causes the material to recover its strain and is capable of imparting large forces. One specific example, NITINOL H (a high temperature range NITINOL) has an austenite transition temperature of 100 degrees Celsius, and may be used in certain embodiments. Certain embodiments utilize a shape memory material structure formed from a material having a martensite to austenite transformation temperature in the range of about 50 to about 300 degrees Celsius. Shape memory materials may include, but are not necessarily limited to, metal alloys having suitable phase transformation properties.
The use of a shape memory material structure enables an active force to be applied to counteract the package warpage forces during reflow temperatures so that the package substrate assembly can remain substantially flat. Conventional approaches provide a passive control to inhibit warpage, whereas the use of a shape memory material structure provides an active control, during the processing operations that generate warpage forces, to inhibit warpage. The use of the active force applied by the shape memory material enables certain embodiments to be formed thinner than conventional stiffeners, while providing the same or a greater level or force to resist warpage (the conventional stiffener applies a passive force after the package substrate begins to warp). As a result, certain embodiments are well suited to being used in applications where limiting thickness is essential, for example, in package assemblies for mobile applications.
In certain embodiments, the shape memory material structure 12 may be formed and the original shape may be set at around 500 degrees Celsius, in the austenite crystalline phase. The shape memory material structure 12 may in certain embodiments be formed to have a zero or near zero warpage. The structure 12 may then be coupled to the package substrate as will be described below in connection with FIG. 2. When the package substrate is exposed to elevated temperatures and starts to warp (for example, during a reflow process), the shape memory material structure 12 produces a counter force to the warpage because the elevated temperature is changing the crystal structure from a martensitic crystal structure to an austenitic crystal structure. This change in crystal structure applies an active force that suppresses the package substrate's tendency to warp during elevated temperature processes.
FIGS. 2(A)-2(C) illustrate coupling the shape memory material structure 12 to the package substrate 10, in accordance with certain embodiments. The shape memory material structure 12 may be coupled to the package substrate using any suitable approach. As seen in FIG. 2(A), for example, an adhesive 16 is applied to the package substrate 10 through an applicator 15. A variety of adhesives may be used, including, but not limited to, an epoxy adhesive. The adhesive 16 is positioned on the surface of the package substrate 10, and then the shape memory material structure 12 is positioned thereon, as illustrated in FIG. 2(B).
Depending on the adhesive used, a heating operation may be carried out, as indicated in FIG. 2(C), to cure the adhesive 16 to form a suitable bond between the shape memory material structure 12 and the package substrate 10. While FIG. 2(A) illustrates the use of a liquid adhesive that is applied to the package substrate, other approaches, for example, a solid, preformed adhesive that is heated after the shape memory material structure is positioned on the substrate, may also be used in certain embodiments. In an alternative embodiment, the shape memory material structure 12 maybe deposited directly onto the package substrate 10, with no separate adhesive layer formed therebetween.
In certain embodiments, after the shape memory material structure 12 has been coupled to the package substrate 10, an electronic device such as the semiconductor die 14 is coupled to the package substrate 10 using a suitable method, for example, a solder bump method.
The shape memory material structure may in certain embodiments have a ring-like structure. By ring-like, it is meant that the structure is formed to extend around (or define) a hole or open region. In FIG. 1, the shape memory material structure 12 defines a hole bounded by the four sides (and curved corner regions) of the shape memory material structure 12. The die 14 is positioned within a portion of the hole bounded by the sides of the shape memory material structure 12. The embodiments illustrated in FIGS. 1, 3, and 4 are all examples of ring-like structures.
FIGS. 3, 4, and 5(A)-5(C) illustrate additional examples of shapes and positions of shape memory material structures on package substrates. In FIG. 3, the shape memory material structure 32 positioned on the package substrate 30 has a structure that is substantially circular when viewed from above. In FIG. 4, the shape memory material structure 42 on the package substrate 40 has a structure that is substantially rectangular in structure, with rounded interior corners. The shape memory material structures 32, 42 of FIGS. 3 and 4 are positioned a distance away from the side edges of the package substrates 30, 40, unlike the shape memory material structure 12 of FIG. 1, which is aligned with the side edges of the package substrate 10.
FIGS. 5(A)-5(C) illustrate the application of a shape memory material structure 52 to a substrate 50 and the resultant assembly after heating, in accordance with another embodiment. In this embodiment, the shape memory structure 52 is formed to have a curvature that opposes that of the substrate 50 to which it is attached. As illustrated in FIG. 5(A), the shape memory structure 52 has a curvature that is opposite the curvature of the substrate 50. FIG. 5(B), the shape memory material structure 52 is coupled to the package substrate 50 and has a concave shape due to the forces applied by the substrate 50. FIG. 5(C) illustrates the shape memory material structure 52 and substrate 50 after heating, where the heating has caused a phase change in the shape memory material structure 52, which applied a force to counteract the force in the substrate 50 and caused the assembly to flatten. Thus, the use of a concave or otherwise bowed shape material structure may also be used in certain embodiments to provide additional force to counteract warpage forces developed during processing operations.
FIG. 6 illustrates a flow chart of certain operations for forming an assembly in accordance with certain embodiments. Box 60 is providing a package substrate to which a shape memory material structure and an electronic device will be coupled. Box 62 is coupling the shape memory material structure to the substrate, using a technique such as described above. Box 64 is coupling an electronic device such as a semiconductor die to the substrate, to form an assembly.
Assemblies as described in embodiments above may find application in a variety of electronic components. In certain embodiments, a device or devices in accordance with the present description may be embodied in a computer system including a video controller to render information to display on a monitor coupled to the computer. The computer system may comprise one or more of a desktop, workstation, server, mainframe, laptop, handheld computer, handheld gaming device, handheld entertainment device (for example, a video player), PDA (personal digital assistant), telephony device (wireless or wired), etc. Alternatively, a device or devices in accordance with the present description may be embodied in a computing device that does not include a video controller, such as a switch, router, etc.
FIG. 7 schematically illustrates one example of an electronic system environment in which aspects of described embodiments may be embodied. Other embodiments need not include all of the features specified in FIG. 7, and may include alternative features not specified in FIG. 7. FIG. 7 illustrates an embodiment of a device including a computer architecture 100 which may utilize integrated circuit devices having a structure including capacitors formed in accordance with embodiments as described above. The architecture 100 may include a CPU 102, memory 104 (including, for example, a volatile memory device), and storage 106 (including, for example, a non-volatile storage device, such as magnetic disk drives, optical disk drives, etc.). The CPU 102 may be coupled to a printed circuit board 107, which in this embodiment, may be a motherboard. The CPU 102 is an example of a package substrate assembly formed in accordance with the embodiments described above and illustrated, for example, in FIG. 1. A variety of other system components, including, but not limited to input/output devices, controllers, memory and other components, may also include structures formed in accordance with the embodiments described above. The system components may be formed on the motherboard, or may be disposed on other cards such as daughter cards or expansion cards.
The storage 106 may comprise an internal storage device or an attached or network accessible storage. Programs in the storage 106 may be loaded into the memory 104 and executed by the CPU 102 in a manner known in the art. The architecture may further include a network controller 108 to enable communication with a network, such as an Ethernet, a Fibre Channel Arbitrated Loop, etc. Further, the architecture may, in certain embodiments, also include a video controller 109, to render information on a display monitor, where the video controller may be embodied on a video card or integrated on integrated circuit components mounted on the motherboard, for example. Other controllers may also be present to control other devices.
An input device 110 may be used to provide input to the CPU 102, and may include, for example, a keyboard, mouse, pen-stylus, microphone, touch sensitive display screen, or any other suitable activation or input mechanism. An output device 112 including, for example, a monitor, printer, speaker, etc., capable of rendering information transmitted from the CPU 102 or other component, may also be present.
While certain exemplary embodiments have been described above and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative and not restrictive, and that embodiments are not restricted to the specific constructions and arrangements shown and described since modifications may occur to those having ordinary skill in the art.

## Claims

1. A method comprising:
providing a package substrate;
coupling a shape memory material structure to the package substrate; and
coupling an electronic component to the package substrate;
wherein the coupling a shape memory material structure is carried out prior to the coupling an electronic component to the package substrate.

2. The method of claim 1, wherein the electrical component and the shape memory material structure are positioned so that the shape memory material structure extends around a periphery of the electronic component.

3. The method of claim 1, wherein the shape memory material structure comprises nickel and titanium.

4. The method of claim 1, wherein the shape memory material has a martensite to austenite transition temperature in the range of 50-300 degrees Celsius.

5. The method of claim 1, wherein the coupling a shape memory material structure comprises adhering the shape memory material structure to the package substrate using an adhesive positioned between the shape memory material structure and the package substrate.

6. The method of claim 1, wherein the coupling a shape memory material structure comprises depositing the shape memory material structure directly onto the package substrate using a vapor deposition method.

7. The method of claim 1, wherein the shape memory material structure comprises a ring-like structure.

8. A method comprising:
providing a package substrate;
positioning only a single shape memory material structure on a surface of the package substrate; and
positioning an electronic component on the package substrate.

9. The method of claim 8, wherein the positioning only a single shape memory material structure comprises depositing the shape memory material structure directly onto the package substrate.

10. The method of claim 9, wherein the depositing the shape memory material structure directly onto the package substrate comprises using a vapor deposition method.

11. The method of claim 8, wherein the positioning only a single shape memory material structure comprises adhering the shape memory material structure to the package substrate using an adhesive positioned between the shape memory material structure and the package substrate.

12. The method of claim 8, wherein the shape memory material structure comprises nickel and titanium.

13. The method of claim 8, wherein the shape memory material structure comprises a ring-like structure.

14. The method of claim 8, wherein the positioning only a single shape memory material structure is carried out prior to the positioning an electronic component on the package substrate.

15. A method comprising:
providing a package substrate including an electronic component attachment area on a surface thereof; and
positioning a shape memory material structure on the package substrate surface so that the shape memory material surrounds the electronic component attachment area in a continuous manner.

16. The method of claim 15, wherein the positioning a shape memory material structure comprises depositing the shape memory material structure directly onto the package substrate surface.

17. The method of claim 15, wherein the positioning a shape memory material structure comprises adhering the shape memory material structure to the package substrate surface using an adhesive positioned between the shape memory material structure and the package substrate surface.

18. The method of claim 15, wherein the shape memory material structure comprises nickel and titanium.

19. The method of claim 15, wherein the shape memory material structure comprises a ring-like structure.

20. The method of claim 15, further comprising positioning an electronic component on the package substrate, wherein the positioning a shape memory material structure is carried out prior to the positioning an electronic component on the package substrate.