Heat Sink Design for Flip Chip Ball Grid Array

Abstract

Embodiments of the present disclosure relate to a heat sink design for a flip chip ball grid array. A flip chip ball grid array (FCBGA) includes a substrate, a cavity-forming annular stiffener, an external heat sink, and a thermal interface material. The cavity-forming annular stiffener is disposed on the substrate. The cavity-forming annular stiffener has a portion that forms a cavity with the substrate and exposes the top of the silicon chip. The external heat sink is disposed on the silicon chip and on a section of the cavity-forming annular stiffener. The thermal interface material separates the section of the cavity-forming annular stiffener and the top of the silicon chip from the external heat sink and conducts heat from the silicon chip to the external heat sink.

Description

[0001] Cross - reference to related applications

[0002] This disclosure claims the benefit of priority to U.S. Provisional Application No. 62 / 803,204, filed on February 8, 2019, entitled "EXPOSED-DIE HEAT-SINK DESIGN", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0003] This disclosure relates to a heat sink design for a flip chip ball grid array (FCBGA), namely, an external heat sink disposed on a cavity-forming annular stiffener that forms a cavity with the substrate of the FCBGA. The cavity-forming annular stiffener supports the external heat sink, exposes the top of the silicon chip on the FCBGA, and increases the mechanical stiffness of the FCBGA. BACKGROUND OF THE DISCLOSURE

[0004] The background description provided herein is for the purpose of generally presenting the disclosure. Within the scope of the work described in this background section, as well as in other cases where the description may not be considered prior art at the time of application, nothing is expressly or implicitly admitted to be prior art with respect to the present disclosure.

[0005] A flip chip ball grid array (FCBGA) is a semiconductor package that has a silicon chip disposed on one side of a substrate and a ball grid array disposed on the other side of the substrate. The ball grid array enables the FCBGA to be mounted on a printed circuit board. The silicon chip generates heat during operation. Heat needs to be dissipated from the silicon chip to a fluid medium such as air so that the silicon chip operates at an optimal temperature. SUMMARY OF THE DISCLOSURE

[0006] This disclosure relates to a heat sink design for a flip chip ball grid array (FCBGA), namely, an external heat sink that is arranged on a cavity-forming annular stiffener that forms a cavity with the substrate of the FCBGA. The cavity-forming annular stiffener supports the external heat sink, exposes the top of the silicon chip on the FCBGA substrate, and increases the mechanical stiffness of the FCBGA substrate. Heat is transferred from the silicon chip to the external heat sink to be dissipated to a fluid medium such as air through a layer of thermal interface material that separates the silicon chip and the cavity annular stiffener from the external heat sink.

[0007] Aspects of the present disclosure provide a flip chip ball grid array (FCBGA) comprising: a substrate having a silicon chip; a cavity-forming annular stiffener disposed on the substrate, the cavity-forming annular stiffener having a portion that forms a cavity with the substrate and exposes the top of the silicon chip; a thermal interface material disposed on a section of the cavity-forming annular stiffener and on the silicon chip; and an external heat sink disposed on the thermal interface material.

[0008] In one example, the section exposes a portion of the top of the silicon chip. In another example, the height of the section of the cavity-forming annular stiffener is lower or higher than the height of the silicon chip. In yet another example, the section is a first section and the cavity-forming annular stiffener includes a second section disposed along the periphery of the substrate, and the second section transitions to the first section by a stepped transition. In another example, the cavity-forming annular stiffener has a uniform height from the periphery of the substrate to the center of the substrate. In yet another example, the section is a first section and the cavity-forming annular stiffener includes a second section attached to the first section. In another example, the second section is disposed along the periphery of the substrate. In yet another example, the thermal interface material is thermal grease or a thermal pad. In another example, the height of the section of the cavity-forming annular stiffener is the same as the height of the silicon chip. In yet another example, the section has a length that exposes an area on the substrate having integrated circuits or probe pads. In another example, the external heat sink includes one or more fins perpendicular to the section of the cavity-forming annular stiffener. In yet another example, the external heat sink includes a groove or a protrusion on the bottom of the external heat sink, and the groove or the protrusion is above the silicon chip.

[0009] Aspects of the present disclosure provide a method that includes: disposing a cavity-forming annular stiffener on a substrate of a flip-chip ball grid array (FCBGA), the cavity-forming annular stiffener having a section that forms a cavity with the substrate and exposes the top of a silicon chip on the substrate; disposing a thermal interface material on the section of the cavity-forming annular stiffener and on the top of the silicon chip; and disposing an external heat sink on the thermal interface material.

[0010] In one example, the section exposes a portion of the top of the silicon chip. In another example, the method of disposing the cavity-forming annular stiffener on the substrate includes: disposing the section of the cavity-forming annular stiffener at a height lower or higher than the silicon chip. In yet another example, the thickness of the thermal interface material is uniform. In another example, the external heat sink includes a groove or a protrusion on the bottom of the external heat sink, and the groove or the protrusion is above the silicon chip. In yet another example, the section is a first section and the method further includes fixing the first section to a second section disposed along the periphery of the substrate. In another example, the section is a first section and the cavity-forming annular stiffener includes a second section disposed along the periphery of the substrate, and the second section transitions to the first section by a stepped transition. In yet another example, the method further includes mounting the FCBGA on a printed circuit board. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figures 1A - 1C Various example views of an example flip-chip ball grid array (FCBGA) having an example fin design are shown.

[0012] Figure 2A andFigure 2B Shows an example top view and an example side view of an example FCBGA having an example cavity-forming annular reinforcement that does not cover an area on a substrate of the example FCBGA.

[0013] Figures 3A - 3B Shows an example side view of an example cavity-forming annular reinforcement having different heights.

[0014] Figure 4 Shows an example side view of an example external heat sink disposed on the example cavity-forming annular reinforcement, the example cavity-forming annular reinforcement being higher than a silicon chip.

[0015] Figure 5A and 5B Shows various example views of an example cavity-forming annular reinforcement having a uniform height.

[0016] Figure 6 Shows an example side view of another example cavity-forming annular reinforcement having a uniform height.

[0017] Figure 7 Is a flowchart of an example function associated with the assembly of an example cavity-forming annular reinforcement and an example external heat sink on a substrate of an FCGBA.

[0018] The drawings are for the purpose of illustrating example embodiments, but it should be understood that the embodiments are not limited to the arrangements and means shown in the drawings. Detailed Description

[0019] The following description includes example systems, methods, techniques, and program flows that embody aspects of the present disclosure. However, it should be understood that the present disclosure may be practiced without these specific details. For example, the present disclosure relates to an example heat sink design for a flip chip ball grid array (FCBGA), namely, an external heat sink and a cavity-forming annular reinforcement that forms a cavity with a substrate of the FCBGA. Aspects of the present disclosure may be applied to semiconductor packages other than FBGA, and in other cases, well-known situations, structures, and techniques are not shown in detail so as not to obscure the description.

[0020] Overview

[0021] An FCBGA with a heat spreader and an external heat sink dissipates heat from a silicon chip on the FCBGA to a fluid medium such as air, enabling the silicon chip to operate at an optimal temperature. The heat spreader is arranged above the silicon chip of the FCBGA to completely cover the top of the silicon chip, where the support ends of the heat spreader are coupled to the substrate of the FCBGA. Additionally, a first layer of thermal interface material such as thermal grease is provided between the silicon chip and the heat spreader to transfer heat from the silicon chip to the heat spreader. To dissipate heat into the air, the external heat sink contacts the heat spreader through a second layer of thermal interface material (e.g., a thermal pad) to transfer heat from the heat spreader to the external heat sink. The external heat sink includes one or more plates oriented perpendicular to the heat sink, such as heat fins, to allow heat to flow into the heat fins for dissipation into the air.

[0022] The heat flowing from the silicon chip to the heat spreader via the first layer of thermal interface material layer is the bottleneck for transferring heat from the silicon chip to the external heat sink. To reduce this bottleneck, a heat sink design for the FCBGA is disclosed. The heat sink design has an external heat sink and a cavity-forming annular reinforcement, and the cavity-forming annular reinforcement forms a cavity with the substrate of the FCBGA. The external heat sink can be disposed on the cavity-forming annular reinforcement and the silicon chip of the FCBGA, and a layer of thermal interface material separates the cavity-forming annular reinforcement and the silicon chip from the external heat sink. Heat is transferred from the silicon chip to the external heat sink via the thermal interface material layer, and thus dissipated into a fluid medium such as air.

[0023] The disclosed heat sink structure eliminates the thermal interface material layer required to manage heat on the FCBGA between the heat sink and the silicon chip, and reduces the thermal resistance of the connection to the housing (e.g., from the silicon chip to the external heat sink). Heat from the silicon chip does not transfer from the silicon chip to the heat spreader through the first layer of thermal interface material and then from the heat spreader to the external heat sink through the second layer of thermal interface material. Instead, heat is transferred from the silicon chip to the external heat sink through a single layer of thermal interface material. The disclosed external heat sink for the FCBGA also provides other advantages.

[0024] Example illustrations

[0025] Figures 1A - 1C Various example views of an example flip chip ball grid array (FCBGA) with an example heat sink design are shown. Figure 1A and Figure 1B show a side view 100 and a top view 150 of the cavity-forming annular reinforcement 128 of the FCBGA, respectively. Additionally, Figure 1C shows the external heat sink 130 of the FCBGA, which is disposed on the cavity-forming annular reinforcement 128. As compared with Figure 1A and Figure 1CAssociated views can be associated with the x or y dimension, which may be the same assuming FCBGA symmetry, but in other examples the views may vary in size. Similar components in the views are labeled with similar reference numerals.

[0026] The FCBGA has a silicon chip 110 disposed on one side of a substrate 120 and a ball grid array 122 disposed on the other side of the substrate 120. The silicon chip 110 can be an integrated circuit disposed on the substrate 120 using controlled collapse chip connection. Controlled collapse chip connection or its abbreviation C4 is a method for interconnecting semiconductor devices such as the silicon chip 110 with a circuit such as the substrate 120 through solder bumps deposited on chip pads. The ball grid array 122 disposed on the other side of the substrate 120 is a surface mount package for an integrated circuit. The ball grid array 122 allows the FCBGA to be surface mounted to a printed circuit board (not shown).

[0027] The silicon chip 110 can generate heat during operation. To enable the silicon chip to operate at an optimal temperature, an external heat sink 130 can be placed on the cavity-forming annular reinforcement 128 and the silicon chip 110. The external heat sink 130 can transfer the heat generated by the silicon chip 110 during operation to a fluid medium such as air for dissipation from the silicon chip 110.

[0028] The cavity-forming annular reinforcement 128 can be a rigid one-piece structure made of a metal such as copper with a nickel plating or aluminum. The cavity-forming annular reinforcement 128 can be defined by a first section 102, a stepped transition 104 or a lower step, and a second section 106, each separated by a dashed line, and for ease of illustration, the first section 102, the stepped transition 104 or the lower step, and the second section 106 are shown for one side of the cavity-forming annular reinforcement 128, but both sides of the cavity-forming annular reinforcement 128 can be similarly configured. In an example, the first section 102, the stepped transition 104 or the lower step, and the second section 106 can each have a thickness of 0.3 mm to 4 mm. At least the second section 106 and the substrate 120 can form a cavity 112, and in an example, the first section 102 can be lower than the second section 106. The first section 102 can be disposed along the periphery of the substrate 120 to support the cavity-forming annular reinforcement, and the second section 106 can be oriented at a height H substantially parallel to the substrate 120. The stepped transition 104 can facilitate the transition from the first section 102 at a different height to the second section 106. As shown in the top view 150, the second section 106 having a length L can expose the top 134 of the silicon chip 110. The exposure can be such that the section 106 covers a portion of the top 134 or does not cover the top 134 at all. In an example, the length L of the second section 106 can define a slot 108 between the silicon chip 110 and the second section 106 in the top view 150.

[0029] The cavity-forming annular reinforcement 128 further supports the external heat sink 130 and increases mechanical stiffness to prevent warping of the substrate 120. The rigidity is increased compared to an annular structure without the cavity 112 formed. As Figure 1C shown, the external heat sink 130 together with the cavity-forming annular reinforcement 128 can also be made of various metals, such as copper or aluminum with nickel plating. The external heat sink 130 can be disposed on the second section 106 of the cavity-forming annular reinforcement 128 and on the top 134 of the silicon chip 110, and is separated by a thermal interface material layer 132. In an example, the thermal interface material layer 132 can have a uniform thickness. The thermal interface material 132 can be a material with a thermal resistance that promotes heat conduction, such as thermal grease with a silicon-based filler or a thermal pad such as a graphite pad, with a thickness in the range of dozens of microns. Thermal grease (also known as thermal paste, heat dissipation compound, heat sink paste, thermal compound, thermal glue, thermal interface material, or heat paste) is a thermally conductive (but usually electrically insulating) compound. The role of thermal grease may be to eliminate air gaps or voids in the interface region (which act as heat insulators) to maximize heat transfer and heat dissipation. The thermal interface material 132 can conduct heat from the silicon chip 110, which is exposed to the external heat sink 130 through the cavity-forming annular reinforcement 128. To dissipate heat into the air, the external heat sink 130 can include one or more plates 124 on the top of the external heat sink 130, such as heat sinks. In some examples, the heat sinks can be oriented perpendicular to the second section 106 of the cavity forming the annular reinforcement 128. Heat flows from the silicon chip 110 through the thermal interface material 132 and from the plates 124 of the external heat sink 130 for dissipation into the air.

[0030] The second section 106 of the cavity-forming annular reinforcement 128 can have a length L that exposes the top 134 of the silicon chip 110 in different amounts. In some examples, the length L of the second section 106 of the cavity-forming annular reinforcement 128 can be dimensioned such that the second section 106 does not cover the top 134 of the silicon chip 110 and does not cover the adjacent area on the substrate 120. As long as the external heat sink 130 and the thermal interface material 132 are not disposed on the cavity-forming annular reinforcement 128, the silicon chip 110 will not be covered. This area is not covered, allowing access to this area from above.

[0031] Figure 2A and Figure 2BShows an example side view 200 and an example top view 250 of an example FCBGA having an example cavity-forming annular reinforcement 128 with a second section 106 that does not cover an area 202 on a substrate 120 of the example FCBGA. In the example, the area 202 may have probe pads coupled to a silicon chip 110 to probe the silicon chip 110 and / or an integrated circuit. The second section 106 of the cavity-forming annular reinforcement 128 may have a length L so as not to extend over the area 202 to cover the area 202. Additionally, the second section 106 may not cover the top of the silicon chip 110. The slot 108 between the silicon chip 110 and the second section 106 may take different shapes. The shape shown in the top view 250 is circular, indicating that the length L may vary along the x or y dimension around the silicon chip 110, but the shape may take other forms including rectangular or oval. When an external heat sink 130 (not shown) is not arranged on the cavity-forming annular reinforcement 128, the slot 108 may allow access to the area 202 from above.

[0032] In the above example, the height of the cavity-forming annular reinforcement 128 and the height of the top of the silicon chip 110 may be the same. For example, the second section 106 and the top of the silicon chip 110 are in the same plane. In other examples, the second section 106 of the cavity-forming annular reinforcement 128 may be below or above the top of the silicon chip 110.

[0033] Figure 3A and Figure 3B Shows an example side view of an example cavity-forming annular reinforcement 128 having different heights. In Figure 3A this, the second section 106 of the cavity-forming annular reinforcement 128 may be higher than the height of the silicon chip 110. In Figure 3B this, the second section 106 of the cavity-forming annular reinforcement 128 may be lower than the height of the silicon chip 110. The external heat sink 130 may be modified to account for the height difference between the top of the silicon chip 110 and the second section 106 of the cavity-forming annular reinforcement 128.

[0034] Figure 4Shows a side view example of an example external heat sink 130, the example external heat sink 130 is disposed on an example cavity forming annular reinforcement 128, and a second section 106 of the example cavity forming annular reinforcement 128 is higher than the height of the silicon chip 110. A protrusion 302 may be formed on the bottom 308 of the external heat sink 130 on the silicon chip 110. The protrusion 302 may be made of the same material or a different material as the external heat sink 130. A thermal interface material 306 may be disposed between the external heat sink 130 and the silicon chip 110 and between the external heat sink 130 and the second section 106. Compared with the external heat sink 130 without the protrusion 302, the protrusion 302 may reduce the thickness of the thermal interface material 306 required between the silicon chip 110 and the external heat sink 130. For example, when the external heat sink is disposed on the second section 106 and on the silicon chip 110, the thickness of the thermal interface material 306 between the silicon chips 110 and the thickness of the thermal material between the support 106 and the external heat sink 130 may be substantially the same or uniform. The second section 106 being higher than the top of the silicon chip 110 may also allow protecting the silicon chip 110 during processing of the FCBGA. Any impact on the FCBGA will be absorbed by the example cavity forming annular reinforcement 128 rather than the silicon chip 110. If the second section 106 of the example cavity forming annular reinforcement 128 is lower than the height of the silicon chip 110, a portion of the bottom 308 of the external heat sink 130 may be formed with a groove on the silicon chip 110 (not shown). The thermal interface material 306 may be disposed between the external heat sink 130 and the silicon chip 110 and between the external heat sink 130 and the second section 106. The groove on the bottom of the external heat sink 130 may provide space for increasing the thickness. Compared with the external heat sink 130 without the groove, the thermal conductivity of the thermal interface material between the silicon chip 110 and the external heat sink 130 is reduced. For example, when the external heat sink is disposed on the second section 106 and on the silicon chip 110, the thickness of the thermal interface material 306 between the silicon chips 110 and the thickness of the thermal material between the support 106 and the external heat sink 130 may be substantially the same or uniform. Other variations are possible.

[0035] Figure 5A and Figure 5BShows an example side view 500 and an example top view 550 of an example cavity-forming annular stiffener 128, which has a uniform height and is disposed on a substrate 120 of an FCBGA. The views can be associated with the x or y dimensions, which can be the same assuming the symmetry of the FCBGA, but in other examples, the views can vary according to the dimensions. The example cavity-forming annular stiffener 128 can be a ridge-like monolithic structure defined by a first section 502 and a second section 504. The first section 502 can be positioned along the periphery 506 of the substrate 120. The second section 504 is shown to be at the same height as the top of the silicon chip 110, but in other examples can be lower or higher than the top of the silicon chip 110. The second section 504 can be oriented substantially parallel to the substrate 120 in the longitudinal direction L of the length direction to form a cavity 112. Additionally, the second section 504 can be at a uniform height from the periphery 506 of the substrate 506 above the substrate 120. The substrate 120 faces the center 508 of the substrate 120, and there is a groove 510 between the silicon chip 110 and the second section 504. In an example, an external heat sink 130 (not shown) can be disposed on the second section 504 of the cavity-forming annular stiffener 128, where a thermal interface material separates the second section 504 of the cavity-forming annular stiffener 128 and the top of the silicon chip 110 from the external heat sink 130. The area of the second section 504 that supports the external heat sink 130 can be larger than the area of the second section 106 because there is no stepped transition 104 in this example of the cavity-forming annular stiffener 128. Furthermore,. In some examples, the first section 502 can have a greater thickness than the second section 504 to increase the stability of the cavity-forming annular stiffener 128 in supporting the external heat sink 130.

[0036] In some examples, the cavity-forming annular stiffener 128 can be made of multiple sections joined together rather than a one-piece structure.

[0037] Figure 6An example side view showing another example of a cavity-forming annular stiffener 128 having a uniform height. The example cavity-forming annular stiffener 128 can be a ridge-like two-piece structure defined by a first section 602 and a second section 604 fixed at an interface 606. The two sections 602, 604 can be fixed, for example, by adhesive connection or mechanical connection at the interface 606. The section 602 can be a conventional annular stiffener along the periphery 608 of the substrate 120, with the section 604 disposed on top thereof to form the cavity-forming annular stiffener 128. The section 604 can be oriented to be substantially parallel to the substrate 120 in the longitudinal direction of the length L view. Further, the section 604 can be at a uniform height above the substrate 120 from the periphery 608 of the substrate 120 towards the center 610 of the substrate 120. For example, an external heat sink 130 (not shown) can be provided on the section 604 of the cavity-forming annular stiffener 128, where a thermal interface material separates the silicon chip 110 and the section 604. The section 604 can be a support for the external heat sink 130.

[0038] In the above example, the example cavity-forming annular stiffener 128 is described as exposing the top 134 of the silicon chip 110. In other examples, the example cavity-forming annular stiffener 128 can further contact the silicon chip 110. For example, the sections 106, 504 or 604 of the example cavity-forming annular stiffener 128 contact the silicon chip 110. The contact with the silicon chip 110 can cause the example cavity-forming annular stiffener 128 to conduct heat from the silicon chip 110 to the substrate 120 of the FCBGA and transfer it from the silicon chip 110 to the external heat sink 130 through the thermal interface material 132.

[0039] Exemplary functions

[0040] Figure 7 Is a flowchart 700 of an example function associated with the assembly of the example cavity-forming annular stiffener 128 and the example external heat sink 130 on the FCGBA.

[0041] At 702, the example cavity-forming annular stiffener 128 is disposed on the substrate 120 of the FCBGA. The example cavity-forming annular stiffener 128 can expose the top of the silicon chip 110 of the FCBGA. The example cavity-forming annular stiffener 128 can also define a cavity relative to the substrate 120. The example cavity-forming annular stiffener 128 can be made of a metal such as copper plated with nickel or aluminum.

[0042] At 704, a thermal interface material is disposed on (i) a section of the example cavity forming the annular reinforcement 128, which is for supporting the external heat sink 130, and (ii) on top of the silicon chip 110 of the FCBGA. An example of this section of the example cavity forming the annular reinforcement is shown and described above. The thermal interface material 132 can be a thermal grease having silicon filler to improve thermal conductivity, or can be other materials such as a thermal pad, which in some examples can be a multiple of ten microns thick.

[0043] At 706, the external heat sink 130 is disposed on the thermal interface material 132 to transfer heat from the silicon chip 110 to the external heat sink 130 via the thermal interface material 132. The external heat sink 130 can also have a plate 124 such as a heat sink to conduct heat from the silicon chip 110 into the air.

[0044] At 708, the FCBGA is surface-mounted on a printed circuit board. In an example, the ball grid array 122 of the substrate 120 can assist in mounting the FCBGA to the printed circuit board.

[0045] Unless explicitly stated, the use of the phrase "at least" before a list with the conjunction "and" should not be regarded as an exclusive list, nor should it be interpreted as a list of categories having one item in each category. Otherwise. A clause that recites "at least one of A, B, and C" can only infringe one of the listed items, multiple of the listed items, and one or more of the listed items and another item not listed.

[0046] Although aspects of the present disclosure have been described in connection with specific embodiments of the present disclosure presented as examples, alternatives, modifications, and variations can be made to the examples. Therefore, the embodiments set forth herein are intended to be illustrative and not limiting. Changes can be made without departing from the scope of the claims set forth below.

Claims

1. A flip chip ball grid array, comprising: a substrate including a ball grid array; a ring-shaped reinforcement disposed on the substrate and forming a cavity with the substrate, the ring-shaped reinforcement including an opening; a silicon chip disposed in the cavity and mounted on a side of the substrate opposite to the side with the ball grid array and in contact with the side of the substrate opposite to the side with the ball grid array, and when the ring-shaped reinforcement is attached to the substrate, the silicon chip is exposed by the opening; a thermal interface material disposed on the silicon chip at the opening in the ring-shaped reinforcement; an external heat sink disposed above the opening and on the thermal interface material; and probe pads disposed on the substrate, wherein the opening of the ring-shaped reinforcement is configured to: expose an area on the substrate having the silicon chip and the probe pads, and provide a channel for probing the silicon chip via the probe pads.

2. The flip chip ball grid array according to claim 1, wherein the thermal interface material contacts the silicon chip in the opening of the ring-shaped reinforcement.

3. The flip chip ball grid array according to claim 1, wherein: the height of the cavity is less than the height of the silicon chip; and the silicon chip at least partially extends into the opening of the ring-shaped reinforcement.

4. The flip chip ball grid array according to claim 1, wherein the ring-shaped reinforcement comprises: a first section; and a second section disposed along the periphery of the substrate and transitioning to the first section by a stepped transition.

5. The flip chip ball grid array according to claim 4, wherein the second section is disposed along the periphery of the substrate.

6. The flip chip ball grid array according to claim 1, wherein the ring-shaped reinforcement has a uniform height from the periphery of the substrate to the center of the substrate and surrounds the silicon chip.

7. The flip chip ball grid array according to claim 1, wherein the thermal interface material comprises thermal grease or is implemented as a thermal conductive pad.

8. The flip chip ball grid array according to claim 1, wherein the height of the ring-shaped reinforcement is equal to the height of the silicon chip.

9. The flip chip ball grid array according to claim 1, wherein the external heat sink comprises one or more fins extending perpendicular to a section of the ring-shaped reinforcement.

10. The flip chip ball grid array according to claim 1, wherein: the external heat sink comprises a protrusion extending into a recess of the thermal interface material above the silicon chip; and the recess of the thermal interface material is disposed in the opening of the ring-shaped reinforcement.

11. The flip chip ball grid array according to claim 1, wherein the height of the cavity is greater than the height of the silicon chip.

12. The flip chip ball grid array according to claim 11, wherein the thermal interface material is partially disposed in the opening of the ring-shaped reinforcement.

13. The flip chip ball grid array according to claim 1, wherein: the thermal interface material contacts the silicon chip; and The external heat sink contacts the thermal interface material and draws heat energy from the silicon chip via the thermal interface material.

14. The flip chip ball grid array according to claim 1, wherein: the annular reinforcement includes a first section and a second section; the first section includes the opening; and the cavity is defined by a bottom surface of the first section and a top surface of the substrate.

15. The flip chip ball grid array according to claim 1, wherein: the substrate includes chip pads; and the silicon chip includes solder bumps disposed on and connected to the chip pads.

16. The flip chip ball grid array according to claim 1, wherein the thermal interface material extends above the opening of the annular reinforcement.

17. The flip chip ball grid array according to claim 1, wherein the flip chip ball grid array does not have a heat spreader.

18. The flip chip ball grid array according to claim 1, wherein the annular reinforcement contacts the substrate.

19. A method, comprising: providing an annular reinforcement on a substrate of a flip chip ball grid array and above a silicon chip, the annular reinforcement forming a cavity with the substrate and including an opening, and when the annular reinforcement is attached to the substrate, the opening exposes the silicon chip, wherein the silicon chip is disposed in the cavity and mounted on the substrate; providing a thermal interface material at the opening in the annular reinforcement and on the silicon chip; providing an external heat sink above the opening in the annular reinforcement and on the thermal interface material; providing probe pads on the substrate; and exposing an area on the substrate having the silicon chip and the probe pads, and providing a channel for probing the silicon chip via the probe pads.

20. The method according to claim 19, wherein providing the annular reinforcement on the substrate comprises: forming the cavity such that a height of the cavity is higher than a height of the silicon chip.

21. The method according to claim 19, wherein providing the thermal interface material at the opening in the annular reinforcement such that a thickness of the thermal interface material is uniform.

22. The method according to claim 19, further comprising extending a protrusion of the external heat sink into a recess of the thermal interface material above the silicon chip.

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