Patent Description:
Electronic devices, such as tablets, computers, copiers, digital cameras, smart phones, control systems and automated teller machines, among others, often employ electronic components which leverage chip package assemblies for increased functionality and higher component density. Conventional chip packaging schemes often utilize a package substrate, often in conjunction with a through-silicon-via (TSV) interposer, to enable a plurality of integrated circuit (IC) dice to be mounted to a single package substrate. The IC dice may include memory, logic or other IC devices.

Out of plane deformation of the package substrate can be problematic to conventional chip packaging schemes. In many instances, a stiffener is utilized to stiffening the package substrate against out of plane deformation. However, particularly in larger chip package assemblies, the stiffener itself may bend or twist, or even become delaminated from package substrate, thus still permitting undesirable warpage and bending during manufacture and/or use. Such warpage and bending of the package substrate can lead to solder connection failure or other damage to the components and devices of the chip package assembly, which may detrimentally effect device performance and reliability.

Therefore, a need exists for an improved chip package assembly, and in particular, to a chip package assembly having an improved stiffener.

<CIT> describes an injection molded metal IC package stiffener and package-to-package interconnect frame. An apparatus is introduced comprising a microelectronic device package substrate, a microelectronic device coupled with a top surface of the package substrate, and an injection-molded, metal stiffener coupled with the package substrate, wherein the stiffener includes a central opening and at least partially surrounds the microelectronic device, and wherein the stiffener includes a plurality of vias that each couple a contact on a bottom surface of the stiffener with a respective contact on a top surface of the stiffener.

<CIT> describes a flip-chip package structure with stiffener including a substrate, a first stiffener positioned on a surface of the substrate, a chip having a plurality of bumps adopted to electrically connect the substrate and the chip, and a second stiffener positioned on the surface of the substrate and connected with the first stiffener. The first stiffener is positioned outside of the second stiffener.

<CIT> describes a method of manufacture of an integrated circuit packaging system which includes: providing a substrate; mounting an integrated circuit over the substrate; mounting a lid base over the substrate, the lid base having a base indentation and a hole with the integrated circuit within the hole; and mounting a heat slug over the lid base, the heat slug having a slug non-horizontal side partially within the base indentation.

<CIT> describes a reinforced semiconductor package with a stiffener. The stiffener is composed of an inner ring disposed on the upper surface of a substrate and surrounding a semiconductor chip, and an outer ring also disposed on the upper surface of the substrate but surrounding the inner ring. The inner ring and the outer ring are connected with each other by means of at least one tie bar, and cooperatively cover a majority portion of the upper surface of the substrate.

According to an aspect of the invention, there is provided a chip package assembly according to the appended claims.

In some embodiments, the stiffener further includes a standoff portion projecting below the second surface of the package substrate.

In some embodiments, , the solder balls extend a distance from the second surface of the package substrate beyond the standoff portion.

In some embodiments, the chip package assembly further includes a lid coupled to the stiffener and extending across the IC die.

The stiffener is bonded to the first surface of the package substrate and in some embodiments is bonded to the lid.

In some examples not forming part of the claimed invention, the stiffener is bonded to the second surface of the package substrate and to the lid.

In some embodiments, the second surface of the stiffener further includes a first portion covering a first corner of the package substrate and a second portion covering a second corner of the package substrate, wherein the second surface of the stiffener is discontinuous between the first and second portions.

In some embodiments, the second surface of the stiffener covers only a portion of the first surface or the second surface of the package substrate.

In some embodiments, the first surface of the stiffener covers only a portion of the side wall of the package substrate.

In some embodiments, the stiffener is bonded to the spacer and the first surface of the package substrate.

In some embodiments, the stiffener is bonded to the spacer and the second surface of the package substrate.

In some embodiments, the chip package assembly of further includes a lid coupled to the spacer and extending across the IC die.

In some embodiments, the stiffener includes a plurality of stiffener segments, each segment bonded to a different portion of the package substrate.

In an example, a method for fabricating a chip package assembly is provided that includes attaching a stiffener to a package substrate prior to attaching one or more IC dice to the package substrate.

So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, which is defined solely by the appended claims, for the invention may admit to other equally effective embodiments.

In the following, <FIG> shows an embodiment of the present invention and <FIG> and <FIG> represent examples that are useful for understanding the present invention.

It is contemplated that elements of one embodiment may be beneficially incorporated in other embodiments.

A chip package assembly and method for fabricating the same are provided which utilize an improved stiffener. The chip package assembly described herein includes at least one integrated circuit (IC) die and stiffener disposed on a package substrate. The stiffener is configured to increase the resistance of the package substrate to out of plane deformation during the fabrication and use of the chip package assembly. Advantageously, the enhanced stiffness of the chip package assembly improves reliability and performance. In various examples described herein one or more advantages may be realized that include stiffening the package substrate both the horizontal and vertical axis, greater area for adhesive attach for reduced delamination, more space for surface mounted circuit elements, such as chip capacitors, thinner package profile and ball grid array (BGA) stand-off height control, among other benefits.

Turning now to <FIG>, an exemplary integrated chip package assembly <NUM> is schematically illustrated. The chip package assembly <NUM> includes at least one or more IC dice <NUM> connected optionally by a silicon-through-via (TSV) interposer <NUM> to a package substrate <NUM>. Although two IC dice <NUM> are shown in <FIG> , the number of IC dice may range from one to as many as can be fit within the chip package assembly <NUM>. In some implementations, the interposer <NUM> may be omitted with the one or more IC dice <NUM> connected directly to a top surface <NUM> of the package substrate <NUM>. A stiffener <NUM> is coupled to at least one side wall <NUM> of the package substrate <NUM> in a manner that enhances the resistance of the package substrate <NUM> against out of plane deformation, as further discussed below.

The interposer <NUM>, when present, includes circuitry for electrically connecting the dice <NUM> to circuitry of the package substrate <NUM>. The circuitry of the interposer <NUM> may optionally include transistors and/or other circuit elements. Package bumps <NUM>, also known as "C4 bumps," are utilized to provide an electrical connection between the circuitry of the interposer <NUM> and the circuitry of the package substrate <NUM>. A bottom surface <NUM> of the package substrate <NUM> may be mounted and connected to a top surface <NUM> of a printed circuit board (PCB) <NUM>, utilizing solder balls <NUM>, wire bonding or other suitable technique. An undermolding <NUM> may be utilized to fill the space not taken by the package bumps <NUM> between the PCB <NUM> and the interposer <NUM>.

The IC dice <NUM> are mounted to one or more surfaces of the interposer <NUM>, or alternatively in implementations wherein an interposer is not utilized, to the package substrate <NUM>. The IC dice <NUM> may be programmable logic devices, such as field programmable gate arrays (FPGA), memory devices, optical devices, processors or other IC logic structures. Optical devices include photodetectors, lasers, optical sources, and the like. In the example depicted in <FIG> , the IC dice <NUM> are mounted to a top surface of the interposer <NUM> by a plurality of micro-bumps <NUM>. The micro-bumps <NUM> electrically connect the circuitry of each IC die <NUM> to circuitry of the interposer <NUM>. The circuitry of the interposer <NUM> connects the micro-bumps <NUM> to selective package bumps <NUM>, and hence, connects selective circuitry of each IC die <NUM> to the package substrate <NUM>, to enable communication of the dice <NUM> with the PCB <NUM> after the chip package assembly <NUM> is mounted within an electronic device (not shown). When the optional interposer <NUM> is not present, the micro-bumps <NUM> connects selective circuitry of each IC die <NUM> to the package substrate <NUM> to enable communication of the dice <NUM> with the PCB <NUM>. An undermolding <NUM> may be utilized to fill the space not taken by the micro-bumps <NUM> between the dice <NUM> and interposer <NUM>.

An optional lid <NUM> (shown in phantom) is disposed over the dice <NUM>. In some implementations, the lid <NUM> may be fabricated from a plastic material or other suitable material. In other implementations particularly where it is desirable to utilize the lid <NUM> to receive heat from the dice <NUM>, the lid <NUM> may be fabricated from a thermally conductive material, such as copper, nickel-plated copper or aluminum, among other suitable materials. The lid <NUM> may have a thickness of between about <NUM> and about <NUM>, although other thicknesses may be utilized. A heat sink, not shown, may optionally be mounted to the lid <NUM>.

The lid <NUM> may be coupled to the stiffener <NUM> to increase the rigidity of the chip package assembly <NUM>. For example, the lid <NUM> may be coupled to the stiffener <NUM> by an adhesive (not shown), such as an epoxy.

An adhesive <NUM> may also be utilized to couple the lid <NUM> to the dice <NUM>. The adhesive <NUM> may be selected to provide a thermally conductive path between the lid <NUM> to the dice <NUM> so that heat generated by the dice <NUM> may be dissipated through the lid <NUM>. The adhesive <NUM> may be a soft or compliant adhesive to allow compensation between mismatched heights of neighboring dice <NUM> within the chip package assembly <NUM>. In one example, the adhesive <NUM> may be a thermal gel or thermal epoxy, such as for example, packaging component attach adhesives available from Al Technology, Inc. , located in Princeton Junction, New Jersey.

The stiffener <NUM> is coupled to the package substrate <NUM> outward the IC dice <NUM>. The stiffener <NUM> extends beyond the side walls <NUM> of the package substrate <NUM> to provide mechanical support that helps prevent the chip package assembly <NUM> from bowing and twisting. The stiffener <NUM> may be a single layer structure or a multi-layer structure. The stiffener <NUM> may be a single one-piece structure or a multi-piece structure. The stiffener <NUM> may circumscribe the package substrate <NUM> as a single structure, or multiple connected or unconnected structures may be used. Although the stiffener <NUM> is only shown in sectional profile in <FIG> , the stiffener <NUM> may have a closed ring shape, an open ring shape, or other shape suitable for increasing the rigidity of the package substrate <NUM>.

The stiffener <NUM> may be made of ceramic, metal or other various inorganic materials, such as aluminum oxide (Al<NUM><NUM><NUM>), aluminum nitride (AIN), silicon nitride (SiN), silicon (Si), copper (Cu), aluminum (Al), and stainless steel, among other materials. The stiffener <NUM> can also be made of organic materials such as copper-clad laminate.

The stiffener <NUM> generally includes an inner wall <NUM> coupled to an outer wall <NUM> by a top wall <NUM>. The stiffener <NUM> also includes a bottom wall <NUM> disposed at the opposite end of the stiffener <NUM> relative to the top wall <NUM>. The bottom wall <NUM> is coupled at least to the outer wall <NUM>.

The stiffener <NUM> includes a side mounting surface <NUM> and a bottom mounting surface <NUM> at the interface between the inner wall <NUM> and the bottom wall <NUM>. In one example, the side mounting surface <NUM> is generally perpendicular to the planar orientation of the package substrate <NUM>, and may be perpendicular to one or both of the top and bottom walls <NUM>, <NUM>. Similarly, the bottom mounting surface <NUM> is generally parallel to the planar orientation of the package substrate <NUM>, and may be parallel to one or both of the top and bottom walls <NUM>, <NUM>. The side mounting surface <NUM> may extend from the inner wall <NUM> and intersect with the bottom mounting surface <NUM>, with the bottom mounting surface <NUM> then extending to the bottom wall <NUM>. The mounting surfaces <NUM>, <NUM> also disrupt the generally rectangular profile of the stiffener <NUM>, thereby increasing the rigidity of the stiffener <NUM>. Additionally, as the bottom mounting surface <NUM> is only a fraction of the width between the inner and outer walls <NUM>, <NUM> of the stiffener <NUM>, the inner wall <NUM> is closer to the side wall <NUM> of the package substrate <NUM>, thereby result in greater area of the top surface <NUM> of the package substrate <NUM> being exposed inward of the stiffener <NUM> as compared to conventional chip package assemblies. The greater top surface area of the package substrate <NUM> increases the area available to accommodate the IC dice <NUM> and surface mounted components, such as diodes, capacitors, resistors and the like.

The mounting surfaces <NUM>, <NUM> are configured contact and secure the stiffener <NUM> to the package substrate <NUM>. In one example, the bottom mounting surface <NUM> contacts and is bonded to the top surface <NUM> of the package substrate <NUM>. The bottom mounting surface <NUM> may be bonded to the top surface <NUM> of the package substrate <NUM> utilizing an epoxy or other suitable adhesive. Examples of suitable adhesives for bonding the bottom mounting surface <NUM> to the top surface <NUM> include Henkel MC-<NUM>, Dow Corning SE-<NUM>, and Shin-Etsu <NUM>-<NUM> , among others.

Similarly, the side mounting surface <NUM> contacts and is bonded to the side wall <NUM> of the package substrate <NUM>. The side mounting surface <NUM> may be bonded to the side wall <NUM> of the package substrate <NUM> utilizing an epoxy or other adhesive suitable for bonding the bottom mounting surface <NUM>. Alternatively, one or both of the mounting surfaces <NUM>, <NUM> may be secured to the package substrate <NUM> utilizing a mechanical technique, such as staking, snap fit, press fit, fastening or other suitable technique.

As the stiffener <NUM> is coupled to the side wall <NUM> of the package substrate <NUM>, the outer wall <NUM> of the stiffener <NUM> is generally farther from the center of the package substrate <NUM> than the side wall <NUM> of the package substrate. In comparison, the outer wall of conventional stiffeners are generally the same distance as the side wall <NUM> from the center of the package substrate <NUM>. As a result, the outer wall <NUM> of the stiffener <NUM> is generally farther from the center of the package substrate <NUM> then outer walls of conventional stiffeners, thereby providing protection to the side wall <NUM> of the package substrate <NUM> against chipping or other damage, while providing a larger surface area for handing the chip package assembly <NUM> during fabrication.

Bonding of the stiffener <NUM> to different planes (i.e., the top surface <NUM> and side wall <NUM>) of the package substrate <NUM> increases the stiffness of the package substrate <NUM> as compared to conventional chip package assemblies having stiffeners solely bonded to the top surface of the package substrate. Moreover, the mounting surfaces <NUM>, <NUM> provide an increased area for bonding the stiffener <NUM>, which also increases the robustness of the stiffener-to-package substrate connection, such as increasing bond strength and minimizing the propensity for delamination. Still another advantage is that the side mounting surfaces <NUM>, interfacing with the side wall <NUM> of the packing substrate <NUM>, precisely locates the stiffener <NUM> on the top surface <NUM> of the packing substrate <NUM>, thereby ensuring adequate room for later fabrication processes and components, while providing an excellent reference surface for automated fabrication and handling equipment and processes.

<FIG> is a cross sectional schematic view of another integrated chip package assembly <NUM> that includes at least one IC die <NUM> and stiffener <NUM> disposed on a package substrate <NUM>. The integrated chip package assembly <NUM> is essentially the same as the integrated chip package assembly <NUM> depicted in <FIG> , except that the stiffener <NUM> includes a standoff portion <NUM> extending below a bottom surface <NUM> of the package substrate <NUM>.

The standoff portion <NUM> of the stiffener <NUM> may be defined as the portion of the outer wall <NUM> and side mounting surface <NUM> of the stiffener <NUM> that is disposed below the bottom surface <NUM> of the package substrate <NUM>. The standoff portion <NUM> of the stiffener <NUM> may extend below the bottom surface <NUM> of the package substrate <NUM> a distance <NUM> to the bottom surface <NUM>. The distance <NUM> may be selected to control the collapse height of the solder balls <NUM> disposed inward of the stiffener <NUM>. In one implementation the distance <NUM> is selected be about <NUM> percent of the pre-collapse height of the solder balls <NUM>. For example, during reflow, the solder balls <NUM> collapse during mounting of the chip package assembly <NUM> to the PCB <NUM>. During mounting, the bottom wall <NUM> of the stiffener <NUM> contacts the top surface <NUM> of the PCB <NUM>, thereby controlling the collapse height of the solder balls <NUM> to a predefined amount. Another advantage of the standoff portion <NUM> is that the standoff portion <NUM> protects the solder balls <NUM> prior to mounting to the PCB <NUM>.

<FIG> is a cross sectional schematic view of another integrated chip package assembly <NUM> that includes at least one IC die <NUM> and stiffener <NUM> disposed on a package substrate <NUM>. The integrated chip package assembly <NUM> is essentially the same as the integrated chip package assembly <NUM> depicted in <FIG> , except that the stiffener <NUM> is mounted to both the side wall <NUM> and the bottom surface <NUM> of the package substrate <NUM>.

For example, the side mounting surface <NUM> of the stiffener <NUM> contacts and is bonded to the side wall <NUM> of the package substrate <NUM> discussed above, while a top mounting surface <NUM> contacts and is bonded to the bottom surface <NUM> of the package substrate <NUM>. The mounting surfaces <NUM>, <NUM> may be bonded to the package substrate <NUM> utilizing an epoxy or other adhesive as discussed above.

In one implementation, the inner wall <NUM> of the stiffener <NUM> is advantageously outward of the side wall <NUM> of the package substrate <NUM>, maximizing the area of the top surface <NUM> of the package substrate <NUM> available for die mounting or for surface mounted circuit components. Another advantage of the implementation depicted in <FIG> is that the bottom wall <NUM> of the stiffener <NUM> extends below the bottom surface <NUM> of the package substrate <NUM>, thereby protecting the solder balls <NUM> prior to mounting to the PCB <NUM>.

In the example illustrated in <FIG>, the stiffener <NUM> is shown coupled to the optional lid <NUM>. However, in other examples, the lid <NUM> may not be present. In still other examples, the top wall <NUM> of the stiffener <NUM> may be flush with, or slightly below the top surface <NUM> of the package substrate <NUM>.

<FIG> is a cross sectional schematic view of another integrated chip package assembly <NUM> that includes at least one IC die <NUM> and stiffener <NUM> disposed on a package substrate <NUM>. The integrated chip package assembly <NUM> is essentially the same as the integrated chip package assembly <NUM> depicted in <FIG> , except that the stiffener <NUM> includes a standoff portion <NUM> extending below a bottom surface <NUM> of the package substrate <NUM>. In other respects, the stiffener <NUM> is essentially the same as the stiffener <NUM>.

In the implementation depicted in <FIG>, the standoff portion <NUM> extends a distance <NUM> below the bottom surface <NUM> of the package substrate <NUM>. As discussed above, the distance <NUM> may be selected to control the collapse height of the solder balls <NUM> disposed inward of the stiffener <NUM>. In one implementation the distance <NUM> is selected be about <NUM> percent of the precollapse height of the solder balls <NUM>. Another advantage of the standoff portion <NUM> is that the standoff portion <NUM> protects the solder balls <NUM> prior to mounting to the PCB <NUM>.

<FIG> is a partial sectional view of an alternative example of a stiffener <NUM> which may be utilized in an integrated chip package assembly, such as the integrated chip package assemblies <NUM>, <NUM>, <NUM>, <NUM> of <FIG>, among others. Optionally, the stiffener <NUM> may include a standoff portion <NUM>, as shown in <FIG> or <FIG>.

Similar to the other stiffeners described herein, the stiffener <NUM> includes a top wall <NUM>, a bottom wall <NUM>, an outer wall <NUM> and an inner all <NUM>. The inner wall <NUM> of the stiffener <NUM> includes a substrate edge receiving pocket <NUM> that is configured to capture the side wall <NUM> of the package substrate <NUM>. The substrate edge receiving pocket <NUM> may be a groove or area between projections extending from the inner all <NUM> of the stiffener <NUM>. In the implementation depicted in <FIG>, the substrate edge receiving pocket <NUM> is defined between two barbs <NUM>, <NUM> extending from the inner wall <NUM> of the stiffener <NUM>. The barbs <NUM>, <NUM> include an entrance angle <NUM> that facilitates the side wall <NUM> of the package substrate <NUM> to be slid and snap-fit into the substrate edge receiving pocket <NUM>. In some implementations, use of an adhesive to bond the package substrate <NUM> into the substrate edge receiving pocket <NUM> may be omitted.

<FIG> is top view of stiffeners <NUM> that may be utilized in an integrated chip package assembly, such as the integrated chip package assemblies <NUM>, <NUM>, <NUM>, <NUM> of <FIG>, among others. The stiffeners <NUM> may be secured to the package substrate <NUM> of the chip package assembly <NUM> in any manner as described above, or other suitable manner.

The stiffeners <NUM> are disposed along edges of the side walls <NUM>. Optionally, the stiffeners <NUM> may extend along edges of the side walls <NUM> to engage the corners <NUM> of the package substrate <NUM>. The stiffeners <NUM> may have any of the profiles described above for the stiffeners <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or other suitable profile. Although only one stiffener <NUM> is shown engaged with every other side wall <NUM> of the package substrate <NUM> in <FIG>, one or more stiffeners <NUM> may be engaged with at least one side wall <NUM> of the package substrate <NUM>. For example, one or more stiffeners <NUM> may be engaged with each of the four side walls <NUM> of the package substrate <NUM>.

Additionally, although the stiffeners <NUM> are shown engaging the top surface <NUM> and side walls <NUM> of the package substrate <NUM>, the stiffeners <NUM> may alternatively be engage the bottom surface <NUM> and side walls <NUM> of the package substrate <NUM> as shown in <FIG>, or engage the package substrate with a receiving pocket <NUM> as shown in <FIG>. Optionally, the stiffeners <NUM> may include a standoff portion <NUM>, as shown in <FIG> or <FIG>.

The stiffeners <NUM> are disposed along edges of the side walls <NUM> and engage at least one corner <NUM> of the package substrate <NUM>. The stiffeners <NUM> may have any of the profiles described above for the stiffeners <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or other suitable profile. Although only two stiffeners <NUM> are shown circumscribing the perimeter of the side walls <NUM> of the package substrate <NUM> in <FIG>, three or more stiffeners <NUM> may be utilized.

Additionally, although the stiffeners <NUM> are shown engaging the top surface <NUM> and side walls <NUM> of the package substrate <NUM>, the stiffeners <NUM> may alternatively be engage the bottom surface <NUM> and side walls <NUM> of the package substrate <NUM> as shown in <FIG>, or engage the package substrate with a receiving pocket <NUM> as shown in <FIG>.

<FIG> is top view of a stiffener <NUM> that may be utilized in an integrated chip package assembly, such as the integrated chip package assemblies <NUM>, <NUM>, <NUM>, <NUM> of <FIG>, among others. The stiffener <NUM> may be secured to the package substrate <NUM> of the chip package assembly <NUM> in any manner as described above, or other suitable manner. Although only a single ring-shaped stiffener <NUM> is shown circumscribing the perimeter of the side walls <NUM> of the package substrate <NUM> in <FIG>, multiple stiffeners <NUM> may be utilized.

The stiffener <NUM> is disposed along edges of the side walls <NUM> and engages the corners <NUM> of the package substrate <NUM>. The stiffener <NUM> generally may have any of the profiles described above for the stiffeners <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or other suitable profile. Additionally, although the stiffener <NUM> is shown engaging the top surface <NUM> and side walls <NUM> of the package substrate <NUM>, the stiffener <NUM> may alternatively be engage the bottom surface <NUM> and side walls <NUM> of the package substrate <NUM> as shown in <FIG>, or engage the package substrate with a receiving pocket <NUM> as shown in <FIG>.

In the implementation depicted in <FIG>, the stiffener <NUM> includes at least one portion, for example a surface mounting pad <NUM>, that overlays the top surface <NUM> at least one of the corners <NUM> of the package substrate <NUM>. Other portions <NUM> of the stiffener <NUM> between the surface mounting pad <NUM> do overlays the top surface <NUM>. In the illustrated example, the stiffener <NUM> includes four mounting pads <NUM> that overlay the top surface <NUM> at each of the corners <NUM> of the package substrate <NUM>. The surface mounting pads <NUM> do not overlay the entire region (i.e., the portion <NUM>) of the side wall <NUM> between adjacent corners <NUM>.

As better illustrated in the sectional view of <FIG> taken along section lines <NUM> - - <NUM> of <FIG>, the stiffener <NUM> includes a side mounting surface <NUM> and an outer wall <NUM>. The side mounting surface <NUM> is bonded to the side wall <NUM> of the package substrate <NUM> as described above. As additionally illustrated in the sectional view of <FIG> taken along section lines <NUM> - - <NUM> of <FIG>, the stiffener <NUM> includes a bottom mounting surface <NUM> that is bonded to the top surface <NUM> of the package substrate <NUM> as described above.

Alternatively, the mounting pads <NUM> may overlay the bottom surface <NUM> of the package substrate <NUM>. In such an implementation, the stiffener <NUM> is configured to include a top mounting surface <NUM> that is bonded to the bottom surface <NUM> of the package substrate <NUM>, as described above with reference to <FIG>.

<FIG> is a top view of a stiffener <NUM> that may be utilized in an integrated chip package assembly, such as the integrated chip package assemblies <NUM>, <NUM>, <NUM>, <NUM> of <FIG>, among others. The stiffener <NUM> is similar to the stiffener <NUM> describe above, except that stiffener <NUM> includes at least one surface mounting pad <NUM> that overlays the top surface <NUM> between the corners <NUM> of the package substrate <NUM>. The corners <NUM> of the package substrate <NUM> are generally exposed by the stiffener <NUM>.

In the illustrated example, the stiffener <NUM> includes four mounting pads <NUM> that overlay the top surface <NUM> between each of the corners <NUM> of the package substrate <NUM>. The surface mounting pads <NUM> of the stiffener <NUM> do not overlay the corners <NUM> of the package substrate <NUM>. The portion of the stiffener <NUM> not overlaying the top surface <NUM> is configured as shown in the sectional view of the stiffener <NUM> illustrated in <FIG>. The portion of the stiffener <NUM> overlaying the top surface <NUM> (i.e., the surface mounting pad <NUM>) is configured as shown in the sectional view of the stiffener <NUM> illustrated in <FIG>.

The stiffener <NUM> may be secured to the package substrate <NUM> of the chip package assembly <NUM> in any manner as described above, or other suitable manner. Although only a single ring-shaped stiffener <NUM> is shown circumscribing the perimeter of the side walls <NUM> of the package substrate <NUM> in <FIG> , multiple stiffener <NUM> may be utilized.

In the implementation depicted in <FIG> , the stiffener <NUM> includes at least one surface mounting pad <NUM> that overlays the top surface <NUM> between at least two of the corners <NUM> of the package substrate <NUM>. In the illustrated example, the stiffener <NUM> includes four mounting pads <NUM> that overlay the top surface <NUM> between each of the corners <NUM> of the package substrate <NUM>. The surface mounting pads <NUM> do not overlay the corners <NUM> of the package substrate <NUM>.

<FIG> are partial sectional views of a stiffener <NUM> interfaced with an adapter <NUM> or an adapter <NUM> that may be utilized in an integrated chip package assembly, such as the integrated chip package assemblies <NUM>, <NUM>, <NUM>, <NUM> of <FIG>, among others. Although the adapters <NUM>, <NUM> are illustrated in <FIG> as interfacing with the stiffener <NUM>, the adapters <NUM>, <NUM> may be utilized with the other stiffeners described herein. For example, the stiffener <NUM> may include a standoff portion <NUM> as shown in <FIG>.

The adapter <NUM> may be fabricated from the same materials as the stiffener <NUM>. The adapter <NUM> is bonded to the stiffener <NUM> to increase the rigidity of the package substrate <NUM>. The adapter <NUM> may be bonded to the stiffener <NUM> utilizing any suitable adhesives, such as the adhesives utilized to bonded the stiffener <NUM> to the package substrate <NUM>. Alternatively, the adapter <NUM> may be mechanically coupled to the stiffener <NUM>. If an optional lid <NUM> is incorporated into the chip package assembly, the lid <NUM> may be bonded to the adapter <NUM>.

Referring first to the implementation depicted in <FIG>, the adapter <NUM> includes a top wall <NUM>, a bottom wall <NUM>, an inner wall <NUM> and an outer wall <NUM>. The adapter <NUM> also includes an outer mounting surface <NUM> and a bottom mounting surface <NUM>. At least one or both of the mounting surfaces <NUM>, <NUM> are bonded to the adjacent surface of the stiffener <NUM>, thereby increasing the overall stiffness of the stiffener/adaptor assembly, and consequently, the increasing the stiffness of the package substrate <NUM> mounted thereto. The interface between the outer mounting surface <NUM> and the inner wall <NUM> of the stiffener <NUM> precisely locates the adapter <NUM> on the stiffener <NUM>.

Referring now to the implementation depicted in <FIG>, the adapter <NUM> includes a top wall <NUM>, a bottom wall <NUM>, an inner wall <NUM> and an outer wall <NUM>. The adapter <NUM> also includes an inner mounting surface <NUM> and a bottom mounting surface <NUM>. At least one or both of the mounting surfaces <NUM>, <NUM> are bonded to the adjacent surface of the stiffener <NUM>, thereby increasing the overall stiffness of the stiffener/adaptor assembly, and consequently, the increasing the stiffness of the package substrate <NUM> mounted thereto. The interface between the inner mounting surface <NUM> and the outer wall <NUM> of the stiffener <NUM> precisely locates the adapter <NUM> on the stiffener <NUM>.

The adapters <NUM>, <NUM> allow a standardized stiffener to be utilized with a predefined package substrate in a large variety of IC package assembly configurations, with only the simple and inexpensive adapter needing to be customized for a specific design. For example, the adapters <NUM>, <NUM> may be utilized with any of the stiffeners <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> described above, with or without lids <NUM>. Use of a standardized stiffener and package substrate size allows different chip package assemblies to be fabricated more rapidly with less expense.

<FIG> is a block diagram of one example of a method <NUM> for forming a chip package assembly <NUM> having improved stiffener. The stiffener may be any of the stiffeners described above, or other suitable stiffener. The method <NUM> begins at block <NUM> by printing surface mounting paste on a substrate, such as the package substrate <NUM>, at pad locations where surface components are to be placed. The surface mounting paste may be printed using screen printing, ink jet printing or other suitable process.

At block <NUM>, surface components, such as diodes, capacitors, resistors and the like, are mounted to the surface mounting paste. At block <NUM>, a first reflow process is performed to reflow solder to electrically connect the component leads of the surface components to the pads on the package substrate <NUM>. The first reflow process may be performed in a conveyor oven or using other suitable technique. At block <NUM>, solder bumps formed on the package substrate <NUM> are coined. Package bumps <NUM> are then formed on the coined surface.

At block <NUM>, the stiffener is attached to the package substrate <NUM>. As discussed above, the stiffener may be attached to the side wall <NUM> and at least one of the top and bottom surfaces <NUM>, <NUM> of the package substrate <NUM> using an epoxy or other suitable adhesive. At block <NUM>, IC chips, such as the IC dice <NUM>, are attached to the package substrate <NUM>. The IC dice <NUM> may be directly attached to the package substrate <NUM>, or an interposer <NUM> already having the IC dice <NUM> mounted thereon may be attached to the package substrate <NUM>. As the stiffener is already attached to the package substrate <NUM>, the package substrate <NUM> is less susceptible to warpage and/or bowing during the chip attach process at block <NUM>.

At block <NUM>, a second reflow process is performed to reflow solder in the package bumps <NUM> to electrically connect the IC dice <NUM> to the package substrate <NUM>. The second reflow process may be performed in a conveyor oven or using other suitable technique. As the stiffener is already attached to the package substrate <NUM>, the package substrate <NUM> is less susceptible to warpage and/or bowing due to thermal expansion during the second reflow process performed at block <NUM>.

At block <NUM>, underfill, such as the undermolding <NUM>, is dispensed between the package substrate <NUM> and interposer <NUM>. If the IC dice <NUM> are directly mounted to the package substrate <NUM>, the underfill may be directly disposed between the IC dice <NUM> and the package substrate <NUM>. Optionally, if a lid <NUM> is utilized, the lid <NUM> may be disposed over the IC dice <NUM> and coupled to the stiffener after the underfill process is complete at block <NUM>.

At block <NUM>, solder balls <NUM> are attached to a side of the package substrate <NUM> opposite the IC dice <NUM>. As the stiffener is already attached to the package substrate <NUM>, the package substrate <NUM> is less susceptible to warpage and/or bowing during the solder ball attach process performed at block <NUM>.

At block <NUM>, a third reflow process is performed to reflow solder in the solder balls <NUM> to electrically connect the package substrate <NUM> to the PCB <NUM>. The third reflow process may be performed in a conveyor oven or using other suitable technique. As the stiffener is already attached to the package substrate <NUM>, the package substrate <NUM> is less susceptible to warpage and/or bowing due to thermal expansion during the third reflow process performed at block <NUM>.

<FIG> is a block diagram of another example of a method <NUM> for forming a chip package assembly <NUM> having improved stiffener. The stiffener may be any of the stiffeners described above, or other suitable stiffener. The method <NUM> begins at block <NUM> wherein a stiffener is attached to a package substrate <NUM>. As discussed above, the stiffener may be attached to the side wall <NUM> and at least one of the top and bottom surfaces <NUM>, <NUM> of the package substrate <NUM> using an epoxy or other suitable adhesive.

At block <NUM> by printing surface mounting paste on a substrate, such as the package substrate <NUM>, at pad locations where surface components are to be placed. The surface mounting paste may be printed using screen printing, ink jet printing or other suitable process. At block <NUM>, surface components, such as diodes, capacitors, resistors and the like, are mounted to the surface mounting paste.

At block <NUM>, IC chips, such as the IC dice <NUM>, are attached to the package substrate <NUM>. The IC dice <NUM> may be directly attached to the package substrate <NUM>, or an interposer <NUM> already having the IC dice <NUM> mounted thereon may be attached to the package substrate <NUM>. As the stiffener is already attached to the package substrate <NUM>, the package substrate <NUM> is less susceptible to warpage and/or bowing during the chip attach process at block <NUM>.

At block <NUM>, a reflow process is performed to reflow solder in the package bumps <NUM> to electrically connect the IC dice <NUM> to the package substrate <NUM>. The reflow process may be performed in a conveyor oven or using other suitable technique. As the stiffener is already attached to the package substrate <NUM>, the package substrate <NUM> is less susceptible to warpage and/or bowing due to thermal expansion during the reflow process performed at block <NUM>.

At block <NUM>, solder balls <NUM> are attached to a side of the package substrate <NUM> opposite the IC dice <NUM>. As the stiffener is already attached to the package substrate <NUM>, the package substrate <NUM> is less susceptible to warpage and/or bowing during the solder ball attach process performed at block <NUM>. At block <NUM>, another reflow process is performed to reflow solder in the solder balls <NUM> to electrically connect the package substrate <NUM> to the PCB <NUM>. The reflow process performed at block <NUM> may be performed in a conveyor oven or using other suitable technique. As the stiffener is already attached to the package substrate <NUM>, the package substrate <NUM> is less susceptible to warpage and/or bowing due to thermal expansion during the reflow process performed at block <NUM>.

One advantage of the methods <NUM>, <NUM> is that the stiffener attach at block <NUM> occurs prior to the chip attach at block <NUM>, which happens in reverse order when practicing a conventional fabrication process. Attaching the stiffener prior to the chip reduces warpage that may be induced during the subsequent solder reflows. Thus, the methods <NUM>, <NUM> keeps the substrate flat during chip-attach reflow, ensuring proper C4 joint formation. Additionally, the flatter chip package assembly <NUM>, imparts less stress on the C4 solder joints, as compared to conventionally fabricated chip packages, and thus, helps prevent post-reflow solder joint defects from occurring.

Thus, a chip package assembly and method for fabricating the same have been provided which utilize a stiffener to improve the resistance of a package substrate to out of plane deformation. The implementations described above advantageously provide one or more of the following benefits: enhanced warpage control while maintaining lower package profile; BGA solder ball height collapse control; stiffener standardization through use of customizable adaptors; pre-attached stiffeners for enhanced warpage control at chip-attach reflow; larger stiffeners that provide greater surface area for clamping during package fabrication; edge protection for the package substrate during handling and processing; and mechanical damage protection for BGA solder balls, among other benefits.

Claim 1:
A chip package assembly (<NUM>) comprising:
a package substrate (<NUM>) having a first surface (<NUM>) and a second surface (<NUM>) coupled by a side wall (<NUM>);
at least one integrated circuit, IC, die (<NUM>) disposed on the first surface of the package substrate;
a stiffener (<NUM>) having a first surface (<NUM>) disposed outward of and bonded to the side wall of the package substrate, the stiffener having a second surface (<NUM>) bonded to the first surface of the package substrate, the stiffener circumscribing the IC die, the stiffener further including: a third surface (<NUM>) disposed opposite the first surface of the stiffener and parallel thereto; an inner wall (<NUM>) parallel to the first and third surfaces (<NUM>,<NUM>) and coupled to the third surface (<NUM>) by a top wall (<NUM>); and a bottom wall (<NUM>) coupled to the third surface (<NUM>) and the first surface (<NUM>);
an adapter (<NUM>) coupled to the stiffener, the adapter including:
an outer wall (<NUM>) aligned with the third surface of the stiffener, a top wall (<NUM>), a bottom wall (<NUM>), an inner wall (<NUM>), an outer mounting surface (<NUM>) and a bottom mounting surface (<NUM>), whereby: the outer wall (<NUM>), the outer mounting surface (<NUM>) and the inner wall (<NUM>) are parallel; the inner wall (<NUM>) is coupled to the outer wall (<NUM>) by the top wall (<NUM>); the bottom wall (<NUM>) being aligned with the second surface (<NUM>) of the stiffener; the inner wall (<NUM>) coupling the top wall (<NUM>) and the bottom wall (<NUM>); and whereby the bottom mounting surface (<NUM>) extends from the inner wall (<NUM>) of the stiffener to the third surface (<NUM>) of the stiffener (<NUM>);
at least one of the outer mounting surface (<NUM>) and the bottom mounting surface (<NUM>) of the adapter is bonded or mechanically coupled to the respective adjacent inner wall (<NUM>) or the top wall (<NUM>) of the stiffener (<NUM>); whereby the interface between the outer mounting surface (<NUM>) of the adapter and the inner wall (<NUM>) of the stiffener precisely locates the adapter on the stiffener; and
a plurality of solder balls (<NUM>) disposed on the second surface of the package substrate.