SEMICONDUCTOR ASSEMBLY INCLUDING MULTIPLE SOLDER MASKS

A semiconductor device includes a substrate and a conductive pad coupled to the substrate. A first solder mask is coupled to the substrate and to a portion of the conductive pad so the first solder mask covers the portion of the conductive pad and extends above the conductive pad. A second solder mask is coupled to a portion of the first solder mask and extends above the first solder mask.

BACKGROUND

In semiconductor assemblies, such as package assemblies or printed circuit boards, solder joints are used to connect components to each other. As a number of components included in a semiconductor assembly increases, distance between solder joints decreases. This increases a likelihood of solder bridging between adjacent connections where solder creates an electrical short between adjacent components when a solder joint is being formed.

DETAILED DESCRIPTION

When fabricating a semiconductor package or a printed circuit board design, solder joints may be used to electrically connect different components. Solder joints are formed by applying a solder ball to a conductive pad and heating the solder ball to form a solder joint. As an increasing number of components are included in a semiconductor package or on a printed circuit board, a likelihood of solder ball bridging, where adjacent solder joints bridge together and cause a short circuit, also increases.

Conventional fabrication techniques reduce a risk of solder ball bridging by reducing a size of a solder ball or a size of an opening in the substrate for the solder ball. However, such reductions reduce reliability of a resulting solder joint. Similarly, for printed circuit boards, the opening for a solder ball or a thickness of the solder ball is reduced to mitigate the risk of solder ball bridging, which similarly decreases reliability of the resulting solder joint.

To that end, the present specification sets forth various implementations of a semiconductor device including a substrate and a conductive pad coupled to the substrate. The semiconductor device also includes a first solder mask coupled to the substrate and coupled to a portion of the conductive pad, where the first solder mask covers the portion of the conductive pad and extends above the conductive pad. The semiconductor device further includes a second solder mask coupled to a portion of the first solder mask, where the second solder mask extends above the first solder mask. In some implementations, the first solder mask and the second solder mask comprise different materials.

In some implementations, the semiconductor device further includes a solder ball contacting an additional portion of the conductive pad that is not covered by the solder mask, where the solder ball is within an area having a boundary formed by the second solder mask. The second solder mask is positioned to prevent solder from the solder ball spreading outside the area bounded by the second solder mask in some implementations. In some implementations, a combined height of the first solder mask and the second solder mask is within a threshold amount of a height of the solder ball. In other implementations, the second solder mask is coupled to the first solder mask in a location within a threshold distance of a plane perpendicular to the edge of the conductive pad.

In some implementations, a portion of the second solder mask is coupled to an additional portion of the conductive pad of the semiconductor device, where the additional portion of the conductive pad is not covered by the first solder mask.

In some implementations, the first solder mask and the second solder mask comprise a common material. In other implementations, the first solder mask and the second solder mask comprise different materials. In some implementations, the portion of the solder mask coupled to the additional portion of the conductive pad decreases a diameter of a solder joint formed from a solder ball contacting another portion of the conductive pad that is not covered by the solder mask and that is not covered by the second solder mask.

In some embodiments, the semiconductor device further includes an additional second solder mask opposite the second solder mask and parallel to the second solder mask, where the additional second solder mask is coupled to an additional portion of the first solder mask and extends above the first solder mask. In some implementations, the additional second solder mask is positioned between the conductive pad and an additional conductive pad adjacent to the conductive pad. The second solder mask is coupled to the first solder mask in a location within a threshold distance of a plane perpendicular to the edge of the conductive pad in some implementations.

The present specification also describes a method that includes applying a first solder mask to a substrate and to a conductive pad coupled to the substrate, where the first solder mask covers a portion of the conductive pad and extends above the conductive pad. The method further includes applying a second solder mask to the first solder mask, where the second solder mask is coupled to a portion of the first solder mask and extends above the first solder mask.

In some implementations, applying the second solder mask to the first solder mask includes coupling a portion of the second solder mask to an additional portion of the conductive pad, where the additional portion of the conductive pad is not covered by the first solder mask. In some implementations, the portion of the second solder mask coupled to the additional portion of the conductive pad decreases a diameter of a solder joint formed from a solder ball contacting another portion of the conductive pad that is not covered by the first solder mask and that is not covered by the second solder mask. In some implementations, applying the second solder mask to the first solder mask includes coupling the second solder mask to the first solder mask in a location within a threshold distance of a plane perpendicular to the edge of the conductive pad.

In some implementations, the method further includes applying a solder ball to the conductive pad, so the solder ball contacts an additional portion of the conductive pad that is not covered by the solder mask and the solder ball is within an area having a boundary formed by the second solder mask. The method further includes melting the solder ball, with melted solder remaining within the area having the boundary formed by the second solder mask in some implementations.

In some implementations applying the second solder mask to the first solder mask includes applying a second solder mask layer to a surface of the first solder mask and to a surface of the conductive pad not covered by the first solder mask and forming the second solder mask by removing one or more portions of the second solder mask layer from the surface of the first solder mask and the surface of the conductive pad not covered by the first solder mask.

In some implementations, the first solder mask and the second solder mask comprise different materials.

The following disclosure provides many different implementations, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows include implementations in which the first and second features are formed in direct contact, and also include implementations in which additional features formed between the first and second features, such that the first and second features are in direct contact. Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper,” “back,” “front,” “top,” “bottom,” and the like, are used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Similarly, terms such as “front surface” and “back surface” or “top surface” and “back surface” are used herein to more easily identify various components, and identify that those components are, for example, on opposing sides of another component. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures.

FIGS.1A-1Dshow steps in an example manufacturing process for a semiconductor assembly including multiple solder masks. Beginning withFIG.1A, one or more conductive pads105are coupled to, or applied to, a substrate100. Each conductive pad105comprises an electrically conductive material. For example, a conductive pad105comprises copper, while in other examples the conductive pad105comprises one or more other conductive materials. In various embodiments, the substrate100comprises materials such as glass fiber core material, pre-preg, build up material, epoxy, conductive material (e.g., copper), or other suitable materials. A first solder mask layer110is applied to a surface of the substrate100and to a surface of the one or more conductive pads105. The first solder mask layer110has a thickness so an upper surface of the first solder mask layer110(relative to the substrate100) has a height above the surface of the substrate100and the surface of the one or more conductive pads105to which the first solder mask layer110was applied. The first solder mask layer110has different thicknesses in different implementations. The first solder mask layer110is a non-electrically conductive material. For example, the first solder mask layer110is epoxy or polymer in some implementations.

As shown inFIG.1B, portions of the first solder mask layer110are removed, resulting in a first solder mask115, with openings in the first solder mask115where portions of the one or more conductive pads105are exposed, being coupled to the substrate. In various embodiments, the portions of the first solder mask layer110are removed using photolithography, while other methods are used to remove portions of the first solder mask layer110in other implementations. A pattern is used to identify portions of the first solder mask layer110to remove in various implementations. As shown inFIG.1B, the first solder mask115covers a portion117of a conductive pad105. The solder mask115also extends above the conductive pad105. In different implementations, the height with which the first solder mask115extends above the conductive pad105differs.

Referring toFIG.1C, a second solder mask layer120is applied to the first solder mask115. As shown in the implementation ofFIG.1C, the second solder mask layer120is applied to a surface of the first solder mask115and to a surface of the one or more conductive pads105. The second solder mask layer120has a thickness so an upper surface of the second solder mask layer120(relative to the one or more conductive pads105) has a height above the surface of the first solder mask115and the surface of the one or more conductive pads105to which the second solder mask layer120was applied. The second solder mask layer120has different thicknesses in different implementations. The second solder mask layer120is a non-electrically conductive material. For example, the second solder mask layer120is epoxy or polymer in some implementations. In some implementations, the second solder mask layer120a film material, while in other implementations the second solder mask layer120is a liquid material (e.g., epoxy liquid, liquid ink). In some implementations, the first solder mask115and the second solder mask layer120are a common material, while in other implementations, the first solder mask115comprises a different material than the second solder mask layer120.

InFIG.1D, portions of the second solder mask layer120are removed, resulting in a second solder mask125, with openings in the second solder mask125where portions of the one or more conductive pads105are exposed. In various embodiments, the portions of the second solder mask layer120are removed using photolithography, while other methods are used to remove portions of the second solder mask layer120in other implementations. A pattern is used to identify portions of the second solder mask layer120to remove in various implementations. The second solder mask125is coupled to a portion of the first solder mask115, with the second solder mask125extending above the first solder mask115. In different implementations, the height with which the second solder mask125extends above the first solder mask115differs. Extending above the first solder mask115allows the second solder mask125, along with the first solder mask115, to form a boundary for solder applied to the position of a conductive pad105that is not covered by the first solder mask115. Such a boundary prevents solder applied to the exposed portion of a conductive pad105from bridging to an adjacent conductive pad105and creating an electrical short. In some implementations a combined height of the first solder mask115and the second solder mask125is within a threshold amount of a height of a solder ball applied to the exposed portion of the conductive pad105. In other implementations, the combined height of the first solder mask115and the second solder mask125equals the height of the solder ball applied to the exposed portion of the conductive pad105, while in other implementations, the combined height of the first solder mask115and the second solder mask exceeds the height of the solder ball applied to the exposed portion of the conductive pad.

In various implementations, the height of the second solder mask125ranges between 20 microns and 50 microns. The second solder mask125has different widths in different implementations, with a size of a ball grid array and solder resist opening for a conductive pad105affecting a width of the second solder mask. For example, the second solder mask125has a range of widths between 100 microns and 400 microns.

In some implementations, such as shown inFIG.1D, an additional second solder mask130is opposite the second solder mask125and parallel to the second solder mask125. For example, the second solder mask125and the additional second solder mask130are on opposing sides of a conductive pad105to form a boundary for solder on multiple sides of the conductive pad105. The additional second solder mask130is coupled to an additional portion of the first solder mask115and extends above the first solder mask115. In various implementations, the additional second solder mask130is positioned between the conductive pad105and an additional conductive pad105that is adjacent to the conductive pad105to prevent solder from contacting the additional conductive pad105.

WhileFIGS.1A-1Dshow a first solder mask115and a second solder mask125coupled to the second solder mask125, in some implementations, additional solder masks may be coupled to the second solder mask125to further increase a height above a conductive pad105to which the combination of solder masks extends. AlthoughFIGS.1A-1Dshow the formation of the first solder mask115and the second solder mask125with respect to a substrate100, in other implementations the one or more conductive pads105are coupled to a printed circuit board, so the first solder mask115is coupled to the printed circuit board and to portions of the one or more conductive pads in such implementations.

Various implementations may employ different structures for the first solder mask115or for the second solder mask125.FIGS.2and3depict different example structures for the first solder mask115and for the second solder mask125for purposes of illustration. For clarity,FIGS.2and3do not show the substrate100to which the one or more conductive pads105are coupled. In the example ofFIG.2, a first solder mask205is coupled to a substrate (not shown) and covers a portion207of a conductive pad105. As shown inFIG.2, the first solder mask205extends above the conductive pad105by a height. In the example shown byFIG.2, a second solder mask210is coupled to a portion of the first solder mask210and extends above the first solder mask205by an amount. Further, in the implementation ofFIG.2, the second solder mask210is also coupled to an additional portion215of the conductive pad105, where the additional portion215of the conductive pad105is not covered by the first solder mask205. Coupling the second solder mask210to the additional portion215of the conductive pad105reduces an amount of the conductive pad105that is exposed, which reduces a diameter of a solder joint formed from a solder ball220that contacts the portion of the conductive pad105that is exposed (i.e., not covered by the first solder mask205and not covered by the second solder mask210). Additionally, the second solder mask210is positioned relative to the conductive pad105so the solder ball220is within an area bounded by the second solder mask210and so solder from the solder ball220is prevented from spreading outside the area bounded by the second solder mask210. Thus, in the example shown byFIG.2, solder from the solder ball220is blocked from reaching a conductive pad105adjacent to the conductive pad the solder ball220contacts by the second solder mask210, preventing solder bridging.

In the example ofFIG.3, a first solder mask305is coupled to a substrate (not shown) and covers a portion307of a conductive pad105. As shown inFIG.3, the first solder mask305extends above the conductive pad105by a height. In the example shown byFIG.3, a second solder mask310is coupled to a portion of the first solder mask305and extends above the first solder mask305by an amount. In the implementation ofFIG.3, the second solder mask310is not coupled to a portion of the conductive pad105. For example, the second solder mask310is coupled to the first solder mask305in a location corresponding to an edge of the conductive pad105or in a location within a threshold distance of a plane perpendicular to the edge of the conductive pad105. When a solder ball315contacts a conductive pad105, the solder ball315is an area that has a boundary formed by the second solder mask310, which prevents solder from the solder ball315from spreading outside the area bounded by the second solder mask310, preventing solder from the solder ball315from reaching a conductive pad105adjacent to the conductive pad the solder ball315contacts by the second solder mask310. WhileFIGS.2and3show example configurations of the first solder mask and the second solder mask, different configurations of the first solder mask and the second solder mask are possible in other implementations.

FIG.4is a cross-sectional diagram of an example integrated circuit device400including multiple solder masks in accordance with some implementations of the present disclosure. The example integrated circuit device400can be implemented in a variety of computing devices, including mobile devices, personal computers, peripheral hardware components, gaming devices, set-top boxes, smart phones, and the like (as shown inFIG.5). The example integrated circuit device400ofFIG.4includes a die405. The die405is a block of semiconducting material such as silicon onto which a functional integrated circuit is fabricated. As an example, the die405includes a processor such as a Central Processing Unit (GPU), a Graphics Processing Unit (GPU), or other processor as can be appreciated.

As an example, the die405includes a processor505of a computing device500as shown inFIG.5. The computing device500is implemented, for example, as a desktop computer, a laptop computer, a server, a game console, a smart phone, a tablet, and the like. In addition to one or more processors505, the computing device500includes memory510. The memory510includes Random Access Memory (RAM) or other volatile memory. The memory510also includes non-volatile memory such as disk storage, solid state storage, and the like.

In some implementations, the computing device500also includes one or more network interfaces515. In some implementations, the network interfaces515include a wired network interface515such as Ethernet or another wired network connection as can be appreciated. In some implementations, the network interfaces515include wireless network interfaces515such as WiFi, BLUETOOTH®, cellular, or other wireless network interfaces515as can be appreciated. In some implementations, the computing device500includes one or more input devices520that accept user input. Example input devices520include keyboards, touchpads, touch screen interfaces, and the like. One skilled in the art will appreciate that, in some implementations, the input devices520include peripheral devices such as external keyboards, mouses, and the like.

In some implementations, the computing device500includes a display525. In some implementations, the display525includes an external display connected via a video or display port. In some implementations, the display525is housed within a housing of the computing device500. For example, the display525includes a screen of a tablet, laptop, smartphone, or other mobile device. In implementations where the display525includes a touch screen, the display525also serves as an input device520.

The die405is coupled to a substrate410. The substrate410is a portion of material that mechanically supports coupled components such as the die405. In some implementations, the substrate410also electrically couples various components mounted to the substrate410via conductive traces, tracks, pads, and the like. For example, the substrate410electrically couples a component of the die405to one or more other components via a connective trace and a solder joint formed from a solder ball415coupled to a conductive pad105. As further described above in conjunction withFIGS.1A-1D, to prevent the solder joint from bridging to another solder joint, the substrate410includes a first solder mask115and a second solder mask125. As further described above in conjunction withFIGS.1A-3, the second solder mask125is coupled to the first solder mask115and extends above the first solder mask115to form a boundary of an aera where the solder ball415, and solder from the solder ball415, occupies. This prevents solder from the solder ball415reaching a conductive pad105other than the conductive pad105that the solder ball415contacts.

In some implementations, the substrate410includes a printed circuit board (PCB), while in other implementations the substrate410is another semiconductor device, like die405(which may include active components therein). In some implementations, the die405is coupled to the substrate410via a socket (not shown), where the die405is soldered to or otherwise mounted in the socket. In other implementations, as shown inFIG.4, the die405is directly coupled to the substrate410via a direct solder connection or other connection as can be appreciated. In some implementations, the die405is coupled to the substrate410using a land grid array (LGA), pin grid array (PGA), or other packaging technology as can be appreciated.

For further explanation,FIG.6sets forth a flow chart illustrating an example method for manufacturing an integrated circuit device assembly for a semiconductor assembly including multiple solder masks according to implementations of the present disclosure. The method ofFIG.6includes applying605a first solder mask115to a substrate100and to a conductive pad105that is coupled to the substrate100. The first solder mask115covers a portion of the conductive pad105and extends above the conductive pad105, as shown inFIGS.1A and1B.

A second solder mask125is applied610to the first solder mask115, with the second solder mask125coupled to a portion of the first solder mask115and extending above the first solder mask115, as shown inFIGS.1C-3. Hence, the second solder mask125is coupled to the first solder mask115, while extending above the first solder mask115. In some implementations, a second solder mask layer120is applied to a surface of the first solder mask115and to a surface of the conductive pad105that is not covered by the first solder mask115, and the second solder mask125is formed by removing one or more portions of the second solder mask layer120from the surface of the first solder mask115and from the surface of the conductive pad105that is not covered by the first solder mask115. Further, in some implementations, such as the example shown inFIG.1B, when applying the second solder mask125to the first solder mask115, a portion of the second solder mask125is coupled to an additional portion of the conductive pad105that is not covered by the first solder mask115. The first solder mask115and the second solder mask125comprise different materials in some implementations, while in other implementations the first solder mask115and the second solder mask125comprise different materials.

When a solder ball is applied to the conductive pad105, the solder ball contacts the conductive pad105that is not covered by the first solder mask115(or by the second solder mask125). The solder ball remains within an area that has a boundary formed by the second solder mask125, allowing the first solder mask115and the second solder mask125to prevent the solder ball from contacting an adjacent solder ball or an adjacent conductive pad105. When the solder ball is melted, melted solder remains within the area having the boundary formed by the second solder mask125, preventing the melted solder from contacting other conductive pads105or other components.

In view of the explanations set forth above, readers will recognize that manufacturing an integrated circuit device assembly including multiple solder masks allows solder joints to be isolated from other solder joints or conductive pads, such as adjacent solder joints or adjacent conductive pads. This reduces a likelihood of solder bridging in the integrated circuit device assembly that electrically shorts different components. Using multiple solder masks reduces the likelihood of solder bridging without compromising solder joint reliability.

It will be understood from the foregoing description that modifications and changes can be made in various implementations of the present disclosure. The descriptions in this specification are for purposes of illustration only and are not to be construed in a limiting sense. The scope of the present disclosure is limited only by the language of the following claims.