CONDUCTIVE MEMBER WITH METAL CORE FOR SUBSTRATE CONNECTIONS

In examples, a semiconductor package comprises a semiconductor die including a circuit, a housing covering the semiconductor die, and a conductive terminal coupled to the semiconductor die and exposed to an exterior surface of the housing. The package also comprises a sensor exposed on the exterior surface of the housing, a flux layer on the conductive terminal and a conductive member on the flux layer. The conductive member includes a copper core, a nickel layer covering the copper core, and a solder layer covering the nickel layer.

BACKGROUND

A semiconductor package may include a semiconductor die and a housing to cover the semiconductor die. The package may further include conductive terminals exposed to an exterior surface of the housing. The conductive terminals are coupled to the semiconductor die. The conductive terminals provide electrical pathways between circuitry on the semiconductor die and components (e.g., printed circuit boards) outside of the package.

SUMMARY

In examples, a semiconductor package comprises a semiconductor die including a circuit, a housing covering the semiconductor die, and a conductive terminal coupled to the semiconductor die and exposed to an exterior surface of the housing. The package also comprises a sensor exposed on the exterior surface of the housing, a flux layer on the conductive terminal and a conductive member on the flux layer. The conductive member includes a copper core, a nickel layer covering the copper core, and a solder layer covering the nickel layer.

In examples, a method for manufacturing a semiconductor package comprises coupling a semiconductor die to a conductive terminal; covering the semiconductor die with a housing, the conductive terminal and a sensor exposed to an exterior surface of the housing; and applying a metal layer to the conductive terminal. The method also comprises applying a flux layer to the metal layer and positioning a conductive member on the flux layer, the conductive member including a metal core and a solder layer covering the metal core. The method also comprises performing a first reflow process of the solder layer. The solder layer has a volume such that, upon a second reflow of the solder layer, the conductive member is able to reach a plane coincident with an edge of the exterior surface and perpendicular to the exterior surface of the housing.

DETAILED DESCRIPTION

Many semiconductor packages include conductive terminals that are positioned for easy coupling to a substrate, such as a printed circuit board (PCB). But in some semiconductor packages, including sensor applications, the conductive terminals are on a side exterior surface of the package that extends vertically from the PCB. These conductive terminals are located several millimeters above the PCB. The conductive terminals are coupled to the PCB using a solder reflow process. Specifically, solder that is placed on the conductive terminals is reflowed, causing the solder to flow toward the PCB due to gravity. In this way, a solder connection is formed between the conductive terminals and the PCB. But in many cases, the solder fails to reach the PCB and form a proper connection. Further, the steps used to form the conductive terminals to which the solder couples are time-consuming and expensive.

This disclosure describes various examples of a semiconductor package having a conductive member with a metal core to facilitate connections between conductive terminals of the package and a substrate on which the package is mounted. In examples, the semiconductor package includes a semiconductor die including a circuit and a housing covering the semiconductor die. The package also includes a conductive terminal coupled to the semiconductor die and exposed to an exterior surface of the housing, the conductive terminal located between 20 microns and 100 microns from an edge of the housing. The package also includes a flux layer on the conductive terminal and a conductive member on the flux layer. The conductive member includes a metal core and a solder layer covering the metal core. The conductive member has a volume ranging from 14 kilomicrons3to 524 kilomicrons3, and the solder layer has a volume that is a percentage of the metal core volume ranging from 40% to 80%. The weight and shape of the metal core encourages solder flow toward a substrate to which the package is coupled. The surface area of the core also facilitates the use of larger amounts of solder than would otherwise be possible, thus further encouraging solder flow and the formation of strong, reliable connections between conductive terminals and the substrate to which the package is mounted. Because a metal (e.g., copper) core is used, metal (e.g., copper) layers that would otherwise have been included as part of the conductive terminals may be omitted, thus significantly reducing manufacturing time and expense.

FIG.1is a block diagram of a semiconductor package configured to couple to a conductive member with a metal core for substrate connections, in accordance with various examples. Specifically,FIG.1shows a semiconductor package100including a semiconductor die102and a conductive terminal104coupled to the semiconductor die102. The conductive terminal104is exposed to a lateral exterior surface106of the semiconductor package100. As described below, a spherical or ovoid conductive member having a metal (e.g., copper) core, a protective (e.g., nickel) layer covering the metal core, and a solder layer covering the protective layer and the metal core may be coupled to the conductive terminal104and then reflowed to couple the conductive terminal104to a metal trace on a PCB.

FIG.2Ais a perspective view of a semiconductor package, in accordance with various examples. Specifically,FIG.2Ashows the semiconductor package100having multiple conductive terminals104on the surface106. The semiconductor package100may also include a photo sensor200, for example, in case the semiconductor package100is a sensor package in a light sensing application. A distance202between each conductive terminal104and the closest point on the bottom edge204of the surface106ranges between 20 microns and 100 microns, with a distance greater than this range being disadvantageous because the solder volume of the conductive member will collapse and fail to form a proper connection between the conductive terminal104and a PCB, and with a distance lesser than this range causing a disadvantageous displacement of the metal core of the conductive member.FIG.2Bis a frontal view of the semiconductor package100ofFIG.2A, in accordance with various examples.

FIG.3Ais a cross-sectional profile view of the semiconductor package conductive terminal104configured to couple to a conductive member with a metal core to facilitate substrate connections, in accordance with various examples. The detailed features shown inFIG.3Aare not expressly shown inFIGS.1,2A, and2B. The conductive terminal104includes a protective layer300(e.g., a polyimide layer). The protective layer300has been patterned using a photolithography process (e.g., using suitable masks, exposures, bakes, developers, etc.) to produce an opening302in the protective layer300. A metal layer304(e.g., a bond pad) is exposed and accessible through the opening302. In examples, the metal layer304is aluminum, copper, gold, or any other suitable metal or alloy.FIG.3Bis a top-down view of the structure ofFIG.3A.FIG.3Cis a perspective view of the structure ofFIG.3A.

FIG.4Ais a cross-sectional profile view of the semiconductor package conductive terminal104, in accordance with various examples. The conductive terminal104as shown inFIG.4Ais identical to that shown inFIG.3A, but with the addition of a metal seed layer306on the protective layer300and on the metal layer304. The metal seed layer306may be applied using any suitable technique, including sputtering. As described below, a conductive member (e.g., a relatively large, spherical or ovoid conductive member) may later be positioned above the metal seed layer306, and the metal seed layer306provides a broad surface area to adequately couple to the conductive member to transfer electrical signals between the conductive member and the metal layer304. To achieve such electrical communication, the metal seed layer306may have a thickness ranging from 1 kiloAngstrom to 4 kiloAngstroms, with a thickness outside this range being disadvantageous because of deleterious effects on resistivity and/or drain-source on resistance (RDSON) performance.

FIG.4Bis a top-down view of the semiconductor package conductive terminal104ofFIG.4A, in accordance with various examples.FIG.4Cis a perspective view of the semiconductor package conductive terminal104, in accordance with various examples.

FIG.5Ais a cross-sectional profile view of the semiconductor package conductive terminal104ofFIG.4A, but with the addition of a flux layer308above and abutting the seed layer306. The flux layer308is conductive and may be composed of organic adhesives. The flux layer308serves as an adhesive between the conductive member (which is described below) and the metal layer304, and the flux layer308further serves to activate the solder in the conductive member upon a reflow (e.g., heating) process. The flux layer308has a thickness ranging from 20 microns to 40 microns, with a greater thickness being disadvantageous because the flux will smear across different metal contacts due to the increased flux volume, and with a lesser thickness being disadvantageous because the flux will be unable to activate the solder in the conductive member. The flux layer308has an area that is 120%-180% of the area of the opening in the protective layer300to expose the metal layer304. The flux layer308may be applied by screen printing using stencils. After the flux layer308is applied to the metal seed layer306, the flux layer308may be heated to a temperature ranging from 220 degrees Celsius to 250 degrees Celsius for a liquidus time ranging from 30 seconds to 60 seconds, thereby causing the flux layer308to adhere to the underlying metal seed layer306. Heat application outside of these ranges will result in damage to the flux layer308and/or a flux layer308that is ineffective to maintain the conductive member in position, as described in more detail below.

FIG.5Bis a top-down view of the semiconductor package conductive terminal104ofFIG.5A, in accordance with various examples.FIG.5Cis a perspective view of the semiconductor package conductive terminal104ofFIG.5A, in accordance with various examples.

FIG.6Ais a cross-sectional view of a conductive member with a metal core to facilitate substrate connections, in accordance with various examples. Specifically,FIG.6Ashows a conductive member600that may be coupled to the semiconductor package conductive terminal104described above. The conductive member600may have a spherical or ovoid shape, although other shapes are contemplated and included in the scope of this disclosure. The conductive member600may include a metal core602(e.g., copper). The conductive member600may include a protective layer604(e.g., nickel) covering the metal core602. The protective layer604may prevent oxidation of the metal core602, should the metal core602be exposed to ambient air or other deleterious influences. In some examples, the protective layer604is omitted. The conductive member600may include a solder layer606covering the metal core602.FIG.6Bis a perspective view of the conductive member600, in accordance with various examples.

As described below, the conductive member600is applied to the flux layer308(FIG.5A) and a reflow process is performed to cause the flux layer308to activate the solder layer606. The flux layer308adheres to the solder layer606, thus holding the conductive member600in place. The flux layer308holds the conductive member600in place even if the semiconductor package100were moved, turned upside down, shaken, etc. Later, the semiconductor package100may be positioned on a PCB and another reflow process performed. This reflow process dislodges the conductive member600, causing the solder layer606to flow with gravity toward a metal trace on the PCB. The volume of solder in the solder layer606is adequate to encourage contact with both the conductive terminal104and the metal trace on the PCB. Similarly, the weight and/or mass of the metal core602is adequate to encourage flow of the solder layer606and to establish contact with both the conductive terminal104and the metal trace on the PCB. Such a reflow process is now described in more detail with reference toFIGS.7A-11C.

FIG.7Ais a cross-sectional profile view of a semiconductor package conductive terminal coupled to a conductive member with a metal core to facilitate substrate connections, in accordance with various examples. More specifically,FIG.7Ashows the conductive member600positioned on the flux layer308of the conductive terminal104. A reflow process may be performed to cause the conductive terminal104to adhere to the flux layer308and to activate the solder layer606. Such a reflow process includes heating the flux layer308and the solder layer606to a temperature between 220 degrees Celsius and 250 degrees Celsius for a liquidus time ranging from 30 seconds to 60 seconds, with heat applications outside of these ranges resulting in damage to the flux layer308and/or poor adhesion between the solder layer606and the flux layer308, and/or inappropriate activation of the solder layer606.FIG.7Bis a top-down view of the structure ofFIG.7A, in accordance with various examples.FIG.7Cis a perspective view of the structure ofFIG.7A, in accordance with various examples.

FIG.8Ais a cross-sectional profile view of a semiconductor package coupled to a conductive member with a metal core to facilitate substrate connections, in accordance with various examples. More specifically,FIG.8Ashows the structure ofFIG.7A, but rotated90degrees to demonstrate the adhesion of the conductive member600to the conductive terminal104. InFIG.8A, the bottom of the figure is downward toward the earth, and thus in the absence of adhesion of the conductive member600to the conductive terminal104, the conductive member600would fall out of place and downward due to gravity. However, because the flux layer308adheres to the conductive member600, the conductive member600remains in place.FIG.8Bis a frontal view of the structure ofFIG.8A, in accordance with various examples.FIG.8Cis a perspective view of the structure ofFIG.8A, in accordance with various examples.

FIG.9Ais a perspective, zoomed-out view ofFIGS.8A-8C, meaning the entirety of the semiconductor package100(FIG.2A) is visible, with a different conductive member600coupled to each of the conductive terminals104.FIG.9Bis a frontal view of the structure ofFIG.9A.

After the conductive members600have been adhered to the flux layers308on respective conductive terminals104, the semiconductor package100may be coupled to a PCB by a reflow process.FIG.10Ashows the semiconductor package100positioned on a PCB1000. For example, each of the conductive terminals104may be positioned above a different metal trace of the PCB1000. The metal traces of the PCB1000are not expressly shown. The conductive members600have been reflowed such that the solder layers606have flowed with gravity toward the PCB1000and have coupled to the PCB1000. As the solder layers606cool, they solidify and form electrical pathways between the conductive terminals104and the PCB1000.

As described above, various features of the conductive members600facilitate solder flow and the establishment of electrical pathways between the conductive terminals104and the PCB1000. The conductive member600has a volume ranging from 54 kilomicrons3to 3600 kilomicrons3, with a greater volume being disadvantageous because it unacceptably raises the risk of unintended electrical connections to nearby solder bumps or balls, and with a lesser volume being disadvantageous because of the unacceptable risk of inadequate connection to the underlying substrate or PCB. As the solder layer606is heated during the reflow process, the metal core602is permitted to move, and gravity pulls the metal core602downward toward the PCB1000. The weight (or mass) of the metal core602as the metal core602moves toward the PCB1000encourages movement of the solder layer606toward the PCB1000. The diameter of the metal core602may similarly encourage solder flow. The diameter of the metal core602is between 30 microns and 100 microns, with a larger diameter being disadvantageous because it unacceptably raises the risk of unintended electrical connections to nearby solder bumps or balls, and with a smaller diameter being disadvantageous because of the unacceptable risk of inadequate connection to the underlying substrate or PCB . The shape of the metal core602may also affect solder flow. A spherical shape of the metal core602facilitates solder flow. A cuboid shape of the metal core602restricts solder flow. An ovoid shape of the metal core602facilitates solder flow, but to a lesser degree than a spherical shape of the metal core602. The metal core602may be composed of metals such as copper or alloys that contain copper as the primary metal. The protective layer604may be composed of metals such as nickel or alloys that contain nickel as the primary metal. In the event that the protective layer604becomes exposed to ambient environment due to the pattern of solder flow of the solder layer606, the protective layer604protects the metal core602from oxidation and other types of damage. The thickness of the protective layer604ranges from 2 microns to 5 microns, with a thicker protective layer604being disadvantageous because it would increase complexity of manufacture without providing any benefit, and with a thinner protective layer604being disadvantageous because it would not prevent diffusion between the metal core602and the solder layer606. The solder layer606has a thickness ranging from 20 microns to 100 microns, with a thicker solder layer606being disadvantageous because of the unacceptably increased risk of unintended connections to nearby bumps or balls, and with a thinner solder layer606being disadvantageous because of the unacceptable risk of inadequate connection to the underlying substrate or PCB. The volume of the solder layer606ranges from 40 kilomicrons3to 300 kilomicrons3to achieve adequate connections between the connective terminals104and the PCB1000, with a volume greater than this range being disadvantageous because of inadvertent coupling to nearby electrically conductive components, and with a volume less than this range being disadvantageous because of the risk that the solder layer606will not reach the PCB1000to form an electrical connection. The volume of the solder layer606is a percentage of the conductive member600volume ranging from 30% to 60%, with a smaller percentage being disadvantageous because of a lack of adequate solder to form electrical connections to the PCB1000, and with a percentage larger than this range being disadvantageous because of a lack of current carrying capacity due to the relatively low core volume. The volume of the solder layer606depends at least in part on the distance202(FIG.2A) between the conductive terminal104(and, more specifically, the bottom-most end of the metal seed layer306and/or the flux layer308) and the edge204(FIG.2A), with a greater distance202requiring a larger volume of the solder layer606, and a lesser distance202requiring a smaller volume of the solder layer606.

FIG.10Bis a frontal view of the structure ofFIG.10A, in accordance with various examples.FIG.10Cis a perspective view of the structure ofFIG.10A, in accordance with various examples.

FIG.11Ais a perspective, zoomed-out view of the structure ofFIGS.10A-10C, showing the entirety of the semiconductor package100coupled to the PCB1000, in accordance with various examples.FIG.11Bis a frontal view of the structure ofFIG.11A, in accordance with various examples.FIG.11Cis a profile cross-sectional view of the structure ofFIG.11A, in accordance with various examples.

FIG.12is a flow diagram of a method1200for manufacturing a semiconductor package and coupling the package to a substrate by way of a conductive member with a metal core, in accordance with various examples. The method1200includes coupling a semiconductor die to a conductive terminal (1202). For example,FIG.1shows the semiconductor die102coupled to the conductive terminal104. The method1200includes covering the semiconductor die with a housing, where the conductive terminal is exposed to an exterior surface of the housing, and the conductive terminal is located between 20 microns and 100 microns from an edge of the housing (1204). AsFIG.2Ashows, the semiconductor die102is covered by the walls (e.g., formed of a mold compound) of the semiconductor package100, the conductive terminal104is exposed to the surface106, and the conductive terminal104is located a distance202from the edge204, where the distance202falls within the range specified in step1204.

The method1200includes applying a metal layer to the conductive terminal (1206).FIG.4Ashows the application of the metal seed layer306to the conductive terminal104. The method1200includes applying a flux layer to the metal layer (1208).FIG.5Ashows the application of the flux layer308to the metal seed layer306. The method1200includes positioning a conductive member on the flux layer, where the conductive member includes a metal core and a solder layer covering the metal core (1210).FIG.7Ashows the conductive member600positioned on the flux layer308and further shows the conductive member600including the metal core602and the solder layer606.

The method1200includes performing a first reflow process of the solder layer (1212). The method1200includes performing a second reflow process of the solder layer to cause the conductive member to reach a plane coincident with the edge and perpendicular to the exterior surface of the housing (1214).FIGS.10A and11Ashow the solder layer606flowing due to gravity and reaching a plane coincident with the edge204(FIG.2A), the plane being perpendicular to the surface106(FIG.2A).

In this description, the term “couple” may cover connections, communications or signal paths that enable a functional relationship consistent with this description. For example, if device A provides a signal to control device B to perform an action, then: (a) in a first example, device A is directly connected to device B; or (b) in a second example, device A is coupled to device B through intervening component C if intervening component C does not alter the functional relationship between device A and device B, so device B is controlled by device A via the control signal provided by device A.

In this description, unless otherwise stated, “about,” “approximately” or “substantially” preceding a parameter means being within +/−10 percent of that parameter. Modifications are possible in the described examples, and other examples are possible within the scope of the claims.