Patent Description:
<CIT> discloses techniques for installing a module on a circuit board by simultaneously heating a perimeter portion of the module, and bringing an inner portion of the module to temperature that is lower than that of the perimeter portion. Heating the perimeter portion of the module melts solder disposed between contact members of the module and corresponding contact members of the circuit board in order to form solder connections. Bringing the inner portion of the module to temperature that is lower than that of the perimeter portion reduces the likelihood of causing heat-related damage to the module itself.

<CIT>discloses a repair apparatus for a circuit board assembly including a cooling device for a surface of the circuit board assembly opposite to the surface to be repaired. The cooling device defines a chamber for receiving the circuit board assembly. The circuit board assembly is disposed within the chamber to define a heat exchange space between the circuit board assembly and the bottom of the chamber. The cooling device includes a backer plate including an air inlet port and an air inlet ducting connected to the air inlet port, and a plurality of vents extending from the air inlet ducting to a first surface of the backer plate.

The presently claimed subject-matter is defined in independent claim <NUM>. There is disclosed a heatshield with active cooling capability to a first ball grid array ("BGA") package during rework of a second BGA package of a clamshell BGA. The first BGA package may be the bottom-side BGA package and the second BGA package may be the top-side BGA package. The first and second BGA packages may be located on opposite sides of a printed circuit board ("PCB"), creating a clamshell BGA structure. The first BGA package may be on the side of the PCB board that faces the heatshield. The heatshield includes a backer plate and a metal plate. In some examples, the heatshield may also include a package pedestal. The backer plate includes one or more air inlet ports that are configured to be coupled to an air compressor. Air inlet ducting extends from the air inlet ports through at least a portion of the backer plate. One or more vents extend from the air inlet ducting to a top surface of the backer plate. The air inlet ducting and one or more vents direct cooling gas towards the metal plate. The metal plate may be a finned metal plate. The heatshield may absorb thermal energy, or heat, during rework of the second BGA package.

To cool the first BGA package during the rework of the second BGA package and, therefore, to prevent hot tears, separation, joint failure, defects, etc. of the solder joints of the first BGA package, cooling gas may be forced into the heatshield via the air inlet port and/or air inlet ducting. The cooling gas is directed towards the metal plate and the first BGA package, rather than directly towards the solder joint area. By directing the cooling gas towards the metal plate and the first BGA package instead of the solder joint area, the PCB and second BGA may maintain the heat necessary to allow rework to occur. The active cooling of the heatshield using cooling gas may maintain the solder joint temperature of the first BGA package below the reflow temperature and below the solidus temperature of the solder joints.

The system may further comprise a printed circuit board ("PCB") and a first ball grid array ("BGA") package positioned between the metal plate and the PCB, wherein the first BGA is coupled to a bottom surface of the PCB. The system may further comprise a second BGA package soldered to a top surface of the PCB. At least one of the backer plate or the metal plate may be configured to absorb heat from the first BGA package during rework of a second BGA package.

The metal plate may be a finned metal plate. The cooling gas may be configured to exit the system through at least one fin of the finned metal plate.

The system may further comprise a package pedestal coupled to the backer plate. The package pedestal may be positioned between the backer plate and the metal plate. The one or more outlets formed by the metal plate and the backer plate may extend along a top surface of the package pedestal. The one or more outlets may include a recess in the package pedestal extending from a center of the package pedestal to a perimeter edge of the package pedestal. The backer plate may further include air inlet ducting connected to the at least one air inlet port, and a first plurality of vents extending from the air inlet ducting to a first surface of the backer plate. The package pedestal may include a second plurality of vents extending from a bottom surface of the package pedestal to a top surface of the package pedestal, and the second plurality of vents may align with the first plurality of vents when the package pedestal is coupled to the backer plate.

The technology relates generally to a system that provides a heatshield on the top side of a first ball grid array ("BGA") package of a clamshell BGA structure to keep the solder joint temperature of the first BGA package below the reflow temperature and below the solidus temperature of the solder joint alloy such that the solder joints of the first BGA package do not become liquidus and/or soft enough to allow solder separation or other reflow-related solder defects during rework of a second BGA package. The clamshell BGA structure may include the first BGA package coupled to a first side of a printed circuit board ("PCB"). The second BGA package may be coupled to a second side of the PCB opposite the first side such that the first and second BGA packages make a clamshell around the PCB. A bottom side of the first BGA package may be coupled to the PCB. The bottom side of the first BGA package may be the side of the BGA package with the solder balls.

During manufacture of the clamshell BGA structure, rework of the second BGA package may be necessary. The heatshield on the top side of the first BGA package may prevent the solder coupling the first BGA package to the PCB from becoming liquidus during the rework of the second BGA package. This may prevent hot tears, separation, joint failure, defects, etc. of the solder joints of the first BGA package.

The heatshield may include a backer plate and a metal plate. According to some examples, the heatshield may additionally or alternatively include a package pedestal. The backer plate may include one or more air inlet ports connected to interior ducting as well as one or more vents. The air inlet ports are configured to be coupled to an air source, such as a compressor. The air source may cause a cooling gas, such as air or nitrogen, to flow through air inlet ducting within the backer plate and through the vents. The cooling gas may come in contact with the metal plate and/or additional components of the clamshell BGA, such as the first BGA package. As the cooling gas comes into contact with the metal plate and/or additional components of the clamshell BGA during rework of the second BGA package, the cooling gas may become heated. For example, thermal energy produced during the rework of the second BGA package may be transferred to the first BGA package, metal plate, and/or printed circuit board ("PCB"). The cooling gas reduces the thermal energy transferred to the first BGA package, metal plate, and/or PCB by cooling those components. By cooling those components, the solder of the first BGA package remains at a temperature that prevents the solder from becoming liquidus.

The cooling gas exits the system through one or more outlets in the backer plate, package pedestal, and/or metal plate. According to some examples, the metal plate and backer plate may form one or more outlets which allow the cooling gas to exit the system. The cooling gas may exit the system through fins of the metal place. In some examples, the backer plate may include one or more recesses, or outlets, extending from the center of the package pedestal to a perimeter edge of the package pedestal. The recesses may direct the heated cooling gas away from the heatshield.

According to some examples, there may be one or more exit vents, similar to the vents connected to the inlet ducting, that allow the now heated cooling gas to exit the system through air outlet ducting. The air outlet ducting may be connected to or extend from an air outlet port. According to some examples, the air outlet port may be coupled to a vacuum such that the heated gas may be removed from the system.

The metal plate may pull heat away from the first BGA package during the rework of the second BGA package. According to some examples, thermal energy produced by the rework of the second BGA package may be transferred to, or absorbed by, the metal plate. When thermal energy is transferred to the metal plate, the metal plate may increase in temperature. According to some examples, the metal plate may be made of a metal that has a high thermal conductivity. For example, the metal plate may be made of copper, aluminum, silver, gold, etc. A high thermal conductivity may allow the metal plate to absorb or receive more thermal energy produced during the rework of the second BGA package.

The metal plate may be coupled to a BGA or die. According to some examples, the backer plate may be coupled to a first side of the metal plate and the BGA may be coupled to a second side of the metal plate opposite the first side.

The metal plate may have one or more fins to maximize the surface area of the metal plate. According to some examples, increasing the surface area of the metal plate may increase the amount of contact the cooling gas has with the metal plate. By increasing the amount of contact between the metal plate and the cooling gas, the performance of the heatshield may increase as compared to a metal plate without fins. The performance of the heatshield may be how much heat is removed or dissipated by the heatshield.

According to some examples, as the cooling gas is injected or forced into the backer plate through the air inlet port, the cooling gas comes into contact with the metal plate as the cooling gas leaves the vents in the air inlet ducting. The cooling gas cools the metal plate that absorbed the heat from the rework of the second BGA package. As the cooling gas comes into contact with the metal plate, the now heated gas may exit through one or more fins in the metal plate and/or exit through the outlets in the backer plate. As the heated gas exits the system, the temperature of the first BGA package may remain below liquidus. This may prevent the solder joints of the first BGA package from melting during the rework of the second BGA package. The active cooling of the heatshield draws heat away from the first BGA package without inhibiting the rework process of the second BGA package.

<FIG> illustrates a cross section of a clamshell ball grid array ("BGA") structure. The clamshell BGA structure <NUM> may include two BGA packages <NUM>, <NUM>. According to some examples, the clamshell BGA structure100 may further include a backer plate <NUM>, a package pedestal <NUM>, and a metal plate <NUM>. The combination of the backer plate <NUM> and metal plate <NUM> may form a heatshield. According to some examples, the heatshield may additionally or alternatively include package pedestal <NUM>.

The backer plate <NUM> includes one or more air inlet ports <NUM> connected to air inlet ducting <NUM>. Air inlet ports <NUM> may be configured to be coupled to a gas source, such as a compressor. The compressor may force cooling gas into the air inlet ports <NUM>. The cooling gas may be air or nitrogen. Air inlet ducting <NUM> extends from air inlet ports <NUM>. The air inlet ducting <NUM> may extend inward from an edge of the backer plate <NUM> where air inlet port <NUM>. The air inlet ducts <NUM> may extend from the edge of the backer plate <NUM> towards the center of backer plate <NUM>. According to some examples, air inlet ducting <NUM> may extend past the center of backer plate <NUM>. The distance air inlet ducting <NUM> extends along and/or through a predetermined distance of backer plate <NUM>. According to some examples, the determined distance may be determined based on the size and/or shape of metal plate <NUM>. In some examples, the predetermined distance may be half, two-thirds, three-quarters, etc. of the length of the backer plate <NUM>. However, those are merely some examples and are not intended to be limited. There may be one or more vents <NUM> extending from air inlet ducting <NUM> to a first surface <NUM> of backer plate <NUM>. The air inlet ducting <NUM> and vents <NUM> may allow the cooling gas to travel through backer plate <NUM> towards metal plate <NUM>.

The heatshield may include a package pedestal <NUM>. The package pedestal <NUM> may be coupled to backer plate <NUM>. According to some examples package pedestal <NUM> may be integral with backer plate <NUM>. Package pedestal <NUM> may include one or more vents <NUM>. The one or more vents <NUM> of package pedestal <NUM> may align with the one or more vents <NUM> of backer plate <NUM> when package pedestal <NUM> is coupled to backer plate <NUM>. In examples where the package pedestal <NUM> is integral with backer plate <NUM>, the one or more vents <NUM> of package pedestal <NUM> are a continuation of the one or more vents <NUM> of backer plate <NUM>. The vents <NUM> of package pedestal <NUM> direct the cooling gas towards metal plate <NUM>.

Package pedestal <NUM> may include one or more outlets <NUM> to allow heated gas to escape. The cooling gas from the compressor that is injected or forced into air inlet ports <NUM> may become heated gas once the cooling gas comes in contact with metal plate <NUM> during the rework process of the second BGA package <NUM>. The heated gas may leave or dissipate from the heatshield by the one or more outlets <NUM>. According to some examples, the one or more outlets <NUM> may be recesses or cutouts in package pedestal. The one or more outlets <NUM> may extend from metal plate <NUM> to edges <NUM> of package pedestal <NUM>. For example, the one or more outlets <NUM> may be channels in package pedestal <NUM>, as best seen in <FIG>.

The metal plate <NUM> may be coupled to package pedestal <NUM>. Alternatively, in examples where the package pedestal <NUM> is part of backer plate <NUM> or where there is no package pedestal <NUM>, the metal plate <NUM> may be coupled to backer plate <NUM>. The metal plate <NUM> may be coupled to the package pedestal <NUM> and/or backer plate <NUM> via one or more screws.

During the rework of the second BGA package <NUM>, the metal plate <NUM> may pull heat away from the first BGA package <NUM>. For example, the thermal energy produced during the rework of the second BGA package <NUM> may be absorbed by or transferred to the metal plate <NUM>. As the metal plate <NUM> absorbs thermal energy and/or pulls heat away from the first BGA package <NUM>, the metal plate <NUM>, as part of the heatshield, may prevent reflow-related solder defects from occurring with respect to the first BGA package <NUM> during rework of the second BGA package <NUM>.

The metal plate <NUM> may be made of a material with a high thermal conductivity. A high thermal conductivity may allow the metal plate <NUM> to absorb or receive a greater amount of thermal energy. For example, the metal plate <NUM> may be made of copper, aluminum, silver, gold, etc..

Metal plate <NUM> may be cooled by the cooling gas injected or forced into air inlet port <NUM>. The metal plate <NUM> may have one or more fins <NUM>, as shown in <FIG>. The one or more fins 252may increase the surface area of metal plate <NUM>. Increasing the surface area of metal plate <NUM> may increase the amount of contact the cooling gas has with the metal plate <NUM> such that the performance of the heatshield increases as compared to a metal plate <NUM> without fins <NUM>. The performance of the heatshield, which includes metal plate <NUM>, may be how much heat, or thermal energy, is dissipated by the heatshield. According to some examples, the cooling gas may leave or dissipate from the heatshield by the one or more fins <NUM>.

The first BGA package <NUM> may be located between the metal plate <NUM> and PCB <NUM>. As shown, the first BGA package <NUM> may include a stiffener ring <NUM> and exposed die <NUM>. The first BGA package <NUM> may be soldered to a first side <NUM> of PCB <NUM> via solder balls <NUM>.

The second BGA package <NUM> may be coupled to a second side <NUM> of PCB <NUM> using solder balls <NUM>. The second side <NUM> of PCB <NUM> may be opposite the first side <NUM> of PCB <NUM>.

The heatshield, including the backer plate <NUM>, metal plate <NUM>, and/or package pedestal <NUM>, may absorb the thermal energy during the rework of the second BGA package <NUM> to prevent the solder joints coupling the first BGA package <NUM> to PCB <NUM> from becoming liquidus and/or soft enough to allow reflow-related solder defects to occur. The solder joints coupling the first BGA package <NUM> to PCB <NUM> may include solder balls <NUM>.

The PCB <NUM> may be connected, or coupled, to the backer plate <NUM> via one or more posts <NUM>. Posts <NUM> may be screw-mounted to allow for easy removal after the rework process. According to some examples, using screw mounted posts <NUM> may leverage tooling holes in the PCB <NUM>. The tooling holes may be the holes in PCB <NUM> that are used to attach the heatsink.

<FIG> and <FIG> illustrate a perspective view of a heatshield <NUM>. As shown, only some of the components of clamshell BGA structure <NUM> is shown in heatshield <NUM>. For example, <FIG> illustrates a perspective view of the backer plate <NUM>, the package pedestal <NUM>, and the metal plate <NUM>. <FIG> illustrates a perspective view of backer plate <NUM>, the package pedestal <NUM>, the metal plate <NUM>, and the first BGA package <NUM>.

Backer plate <NUM> includes one or more air inlet ports <NUM>. While three air inlet ports <NUM> are shown, there may be any number of air inlet ports <NUM>. According to some examples, there may be one, four, five, etc. air inlet ports. Thus, the example of three air inlet ports <NUM> is only one example and is not intended to be limiting.

The thickness of the backer plate <NUM> may in some examples be relational to the diameter of the air inlet ports <NUM>. For example, the thickness of the backer plate must be larger than the diameter of the air inlet ports <NUM>. If the diameter of the air inlet ports <NUM> is reduced, the thickness of the backer plate <NUM> may be reduced also.

The package pedestal <NUM> may extend from the first surface <NUM> of backer plate <NUM>. According to some examples, the package pedestal <NUM> may be integral with backer plate <NUM>. In some examples, package pedestal <NUM> may be a separate component that is coupled to backer plate <NUM>. As shown, package pedestal <NUM> is coupled to backer plate <NUM> via a plurality of screws <NUM>.

The package pedestal <NUM> may include one or more outlets <NUM>. The outlets <NUM> may extend, or radiate, outward from the center of package pedestal <NUM>. According to some examples, outlets <NUM> may be a cut out or recess in package pedestal <NUM>. While shown as rectangular recesses within package pedestal <NUM>, outlets <NUM> may have any shape or size, such as semicircular. According to some examples, there may be an outlet <NUM> that extends outward to each edge, or side, of the package pedestal. In the example shown in <FIG>, there are four outlets <NUM>. However, this is merely one example and is not intended to be limiting, and in other examples any number of outlets may be included. In some examples, the outlets <NUM> may extend non-linearly. According to some examples, the outlets <NUM> may form a star burst such that outlets <NUM> extend from the center of package pedestal <NUM> outwardly in all directions.

The metal plate <NUM> may be coupled to package pedestal <NUM> between the package pedestal <NUM> and first BGA package <NUM>. Metal plate <NUM> may be coupled to package pedestal <NUM> via one or more screws <NUM>. As shown, at least a portion of metal plate <NUM> may extend into outlets <NUM>.

The metal plate <NUM> may include a plurality of fins <NUM>. The plurality of fins <NUM> may increase the surface area of metal plate <NUM>. Increasing the surface area of metal plate <NUM> may increase the amount of contact the cooling gas has with the metal plate. The greater the amount of cooling gas that comes in contact with metal plate <NUM>, the better the heatshield may perform as compared to a metal plate <NUM> without fins. The heatshield may be the combination of the metal plate <NUM> and backer plate <NUM>.

As cooling gas is forced into heatshield <NUM> the cooling gas may become heated once it comes in contact with metal plate <NUM> and/or first BGA package <NUM>. The outlets <NUM> may direct the heated gas away from metal plate <NUM>, first BGA package, and/or heatshield <NUM>. The heated gas may also escape heatshield <NUM> by traveling through fins <NUM> and outlets <NUM>.

As shown in <FIG>, the first BGA package <NUM> may be layered on top of package pedestal <NUM> and/or metal plate <NUM>. As described with respect to <FIG>, the first BGA package <NUM> may include a stiffener ring and/or an exposed die. Both the stiffener ring and/or exposed die may be on the side of the first BGA package <NUM> closest to the package pedestal <NUM> and metal plate <NUM> and, therefore, are not shown in <FIG>. According to some examples, a thermal interface material may be used between the exposed die of the first BGA package <NUM> and the metal plate <NUM> of the heatshield to reduce thermal resistance. The thermal interface material may be, for example, a thermal pad or grease. In some examples, a foam pad may be used to provide mechanical protection for the die to prevent cracking, etc. Additionally or alternatively, there may be a small air gap between the exposed die of the first BGA package <NUM> and the metal plate <NUM>.

<FIG> illustrates a cross-sectional perspective view of the portion of the heatshield shown in <FIG> as cooling gas is forced into heatshield <NUM>. Air inlet ducting <NUM> extends from air inlet port <NUM>. A plurality of vents <NUM> may extend from air inlet ducting <NUM> to the first surface <NUM> of backer plate <NUM>. For clarity purposes, only one vent <NUM> of the plurality of vents <NUM> is labeled in <FIG>. The air inlet ducting <NUM> and vents <NUM> may direct the cooling gas <NUM> that is injected, or forced, into the heatshield <NUM> towards the metal plate <NUM>.

Package pedestal <NUM> may include a plurality of vents <NUM>. For clarity purposes, only one vent <NUM> of the plurality of vents <NUM> is labeled in <FIG>. When package pedestal <NUM> is coupled to backer plate <NUM>, the plurality of vents <NUM> in package pedestal <NUM> may align with the plurality of vents <NUM> in backer plate <NUM>. The vents <NUM>, <NUM> may direct the cooling gas <NUM> towards the bottom of metal plate <NUM>.

For example, during manufacture of the clamshell BGA structure <NUM>, rework of the second BGA package <NUM> may be necessary. The heat, or thermal energy, produced during the rework of the second BGA package <NUM> may cause the solder joints of the first BGA package <NUM> to become liquidus and/or soft enough to allow reflow-related solder defects to occur. To prevent the solder joints of the first BGA package from becoming liquidus, cooling gas <NUM> may be forced into the heatshieldto cool the metal plate <NUM>, during the rework process of the second BGA package <NUM>. The cooling gas <NUM> may cool the metal plate <NUM> such that the solder joint temperature of the first BGA package <NUM> is kept below the reflow temperature and below the solidus temperature of the solder joint alloy. This may prevent hot tears, separation, joint failure, reflow-related defects, etc. of the solder joints of the first BGA package.

The cooling gas <NUM> may be forced into heatshield <NUM> via an air compressor. The cooling gas <NUM> may be air or nitrogen gas.

<FIG> illustrates a cross-sectional perspective view of the portion of the heatshield shown in <FIG> as heated gas leaves the heatshield <NUM>. As described with respect to <FIG>, cooling gas <NUM> may be forced into heatshield <NUM> during the rework of the second BGA package <NUM>. As the cooling gas <NUM> comes in contact with the metal plate <NUM> and/or the first BGA package <NUM>, the cooling gas <NUM> may be heated. The heated gas <NUM> exits the heatshield <NUM> via one or more outlets <NUM>. For example, as the cooling gas <NUM> comes in contact with the metal plate <NUM>, the heated gas <NUM> may leave through fins <NUM> of metal plate <NUM>. According to some examples, the fins <NUM> of metal plate <NUM> may be located in outlet <NUM>. Therefore, outlet <NUM> may direct the heated gas <NUM> away from heatshield <NUM>.

According to another example, a heatshield that can be actively cooled during a rework process is disclosed. The heatshield may include a backer plate, a metal plate, and/or a package pedestal. The backer plate may include one or more air inlet ports configured to be connected to an air compressor. Air inlet ducts may extend from the air inlet ports through at least a portion of the backer plate. A plurality of vents may extend from the air inlet ducts to a top surface of the backer plate such that the plurality of vents directs cooling gas forced into the heatshield towards the metal plate and a first BGA. The cooling gas may maintain the solder joint temperature of the first BGA package below the reflow temperature and below the solidus temperature of the solder joints to prevent reflow-related solder joint defects from occurring in the first BGA package during rework of a second BGA package.

Claim 1:
A system, comprising:
a heatshield for cooling a first ball grid array, BGA, package (<NUM>) of a clamshell BGA structure (<NUM>), the heatshield comprising:
a backer plate (<NUM>) including at least one air inlet port (<NUM>) and air inlet ducting (<NUM>) connected to the at least one air inlet port (<NUM>), and a first plurality of vents (<NUM>) extending from the air inlet ducting (<NUM>) to a first surface (<NUM>) of the backer plate (<NUM>); and
a metal plate (<NUM>) coupled to the backer plate (<NUM>),
wherein the metal plate (<NUM>) and the backer plate (<NUM>) form one or more outlets (<NUM>),
wherein the at least one air inlet port (<NUM>) is configured to receive cooling gas (<NUM>) to decrease a temperature of at least one of the metal plate (<NUM>), and the backer plate (<NUM>), and
wherein the cooling gas (<NUM>) is configured to exit the system through at least one of the one or more outlets (<NUM>).