The present invention relates to semiconductor packages, and more specifically to ball grid array packages with heat spreaders, such as a thermally enhanced ball grid array.
A semiconductor package includes a semiconductor die that is attached to a substrate and wire bonded to connection points on the substrate to form electrical connections with contacts that may be soldered to a printed circuit board (PCB). The die is encapsulated in an encapsulant material, such as a thermosetting resin mold compound, to provide protection to the die and the electrical interconnections.
During operation of the semiconductor package, heat generated by the die must be removed to ensure correct operation of the die. To assist with heat removal, some semiconductor packages incorporate a heat spreader that is typically encapsulated in the mold compound.
One example of a conventional semiconductor package is described in U.S. Pat. No. 7,126,218. U.S. Pat. No. 7,126,218 describes a semiconductor package that includes a heat spreader attached directly to an upper surface of a ball grid array package with a thin adhesive layer. The shape of the heat spreader conforms to the topographical profile of the underlying die. According to U.S. Pat. No. 7,126,218, attaching the heat spreader directly to the die results in a very low thermal resistance at the interface between the die and the heat spreader. However, directly attaching the heat spreader to the die may obstruct plasma cleaning (prior to molding) and also obstruct mold flow of the mold compound during a side gate molding process. Obstruction of plasma cleaning may have the undesirable result of reducing the effectiveness of the cleaning process and thus also reduce mold compound adhesion. Obstruction of the mold flow may result in unbalanced mold flow.
It is believed that reducing the effectiveness and unbalanced mold flow may contribute to delamination of either the heat spreader or the die from the substrate. Accordingly, it would be desirable to have a heat spreader the does not impair mold flow or plasma cleaning for a side gate molding process.
The present invention will now be described in relation to preferred embodiments as illustrated in the accompanying drawings. However, it is to be understood that the following description is not to limit the generality of the above description.
The present invention provides a semiconductor package that incorporates a heat spreader configured to provide improved mold flow and cleaning processes during manufacture of the semiconductor package.
In one aspect the present invention provides a semiconductor package, comprising a substrate, a die attached to substrate and a heat spreader. The heat spreader comprises a heat dissipating portion comprising an upper surface, a lower surface and a perimeter. The lower surface overlies and is spaced apart from the die to provide a clearance therebetween. Plural supports are spaced about the perimeter of the heat dissipating portion and depend downwardly thereof. Each support is located on the substrate to establish an opening between adjacent supports.
In an embodiment, the upper surface of the heat dissipating portion is exposed and thus not covered by the encapsulant. Not covering the upper surface of the heat dissipating portion with encapsulant may enhance the thermal conductivity of the heat spreader and thus provide an improved ability to remove heat from the die.
Each opening will provide a vertical extent which extends between the lower surface of the heat dissipating portion and the substrate, and a horizontal extent which extends extending between opposite side edges of the adjacent supports. The horizontal and vertical extents are adapted to permit flow of a molding compound through the openings to encapsulate the die and fill the clearance. The openings also permit plasma cleaning of the die prior to the encapsulation.
The supports may be uniformly spaced about the perimeter of the heat dissipating portion. In an embodiment, each support subtends a central angle δ about a respective extent of the perimeter of the heat dissipating portion. It is preferred that each opening subtends a central angle θ about a respective extent of the perimeter of the heat dissipating portion which is substantially the same as or greater than the central angle δ. Furthermore, at each opening it is preferred that the heat spreader has a peripheral or outermost extent which corresponds with the perimeter of the heat dissipating portion.
The present invention also provides a plastic ball grid array semiconductor package, comprising a substrate, a die attached to substrate and a heat spreader. The heat spreader comprises a heat dissipating portion comprising an upper surface, a lower surface and a perimeter. The lower surface overlies and is spaced apart from the die to provide a clearance therebetween. Plural supports spaced about the perimeter of the heat dissipating portion and depend downwardly thereof. Each support is located on the substrate to establish an opening between adjacent supports. Each opening has a vertical extent which extends between the lower surface of the heat dissipating portion and the substrate, and a horizontal extent which extends between opposite side edges of the adjacent supports.
The vertical extent and the horizontal extent of the openings are adapted for flow therethough of a molding compound for filling the clearance and encapsulating the die.
The present invention also provides a method of packaging a semiconductor die, comprising providing a substrate, attaching the die to the substrate, attaching a heat spreader to the substrate. The heat spreader comprises a heat dissipating portion comprising an upper surface, a lower surface and a perimeter. The lower surface overlies and is spaced apart from the die to provide a clearance therebetween. Plural supports are spaced about the perimeter of the heat dissipating portion and depend downwardly thereof. Each support is located on the substrate to establish an opening between adjacent supports. After the heat spreader has been attached to the substrate a molding compound is injected to flow through the openings to fill the clearance and encapsulate the die.
The present invention also provides a heat spreader for attaching to a substrate of a semiconductor package, the heat spreader comprising a heat dissipating portion comprising an upper surface, a lower surface and a perimeter. Plural supports are spaced about the perimeter of the heat dissipating portion and depend downwardly thereof. Each support is adapted to locate the heat spreader on the substrate to establish an opening between adjacent supports, such that each opening has a vertical extent extending between the lower surface of the heat dissipating portion and the substrate and a horizontal extent extending between opposite side edges of the adjacent supports. The vertical extent and the horizontal extent of the openings are adapted for flow therethough of a molding compound, said molding compound for filling the clearance and encapsulating the die.
Referring now to
The semiconductor package 100 is illustrated as a thermally enhanced plastic ball grid array (TEPGA) device. However, although the following embodiment relates to a TEPGA device, it will be appreciated that a heat spreader according to an embodiment may be used in other type of semiconductor devices which are manufactured using a process that involves “over molding”, such as side gate molding, of the encapsulant 108.
The substrate 102 provides the semiconductor package 100 with a base for mechanically supporting the die 104 and also provides an electrical interface for forming suitable electrical connections with the die 104. Typically, the electrical connections are formed using interconnecting elements, such as wires, which are connected by way of a suitable connection process between an electrically conductive terminal, such as a die pad, disposed on the die 104, and an electrically conductive terminal, which may also be a pad, disposed on the substrate 102. The wires may be made of, for example, gold (Au), copper (Cu), aluminium (Al) or other suitable conductive materials. Suitable connection processes would be well known to a skilled addressee.
The substrate 102 will typically be a laminated structure comprising multiple layers (not shown). The layers preferably include power and ground planes, and one or more planes of a highly thermal conductive material, such as copper, to assist with dissipating heat from the die. Suitable substrate structures including layer arrangements would be well known to a skilled addressee.
Referring initially to
As shown in
The heat spreader 106 may be manufactured by a conventional process, such as, stamping and forming, etching, mechanical cutting, laser cutting or the like. Other suitable manufacturing processes would be well known to a skilled addressee. The heat spreader 106 material may be copper or another highly thermal conductive material could also be used. An example of a suitable material is copper alloy C1100 3/4H with a material thickness of 0.30 mm. Other suitable materials may include, for example, aluminium, silver, or other materials having suitable thermal conductivity properties. A suitable thermal conductivity in the range of about 350 to 400 W/m.K will be suitable.
As shown in
The heat spreader 106 includes plural supports 506 which are connected to or integrally formed with the heat dissipating portion 112. The supports 506 are spaced about the perimeter 402 of the dissipating portion 112 and depend downwardly therefrom to retain the heat dissipating portion 112 in use above the die 104 and thus provide a clearance D therebetween.
In the heat spreader 106 depicted in
In the present case, the first central angle δ is about forty-four degrees and the second central angle θ is about forty-six degrees. However, it will of course be appreciated that the circumferential extent of each support 506 and the spacing between circumferentially adjacent supports 506 may vary. Indeed, the above configuration and spacing of the spaced apart supports 506 is only one example of a possible configuration and thus other configurations and spacings may also be suitable. Moreover, although in the embodiment illustrated the supports 506 have a uniform width and uniform spacing, it is possible that the width of the supports 506 and/or the spacing therebetween may be non-uniform.
As shown in
In the embodiment illustrated, each leg 508 depends downwardly (that is, in the direction of the substrate 102) from the perimeter 402 of the heat dissipating portion 112 at a right angle relative to the plane of the upper surface 502 of the heat dissipating portion 112. However, it is possible that each leg 508 may form an acute angle relative to the upper surface 502 of the heat dissipating portion 112.
In the heat spreader 106 illustrated in
Referring now to
Continuing now with reference to
The dimension of the clearance D will vary according to package requirements, such as the package thickness or height (H) of the encapsulated die 104 (‘the package’), the material thickness (T) of the heat spreader 106, and the height of the die (h). In the present example, the package thickness H is about 1.15 mm ±0.1 mm, the material thickness T of the heat spreader 106 is about 0.3 mm, and the height of the die 104 is about 0.33 mm. In this example, the clearance D is about 0.52±0.1 mm. Care needs to be taken to ensure that the tolerance of the clearance dimension is not larger than the tolerance of the package thickness H.
As shown in
As best shown in
As is evident from
The above described arrangement may provide for a larger vertical extent than would otherwise be provided if the opening was formed as a slit or cut-out in a vertical peripheral wall of a prior art heat spreader having a top hat type configuration (i.e. one with a single continuous foot).
Providing the above described openings 600 may allow larger amounts of cleaning gases in and out of the die area and also improve mold flow uniformity. In addition, the openings 600 may permit a lower mold flow rate of mold compound into the die area and thus subject the wire bonds to a reduced flow mold speed, and thus a reduction in wire sweep. The significance of a reduced wire sweep would be understood to a skilled person.
In the embodiment illustrated in
As shown in
The heat spreader 700 may be attached to the substrate 102 using any suitable process. One suitable process includes dispensing or applying droplets of a suitable bonding agent 900 (ref.
As shown in
As will be appreciated, in embodiments that do not include projections 702, it is possible that the heat spreader may “tilt” or “float” during the bonding process since the heat spreader may be separated from the substrate 102 by a layer of the bonding agent, which is typically a liquid layer, prior to curing. Thus, in embodiments without projections 702 the heat spreader may be incorrectly positioned so that it is not flat or co-planar with respect to the substrate 102. Hence, in such embodiments care needs to be taken when bonding the heat spreader to the substrate 102 to ensure that the heat spreader is positioned on and/or aligned with the substrate 102 correctly. In other words, unless care is taken, the heat spreader may “tilt” during the bonding process. Unfortunately, such tilting may cause adhesive to “seep” onto an upper surface of the heat spreader and thus form a defect known to those skilled in the art as ‘mold flash’.
As shown in
Embodiments of the present invention are expected to permit a reduced contact angle during pre-encapsulation cleaning, and a reduced wire sweep angle during the encapsulation process. In terms of the reduced contact angle, and as will be appreciated by a skilled reader, after the heat spreader 106/700 has been attached to the substrate 102, but prior to encapsulation, the surface of the die 104 is typically cleaned to remove impurities and contaminants using a suitable cleaning process, such as a gaseous cleaning process involving plasma cleaning. The configuration of the openings 600 may reduce obstructions to plasma gas flow though the openings 600 and thus may permit embodiments of the present invention to allow a larger amount of plasma gas to enter the openings and thus provide for more effective cleaning of the die surface.
Finally, it is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention.