This application claims priority under 35 U.S.C. 119 to German Application Number DE10 2011 012 186.2 filed on Feb. 23, 2011, hereby incorporated in its entirety herein by reference.
The invention relates in general to integrated circuits and more specifically to a chip module comprising a semiconductor die that is embedded in a PCB-substrate and to a method for providing a chip module.
Modern semiconductor devices have a high packing and power density, accordingly, heat dissipation is an important issue. Thermal properties of the package are especially crucial for chip modules comprising a plurality of integrated circuits and/or semiconductor devices. Chip modules come in a variety of different forms depending on the complexity and development philosophies of their designers. These can range from using pre-packed integrated circuits on a small printed circuit board (PCB) to fully custom chip packages integrating many chips dies on a high density interconnection substrate. Chip or multichip modules are also known as a system in package or a chip stack.
For mobile devices, modern chip modules having a small size and a high packing density have been developed. Especially for these modern packages, thermal coupling between the semiconductor die or a plurality of dies and the outside of the chip module is an important issue.
It is an object of the invention to provide a chip module and a method for providing a chip module that are improved with respect to thermal coupling between a surface of the chip module and a semiconductor die that is embedded in the chip module.
In an aspect of the invention, a chip module comprising a semiconductor die that is embedded in a printed circuit board-substrate (PCB-substrate) is provided. The die has a backside and an active front side comprising a plurality of contact pads, wherein the backside of the die is coupled to a surface of the chip module via a thermal bridge. Preferably, the backside of the die is a grinded surface that is a result of a grinding process for decreasing the thickness of the die to a desired value.
Advantageously, the thermal coupling between the embedded semiconductor die and a surface of the chip module is improved and higher heat dissipation is provided. Consequently, a higher integration density or more power integration is possible.
In another aspect of the invention, at least a portion of the backside of the die is coated with a thermally highly conductive coating. An inner end portion of the thermal bridge is adjacent to this coating. Preferably, the coating extends over the entire surface of the backside of the die. The coating may be a closed layer or a patterned layer, wherein according to another aspect, the density of the pattern may by varying. In other words, the density of the pattern may be higher in some areas of the backside of the die when compared to an average density or to a density of the pattern in the rest of the surface. According to an aspect of the invention, the density of the pattern is higher in a region of the die that produces more heat compared to other regions, e.g. the pattern density is increased in an area comprising the power transistors. A preferred material for the coating is a metal, preferably a thermally highly conductive metal e.g. copper. Advantageously, an additional copper metallization on the wafer backside improves heat dissipation from the die into the thermal bridge. Preferably, the copper layer is deposited after grinding the wafer to its final thickness. A closed layer provides the highest heat dissipation; however, it may also put mechanic stress to the die. A structured layer is advantageous due to its lower mechanical stress impact. Preferable patterned layers are dots or cross hatched lines. Further, the thermally highly conductive coating may be limited to some areas of the backside of the die, preferably areas offering a high thermal output like, e.g. the output transistors.
In another aspect of the invention, the thermal bridge is a monolithic block laterally extending over at least the entire surface of the backside of the die. Preferably, the monolithic block is made from a thermally highly conductive material that is e.g. filled with a thermally highly conductive particles. The material of the monolithic block may be filled with metal particles or metal clusters, further preferably a thermally highly conductive metal such as copper is applied. Advantageously, a monolithic block provides an effective thermal bridge for heat transfer between the backside of the semiconductor die and the outside of the chip module. Further, the generation of the monolithic block may be integrated into the embedding process easily.
According to another embodiment of the invention, the thermal bridge comprises a plurality of thermally highly conductive channels, wherein each channel provides a thermal bridge between the backside of the die and a surface of the chip module. Preferably, the thermally highly conductive channels are vias that are filled with a thermally highly conductive material preferably a thermally highly conductive metal such as copper. The vias or bores may be drilled from a surface, preferably a backside surface of the chip module down to the die or at least down to a region near to the backside surface of the die. Drilling may be performed e.g. by mechanical drilling or by laser drilling.
According to another advantageous aspect of the invention, at least a portion of the surface of the chip module is coated with a thermally highly conductive outside coating. An outer end portion of the thermal bridge is adjacent to the outside coating. This outside coating of the chip module allows improving heat dissipation from the package into a heat sink e.g. a customer printed circuit board or a part of the same. The coating is preferably made from a thermally highly conductive metal; a preferred metal is copper due to its high thermal conductivity. The backside coating or plating may be coupled to a heat sink by help of a suitable glue or solder.
In another aspect of the invention, the backside of the semiconductor die may be electrically contacted via the thermal bridge. Advantageously, this electric contact may be provided by a metal for filling the vias or bores or by a thermally highly conductive material for providing the monolithic block.
According to another aspect of the invention, a method for providing a chip module is provided. The method comprises the steps of: contacting contact pads at a front side of a semiconductor die and embedding the semiconductor die in a PCB-substrate. Drilling a plurality of vias in a backside of the PCB-substrate that is averted from the front side of the semiconductor die and filling the vias with a thermally highly conductive material so as to form a thermal bridge between the backside of the die and a surface of the chip module. Preferably, a thermally highly conductive metal, e.g. copper, is applied.
It is understood, a backside of the semiconductor die that is averted from its active front side may be thermally coupled/contacted to an outside surface of the chip module before electrically contacting the active front side of the die.
According to an advantageous embodiment, the method further comprises the step of coating at least a part of the backside of the semiconductor die so as to form a thermally highly conductive layer.
Same or similar advantages already mentioned for the semiconductor device according to the invention apply to the method for packing the semiconductor die.
Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
In a further step that is illustrated in
In a further processing step, shown in
Further, an electric contact between the backside 29 of the chip module 20 and a backside 16 of the semiconductor die 2 may be provided by the filled vias 24. The thermally highly conductive filling material 26 that is preferably copper is also suitable for providing an electric contact at the same time.
There are mainly two way for assembling the chip module 20. First, the die 2 may be placed onto a PCB-substrate 8 and electric and thermal coupling is provided according to
In another simplified cross-sectional view of
According to another embodiment of the invention that is shown in a further simplified cross-sectional view of
As already mentioned, the thermal coupling may be made up before electrically contacting the semiconductor die 2. Advantageously, a transparent thermally highly conductive PCB substrate-material 36 may be applied for manufacturing the thermal bridge 38. This allows aligning the semiconductor die 2 to an exact position for electrically contacting the active front side.
Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions, and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
Number | Date | Country | Kind |
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102011012186.2 | Feb 2011 | DE | national |