A combined heat sink/electromagnetic shield

A COMBINED HEAT SINK/ELECTROMAGNETIC SHIELDTECHNICAL FIELDThe invention relates generally to flip chip semiconductor components and more specifically to a combined heat sink/electromagnetic shield for such components.

BACKGROUND OF THE INVENTIONA major trend in microelectronics today is size reduction of semiconductor components and assemblies of such components. This development is enabled by various technologies related to the fabrication of the semiconductor components and the assembly of them into electronic systems.

One such assembly technology, which enables both size and cost reduction is flip chip technology. In accordance with that technology, the semiconductor component or chip is mounted upside down, and the electrical connections from the component are established by so-called flip chip solder bumps. The upside down mounting of the component imposes a problem related to heat dissipation and cooling of the component. The normal or traditional method of cooling components is to mount them onto a material with high thermal conductivity, which effectively transports the heat away from the component. In flip chip technology, the solder bumps have a very limited ability to conduct the heat away from the chip due to the limited area they constitute relative to the total component area.

Another important problem in microelectronic systems today is electromagnetic shielding of components operating at high frequency. Such components are common today as they are unavoidable in mobile phones and other radio communication equipment. Strong regulations have been issued by, in particular, the EuropeanUnion on the electromagnetic compatibility of electronic equipment and these regulations generate a need for effective electrical shielding of high frequency components.

SUMMARY OF THE INVENTIONThe object of the invention is to improve the cooling as well as the shielding of semiconductor components assembled by flip chip technology.

This is attained in accordance with the invention, mainly by means of a strip of a metal having high thermal and electrical conductivity fixed to the whole backside of the component, extending outside the component, and fixed to the substrate around the component to conduct heat from the component to the substrate and enclose at least the component to electrically shield the component and any other component mounted thereunder.

Thus, by means of a single structural part in the form of a metal strip, both cooling and electrical shielding of a flip chip component on a substrate is accomplished.

BRIEF DESCRIPTION OF THE DRAWINGThe invention will be described more in detail below with reference to the appended drawings on which Fig. 1 shows an embodiment of a combined heat sink/electrical shield according to the invention.

DESCRIPTION OF THE INVENTIONFig. 1 shows an embodiment of a combined heat sink/electromagnetic shield 1 for a flip chip semiconductor component 2 mounted upside down by means of solder bumps 3 on a circuit board or substrate 4.

As mentioned in the introductory portion, the solder bumps 3 have a very limited ability to conduct heat away from the component 2 due to the fact that the contact area of the bumps 3 are much smaller than the area of the component 2.

In accordance with the invention, to conduct heat from the component 2 and at the same time electromagnetically shield the component 2, the combined heat sink/electromagnetic shield 1 comprises a strip of a metal, preferably Cu, having high thermal and electrical conductivity, and extending outside the component 2.

The thickness of the metal strip 1 can be about 0.2 mmIn accordance with the invention, the metal strip 1 is fixed both to the whole backside of the component 2 and to the substrate 4 around the component 2.

The metal strip 1 can be fixed to the component 2 and the substrate 4 by means of solder or electrically conductive adhesive or a combination thereof. Typically, the metal strip 1 is fixed to the backside of the component 2 by means of electrically conductive adhesive 5 and to the substrate 4 by means of solder 6.

The solder 6 will be applied in the same operation as for other components to be mounted on the substrate 4, while the electrically conductive adhesive 5 will typically be printed onto the metal strip 1 prior to the assembly of the strip 1 onto the component 2. Typically, the adhesive 5 will be printed onto the strip 1 as part of the fabrication of the strip 1.

Thus, in the embodiment in Fig. 1, the solder 6 extends all around the component 2.

This means that the metal strip 1 in Fig. 1 functions not just as a heat sink but also as an electromagnetic shield to effectively shield high frequency components mounted on the flip chip semiconductor component 2 or on the substrate 4, such as a component 7 mounted under the metal strip 1.