Component with improved heat dissipation

Abstract

In a component with component structures generating dissipation heat, it is proposed to apply on an active side of the substrate a heat-conducting means to the back side of the component substrate, which has a second thermal conductivity coefficient α.sub.LS, which is substantially higher than the first thermal conductivity coefficient α.sub.S of the substrate. The heat dissipation then succeeds via the heat-conducting means and via connecting means which connect the substrate to a carrier.

Claims

1. A component, comprising: a substrate having a first thermal conductivity coefficient α.sub.S; component structures on an active side of the substrate, the component structures configured to generate dissipation heat; a carrier; metallic connecting means, with which the active side of the substrate is mounted on the carrier; and heat-conducting means applied to a back side of the substrate located opposite to the active side, wherein the heat-conducting means comprises a material having a second thermal conductivity coefficient α.sub.LS, and α.sub.LS>>α.sub.S; wherein vertical heat transport through the substrate in structured areas of the substrate from the component structures to the heat-conducting means and/or the heat-conducting means to the metallic connecting means is facilitated, wherein a layer thickness of the substrate is reduced in the structured areas.

2. The component according to claim 1, wherein the heat-conducting means on the back side connects at least one or a plurality of areas above the component structures to the areas above the metallic connecting means.

3. The component of claim 1, wherein the metallic connecting means are connected to a heat sink in the carrier.

4. The component of claim 1, wherein the substrate comprises a piezoelectric material, in which the component is a component working with acoustic waves.

5. The component of claim 4, wherein the heat-conducting means comprise an electrically conductive layer applied on the back side, which is structured in two separate areas, which are arranged above different component structures, so that a capacitive coupling of the different component structures through the layer of the heat conducting means is avoided.

6. The component of claim 1, wherein the heat-conducting means comprises a layer applied across the entire surface area on the back side.

7. The component of claim 6, wherein the layer applied as a heat-conducting means on the back side extends down to at least one side surface of the substrate towards the carrier and is connected there to a heat sink.

8. The component of claim 3, wherein the metallic connecting means are formed as bumps or solder pads, which connect contact surfaces on the substrate with corresponding connection points on the upper side of the carrier.

9. The component of claim 7, wherein the heat-conducting means comprises a material selected from Al, Ag, Cu, Au, AlN and SiC.

Description

(1) The invention will be explained in greater detail below with reference to exemplary embodiments and the associated figures. The figures shown are only schematic and not true to scale. The figures therefore represent neither absolute nor relative dimensions, since individual parts may be shown enlarged for better clarity.

(2) FIG. 1 shows, in cross-section, a per se known component working with surface acoustic waves, together with the paths along which the generated dissipation heat is discharged,

(3) FIG. 2 shows a simple embodiment of the invention with reference to a schematic cross-section through the component,

(4) FIG. 3 shows a further embodiment of the invention with reference to a cross-section,

(5) FIG. 4 shows an embodiment with first structured areas on the basis of a schematic cross-section,

(6) FIG. 5 shows an embodiment with first and further structured areas in schematic cross-section,

(7) FIG. 6 shows a fifth embodiment in schematic cross-section,

(8) FIG. 7 shows the temperature of a measuring point of a known component as a function of the frequency of the applied electrical signal,

(9) FIG. 8 shows the temperature of a measuring point of a component according to the invention as a function of the frequency of the applied electrical signal.

(10) FIG. 1 snows a per se known component which operates with surface acoustic waves, i.e., a SAW component (SAW=Surface Acoustic Wave). This comprises a piezoelectric substrate SU which is bonded in flip-chip design via bumps serving as connecting means VM to a carrier TR comprising, for example, a ceramic plate. On the active side of the substrate SU, which faces the carrier TR, schematic component structures BES in the form of metallizations are indicated. Not shown are electrical connections that connect the component structures BES with contact surfaces on the active side of the substrate SU. The contact surfaces are used for electrical and mechanical coupling by means of connecting means VM here illustrated as bumps. The device may also be protected by a protective layer GT, for example, with a globe top coating comprising an epoxy resin. A cavity between the active side of the substrate SU and the carrier TR, within which the component structures BES are arranged, can be hermetically sealed with this coating.

(11) As can be seen from the figure, the component is electrically and mechanically connected, for example soldered, to a printed circuit board PCB via electrical connections on the underside of the carrier TR.

(12) Curved arrows within the substrate SU indicate the heat flow with which the dissipation heat generated by the component structures BES extends over the substrate within the layer plane of the substrate SU and is ultimately dissipated via the connecting means VM to the carrier TR and further to the printed circuit board PCB. Due to the poor thermal conductivity coefficient α.sub.S of the piezoelectric substrate SU, a strong heating of the substrate may occur. Heat dissipation is delayed and the component may overheat.

(13) FIG. 2 shows a first embodiment with reference to a schematic cross-section through a component according to the invention. Here too, a piezoelectric substrate SU is again mounted via connecting means VM (bumps) on a carrier TR, which in turn is applied to a printed circuit board PCB. However, the rear side of the substrate SU is coated with a layer of a heat-conducting means CL.sub.T, for example, with a metallic layer. In this case, this layer of the heat-conducting means also extends over a section CL.sub.S which extends over the side surfaces of the substrate SU down towards the carrier TR. In the carrier, in turn, the layer of the conductive material CL or its lateral section CL.sub.S is connected to an additional through-connection VI.sub.Z or a via VI, which likewise has good heat conductivity due to its metallic cladding or filling and allows good heat transport through the carrier TR. The additional through-connection VI.sub.Z may be reserved for heat transfer alone. However, it is also possible to connect the additional through-connection VI.sub.Z to ground potential.

(14) Again, the heat flow is shown schematically by arrows. It can be seen that heat flow now predominantly takes place from the component structures transversely through the substrate SU into the layer of the heat-conductive material CL.sub.T. Within this layer, a rapid heat transfer takes place, so that during operation of the component under load a rapid heat distribution and thus a uniform heating of the heat-conducting means CL takes place. The heating of the substrate is correspondingly more uniform.

(15) From the layer of the heat-conducting means CL.sub.T on the back side of the substrate SU, the heat is dissipated on two routes towards the carrier TR and onwards to the printed circuit board PCB on two fundamentally different paths. A first path extends from the heat-conducting means transversely through the substrate to a connecting means and via the connecting means to a through-connection through the carrier TR towards the circuit board PCB. The further heat dissipation path already described takes place through the lateral sections CL.sub.S of the heat-conducting means towards corresponding through-connections in the carrier.

(16) The illustrated component shows an efficient heat dissipation and a reduced temperature increase under load. Hence it is improved in frequency accuracy, aging resistance and reliability over the known component shown in FIG. 1.

(17) FIG. 3 shows a second embodiment of the invention, in which the layer applied to the back side of the substrate of the heat-conducting means CL is divided into two areas CL.sub.1 and CL.sub.2. The two areas are galvanically separated from one another by a galvanic separation GS, so that a capacitive coupling of different component structures via a continuous, electrically conductive layer to heat-conducting means is avoided. Although not shown, the layer of heat-conducting means CL.sub.1, CL.sub.2 can be continued here via corresponding side sections across the side surfaces of the substrate SU towards the carrier, in order to allow additional heat dissipation in this way.

(18) FIG. 4 shows a third embodiment of the invention. In contrast to FIG. 3, here the heat-conducting means is applied to the back side of the substrate SU as a layer across the entire surface area. In order to shorten the heat path through the substrate, which has a poor first thermal conductivity coefficient α.sub.S, the layer thickness of the substrate SU is reduced in structured areas SB.sub.VM. In this embodiment, these structured areas SB.sub.VM are arranged exclusively above the connecting means VM and not above acoustically active component structures BES, so that their function is not disturbed by the reduced layer thickness in the structured areas SB.sub.VM.

(19) The heat path therefore now extends from the point of heat generation at the component structures BES transversely through the substrate SU into the heat-conducting layer CL.sub.T, there laterally up to the structured areas SB and there through the reduced layer thickness of the substrate SU to the connecting means VM and through these into the carrier TR. Since the section through the substrate, i.e., the section of the heat path through the material with the lowest thermal conductivity coefficient α.sub.S, is shortened compared to the previous exemplary embodiments, an improved heat dissipation takes place via the structured areas and the connecting means VM arranged underneath.

(20) In one embodiment, e.g., the substrate material is LiNbO.sub.3, which has a thermal conductivity coefficient α.sub.S of 4.6 W/mK. The thermal conductivity coefficient of an existing epoxy cover GT is actually only 0.5 W/mK. The thermal conductivity coefficient α.sub.LS of a layer of the heat-conducting means CL made, for example, of aluminum, is on the other hand 237 W/mK—about 50 times as high.

(21) FIG. 5 shows, in a schematic cross-section, a component according to a fourth embodiment, in which both first structured areas SB.sub.VM are placed above the connecting means VM and second structured areas SB.sub.BES above the component structures BES on the back side of the substrate. These two structured areas may differ in terms of the depth of the recess and the reduced layer thickness of the substrate. Furthermore, the recess may be larger above the component structures BES to allow a reduced layer thickness over the entire area of the component structures. The layer thickness of the substrate may be greater above the component structures BES than above the connecting means VM.

(22) Since here the path from the component structures into the heat-conducting means and the path from the heat-conducting means through the substrate into the connecting means VM is now shortened, the heat dissipation of the component according to the fourth embodiment is further improved compared to the third embodiment shown in FIG. 4. By the structuring in a relatively small area of the substrate, the stability of the substrate is not inadmissibly reduced by the recesses. A risk of fracture is ruled out, especially as the electrically conductive layer or the layer of the heat-conducting means is positively applied to the back side of the substrate and thus increases its structural strength. Although not shown, the layer of the heat-conducting means CL may also extend across the side surfaces of the substrate toward the carrier to allow for direct heat dissipation, which need not occur exclusively through the substrate.

(23) In the second to fourth embodiments, the layer of the heat-conducting means CL is preferably positively applied to the back side of the substrate SU. This can be achieved by suitable metallization, for example a base metallization generated via the gas phase and a galvanic or currentless reinforcement thereof.

(24) However, it is also possible, as illustrated in a fifth embodiment with reference to FIG. 6, to adhesively bond the heat-conducting means CL.sub.T as a compact layer onto the back side of the substrate SU. The adhesive used here is preferably an adhesive filled with thermally highly conductive particles, which thus has a good overall heat conductivity.

(25) Through the adhesion of the heat-conducting means in the form of a metal sheet or a foil, the step of metal deposition or the deposition of an insulating heat-conducting means from the gas phase can be dispensed with. At the same time, the layer of heat-conducting means applied with adhesive can form part of the seal or of the protective layer or of the package of the component. Shown in the figure are edge regions of a protective layer GT, which laterally delimit the substrate and hermetically seal the cavity between the carrier and the substrate. The heat-conducting means CL.sub.T then sits flush on these side parts and is tightly connected to the substrate with the aid of the adhesive or the adhesive layer AL. This embodiment too may be combined with the first, second, third or fourth embodiment, without departing from the idea of the fifth embodiment.

(26) The layer of the heat-conducting means, which is an additional advantage over known components, can be generated or applied in one step, which can be easily integrated into the manufacturing process of the component. The risk of inadmissible self-heating of components can therefore be reduced in a cost-effective manner by the invention and leads in a cost-effective manner to components with improved thermal stability, lower drift of the properties by reduced self-heating and to an extended life and increased reliability.

(27) FIG. 7 shows the measured temperature increase of a measuring point on the substrate of a known component in K/W as a function of the frequency of an electrical signal applied to the component structures. In the figure, three curves at different power levels are superimposed.

(28) The component here is a duplexer for Band 3. It turns out that at resonant frequencies of the duplexer a particularly great amount of dissipated heat is generated, which can raise the temperature by up to about 120° C. At a temperature coefficient of the center frequency of the substrate material used of 27.1 ppm/K, this corresponds to a frequency shift of about 2700 ppm, corresponding to an absolute frequency shift of about 5.8 MHz. The highest increase in temperature due to dissipation heat and heating up is measured at a frequency of 1785 MHz, which corresponds to the righthand passband edge.

(29) FIG. 8 shows the measured temperature increase of a measuring point on the substrate of a component according to the invention in K/W as a function of the frequency of an electrical signal applied to the component structures. In the figure, three curves at different power levels are superimposed.

(30) Here again, the component is the duplexer for Band 3, which, however, as shown in FIG. 6, is illustrated with an aluminum foil applied by an adhesive. The highest heating or temperature increase is again in the range of the righthand passband edge, but is much lower under otherwise identical measurement conditions and reaches only about 75° C. With the same temperature coefficient, this results in a temperature-induced frequency drift of about 3.6 MHz, i.e., a reduction of 38%.

(31) Although the invention is described only for components working with acoustic waves, the invention is suitable for all electrical and microelectronic components, which are applied to a carrier in a flip-chip arrangement and have a substrate with poor heat conductivity, i.e., with a low thermal conductivity coefficient. The invention is not therefore limited to the embodiments.

(32) The invention is applicable to various types of components, can be adapted to different housing technologies, may be geometrically shaped differently than shown and can be combined with different materials with respect to the carrier, substrate or printed circuit board. In addition, a component according to the invention may comprise further covering layers, which may be arranged above or below the covering layers described.

LIST OF REFERENCE SIGNS

(33) AL adhesive layer BES component structures on active side CL.sub.S heat-conducting means laterally to substrate CL.sub.T, CL.sub.1, CL.sub.2 heat-conducting means on the back side GS galvanic isolation GT cover/protective layer PCB circuit board SB.sub.BES structured areas of the substrate via component structures SB.sub.VM structured areas of the substrate via connecting means SU substrate TR carrier VI via or through-connection VI.sub.Z additional via or through-connection VM metallic connecting means for heat dissipation α.sub.LS second thermal conductivity coefficient (heat conducting means) α.sub.S first thermal conductivity coefficient (substrate)