Integrated Circuit Package Heat Sink

Abstract

Integrated circuit (1) comprising: - at least one electronic chip (2) having a face (22) covered with a layer of a thermal interface material (6), - a heat sink (7) comprising a mounting area (71) fixed to the chip (2) by means of the layer of thermal interface material (6), the heat sink (7) comprising open notches (73) extending into the mounting area (71) so as to form fins (711, 712, 713, 714) separated from each other by the notches (73). Figure for abstract: Fig 1

Description

Title of the invention: INTEGRATED CIRCUIT PACKAGE HEAT SINK

[0001] Implementation and embodiment methods relate to the field of microelectronics, in particular the field of packaging of integrated circuits, and more particularly heat sinks in encapsulation packages.

[0002] Heat sinks are used to dissipate the heat produced by the chip of an integrated circuit during its operation to the outside of the package. In particular, the heat sink is bonded to the chip with a thermally conductive material allowing the heat to be transferred from the chip to the heat sink.

[0003] Nevertheless, conventional heat sinks are subject to mechanical stresses throughout the life of the package, in particular during the manufacture of the package and the operation of the electronic chip. Indeed, the heat produced by the annealing steps during the manufacture of the package, or by the electronic chip, causes expansions of the heat sink and the chip. That being said, the heat sink and the chip are made of materials having different coefficients of thermal expansion, and this difference generates mechanical stresses which can cause delaminations (detachments) at the interface between the heat sink and the chip. Delaminations can result from the presence of a layer of air, which is very poorly thermally conductive, greatly degrading heat dissipation.

[0004] Consequently, the detachment of the heat sink no longer allows the sink to perform its heat dissipation function and can cause a degradation of the thermal performance of the package. The integrated circuit can therefore overheat and become unusable.

[0005] There is a need to reinforce the mechanical strength of the heat sink to avoid these detachment phenomena, and to avoid a degradation of the thermal performance of the integrated circuit package.

[0006] According to one aspect, there is provided an integrated circuit comprising at least one electronic chip having a face covered with a layer of a thermal interface material, a heat sink comprising a mounting area fixed to the chip via the layer of thermal interface material.

[0007] The heat sink includes open notches extending into the mounting area so as to form fins separated from each other by the notches.

[0008] The fins formed in the heat sink mounting area have the advantage of reducing mechanical stresses, in particular the stresses experienced by the heat sink at the corners of the electronic chip. In fact, each fin is separated from the neighboring fins by the notches which prevent stresses from being transmitted between the fins. For example, a fin expanding during a thermal cycle of the package does not generate any or little stress on the part of the chip located opposite the other fins.

[0009] Therefore, the heat sink according to this aspect undergoes little mechanical stress and has a reduced risk of delamination, particularly at the corners of the chip on which it is fixed.

[0010] According to one embodiment, the notches comprise radial notches extending between a central region of the mounting area and a peripheral region of the heat sink and peripheral notches extending circumferentially between the mounting area and the peripheral region.

[0011] The radial notches allow the fins to be spaced so as to limit the expansion stresses transmitted between them in the mounting area of ​​the heat sink. The peripheral notches allow each fin to be spaced from the peripheral region so as to limit the stresses transmitted to the fins by the peripheral region of the heat sink.

[0012] In fact, the open notches in the heat sink are advantageously arranged so that said fins each have degrees of freedom with respect to the other fins, sufficiently large to absorb the differences in thermal expansion undergone by the sink and by the chip.

[0013] According to one embodiment, the fins are connected to the central region of the mounting zone and to the peripheral region by connecting tabs located in the width of the peripheral notches.

[0014] The fins are therefore supported on the one hand by the peripheral region via the connecting tabs and on the other hand between them, by the central region of the mounting zone.

[0015] The tabs are further advantageously configured to tolerate plastic deformation capable of providing the degrees of freedom of the fins with respect to the other fins, as mentioned previously.

[0016] According to one embodiment, the mounting area comprises an at least partially striated surface comprising grooves and being in contact with the layer of thermal interface material.

[0017] The mounting area may provide grooves for deforming the thermal interface material layer to increase the gripping surface area and reduce delamination between the heat sink mounting area and the thermal interface material layer while allowing heat to escape from the housing.

[0018] According to one embodiment, said grooves are arranged in circles concentric.

[0019] The arrangement of the grooves in concentric circles makes it easier to attach the mounting area to the electronic chip and limits delamination over the entire surface of the mounting area in the direction of the expansion stresses.

[0020] According to one embodiment, the depth of the grooves is between 50 and 300 pm.

[0021] The surface of the mounting area attached to the electronic chip may include microscopic or macroscopic grooves to limit the propagation of delamination on this surface. The grooves in particular make it possible to slow down the propagation of delamination more or less depending on their depth.

[0022] Other advantages and characteristics of the invention will appear on examining the detailed description of embodiments and implementations, which are in no way limiting, and the appended drawings in which:

[0023] [Fig.l],

[0024] [Fig.2],

[0025] [Fig.3] and

[0026] [Fig.4] schematically illustrate embodiments of the invention.

[0027] [Fig.l] schematically illustrates a sectional view of an embodiment of a package for an integrated circuit 1. The package encapsulates the integrated circuit 1 which comprises an electronic chip 2 mounted on a support substrate 3.

[0028] The electronic chip 2 has an upper face 21 fixed on a mounting face 31 of the support substrate 3. The upper face 21 of the chip 2 can be provided with connection balls 4 for example, in a “flip-chip” type assembly. The connection balls 4 can be embedded in a filling material called “underfill” in English and make it possible to electrically connect the electronic chip 2 to the substrate 3.

[0029] The electronic chip 2 also comprises a lower face 22 covered with a layer of thermal interface material 6. The thermal interface material 6 (usually designated by the acronym “TIM” for “Thermal Interface Material” in English) is a material having thermal conduction properties suitable for dissipating heat from the chip, and mechanical bonding properties by bonding suitable for securing the elements assembled in the package (i.e. bonding the chip 2 to the heat sink 7).

[0030] The integrated circuit 1 further comprises a heat sink 7 which is typically made of metal having a sufficiently large thermal conduction coefficient, for example copper. The heat sink 7 comprises a mounting area 71 and a peripheral region 72. The mounting area 71 has an upper face 700 and a lower face 701. The lower face 701 of the mounting area 71 is attached to chip 2 via the thermal interface material layer 6.

[0031] The mounting area 71 of the heat sink 7 allows the heat coming from the electronic chip 2 to be evacuated via the layer of thermal interface material 6 towards the outside of the integrated circuit package 1.

[0032] The peripheral region 72 of the heat sink 7 is fixed to the support substrate 3 by means of a layer of an adhesive material 8, for example glue. The peripheral region 72 has a collar shape, and extends vertically from the mounting area 71 towards the support substrate 3, and can also extend obliquely as shown in [Fig.l].

[0033] [Fig.2] schematically illustrates a top view of the heat sink of the integrated circuit 1 described previously in relation to [Fig.l].

[0034] The heat sink 7 comprises open notches 73 passing through the entire thickness of the heat sink 7. The open notches 73 extend into the mounting area 71 so as to form fins, for example four fins 711, 712, 713, 714 in the mounting area 71. The fins 711, 712, 713, 714 are separated from each other by the open notches 73 which delimit the outline of each of the fins.

[0035] The fins 711, 712, 713, 714 formed in the mounting zone 71 of the heat sink 7 have the advantage of reducing the mechanical stresses, in particular at the corners of the electronic chip 2. More particularly, the expansion stresses are greatly reduced at the edge of the chip 2, which makes it possible to avoid detachment of the thermal interface material 6 and, at the same time, of the heat sink 7, in particular at the locations where the risk of detachment is highest.

[0036] Each fin is separated from neighboring fins by the open notches 73 which prevent stresses from being transmitted between the fins 711, 712, 713, 714. For example, the fin 711 may expand when the heat sink 7 is exposed to high temperatures and then to cooling to room temperature, particularly during annealing. Since the fins 711, 712, 713, 714 are separated from each other, the expansion of the fin 711 does not cause mechanical stress in other fins, particularly the closest fins 712 and 714.

[0037] Consequently, the heat sink 7 according to this aspect undergoes little mechanical stress and the thermal interface material 6 according to this same aspect has a reduced risk of delamination, in particular at the corners of the chip 2 on which the mounting area 71 is fixed.

[0038] For example, the open notches 73 comprise radial notches 730 and peripheral notches 731 and 732. The radial notches 730 extend between a central region 710 of the mounting area 71 and the peripheral region 72. The radial notches 730 make it possible to space the fins 711, 712, 713, 714 so as to limit the expansion stresses transmitted between them in the mounting zone 71. The radial notches 730 may have a width of between 500 and 2000 pm.

[0039] The peripheral notches 731 and 732 extend in the circumference of the mounting zone 71, between the mounting zone 71 and the peripheral region 72 of the heat sink 7. The peripheral notches 731 and 732 make it possible to space each fin from the peripheral region 72 so as to limit the transmission of stresses between fins 711, 712, 713, 714 via the peripheral region 72. The peripheral notches 731 and 732 may have a width of between 500 and 2000 μm.

[0040] The fins 711, 712, 713, 714 are connected together by the central region 710 of the mounting zone 71 and to the peripheral region 72 by connecting tabs 74. For example, each fin is connected locally to the peripheral region 72 by a connecting tab 74.

[0041] The fins 711, 712, 713, 714 are therefore supported on the one hand by the peripheral region 72 via the connecting tabs 74 and on the other hand between them by the central region 710 of the mounting zone 71.

[0042] The connecting tabs 74 and the central region 710 are configured to allow plastic deformation of the respective fins 711, 712, 713, 714 to limit the transmission of mechanical stresses from one fin to another. In particular, the metal thickness of the heat sink may be reduced at the tabs 74 in this regard (the reduced thickness tabs 74 being shown in the section planes of FIGS. 1 and 4).

[0043] By way of example, the mechanical stresses were simulated by computer on the heat sink 7 as described in relation to [Fig. 2], in particular on the mounting face 71 fixed on the chip 2, and compared to simulation results obtained for stresses undergone by a conventional heat sink having neither notches nor fins, and under the same conditions, that is to say with the same dimensions, the same materials and according to the same causes of mechanical stresses (annealing, temperature variations). The mounting area 71 of the heat sink 7 has a maximum mechanical stress simulated by computer at 17.9 MPa (mega Pascal) and that of the conventional heat sink has a maximum mechanical stress simulated by computer at 23.2 MPa.

[0044] [Fig. 3] schematically illustrates a view from below of the heat sink of the housing 1 described previously in relation to Figures 1 and 2.

[0045] The mounting area 71 comprises an at least partially striated surface 75. The at least partially striated surface 75 is in contact with the layer of thermal interface material 6 covering the electronic chip 2.

[0046] Indeed, the surface of the lower face 701 of the mounting zone 71 may provide grooves allowing the layer of thermal interface material 6 to be deformed. In particular, each groove has a depth into which the thermal interface material 6 can penetrate and makes it possible to form a rough gripping surface. The at least partially grooved surface 75 therefore makes it possible to reduce delamination between the mounting area 71 and the layer of thermal interface material 6. In the same way, the thermal interface material 6 can also penetrate into the notches 730 and rise up to halfway up the notches 730. This makes it possible to improve the adhesion of the thermal interface material 6 to the heat sink 7.

[0047] Furthermore, the grooves of the at least partially striated surface 75 are advantageously arranged in concentric circles. The arrangement of the grooves in concentric circles makes it easier to attach the mounting area 71 to the electronic chip 2 and to limit the propagation of delamination over the entire surface of the mounting area 71 in the direction of the expansion stresses, i.e. from the central region 710 to the peripheral region 72 of the heat sink 7. The concentric circles may be spaced apart by a distance of between 1 and 3 mm.

[0048] Thus, the mechanical stresses are not only reduced on the assembly zone 71 but in addition the resistance to delamination of the assembly is greater.

[0049] [Fig. 4] schematically illustrates a sectional view of the heat sink 7 described previously in relation to Figures 1, 2 and 3, along axis II of Figures 2 and 3.

[0050] The depth of the grooves is between 50 and 300 μm. The at least partially striated surface 75 of the mounting zone 71 may in particular comprise microscopic or macroscopic grooves to limit the propagation of the delamination in the mounting zone 71. The macroscopic grooves may correspond to grooves having a depth greater than 500 μm and the microscopic grooves may correspond to grooves having a depth less than 50 μm. The microscopic and macroscopic grooves increase the roughness of the at least partially striated surface 75 by their particular shape but also make it possible to lengthen the path traveled on the surface by the delaminations. Indeed, the delaminations find it more difficult to cross a groove than a flat surface of the mounting zone 71 through which the propagation is direct.Macroscopic grooves can more effectively slow the propagation of delaminations but can be more restrictive to form than microscopic grooves which can be more numerous in the same space of the mounting area 71.

Claims

Claims

1. Integrated circuit (1) comprising: - at least one electronic chip (2) having a face (22) covered with a layer of a thermal interface material (6), - a heat sink (7) comprising a mounting area (71) fixed to the chip (2) via the layer of thermal interface material (6), the heat sink (7) comprising open notches (73) extending into the mounting area (71) so as to form fins (711, 712, 713, 714) separated from each other by the notches (73).

2. A circuit according to claim 1, wherein the notches (73) comprise radial notches (730) extending between a central region (710) of the mounting area (71) and a peripheral region (72) of the heat sink (7) and peripheral notches (731, 732) extending circumferentially between the mounting area (71) and the peripheral region (72).

3. A circuit according to claim 2, wherein the fins (711, 712, 713, 714) are connected to the central region (710) of the mounting area (71) and to the peripheral region (72) by connecting tabs (74) located in the width of the peripheral notches (731, 732).

4. Circuit according to one of the preceding claims, in which the mounting area (71) comprises an at least partially grooved surface (75) having grooves and being in contact with the layer of thermal interface material (6).

5. A circuit according to claim 4, wherein said grooves are arranged in concentric circles.

6. Circuit according to one of claims 4 and 5, in which the depth of the grooves is between 50 and 300 pm.

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