NL2027463B1

NL2027463B1 - Integrated circuit

Info

Publication number: NL2027463B1
Application number: NL2027463A
Authority: NL
Inventors: Dorrestein Sander
Original assignee: Chip Integration Tech Centre
Priority date: 2021-01-29
Filing date: 2021-01-29
Publication date: 2022-09-02
Also published as: WO2022164317A2; WO2022164317A3

Abstract

The invention relates to an integrated circuit comprising: a die (30) having a first elastic modulus and a first coefficient of thermal expansion, comprising an electronic circuit and generating heat in use, a substrate (10) having a second elastic modulus and a second coefficient of thermal expansion, and for dissipating heat from the die, an attachment layer (20) arranged between the die and substrate; wherein the attachment layer comprises: a mesh (21) with openings, and having a fourth elastic modulus, and an attachment material (22) having a third elastic modulus, and substantially filling the openings of the mesh, wherein the third elastic modulus is lower than the fourth elastic modulus.

Description

INTEGRATED CIRCUIT

FIELD OF THE INVENTION The invention relates to an integrated circuit (IC). The invention more specifically relates to attaching a die to a substrate in an integrated circuit package. The invention further relates to a method of adapting the attachment layer.

BACKGROUND OF THE INVENTION The present invention is in the field of an integrated circuit (IC) which is attached to a substrate. Thereby an IC-package is formed. Generally, in many IC packages, the devices are situated on top of a substrate. The substrate may serve as a physical interconnection between the devices and a board in a system. Sometimes this is referred to as embedded packaging. The purpose is to embed dies inside or on the substrate using a multi-step manufacturing process. A die, multiple dies, MEMS or passives may be embedded in a side-by-side fashion in the core of an organic laminate substrate. The components can be connected using copper-plated vias. Three broad categories in IC packaging may be mentioned, namely lead-frame, wafer-level packaging (WLP), and substrate. The present invention makes in particular use of a substrate. Substrate- based packages may fall into several categories, such as ceramic and organic laminate packages. Ceramic substrates can be based on aluminium oxide, aluminium nitride and other materials.

Ceramic-based packages can be used for surface-mount devices, CMOS image sensors and multi- chip modules. Organic laminate substrates can be used for volumetric devices, flip-chip devices, and system-in-packages (SiPs). For these packages. the devices reside on top of the substrate. Such substrates may use similar or identical materials as a printed-circuit board (PCB). Organic substrates may also be multi-layer technologies, where at least two organic layers are separated by a metal layer. The metal layers act as an electromigration shield in the package.

Typically, in a conventional die-attach process, only one die-attach material is used to attach die on to the substrate. In an alternative solution of wafer level chip scale packaging (WLCSP) technology, a die is connected to a substrate, which is then referred to as leadframe, via. bumps while the free space in between the bumps (solder, Cu, etc.) and the die-edges and corners are filled with a (soft) tough material. which is called underfill.

One of the most common failures of electronic packages is fracture of die and die- attach materials as can be visualized during reliability testing such as by thermal cycling (TMCL). During TMCL, the package may undergo thermal cycling from low temperatures (<0°C) to high temperatures (>100°C), and back. Quite often a fracture (or crack) is found at the corner of the die (or substrate), and it can propagate in different regions within the package. Also, fractures may occur as a consequence of poor package design, and of external factors, such as humidity.

The present invention therefore relates to an integrated circuit and further aspects thereof, which overcomes one or more of the above disadvantages, without compromising functionality and advantages.

SUMMARY OF THE INVENTION An object of the invention is to overcome one or more of the disadvantages mentioned above. According to a first aspect of the invention, an integrated circuit comprising: - a die having a first elastic modulus and a first coefficient of thermal expansion, comprising an electronic circuit and generating heat in use; - a substrate having a second elastic modulus and a second coefficient of thermal expansion, and for dissipating heat from the die; - an attachment layer arranged between the die and substrate: wherein the attachment layer comprises: - a mesh with openings, and having a fourth elastic modulus; and - an attachment material having a third elastic modulus, and substantially filling the openings of the mesh: wherein the third elastic modulus is lower than the fourth elastic modulus. Heat is generated by the electronica circuit on the die. This heat will be conducted to other parts of the integrated circuit. The heat will typically be conducted to the substrate as this is typically the larger body in the environment and arranged for dissipating the heat from the die. The heat conductance will follow a conductive path through the attachment layer. Heat will cause the die, substrate and attachment layer to expand. The coefficients of thermal expansion (CTE-s) of these parts are typically different. Furthermore, even when one or more of the coefficients of thermal expansion are equal or almost equal, a temperature gradient will be present along the conductive path. Therefore, these parts will expand differently. It may even be that sections of these parts expand differently due to the temperature gradient. These different expansions create tensions inside these parts, but certainly will create tensions between these parts. This tension or mechanical stress may cause fractures or cracks inside the attachment layer or even in the die. The mechanical stress may even cause shearing off partly or whole of the attachment layer from the die and/or the substrate. When fractures, cracks or shearing off occurs. this negatively impacts the heat conduction through the attachment layer. When the heat conduction is reduced the temperature of the die during use will increase. The increased temperature of the die may cause automated safety measures to trigger and shutdown the operation of the die, or even worse may damage the die whereafter the die may malfunction. Thus, the increased temperature of the die will shorten the lifetime of the die and/or limit or prohibit normal operation.

Further, this effect may be enhanced when the die power cycles between periods of use of the die and periods of non-use wherein the die cools down.

Wikipedia defines elastic modulus (also known as modulus of elasticity) as a quantity that measures an object or substance's resistance to being deformed elastically (i.¢., non- permanently) when a stress is applied to it.

The elastic modulus of an object is defined as the slope of its stress—strain curve in the elastic deformation region.

A stiffer material will have a higher elastic modulus.

As mentioned before the attachment layer as a whole will expand differently from the die and/or substrate when conducting heat.

This will cause mechanical stress between the attachment layer and on the other side the substrate and/or the die.

According to the invention, the elastic modulus of the attachment material is selected lower than the elastic modulus of the mesh.

When that attachment material and mesh are conducting heat, both will expand. and both will typically expand at different rates.

The elastic modulus of the mesh is higher compared to the elastic modulus of the attachment material; thus in other words, the mesh is stiffer compared to the attachment material.

During the expansion of the attachment material arranged in an opening of the mesh, as the mesh is stiffer than the attachment material, the mesh will restrain the expansion of the attachment material.

Furthermore, the attachment material arranged in an opening of the mesh may be seen as a pillar of attachment material attaching and/or joining the die and the substrate.

The movement of these pillars relative to each other is restrained by the stiffer mesh.

The restraining of a single pillar of attachment material and/or pillars of attachment material relative to each other by the mesh allows for adapting the expansion of the attachment layer to the expansion of the die and/or substrate.

This adapting of the attachment layer allows to reduce the mechanical stress between the attachment layer on one side and the die and/or the substrate on the other side.

The reducing of the mechanical stress in a stack of the die, the attachment layer and the substrate reduces the change of fractures in or between layers or even partly or in whole shearing off of layers due to expansion and contraction of the layers in the stack due to heat cycling.

Thus, the technical effect of reducing the mechanical stress in the stack is extending the lifetime of the die and/or increasing the time of normal operation.

According to another aspect the invention relates to a method for designing a mesh for an integrated circuit according to an embodiment of the invention, such as the preceding embodiment, comprising: - identifying the hot spot location of a hot spot of the die; and - adapting the mesh based on the hot spot location.

At the location of the hot spot the expansion during use and contraction during non-use will be the highest.

Therefore, the hot spot location is typically the location with higher or even highest mechanical stress.

As a result of this increased mechanical stress at the hot spot location, cracks or fractures in the attachment layer have a higher change of occurring first at this location.

Adapting the mesh to the hot spot location of the hot spot has the effect of preventing or at least reducing the mechanical stress at that location and thus the starting point for possible cracks or fractures. As the likelihood of a starting point of cracks or fractures is reduced at the hot spot location, the technical effect is that the lifetime of the die is extended and/or the time of normal operation is increased, as argued above. According to another aspect the invention the invention relates to a method for manufacturing an integrated circuit according to any of the embodiments of the invention, comprising: - providing a substrate having a second elastic modulus and a second coefficient of thermal expansion; - providing an attachment layer on top of the substrate, wherein the attachment layer comprises: a mesh with openings, and having a fourth elastic modulus; and an attachment material having a third elastic modulus, and substantially filling the openings of the mesh; and - arranging a die having a first elastic modulus and a first coefficient of thermal expansion on top of the attachment layer, and comprising an electronic circuit and generating heat in use; wherein the third elastic modulus is lower than the fourth elastic modulus. This aspect provides the same advantages as mentioned for other aspects of the invention.

According to another aspect of the invention, a preform of die attach material comprising: - a mesh with openings, and having a fourth elastic modulus; and - an attachment material having a third elastic modulus, and substantially filling the openings of the mesh; wherein the preform is arranged for use in an integrated circuit according to any of the embodiments according to the invention as the attachment layer; and/or wherein the preform is arranged for use in a method for manufacturing an integrated circuit according to any of the methods according to the invention as the attachment layer.

According to another aspect of the invention, a method for manufacturing a preform of die attach material for an integrated circuit according to any of the embodiments of the invention, comprising: - applving a first layer of attachment material on a temporal surface, preferably with stencil printing: - placing the mesh on top of the first layer, preferably pressing the mesh into the first layer; - applying a second layer of attachment material on the first layer and/or the mesh, preferably with stencil printing; and - preferably removing the first layer, the mesh, and the second layer from the temporal surface for obtaining the preform. This aspect provides the same advantages as mentioned for other aspects of the invention.

5 According to an alternative aspect of the invention, an integrated circuit comprising: - a die having a first elastic modulus and a first coefficient of thermal expansion, comprising an electronic circuit and generating heat in use; - a substrate having a second elastic modulus and a second coefficient of thermal expansion, and for dissipating heat from the die; - an attachment layer arranged between the die and substrate; wherein the attachment layer comprises: - a mesh with openings, and having a fourth elastic modulus; and - an attachment material having a third elastic modulus, and substantially filling the openings of the mesh; wherein the third elastic modulus is higher than the fourth elastic modulus. The fourth elastic modulus, being lower than the third elastic modulus, provides a more compressible or flexible mesh compared to the attachment material. When the attachment material expands during heating, the attachment layer will expand typically sideways, as it is enclosed below by the substrate and above by the die. The mechanical stress increases radially towards a location where the attachment layer contacts or is joined with the edge of die. The attachment material according to the invention compresses the mesh. This compression relieves the mechanical stress between the attachment layer on one side and the die and/or the substrate on the other side. This stress relieve is especially present where the attachment material contacts the edges of the die or close to the edges of the die. This is typically the area where the fractures or cracks between the attachment layer and the die are found, and/or in the attachment layer start. Thus, the introduction of the mesh according to the invention allows to prevent fractures and cracks as argued before for advantageously extending the lifetime of the die and/or increasing the time of normal operation. In embodiments throughout the description mentioning the restraining of the attachment material by the die, this restraining may be replaced by compression of the mesh according to this aspect of the invention. This aspect may be combined with any other aspect or embodiment of the invention.

According to an alternative aspect of the invention, an integrated circuit comprising: - adie having a first elastic modulus and a first coefficient of thermal expansion, comprising an electronic circuit and generating heat in use: - a substrate having a second elastic modulus and a second coefficient of thermal expansion, and for dissipating heat from the die: - an attachment layer arranged between the die and substrate:

wherein the attachment layer comprises: - a mesh with openings, and having a fourth elastic modulus; and - an attachment material having a third elastic modulus, and substantially filling the openings of the mesh; wherein the third elastic modulus is different from the fourth elastic modulus. The advantages of the fourth elastic modulus to be above or below the third elastic modulus are presented throughout the description. This aspect may be combined with any other aspect or embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION In an embodiment of the invention, the attachment layer has a combined fifth elastic modulus; and the combined fifth elastic modulus is lower than the fourth elastic modulus. Further, the fifth elastic modulus is typically higher than the third elastic modulus. The fifth elastic modulus is typically advantageously bound to a range bordered by the third elastic modulus and fourth elastic modulus. Adapting the mesh in shape, volume, and/or openings advantageously allows the fifth elastic modulus to be adapted to a value within this range.

In an embodiment of the invention, the elastic modulus is a Young's modulus, a bulk modulus, and/or a volumetric elasticity. The respective elastic moduli each individually are selected from a Young's modulus, a bulk modulus, and/or a volumetric elasticity. The elastic modulus, such as the Young's modulus, is typically expressed in GPa. and may be determined using a standard test, such as EN 10002-1, ASTM E8 and ASTM E111, e.g. using an Ametek. It is noted that inaccuracies in testing in practice do not matter much, as the present invention is more concerned with relative values (between elements) than absolute values. The elastic modulus may be expressed as spring rate.

In an embodiment of the invention, the mesh has a fourth coefficient of thermal expansion; the attachment material has a third coefficient of thermal expansion; the attachment layer has a combined fifth coefficient of thermal expansion; and the combined fifth coefficient of thermal expansion is below the first coefficient of thermal expansion. Adapting the mesh in shape. volume, and/or openings advantageously allows the fifth coefficient of thermal expansion to be adapted to a value below the first coefficient of thermal expansion.

In an embodiment of the invention, the attachment layer has a combined fifth coefficient of thermal expansion between the first coefficient of thermal expansion and the second coefficient of thermal expansion. The first coefficient of thermal expansion and the second coefficient of thermal expansion border a range of thermal expansion. The fifth coefficient of thermal expansion is typically selected within this range. Adapting the mesh in shape, volume. and/or openings advantageously allows the fifth coefficient of thermal expansion to be adapted to a value within this range.

In an embodiment of the invention, the fifth coefficient of thermal expansion is typically advantageously bound to a range bordered by the third coefficient of thermal expansion and fourth coefficient of thermal expansion. Adapting the mesh in shape, volume, and/or openings advantageously allows the fifth coefficient of thermal expansion to be adapted to a value within this range.

In an embodiment of the invention, the mesh is advantageously partly or fully embedded in the attachment material. This provides an advantageous integration of the mesh in the attachment material for forming the attachment layer. In an embodiment of the invention, the attachment material advantageously envelops the mesh or wherein the mesh is incorporated in the attachment material. This provides an advantageous integration of the mesh in the attachment material for forming the attachment layer.

In an embodiment of the invention, the mesh is advantageously in physical contact with the substrate. In a further embodiment of the invention, the mesh is an integrated part of the substrate, preferably wherein the mesh is formed from protruding parts of the substrate after removing, such as galvanically growing, milling or etching away. parts of the substrate. Alternatively, the mesh may be fusion bounded to the substrate to form an integrated part. This embodiment provides the advantage of minimizing the parts in the stack of components. Further, this embodiment provides the advantage of a more gradual transition from the substrate to the attachment layer and/or the die. Further, this embodiment provides the advantage less parts able to move relative to each other. Further, this embodiment provides the advantage of a type of holder for holding the attachment material relative to the substrate during manufacturing before the die is placed on top of the attachment layer.

In an embodiment of the invention, the die has a die attachment surface facing the attachment; and wherein the mesh extends beyond the die attachment surface in a plane parallel to the die attach matter. This advantageously allows the die attachment material to contact the edge of the die or close to the edge of the die while the attachment material is restrained by the mesh.

In an embodiment of the invention, the mesh is smaller than the die attachment surface, preferably wherein the mesh forms a region and/or an island where the combined fifth coefficient is locally adapted and/or the combined fifth elastic modulus is locally adapted. This advantageously allows the mesh and/or the attachment layer as a whole to be adapted to the expected amount of heat generated at a particular location in the die, more specific to a hot spot of the die.

In an embodiment of the invention, the mesh comprises mechanical parts. such as springs and/or hinges, configured for recovering its original shape when released after deformation and/or reinforcements for relieving and/or reducing thermal expansion tension in the attachment layer. The deformation is typically elastic deformation. The mechanical parts and/or the reinforcements allow for adapting the elastic modulus beyond the elastic modulus of the solid material. In a further embodiment of the invention, the mechanical parts and/or the reinforcements are arranged such that the thermal expansion tension in the attachment layer is advantageously relieved and/or reduced in at least one predefined direction. A reenforcing element may be a reenforcing bar for reenforcing a part of or the whole mesh for adapting the elastic modulus to a value different from the elastic modulus of the solid material. In an embodiment of the invention, the at least one predefined direction is in a plane parallel to the substrate and/or the die and/or the shape of the substrate.

In an embodiment of the invention, the attachment layer has a thickness in a range of 5 um to 200 um, preferably 15 um to 150 um, more preferably 25 um to 100 um, most preferably 30 um to 90 pm. In an embodiment of the invention, the openings of the mesh have a diameter and/or diagonal in a range of 25 um to 200 um, preferably 35 um to 150 um, more preferably 45 um to 125 um, most preferably 50 um to 100 pm. A diameter and/or diagonal may be associated with round or rectangular, but may also be associated with other shapes. wherein the diameter or diagonal indicates the maximum length from one edge to another edge of the opening. In an embodiment of the invention, the openings of the mesh have an area in a range of 2000 um2 to 125000 um2, preferably 4000 um? to 175000 um2, more preferably 6000 um2 to 250000 um2. most preferably 8000 um2 to 30000 um2. In an embodiment of the invention, the openings of the mesh have a thickness in a range of 2 um to 200 um, preferably 5 um to 150 um, more preferably 10 um to 100 um, most preferably 20 um to 90 um. In an embodiment of the invention, the mesh comprises one or more of copper, nickel, tungsten, iron and molybdenum, CuW, FeNi, or an alloy ong or more of the previous mentioned materials. In an embodiment of the invention, the integrated circuit is a packaged integrated circuit.

In an embodiment of the vention, the first coefficient of thermal expansion, preferably linear thermal expansion, is in a range of 2.0 10° K to 9.0 10% KL. preferably 2.5 10% K' to 8.5 10° K°!. more preferably 2.7 10% K™ to 8.0 10% K7, most preferably 3.0 10% K! to 7.5 10% K"!: the first elastic modulus is in a range of 90 GPa to 500 GPa, preferably 110 GPa to 450 GPa, more preferably 120 GPa to 420 GPa, most preferably substantially 130 GPa or 400 GPa, such as the elastic modulus of Si or SiC; the second coefficient of thermal expansion, preferably linear thermal expansion, is in a range of 10.0 10% K! to 30.0 10° K*!, preferably 12.0 10% Ki to

25.0 10% KL more preferably 13.0 10% K"! to 22.0 10° K"!, even more preferably 14.0 10° K7! to

20.0 10° Kt, most preferably substantially around 17 10% K't; the second elastic modulus is in a range of 80 GPa to 180 GPa, preferably 110 GPa to 150 GPa, more preferably 120 GPa to 140 GPa, most preferably substantially129 GPa, such the elastic modulus of Cu; the third elastic modulus is in a range of 3 GPa to 50 GPa, preferably 4 GPa to 42 GPa, more preferably 5 GPa to 40 GPa, even more preferably 10 GPa to 30 GPa, most preferably the elastic modulus of pure sintered Ag or hybrid sintered Ag; the fourth elastic modulus is in a range of 100 GPa to 350 GPa, preferably 120 GPa to 300 GPa, more preferably 125 GPa to 290 GPa, even more preferably 129 GPa to 280 GPa, most preferably the elastic modulus of Cu, W80Cu, or Pure Nickel; the combined fifth coefficient of thermal expansion , preferably linear thermal expansion, is in a range of 1.0 10° Kl to 17.0 10° KL, preferably 1.5 10° Ki to 14.0 10% Kt, more preferably 2.0 10% K™ to 12.0 10% KL even more preferably 3.0 10% K' to 11.0 10° K°!. most preferably substantially around 10 10% K*'; the attachment layer has a combined thermal conductivity in a range of 30 Wim PK! to 350 W*m KL preferably 40 W*m PK"! to 320 W*mP*K"!, more preferably 50 W*m!=K"! to 300 W*mKL even more preferably 70 W*m PK"! to 250 W*m 10K, most preferably substantially around 100 W*m?*K"': and/or the combined fifth elastic modulus is in a range of between the selected third elastic modulus and the fourth elastic modulus, such as wherein the fifth elastic modulus depends on the weight and/or the volume of the attachment material relative to the weight and/or the volume of the mesh.

In an embodiment of the inventive designing method, wherein adapting comprises: shrinking the opening area of the mesh relative to the area of the mesh when projected from above at the location of the hot spot: and/or enlarging the opening area of the mesh relative to the area of the mesh when projected from above at the location away from the hot spot.

In an embodiment of the inventive manufacturing method, comprising designing the mesh according to any of the inventive designing methods; and wherein arranging the die comprises orienting the die to the mesh in the attachment layer according to the design of the mesh.

In an embodiment of the inventive manufacturing method, providing an attachment layer comprises: applying a first layer of attachment material on the substrate, preferably with stencil printing; placing the mesh on top of the first layer, preferably pressing the mesh into the first layer; and applying a second layer of attachment material on the first layer and/or the mesh, preferably with stencil printing.

In an embodiment of the inventive manufacturing method, the die has an operational die temperature; the method comprises curing the attachment layer after arranging the die on top of the attachment layer; at least curing is performed at a curing temperature; and the curing temperature is between the operational temperature and room temperature. In a further embodiment of the inventive manufacturing method, the die has an expected power on duty cycle: and the curing temperature is selected based on the power on duty cycle.

= < 2 = 3 a 3 =. ae = = = = < = g i: o 0 2 = = & 5 Ì @ 8 = S a = a = 2 Die Si 130 2.5 130 to 130 & 25to 25& 400 400 ~3 5.1 SiC 400 51 Mesh Cu 129 17.3 100 - 300 100 5t018 10 W380Cu 280 8.0 Pure Nickel 200 13.4 DA Pure Sintered 5to 40 19 to 5to 40 20 19 to 19 Ag — Hybrid 40 40 Sintered Ag Substrate Cu 129 173 X 129 x 17.3

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be apparent from and elucidated further with reference to the embodiments described by way of example in the following description and with reference to the accompanying drawings, in which: Figure 1-3 schematically show a cross-section of an embodiment of an integrated circuit: Figures 4a-4b schematically show a top view of an embodiment of the attachment laver; Figures 5a-5b schematically show a top view of meshes; Figures 5c-5d schematically show a top view of enlargements of the mesh; Figure 6a schematically shows a perspective exploded view of a detail of an integrated circuit; and Figure 6b schematically shows a side view of the non-exploded view of the embodiment of Figure 6a of an integrated circuit.

The figures are purely diagrammatic and not drawn to scale. In the figures, elements which correspond to elements already described may have the same reference numerals.

LIST OF REFERENCE NUMERALS

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS The following figures may detail different embodiments. Embodiments can be combined to reach an enhanced or improved technical effect. These combined embodiments may be mentioned explicitly throughout the text, may be hint upon in the text or may be implicit.

Figures 1-3 schematically show a cross-section of an embodiment of an integrated circuit. The integrated circuit comprises a substrate 10, an attachment layer 20 and a die 30. The substrate, the attachment layer and the die form a stack. Only the part directly beneath the attachment layer is shown in the figures, although the substrate typically extends to all sides beyond what is shown in the figures.

The attachment layer comprises attachment material 22 and a mesh 21. The figures show the mesh embedded, incorporated or surrounded by attachment material. In an alternative embodiment, the mesh contacts the die and/or substrate.

Figures 4a-4b schematically show a top view of an embodiment of the attachment layer. In Figure 4a the attachment layer is shown on top of the substrate. The attachment layer comprises a mesh 21. The attachment layer also comprises attachment material, which is left out of the Figures 4a-4b for clarity purposes only. The mesh in Figure 4a has relatively large rectangular openings. The mesh in Figure 4b has relatively small openings.

Figures 5a-5b schematically show a top view of meshes. The mesh in figure 5a has smaller openings in the left bottom comer for providing locally a different fifth elastic modulus. Typically, the left bottom comer of the mesh, when arranged in an attachment layer, is aligned with a hot spot in the die arranged on top of the attachment layer. The hot spot in the die may cause more heat to be conducted by the left bottom corner of the mesh, thereby the left bottom comer in the attachment layer will expand more compared to other parts. To restrain this expansion, the mesh with the smaller openings counters the expansion for relieving or restraining the mechanical stress. In an alternative embodiment, the mesh is arranged for absorbing the expansion of the attachment material.

The mesh in figure 5b has reinforcements 23 in the corners of the mesh. The reinforcements reinforce mechanical stress location in the mesh for improving the restraining character of the mesh.

Figures 5c-5d schematically show a top view of enlargements of the mesh. Figure 5c shows a narrowing 24 in the mesh. The narrowing may act as a hinge 24 hinging the vertical part of the mesh relative to the horizontal part of the mesh. Figure 5d shows a section of the mesh curled up or folded up 25. The curled up or folded up section may act as a spring allowing the vertical section of the mesh to move up and down relative to the horizontal part of the mesh.

Figure 6a schematically shows a perspective exploded view of an embodiment of an integrated circuit. Figure 6b schematically shows a side view of the non-exploded view of the embodiment of Figure 6a of an integrated circuit, Thermal conductivities may be measured using a standard test, such as ASTM 5334, IEEE 442, such as by using a TEMPOS machine. This invention typically provides a solution for high power packages. A typical attachment material is silver sinter material.

Examples, embodiments or optional features, whether indicated as non-limiting or not, are not to be understood as limiting the invention as claimed. It should be noted that the figures are purely diagrammatic and not drawn to scale. In the figures. elements which correspond to elements already described may have the same reference numerals.

The term “substantially” herein, such as in “substantially all emission” or in “substantially consists”, will be understood by the person skilled in the art. The term “substantially” may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in embodiments the adjective substantially may also be removed. Where applicable, the term “substantially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term “comprise” includes also embodiments wherein the term “comprises” means “consists of”.

The term "functionally" will be understood by, and be clear to, a person skilled in the art. The term “substantially” as well as “functionally” may also include embodiments with “entirely”, “completely”. “all”, etc. Hence, in embodiments the adjective functionally may also be removed. When used, for instance in “functionally parallel”, a skilled person will understand that the adjective “functionally” includes the term substantially as explained above. Functionally in particular is to be understood to include a configuration of features that allows these features to function as if the adjective “functionally” was not present. The term “functionally” is intended to cover variations in the feature to which it refers, and which variations are such that in the functional use of the feature, possibly in combination with other features it relates to in the invention, that combination of features is able to operate or function. For instance, if an antenna is functionally coupled or functionally connected to a communication device, received electromagnetic signals that are receives by the antenna can be used by the communication device. The word “functionally” as for instance used in “functionally parallel” is used to cover exactly parallel, but also the embodiments that are covered by the word “substantially” explained above. For instance, “functionally parallel” relates to embodiments that in operation function as if the parts are for instance parallel. This covers embodiments for which it is clear to a skilled person that it operates within its intended field of use as if it were parallel.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

The devices or apparatus herein are amongst others described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device or apparatus claims enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually difterent dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The invention further applies to an apparatus or device comprising one or more of the characterising features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterising features described in the description and/or shown in the attached drawings.

The various aspects discussed in this patent can be combined in order to provide additional advantages. Furthermore, some of the features can form the basis for one or more divisional applications.

EMBODIMENTS I. Integrated circuit comprising: - a die (30) having a first elastic modulus and a first coefficient of thermal expansion, comprising an electronic circuit and generating heat in use; - a substrate (10) having a second elastic modulus and a second coefficient of thermal expansion, and for dissipating heat from the die; - an attachment layer (20) arranged between the die and substrate; wherein the attachment layer comprises: - amesh (21) with openings, and having a fourth elastic modulus; and - an attachment material (22) having a third elastic modulus, and substantially filling the openings of the mesh; wherein the third elastic modulus is lower than the fourth elastic modulus.

2. Integrated circuit according to the preceding embodiment, wherein the attachment layer has a combined fifth elastic modulus; and wherein the combined fifth elastic modulus is lower than the fourth elastic modulus.

3. Integrated circuit according to any of the preceding embodiments, wherein the elastic modulus is a Young's modulus, a bulk modulus, and/or a volumetric elasticity.

4. Integrated circuit according to any of the preceding embodiments, wherein the mesh has a fourth coefficient of thermal expansion; wherein the attachment material has a third coefficient of thermal expansion; wherein the attachment layer has a combined fifth coefficient of thermal expansion; and wherein the combined fifth coefficient of thermal expansion is below the first coefficient of thermal expansion.

5. Integrated circuit according to the preceding embodiment, wherein the attachment layer has a combined fifth coefficient of thermal expansion between the first coefficient of thermal expansion and the second coefficient of thermal expansion.

6. Integrated circuit according to the preceding embodiment, wherein the mesh is partly or fully embedded in the attachment material. 7 Integrated circuit according to any of the preceding embodiments, wherein the attachment material envelops the mesh or wherein the mesh is incorporated in the attachment material.

8. Integrated circuit according to any of the preceding embodiments 1-5, wherein the mesh is in physical contact with the substrate.

9. Integrated circuit according to the preceding embodiment, wherein the mesh is an integrated part of the substrate, preferably wherein the mesh is formed from protruding parts of the substrate after removing, such as galvanically growing, milling or etching away, parts of the substrate.

10. Integrated circuit according to any of the preceding embodiments, wherein the die has a die attachment surface facing the attachment; and wherein the mesh extends beyond the die attachment surface in a plane parallel to the die attach mater.

11. Integrated circuit according to any of the preceding embodiments, wherein the mesh is smaller than the die attachment surface, preferably wherein the mesh forms a region and/or an island where, when depending on embodiment 4, the combined fifth coefficient is locally adapted and/or where, when depending on embodiment 2, the combined fifth elastic modulus is locally adapted.

12 Integrated according to any of the preceding embodiments, wherein the mesh comprises mechanical parts, such as springs and/or hinges, configured for recovering its original shape when released after deformation and/or reinforcements for relieving and/or reducing thermal expansion tension in the attachment layer.

13. Integrated circuit according to the preceding embodiment, wherein the mechanical parts and/or the reinforcements are arranged such that the thermal expansion tension in the attachment layer is relieved and/or reduced in at least one predefined direction.

14. Integrated circuit according to the preceding embodiment, wherein the at least one predefined direction is in a plane parallel to the substrate and/or the die and/or the shape of the substrate.

15. Integrated circuit according to any of the preceding embodiments, wherein the attachment layer has a thickness in a range of 5 um to 200 um, preferably 15 um to 150 um, more preferably 25 um to 100 um, most preferably 30 um to 90 um.

16. Integrated circuit according to any of the preceding embodiments, wherein the openings of the mesh have a diameter and/or diagonal in a range of 25 um to 200 um, preferably 35 um to 150 um, more preferably 45 um to 125 um, most preferably 50 um to 100 um.

17 Integrated circuit according to any of the preceding embodiments, wherein the openings of the mesh have an area in a range of 2000 pm2 to 125000 um2. preferably 4000 um? to 175000 um?2, more preferably 6000 um2 to 250000 um2, most preferably 8000 um2 to 30000 um2.

18. Integrated circuit according to any of the preceding embodiments, wherein the openings of the mesh have a thickness in a range of 2 um to 200 um, preferably 5 um to 150 um, more preferably 10 um to 100 um, most preferably 20 um to 90 um.

19. Integrated circuit according to any of the preceding embodiments, wherein the mesh comprises one or more of copper, nickel, tungsten, iron and molybdenum.

20. Integrated circuit according to any of the preceding embodiments, wherein the integrated circuit 1s a packaged integrated circuit.

21. Integrated circuit according to any of the preceding embodiments, wherein the first coefficient of thermal expansion, preferably linear thermal expansion, is in a range of 2.0 10% Kl to 9.0 10% K't, preferably 2.5 10% Ki to 8.5 10° K't, more preferably 2.7 10° K't to 8.0 10° Kt, most preferably 3.0 10° K to 7.5 10° KL; wherein the first elastic modulus is in a range of 90 GPa to 500 GPa, preferably 110 GPa to 450 GPa, more preferably 120 GPa to 420 GPa. most preferably substantially 130 GPa or 400 GPa, such as the elastic modulus of Si or SiC; wherein the second coefficient of thermal expansion, preferably linear thermal expansion, is in a range of 10.0 10° K! to 30.0 10° K°!, preferably 12.0 10 K°t to 25.0 10° K'!, more preferably 13.0 10% Ktto 22.0 10% KL even more preferably 14.0 10% K! to 20.0 10° K"1, most preferably substantially around 17 10° K7; wherein the second elastic modulus is in a range of 80 GPa to 180 GPa, preferably 110 GPa to 150 GPa, more preferably 120 GPa to 140 GPa, most preferably substantially 129 GPa, such the elastic modulus of Cu; wherein the third elastic modulus is in a range of 3 GPa to 50 GPa, preferably 4 GPa to 42 GPa, more preferably 5 GPa to 40 GPa, even more preferably 10 GPa to 30 GPa, most preferably the elastic modulus of pure sintered Ag or hybrid sintered Ag; wherein the fourth elastic modulus is in a range of 100 GPa to 350 GPa. preferably 120

GPa to 300 GPa, more preferably 125 GPa to 290 GPa, even more preferably 129 GPa to 280 GPa, most preferably the elastic modulus of Cu, W80Cu, or Pure Nickel; wherein the combined fifth coefficient of thermal expansion, preferably linear thermal expansion, is in a range of 1.0 10° K"! to 17.0 105 KL, preferably 1.5 10° K to 14.0 10° K"!, more preferably 2.0 10° K1to 12.0 10° K1, even more preferably 3.0 10° K+ to 11.0 10° KL most preferably substantially around 10 10% K-'; wherein the attachment layer has a combined thermal conductivity in a range of 30 Wm HK! to 350 Wom *K, preferably 40 W*m™*K to 320 W*m™'*K"!, more preferably 50 W*m Kl to 300 W*m™*K™!, even more preferably 70 W*m PK"! to 250 W*m'*K-!, most preferably substantially around 100 W*m?*K"!: and/or wherein the combined fifth elastic modulus is in a range of between the selected third elastic modulus and the fourth elastic modulus, such as wherein the fifth elastic modulus depends on the weight and/or the volume of the attachment material relative to the weight and/or the volume of the mesh.

22. Method for designing a mesh for an integrated circuit according to the preceding embodiments, comprising: - identifving the hot spot location of a hot spot of the die; and - adapting the mesh based on the hot spot location.

23. Method for designing according to the preceding embodiment, wherein adapting comprises: - shrinking the opening area of the mesh relative to the area of the mesh when projected from above at the location of the hot spot; and/or - enlarging the opening area of the mesh relative to the area of the mesh when projected from above at the location away from the hot spot.

24. Method for manufacturing an integrated circuit according to any of the embodiments 1- 21, comprising: - providing a substrate having a second elastic modulus and a second coefficient of thermal expansion; - providing an attachment layer on top of the substrate, wherein the attachment layer comprises: a mesh with openings, and having a fourth elastic modulus; and an attachment material having a third elastic modulus, and substantially filling the openings of the mesh; and - arranging a die having a first elastic modulus and a first coefficient of thermal expansion on top of the attachment layer, and comprising an electronic circuit and generating heat in use; wherein the third elastic modulus is lower than the fourth elastic modulus.

25. Method for manufacturing according to the preceding embodiment, comprising designing the mesh according to any of the embodiments 22-23: and wherein arranging the die comprises orienting the die to the mesh in the attachment layer according to the design of the mesh.

26. Method for manufacturing according to any of the preceding embodiments 24-25, wherein providing an attachment layer comprises: - applying a first layer of attachment material on the substrate, preferably with stencil printing; - placing the mesh on top of the first layer, preferably pressing the mesh into the first layer: and - applying a second layer of attachment material on the first layer and/or the mesh, preferably with stencil printing.

27. Method for manufacturing according to any of the preceding embodiments 24-26, wherein the die has an operational die temperature; wherein the method comprises curing the attachment layer after arranging the die on top of the attachment layer; wherein at least curing is performed at a curing temperature; and wherein the curing temperature is between the operational temperature and room temperature. 28 Method for manufacturing according to the preceding embodiment, wherein the die has an expected power on duty cycle: and wherein the curing temperature is selected based on the power on duty cycle.

29. Preform of die attach material comprising: - amesh with openings, and having a fourth elastic modulus; and - an attachment material having a third elastic modulus, and substantially filling the openings of the mesh; wherein the preform is arranged for use in an integrated circuit according to any of the embodiments 1-21 as the attachment layer; and/or wherein the preform is arranged for use in a method for manufacturing an integrated circuit according to any of the embodiments 24-28 as the attachment layer.

30. Method for manufacturing a preform of die attach material for an integrated circuit according to any of the embodiments 1-21, comprising:

- applying a first layer of attachment material on a temporal surface, preferably with stencil printing;

- placing the mesh on top of the first layer, preferably pressing the mesh into the first layer;

- applying a second layer of attachment material on the first layer and/or the mesh, preferably with stencil printing; and

- preferably removing the first layer, the mesh. and the second layer from the temporal surface for obtaining the preform.

Claims

CONCLUSIONS

An integrated circuit comprising: - a chip (30) having a first elastic modulus and a first coefficient of thermal expansion, which comprises an electronic circuit and generates heat during use; - a substrate (10) having a second elastic modulus and a second coefficient of thermal expansion, and for dissipating heat from the chip; - an attachment layer (20) arranged between the chip and the substrate; the attachment layer comprising: - a mesh (21) with openings, and with a fourth elastic modulus; and - a fixing material (22) having a third elastic modulus, and substantially filling the openings of the mesh; wherein the third elastic modulus is less than the fourth elastic modulus.

An integrated circuit according to the preceding claim, wherein the fixing layer has a combined fifth elastic modulus: and wherein the combined fifth elastic modulus is less than the fourth elastic modulus.

An integrated circuit according to any one of the preceding claims, wherein the elastic modulus is a Young's modulus, a bulk modulus and/or a volumetric elasticity.

An integrated circuit according to any one of the preceding claims, wherein the mesh has a fourth coefficient of thermal expansion; wherein the fastener has a third coefficient of thermal expansion; wherein the fixing layer has a combined fifth coefficient of thermal expansion; and wherein the combined fifth coefficient of thermal expansion is less than the first coefficient of thermal expansion.

The integrated circuit of the preceding claim, wherein the fixing layer has a combined fifth coefficient of thermal expansion between the first coefficient of thermal expansion and the second coefficient of thermal expansion.

An integrated circuit according to the preceding claim, wherein the mesh is wholly or partly embedded in the mounting material.

An integrated circuit according to any one of the preceding claims, wherein the mounting material surrounds the mesh or wherein the mesh is incorporated in the mounting material.

An integrated circuit according to any one of the preceding claims 1-5, wherein the mesh makes physical contact with the substrate.

An integrated circuit according to the preceding claim, wherein the mesh is an integrated part of the substrate, the mesh preferably being formed from protruding parts of the substrate after removal, such as electroplating, milling or etching away parts of the substrate.

An integrated circuit according to any one of the preceding claims, wherein the chip has a chip mounting surface facing the attachment; and wherein the mesh extends beyond the chip mounting surface in a plane parallel to the chip mounting material.

An integrated circuit according to any one of the preceding claims, wherein the mesh is smaller than the chip mounting area, preferably wherein the mesh forms a region and/or an island where, depending on claim 4, the combined fifth coefficient is locally adjusted and/or where, depending on claim 2, the combined fifth elastic modulus is locally adjusted.

Integrated according to any one of the preceding claims, wherein the mesh comprises mechanical parts such as springs and/or hinges configured to return to its original shape when released after deformation and/or reinforcements to relieve and/or reduce thermal expansion stress in the attachment layer.

An integrated circuit according to the preceding claim, wherein the mechanical parts and/or the reinforcements are arranged such that the thermal expansion stress in the fixing layer is relieved and/or reduced in at least one predetermined direction.

An integrated circuit according to the preceding claim, wherein the at least one predetermined direction lies in a plane parallel to the substrate and/or the chip and/or the shape of the substrate.

An integrated circuit according to any one of the preceding claims, wherein the fixing layer has a thickness in a range of 5 µm to 200 µm, preferably 15 µm to 150 µm, further preferably 25 µm to 100 µm, most preferably 30 µm to 90 µm.

An integrated circuit according to any one of the preceding claims, wherein the openings of the mesh have a diameter and/or diagonal in a range of 25 µm to 200 µm, preferably 35 µm to 150 µm, further preferably 45 µm to 125 µm most preferably 50 µm to 100 µm.

An integrated circuit according to any one of the preceding claims, wherein the openings of the mesh have a surface in a range of 2000 µm 2 to 125,000 µm 2 , preferably 4000 µm 2 to 175,000 µm 2 , further preferably 6000 µm 2 to 250,000 µm 2 , most preferably 8000 µm? up to 30000 µm2.

An integrated circuit according to any one of the preceding claims, wherein the apertures of the mesh have a thickness in a range of 2 µm to 200 µm, preferably 5 µm to 150 µm, further preferably 10 µm to 100 µm, most preferably 20 pm to 90 pm.

The integrated circuit of any preceding claim, wherein the mesh comprises one or more of copper, nickel, tungsten, iron and molybdenum.

An integrated circuit according to any one of the preceding claims, wherein the integrated circuit is a packaged integrated circuit.

An integrated circuit according to any one of the preceding claims, wherein the first coefficient of thermal expansion, preferably linear coefficient of thermal expansion, is in the range of 2.0 10% K*t to 9.0 10% K! is preferably 2.5 10% K'! up to 8.5 10% K, more preferably 2.7 10% K! to 8.0 10% K1, most preferably 3.0 106 K'! to 7.5 10K7: wherein the first elastic modulus is in a range of 90 GPa to 500 GPa, preferably 110 GPa to 450 GPa, more preferably 120 GPa to 420 GPa, most preferably substantially 130 GPa or 400 GPa, such as the elastic modulus of Si or SiC; wherein the second coefficient of thermal expansion, preferably linear coefficient of thermal expansion, is in a range of 10.0 10% K to 30.0 10% KL, preferably 12.0 10% K' to 25.0 10% KL, at further preferably 13.0 10% K -1 to 22.0 10% Ki, still further preferably 14.0 10% K -1 to 20.0 10% KL, most preferably substantially around 17 10 K -1 :

wherein the second elastic modulus is in a range of 80 GPa to 180 GPa, preferably 110 GPa to 150 GPa, further preferably 120 GPa to 140 GPa, most preferably substantially 129 GPa, such as the elastic modulus of Cu: wherein the third modulus of elasticity is in a range of 3 GPa to 50 GPa, preferably 4 GPa to 42 GPa, further preferably 5 GPa to 40 GPa, still further preferably 10 GPa to 30 GPa, most preferably substantially the elastic modulus of pure sintered Ag or hybrid sintered Ag; wherein the fourth elastic modulus is in a range from 100 GPa to 350 GPa, preferably 120 GPa to 300 GPa, further preferably 125 GPa to 290 GPa, still further preferably 129 GPa to 280 GPa, most preferably the elastic modulus of Cu, W80Cu, or pure nickel: where is the combined fifth coefficient of thermal expansion. preferably linear coefficient of thermal expansion, in a range of 1.0 10% K to 17.0 10% KL preferably

1.5 10° Kt to 14.0 10° K, more preferably 2.0 10% K to 12.0 10° K™, still further preferably 3.0 10% K" to 11.0 10% K", at most preferably substantially around 10% K* -1 , wherein the fixing layer has a combined thermal conductivity in a range from 30 W*m*K-1 to 350 W*m*K-1 , preferably 40 W*m*K-1 ! up to 320 W*m KL, further preferably 50 W*m*K-! up to 300 W*m KL, even further preferably 70 W*m*K! to 250 Wm *K-1 , most preferably substantially 100 W*m -1 *K -1 : and/or wherein the combined fifth elastic modulus is in a range between the selected third elastic modulus and the fourth elastic modulus, such as wherein the fifth elastic modulus depends on the weight and/or volume of the fastener relative to the weight and/or volume of the mesh.

A method of designing an integrated circuit mesh according to the preceding claims, comprising: - identifying the heat point location of a heat point of the chip; and - adjusting the mesh based on the heat point location.

A method of design according to the preceding claim, wherein the adaptation comprises: - decreasing the opening area of the mesh relative to the area of the mesh when projected from above at the heat point; and/or - increasing the opening area of the mesh relative to the area of the mesh when projected from above at the location remote from the heat point.

A method of manufacturing an integrated circuit according to any one of claims 1 to 21, comprising: - providing a substrate having a second elastic modulus and a second coefficient of thermal expansion; - applying a fixing layer on top of the substrate, the fixing layer comprising: a mesh having openings of, and a fourth elastic modulus: and a fixing material having a third elastic modulus, and substantially filling the openings of the mesh: and - applying a chip having a first elastic modulus and a first coefficient of thermal expansion on top of the mounting layer, and comprising an electronic circuit and generating heat during use; wherein the third elastic modulus is less than the fourth elastic modulus.

A manufacturing method according to the preceding claim. comprising designing the mesh according to any one of claims 22-23; and wherein arranging the chip includes orienting the chip according to the mesh in the mounting layer according to the design of the mesh.

A manufacturing method according to any one of the preceding claims 24-25, wherein the provision of a fixing layer comprises: - applying a first layer of fixing material to the substrate, preferably with stencil pressure: - placing the mesh on the first low. preferably pressing the mesh into the first layer; and - applying a second layer of fixing material to the first layer and/or the gauze, preferably with stencil pressure.

A manufacturing method according to any one of claims 24-26, wherein the chip has an operational chip temperature: the method comprising curing the fixation layer after applying the chip on top of the fixation layer; wherein at least the curing is performed at a curing temperature: and wherein the curing temperature is between the operating temperature and room temperature.

A manufacturing method according to the preceding claim, wherein the chip has an expected power utilization coefficient; and wherein the curing temperature is selected based on the coefficient of use.

29. Chip mounting material preform, comprising: - a mesh with openings, and having a fourth elastic modulus; and - a fastener having a third elastic modulus, and for substantially filling the openings of the mesh: wherein the preform is adapted for use in an integrated circuit according to any one of claims 1-21 as the fastening layer: and/or wherein the preform is adapted for use in an integrated circuit manufacturing method according to any one of claims 24-28 as the mounting layer.

A method for manufacturing a preform of chip mounting material for an integrated circuit according to any one of claims 1-21, comprising: - applying a first layer of mounting material to a temporary surface, preferably with stencil pressure: - placing the mesh on the first layer, preferably pressing the gauze into the first layer: - applying a second layer of fastening material to the first layer and/or the gauze, preferably with stencil pressure; and - preferably removing the first layer, the mesh and the second layer from the temporary surface to obtain the preform.