PRESSURE-SINTERING METHOD EMPLOYING DEFORMATION UPTAKE MEANS

Abstract

A method for fixing an attachment object to a side of a patterned object comprising a plurality of protrusions with tip portions, by pressure-sintering. A deformation uptake means made of a material having a lower yield strength and/or a lower hardness than the tip portions, is arranged between the patterned object and at least a fraction of the tip portions.

Claims

1. A method for fixing an attachment object to a patterned object by pressure-sintering, wherein the attachment object becomes fixed to an attachment side of the patterned object and wherein the patterned object comprises a patterned side facing away from the attachment side, the patterned side including a plurality of protrusions with tip portions, the method including: providing a sintering material between the attachment object and the attachment side of the patterned object; arranging the patterned object and the attachment object in a sintering tool, wherein the patterned object is arranged at a first tool side of the sintering tool and the attachment object is arranged at a second tool side of the sintering tool; arranging an additional deformation uptake means between the first tool side and at least a fraction of the tip portions, wherein the deformation uptake means is made of a deformation material having a lower yield strength and/or a lower hardness than the tip portions; a solidification step including pressing the patterned object and the attachment object towards each other for densifying the sintering material and applying heat to the sintering material, thereby sintering the sintering material and forming a sinter layer between the attachment side and the attachment object.

2. The method according to claim 2, further including plastically deforming the deformation uptake means locally by pressing the deformation uptake means against the patterned object at its patterned side.

3. The method according to claim 1, including plunging at least 20 number-% and/or at least 20 area-% of the tip portions into the deformation uptake means causing local plastic deformation of the deformation uptake means during the solidification step and/or an adaption step preceding the solidification step, by pressing the deformation uptake means against the patterned object at its patterned side.

4. The method according to claim 1, wherein the fraction of the tip portions corresponds to at least 50% of all of the tip portions.

5. The method according to claim 1, wherein a yield strength of the deformation material is at the most 80% of a yield strength of the protrusions.

6. The method according to claim 1, wherein a hardness of the deformation material is at the most 80% of a hardness of the tip portions.

7. The method according to claim 1, wherein the deformation material has a thermal conductivity of at least 30 W/(m.Math.K).

8. The method according to claim 1, wherein the deformation uptake means includes a metal sheet.

9. The method according to claim 1 wherein the deformation material is aluminum with a purity of at least 99.0 weight-%.

10. The method according to claim 1, wherein the yield strength of the deformation material is at least 8 MPa.

11. The method according to claim 1, wherein an elevated sintering temperature is in the range from 200? C. to 300? C. and wherein the deformation material is stable at the elevated sintering temperature.

12. The method according to claim 1, wherein at least cores of the protrusions are made of copper and/or aluminum.

13. The method according to claim 1, wherein a thickness of the deformation uptake means is in the range from 0.5 mm to 5 mm.

14. The method according to claim 1, wherein the patterned object is or comprises a heat dissipator, a heat sink, and/or a part for a cooler, and wherein the attachment object is or comprises at least one of the following: a heat generating component, an electronic component, and a semiconductor power module.

15. The method according to claim 1, wherein the protrusions are fins.

16. An assembly comprising an attachment object and a patterned object, wherein the attachment object is fixed to an attachment side of the patterned object by pressure-sintering, and wherein the patterned object comprises a patterned side facing away from the attachment side, the patterned side including a plurality of protrusions, wherein the attachment object has been permanently fixed to the patterned object by the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0146] Preferred embodiments of the invention will now be described with reference to the drawings, in which:

[0147] FIG. 1 shows a cross-sectional view of a collocation with a patterned object and several attachment objects in a pressure-sintering tool at a first stage of a solidification step for solidifying sintering material arranged between the attachment objects and the patterned object, wherein a deformation uptake means is provided between protrusions (pin fins) of the patterned object and a first tool side of the pressure-sintering tool, and wherein only the longest protrusions engage the deformation uptake means at the first stage;

[0148] FIG. 2 shows a later, second stage of the same solidification step, wherein forces applied by the pressure-sintering tool for pressing the patterned object and the attachments objects towards each other for applying pressure on the sintering material arranged between have become high enough such that the longest protrusion of the patterned object have started to plunge into the deformation uptake means, wherein tip portions of intermediate protrusions with an intermediate protrusion length have started to additionally engage the deformation uptake means;

[0149] FIG. 3 shows an enlarged section of FIG. 2, showing that the longest protrusions have already plunged into the deformation uptake means, wherein the intermediate protrusions have started to abut and hence to engage the deformation uptake means such that the intermediate protrusions now also take part in transferring pressing forces between the first tool side, via the deformation uptake means, and the rest of the patterned object and thus the sintering material;

[0150] FIG. 4 shows an enlarged section of the patterned object for schematically illustrating different protrusion lengths of the longest protrusions, the intermediate protrusions, and shortest protrusions;

[0151] FIG. 5 shows a third stage of the same solidification step, wherein the forces applied by the pressure-sintering tool have become high enough that all protrusions, even the shortest protrusions, engage the deformation uptake means and are plunged into the deformation uptake means;

[0152] FIG. 6 shows a first stage of a solidification step similar as in FIG. 1 in a pressure-sintering method, wherein two attachment objects are provided and wherein the deformation uptake means includes two separate elements, one for each of the attachment objects;

[0153] FIG. 7 shows a perspective view of a patterned side of the patterned object with the protrusion (pin fins);

[0154] FIG. 8 show a perspective view of one of the elements of the deformation uptake means shown in FIG. 6 after the end of the solidification step, wherein the shown side exhibits a plurality of indentations caused by the protrusions plunging into the deformation uptake means with local plastic deformation of the latter during the solidification step; and

[0155] FIG. 9 shows a perspective view onto a patterned side of another embodiment of a patterned object, wherein the protrusions form flow channels for a coolant such that this patterned object is configured for forming a substantial part of a cooler.

DETAILED DESCRIPTION

[0156] FIG. 1 schematically shows a collocation for pressure-sintering in a pressure-sintering tool 10 at a first stage of a solidification step. In this example, the collocation includes one patterned object 30 and three attachment objects 50 that shall be fixed to an attachment side 32 of the patterned object 30 by pressure-sintering. Furthermore, the collocation includes sintering material 40. For each of the attachment objects 50, a corresponding section of sintering material 40 is provided between the respective attachment object 50 and the attachment side 32 of the patterned object 30. The attachment objects 50 become permanently fixed to the attachment side 32 of the patterned object 30 by the disclosed method.

[0157] The attachment side 32 of the patterned object 30 is substantially flat, at least in respective contact areas at which the attachment objects 50 become fixed. A normal direction N is perpendicular to said contact areas. In this example, the whole attachment side 32 is flat. Correspondingly, the normal direction N is perpendicular to the complete attachment side 32.

[0158] Before the situation shown in FIG. 1, i.e. before the solidification step is performed, the sintering material 40 is applied onto the attachment side 32. For each of the attachment objects 50, a corresponding section of sintering material 40 is applied. Additionally or alternatively, the sintering material 40 is applied onto interface sides of the attachment objects 50. The interface side of the respective attachment object 50 is its side facing the attachment side 32 in the solidification step. In FIG. 1, these are the lower sides of the attachment objects 50.

[0159] In FIG. 1, the areas of the sections of the sintering material 40 correspond to (a shape/size of) the interface side of the respective attachment object 50. It should be noted that pressurizing the sintering material has already begun in FIG. 1. It is also possible that the area of the respective section of the sintering material 40 is smaller than the interface side of the corresponding attachment object 50. This might especially apply before applying the forces F11, F12 starts. The sintering material 40 is squeezed during the solidification step. It might thus expand laterally (with respect to the normal direction N) while its height (along the normal direction N) is reduced. The area of the corresponding section of the sintering material 40 may even become larger than the interface side of the respective attachment object 50. This lateral expansion is schematically illustrated in FIG. 3.

[0160] The sintering material 40 can include sintering paste. Additionally or alternatively, it can include one or more sintering pads. The sintering material 40 can include a volatile organic component and silver particles. It may be applied wet.

[0161] The method can further include pre-drying the applied sintering material 40 before the solidification step. During the pre-drying, the volatile organic component at least partly evaporates. In particular, pre-drying can be performed before the attachment objects 50 are placed at the attachment side 32 with the sintering material 40 in between. The pre-drying can be performed outside of the pressure-sintering tool 10.

[0162] In the examples shown in FIG. 1 and FIG. 6, the attachment objects 50 are semiconductor power modules, more precisely molded modules. They can be of the same type or of different types.

[0163] In this example, each attachment object 50 comprises a direct bonded copper (DCB) structure with a ceramic insulation layer 52, an integrated heat spreader 51, and an internal circuit layer 53. The integrated heat spreader 51 is arranged at the interface side of the attachment object 50. The integrated heat spreader 51 is formed on one side of the insulation layer 52 and fixed to the latter. The internal circuit layer 53 is formed on and fixed to an opposite side of the insulation layer 52 (e.g. the upper side in FIG. 3). Semiconductor components 55 are fixed to the internal circuit layer 53 by internal sinter layers 54. The internal sinter layers 54 may include separate sections for each of the semiconductor components 55. The semiconductor components 55 can include, for example, IGBTs and/or MOSFETs. The semiconductor power modules can further comprise bonding wires 56 and/or other means for electrically connecting the semiconductor components 55.

[0164] According to one aspect, (at least some of) the internal sinter layers 54 can be formed from sintering material by solidification in the same solidification step as a sinter layer that is formed from the sintering material 40.

[0165] However, in the exemplary embodiments shown, the attachment objects 50 are molded (semiconductor power) modules. The internal sinter layers 54 are already sintered. Each molded module comprises a resin cover 57. The resin cover 57 covers the whole semiconductor power module except the integrated heat spreader 51 at the interface side. The resin cover 57 exhibits electrical insulation, protection against humidity as well as protection against mechanical and chemical damage.

[0166] The attachment side 32 of the patterned object 30 is substantially flat, at least in contact areas at which the attachment objects 50 become fixed. The normal direction N is perpendicular to said contact areas. In this example, the whole attachment side 32 is flat. Correspondingly, the normal direction N is perpendicular to the complete attachment side 32.

[0167] The patterned object 30 comprises a planar main plate 31, which (at least substantially) extends perpendicular to the normal direction N. One end side of the main plate 31 along the normal direction N is the attachment side 32. A side opposite to the attachment side 32 is a patterned side 33. The patterned side 33 comprises a plurality of protrusions 34. The protrusions 34 protrude along the normal direction N from the main plate 31.

[0168] In this exemplary embodiment, all protrusions 34 are formed as pin fins. The pin fins can be seen best in FIG. 7. As indicated in FIG. 3, the pin fins are distanced from each other in lateral directions (directions perpendicular to the normal direction N), wherein empty spaces 37 are formed between adjacent pin fins.

[0169] Alternatively or in addition, protrusions with other shapes can be formed at the patterned side 33. For example, such other shapes can include oblong fins (e.g. cooling ribs).

[0170] In this exemplary embodiment, the patterned object 30 is a heat sink. It is configured to take up heat from the attachment objects 50 during operation, to spread the heat and further dissipate it by the protrusions (pin fins) 34 to an environmental fluid, e.g. air.

[0171] Additionally or alternatively, the patterned side 33 may include a channel structure for guiding fluid, e.g. a coolant. The patterned object 30 can be a cooler or a component for forming a substantial part of a cooler (a part for a cooler). For example, the patterned object 30 can include or consist of a metal layer with an internal structure for a flow distributor, e.g. according to any one of the embodiments disclosed in EP 2 559 063 Bi. In this context, the inner walls of the metal layer can be considered protrusions 34.

[0172] In the shown embodiments, the protrusions (pin fins) 34 at the patterned side 33 are produced by stamp forging. They are not subjected to additional mechanical postprocessing, e.g. milling, for improving a manufacturing tolerance regarding protrusion lengths of the protrusions 34. Therefore, the protrusion lengths along the normal direction N vary. In FIGS. 1 to 6, this is schematically illustrated by showing longest protrusions 34m having a longest protrusion length L34m (a maximum protrusion length L34m), intermediate protrusions 34i having an intermediate protrusion length L34i, and shortest protrusion 34s having a shortest protrusion length L34s. This can be seen best in FIG. 4 illustrating an enlarged section of FIG. 2. It is understood that the protrusion lengths can actually vary according to a statistical distribution. Accordingly, there are more different individual protrusion lengths. However, the simplified explanation facilitates the understanding.

[0173] The patterned object 30 can be made of copper, e.g. of a copper-based alloy. Copper and copper-based alloys facilitate a strong and reliable fixation of the sinter layer formed from the sintering material 40. At least the protrusions 34 might be coated with a coating, e.g. with a nickel coating (including coatings made of nickel-based alloys).

[0174] Alternatively, the patterned object 30 is basically made of aluminum, e.g. of an aluminum alloy. This facilitates producing the protrusions 34 by stamp forging. Optionally, the patterned object 30 may include at least one inlay 36 at the attachment side 32 where the attachment objects 50 are fixed. The inlay(s) 36 may be made of copper, e.g. of a copper-based alloy. As noted above, this facilitates strong and reliable fixation of the sinter layer. Furthermore, copper has a particularly high heat conduction. The heat taken up from the attachment objects 50 via the sinter layer is efficiently pre-dissipated within the patterned object 30 by the inlay(s) 36. FIG. 6 shows two of such inlays 36. Inlays are described in WO 2020/254143 A1.

[0175] The pressure-sintering tool 10 comprises a first tool side 11 and a second tool side 12. The first tool side 11 and the second tool side 12 are configured to apply forces F.sub.11 and F.sub.12 for pressing the attachment objects 50 and the patterned object 30 towards each other along the normal direction N. In FIG. 1, upper sides (resin sides) of the attachment objects 50 directly abut the second tool side 12. It is expected that the absolute values of the forces F.sub.11 and F.sub.12 are at least substantially the same.

[0176] Conventionally (not shown), the patterned side 33 of the patterned object 30 directly abuts the first tool side 11. Only the tip portions of the longest protrusions 34m (those with the longest protrusion length L34m) abut on and engage the first tool side 11. The first tool side 11 must be hard and strong, e.g. have a high hardness and a high yield strength, because the pressure-sintering tool 10 must not be damaged during the solidification step. The pressure-sintering tool 10 must be reliable, long-lasting, and usable for performing a large plurality of solidification steps. Hence, the first tool side 11 must not yield, at least not plastically, in the course of the solidification step.

[0177] As a consequence, in conventional pressure-sintering (not shown), the force F.sub.11 applied by the first tool side 11 is transferred to the main plate 31 of the patterned object 30 exclusively via the longest protrusions 34m. The intermediate protrusions 34i and the shortest protrusions 34s are not involved in the force transfer. This results in excessive local stresses and deformations of the patterned object 30 during the solidification step. The attachment side 32 can locally bulge. This leads to variations of the pressure applied to the sintering material 40 and to local variations of the sintering quality.

[0178] In addition, depending on a spatial distribution of the longest protrusions 34m laterally to the normal direction N and/or due to different thicknesses of the attachment objects 50 (along the normal direction N), it can happen that the patterned object 30 (especially its attachment side 32) is not aligned properly perpendicularly to the normal direction N during the solidification step. This results in global thickness variations of the sinter layer. For example, at least a section of the sinter layer for one of the attachment objects 50 may have a cross-sectional shape (in a plane parallel to the normal direction) that is more similar to a trapezoid, e.g. a right trapezoid, than to a rectangle. Additionally, the thickness of the sinter layer may vary for the different sections for the different attachment objects 50.

[0179] According to the present invention and as shown in FIG. 1, an additional deformation uptake means 20 is arranged between the first tool side 11 and the patterned object 30. The deformation uptake means 20 compensates manufacturing tolerances, e.g. the manufacturing tolerance regarding the protrusion lengths, and other tolerances, especially tolerances along the normal direction N (height tolerances). Such height tolerances can include differences in the thicknesses of the attachment objects 50, unevenness of the first tool side 11 and/or the second tool side 12, height tolerances of additional fixation means (not shown) for fixing the collocation in the sintering tool 10, and the like.

[0180] The deformational uptake means 20 partially deforms during the solidification step in order to allow more and more of the protrusions 34 to engage with the deformation uptake means 20 while the pressure applied on the sintering material 40 is increased.

[0181] The deformation uptake means 20 is made of a deformation material. The deformation uptake means 20 is softer than the first tool side 11 and softer than the protrusions 34. In the exemplary embodiment shown in FIG. 1, the deformation uptake means 20 is a single metal sheet having a thickness T in the range from 1 mm to 4 mm, e.g. 2 mm. Especially, its yield strength is lower than the one of the protrusions 34, for example 80% at the most or even 60% at the most. Additionally or alternatively, its hardness is lower than the one of the protrusions 34, for example 80% at the most or even only 60% at the most. Its yield strength and hardness can be also lower than those of a material of the first tool side 11, for example by at least 40%.

[0182] Further, the exemplary deformation uptake means 20 shown in FIG. 1 is made of pure aluminum. Pure aluminum may mean aluminum with a purity of at least 99.0 weight %, e.g. with 99.5 weight %. This deformation material exhibits low hardness and low yield strength. In more detail, the deformation material can be aluminum EN AW 1050A. It can be in the H111/0 temper condition.

[0183] The pure aluminum exhibits sufficient heat conduction for applying heat to the sintering material 40 in the solidification step and is chemically stable at an elevated sintering temperature.

[0184] If the patterned object 30, especially its protrusions 34 are made of aluminum, this kind of aluminum has a higher yield strength and hardness than the pure aluminum. For example, the aluminum used for the attachment object 50 is aluminum with less purity, e.g. an aluminum alloy, and/or it is of another temper condition. In every case, it exhibits higher yield strength and hardness than the pure aluminum used as the deformation material.

[0185] FIG. 1 shows a situation in a first stage of the solidification step. Tool-facing sides (upper sides in FIG. 1) of the attachment objects 50 directly abut the second tool side 12. One large flat surface (a lower side in FIG. 1) of the deformation uptake means 20 directly abuts the first tool side 11. The patterned side 33 of the patterned object 30 directly abuts the other large flat surface of the deformation uptake means 20 (an upper side in FIG. 1).

[0186] In the first stage of the solidification step shown in FIG. 1, the forces F.sub.11 applied by the first tool side 11 and F.sub.12 applied by the second tool side 12 for pressing the attachment objects 50 and the patterned object 30 towards each other (along the normal direction N) have reached first levels F.sub.11,1 and F.sub.12,1. Only the tip portions of the longest protrusions 34m directly abut and hence engage the deformation uptake means 20. At this first stage, the complete force F.sub.11,1 is transferred from the deformation uptake means 20 to the main plate 31 of the patterned object 30 and hence to the sintering material 40 via the longest protrusions 34m. During the first stage, neither the intermediate protrusions 34i nor the shortest protrusions 34s do contribute to said force transfer. The tip portions of the intermediate protrusions 34i and the shortest protrusions 34s do not abut and hence do not engage the deformation uptake means 20 during the first stage.

[0187] If the forces F.sub.11 and F.sub.12 are increased further, stresses at the engagement areas of the deformation uptake means 20 with the tip portions of the longest protrusions 34m rise. At first, the deformation uptake means 20 yields (at least predominantly) elastically. When the stresses at the engagement areas exceed a certain threshold, the deformation uptake means 20 yields plastically at the corresponding engagement areas. The deformation material starts to plastically flow around the corresponding tip portions and these tip portions plunge into the deformation uptake means 20 further with local plastic deformation of the latter at the corresponding engagement areas.

[0188] FIG. 2 shows a second stage of the solidification step. The forces F.sub.11 and F.sub.12 have reached second levels F.sub.11,2 and F.sub.12,2 that are higher than the corresponding first levels F.sub.11,1 and F.sub.12,1. The tip portions of the longest protrusions 34m have already plunged into the deformation uptake means 20 to a certain extent with plastic deformation.

[0189] Compared to the first stage shown in FIG. 1, the first tool side 11 and the deformation uptake means 20 on the one hand and the patterned object 30 at the other hand have been displaced along the normal direction N towards each other by a second stage distance H2.

[0190] Naturally, the tip portions of the longest protrusions 34m continue to engage the deformation uptake means 20. Now, the tip portions of the intermediate protrusions 34i have additionally come into direct contact with the deformation uptake means 20. They additionally abut and hence additionally engage the deformation uptake means 20 now. In other words, additional engagement areas are formed between the deformation uptake means 20 and tip portions, which are different from the longest protrusions 34m. From now on, the intermediate protrusions 34i additionally contribute to the transfer of the force F.sub.11 from the first tool side 11 to the rest of the patterned object (particularly to the main plate 31) and hence to the sintering material 40. This prevents that excessive loads are applied onto the longest protrusions 34m only.

[0191] FIG. 5 shows a third stage of the solidification step. The forces F.sub.11 and F.sub.12 have reached third levels F.sub.11,3 and F.sub.12,3 that are higher than the corresponding second levels F.sub.11,2 and F.sub.12,2. The third stage may correspond to a maximum pressure application in the solidification step. In other words, F.sub.11,3 may be a maximum level of the force F.sub.11 applied during the solidification step and F.sub.12,3 may be a maximum level of the force F.sub.12 applied during the solidification step.

[0192] The tip portions of the intermediate protrusions 34i have also plunged into the deformation uptake means 20 to a certain extent with plastic deformation. Even the tip portions of the shortest protrusions 34s have plunged into the deformation uptake means 20 with plastic deformation. Naturally, the tip portions of the shortest protrusions 34s are not plunged as deep into the deformation uptake means 20 as the tip portions of the intermediate protrusions 34i and the tip portions of the intermediate protrusions 34i are not plunged as deep into the deformation uptake means 20 as the tip portions of the longest protrusions 34m.

[0193] Compared to the first stage shown in FIG. 1, the first tool side 11 and the deformation uptake means 20 on the one hand and the patterned object 30 at the other hand have been displaced along the normal direction N towards each other by a third stage distance H3. The third stage distance H3 is larger than the second stage distance H2 shown in FIG. 2.

[0194] Although the maximum pressure in the solidification step is reached in FIG. 5, the deformation uptake means 20 is strong and rigid enough such that the tip portions of the longest protrusions 34m do not protrude completely through the deformation uptake means 20. The thickness T of the deformation uptake material and the hardness and yield strength of the deformation material are high enough to prevent this. Even in FIG. 5, there is no direct contact between the tip portions of the longest protrusions 34m and the first tool side 11.

[0195] In FIG. 5, the tip portions of all the protrusions 34 (including the longest protrusions 34m, the intermediate protrusions 34i, and the shortest protrusions 34s) engage with deformation uptake means 30. As plastic deformation of the deformation uptake means 20 occurs at the engagement areas of all tip portions, all protrusions 34 bear at least substantially the same portions of the force F.sub.11,3. The plastic deformations in the engagement areas ensure that no excessive load transfer is carried by some individual protrusions, e.g. the longest protrusions 34m. This allows compensating various height tolerances while ensuring more uniform stresses within the patterned object 30 and more uniform pressure application onto the sintering material.

[0196] The protrusions 34 do not plastically deform during the solidification step.

[0197] During the solidification step, the sintering material is not only subjected to the high pressure. In addition, the sintering tool 10 also heats up the sintering material 40 to the elevated sintering temperature. For example, the solidification step may include applying the elevated sintering temperature in a temperature range from 200? C. to 300? C. and the pressure in the range from 10 to 40 MPa to the sintering material 40 for a sintering time. The sintering time may be at least 2 minutes in order to ensure proper sintering of the whole sintering material 40. Additionally or alternatively, the sintering time may be 10 minutes at the maximum in order to reduce a risk of thermal degradation of the sinter layer formed from the sintering material 40 and/or of the attachment objects 50. Furthermore, shorter sintering times reduce the costs for heating and allow faster production.

[0198] The heat application from the second tool side 12 is limited in order not to risk thermal damage of the attachment objects 50. As the deformation uptake means 20 exhibits high heat conduction, the sintering material 40 can be heated up quickly by applying a majority of the heat from the first tool side 11.

[0199] FIG. 6 shows a slightly different arrangement. In this case, the deformation uptake means 20 consists of a separate metal sheet 20a, 20b for each of the attachment objects 50. The first metal sheet 20a covers a first set 35a of protrusions (pin fins) 34 for a first one of the attachment objects 50 and the second metal sheet 20b covers a second set 35b of protrusions (pin fins) 34 for a second one of the attachment objects. Apart from that, the description with regard to the arrangement and method described with respect to the other figures applies accordingly and the same reference numbers are used for the same element. For example, both metal sheets 20a, 20b can be made of pure aluminum.

[0200] In general, the method can be performed with other numbers of attachment objects 50 and other numbers of patterned objects 30 as well. For example, only one attachment object 50 may be fixed to the patterned object 30. In another modification, there are three attachments objects 50 and three corresponding separate metal sheets 20a, 20b.

[0201] As shown in FIG. 8 for one of the metal sheets 20a, the large flat surface of the deformation uptake means 20 facing the patterned object 30 in the solidification step includes a plurality of permanent indentations 21 after the solidification step has been finished. The indentations 21 result from the plastic deformation at the engagement areas caused by the tip portions of the protrusions 34. In this example, the tip portions of all protrusions 34 of the first set 35a have plunged into the metal sheet 20a with plastic deformation.

[0202] It is possible that the deformation uptake means 20 covers (overlaps with) only a fraction of all protrusions 34 in the solidification step. For example, in a modification of FIG. 6 (not shown), the metal sheet 20a does not overlap the three most left columns of the protrusions 34 and the metal sheet 20b does not overlap the three most right columns of the protrusions 34. There is also no overlap of the protrusions 34 with any one of the attachment objects 50 in those regions and hence these regions are less relevant for transferring the force F.sub.11. According to one aspect, when referring to a projection in a plane perpendicular to the normal direction N, the deformation uptake means 20 overlaps the protrusions 34 at least in regions where the protrusions 34 overlap the attachment objects 50.

[0203] There are several approaches for quantifying how much percent of the tip portions have plunged into the deformation uptake means 20 with plastic deformation in the solidification step.

[0204] For example, it can be referred to a percentage of a number of the indentations 21 (as shown in FIG. 8), which remain from the last solidification step, relative to a total number of the protrusions 34 (indication in number %). In FIG. 8 and assuming that the metal sheet 20b looks accordingly, this indication would be 100 number %.

[0205] Another approach is to sum up opening areas 22 (unit: m.sup.2 or the like) of all indentations 21 in the deformation uptake means 20, resulting in an area A.sub.p1. In FIG. 8, the opening areas 22 are the areas of the oval openings of the indentations 21 at the upper surface of the metal sheet 20a. A reference value A.sub.ref can be a sum of cross-sectional areas of all of the tip portions in a cross-sectional plane perpendicular to the normal direction N. A.sub.ref may be simply calculated by assuming an ideal patterned object 34 without tolerances. Said cross-sectional plane can be assumed at a position where all of the tip portions (if applicable, all those of the fraction covered by the deformation uptake means 20) are plunged into the deformation uptake means 20 by at least 40 ?m. In this case, a final value R=A.sub.p1/A.sub.ref.Math.100% corresponds to an indication in area %. This approach can be more precise especially in cases where the patterned object 30 includes protrusions 34 with different and/or complex shapes.

[0206] The deformation uptake means 20 can be re-used. For example, when the solidification step is finished and when an assembly, which is formed by fixing the attachment objects 50 to the patterned object 30 by pressure-sintering, is taken out of the sintering tool. The deformation uptake means 20 is simply turned upside down and re-used for a new method cycle, in which new attachment objects 50 are fixed to a new patterned object 30.

[0207] When the solidification step is finished, the sintering material 40 has been transformed to a sinter layer. The resulting assembly includes the patterned object 30, the attachment objects 50, and the sinter layer in-between. The sinter layer permanently fixes the attachment objects 50 to the patterned object 30. With the disclosed method, a very thin and uniform sinter layer is produced, despite of the height tolerances. This allows easier and more cost-efficient production of the patterned object 30. The thin and uniform sinter layer exhibits particularly good heat conduction from the attachment objects 50 to the patterned object 30 and particularly high reliability.

[0208] FIG. 9 shows another embodiment of a patterned object 130 that is known from DE 10 2017 101 126 A1. In this case, the protrusions 34 form a wall structure on the patterned side 33 of the main plate 31. In more details, the protrusions 34 form a cooling structure with flow channels 138 for guiding a coolant. The cooling structure includes an outer wall structure 139a and a plurality of inner walls 139b, wherein the inner walls 139b (and also parts of the outer wall structure 139a) are arranged to exhibit an interleaved comb pattern for guiding a flow of the coolant along the cooling structure. A cooler can be completed by covering and sealing the cooling structure at the patterned side 33, e.g. with a cover plate (not shown). By this, the channels 138 can be closed.

[0209] While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.