Device and method for optical quality control of a pressure sintered joint

Abstract

A method and a device for pressure sintering and checking the quality of this pressure sintering joint of a first and a second joining partner are presented, comprising a first sub-device for arranging a first joining group consisting of the first and second joining partner with sintering paste arranged between them, directly or indirectly on a lower tool of a second sub-device; the second sub-device comprising an upper tool which is designed to be movable towards it from the normal direction of the lower tool and is intended to exert pressure on the second joining partner in order to convert the sintering paste into a sintered metal and to form a second joining group from the first, in which the joining partners are materially bonded to each other by means of a sintered joint;a third sub-device for arranging a cover film which covers the first joining group after its arrangement in the second sub-device on the side of the first joining group facing the upper tool, preferably directly; a fourth sub-device for optically checking the quality of the sintered pre-bonding of the second joining group by means of a control device for checking an optical property of a control section of the cover film that is aligned with the sintered metal.

Description

[0001] The invention describes a device and a method for this purpose for pressure sintering a first joining group with a first and a second joining partner and a sintering paste arranged therebetween, with a plurality of sub-devices, wherein a second sub-device is designed to convert the sintering paste into a sintered metal and thus the first into a second joining group.

[0002] DE 10 2015 120 156 A1 discloses a generic device with a press die having an elastic cushion element for the material-locking pressure sintering connection of a first connection partner to a second connection partner of a power electronics component, wherein the elastic cushion element of the press die is surrounded by a dimensionally stable frame, within which the cushion element and a guide part of the press die are guided in a linearly movable manner such that the dimensionally stable frame is lowered onto the first connection partner or a workpiece carrier with the first connection partner arranged therein and, after resting against the latter, the press die together with the elastic cushion element is lowered onto the second connection partner and the necessary pressure is exerted on the elastic cushion in order to connect the first connection partner to the second connection partner.During the sintering process, a cover film is typically placed between the cushion element, more generally the upper tool, and at least the second joining partner. Following the sintering process, this cover film often adheres to the second, usually both, joining partners.

[0003] DE 10 2020 206 978 A1 discloses a method for checking a connection between two elements on an assembly, in which a stamp is pressed against an element of the assembly with a separating film (5) interposed in order to connect the element to the other element of the assembly, preferably under simultaneous heat exposure, wherein the separating film changes optically under the influence of the stamp pressure generated by the stamp on the separating film.

[0004] DE 10 2021 118 949 A1 discloses a method and a device for pressure-sintering a first and a second connection partner, comprising a first sub-device for arranging a first joining group consisting of the first and second connection partners with sintering paste arranged therebetween, directly or indirectly, on a lower tool of a second sub-device; the second sub-device having an upper tool which is designed to be movable from the normal direction of the lower tool towards the latter and is intended to exert pressure on the second connection partner in order to convert the sintering paste into a sintered metal and to form a second joining group from the first, in which the connection partners are integrally connected to one another by means of a sintered connection;a third sub-device for arranging a first cover film, which covers the first joining group after its arrangement in the second sub-device on the side of the first joining group facing the upper tool, preferably directly, and additionally overlaps it at two opposite edges to form a first overlap section;

[0005] DE 10 2022 102 745 A1 discloses a method and a device for pressure-sintering a first and a second connection partner, comprising a first sub-device for arranging a first joining group comprising the first and second connection partners with sintering paste arranged therebetween on a lower tool of a second sub-device; the second sub-device having an upper tool and a lower tool which are designed to be movable towards one another and wherein the upper tool is provided for exerting pressure on the second connection partner in order to convert the sintering paste into a sintered metal and to form a second joining group from the first; a third sub-device for providing and arranging a cover film which covers the first joining group after its arrangement in the second sub-device on the side of the first joining group facing the upper tool;a fourth sub-device configured to treat a second surface of the cover film by means of plasma from a plasma treatment device, wherein this second surface is provided to face the first joining group and to lie on a first surface of the first joining group;

[0006] In view of the state of the art, the object of the invention is to provide a device and a method for determining the quality of the pressure sintered joint in a simple, rapid and non-destructive manner.

[0007] This object is achieved according to the invention by a device for pressure sintering and checking the quality of this pressure sintering connection of a first and a second connection partner, with a) a first sub-device for arranging a first joining group comprising the first and second connecting partners with sintering paste arranged therebetween, directly or indirectly, on a lower tool of a second sub-device; b) the second sub-device with an upper tool which is designed to be movable from the normal direction of the lower tool towards the latter and is intended to exert pressure on the second connection partner in order to convert the sintering paste into a sintered metal and to form a second joining group from the first, in which the connection partners are materially connected to one another by means of a sintered connection; c) a third sub-device for arranging a cover film which covers the first joining group, preferably directly, after its arrangement in the second sub-device on the side of the first joining group facing the upper tool; d) A fourth sub-device for optically checking the quality of the sintered connection of the second joining group by means of a control device for checking an optical property of a control section of the cover film aligned with the sintered metal, wherein the control device (40) is designed as an interferometer.

[0008] In this case, it may be advantageous if the second sub-device has a cutting tool which is designed and intended to cut the cover film.

[0009] It is generally advantageous if the upper tool is designed as an elastic sintering cushion, preferably with a frame element surrounding it, or as one or more rigid sintering stamps.

[0010] Likewise, it is fundamentally advantageous if the cover film is designed as a PTFE film and preferably has a thickness between 10 µm and 200 µm, in particular between 30 µm and 100 µm.

[0011] It may be advantageous if the fourth sub-device is arranged immediately after, but outside, the second sub-device.

[0012] It may also be advantageous if the first connection partner is designed as a power electronic substrate and the second connection partner is designed as a power semiconductor component or as a power electronic connection device comprising a foil stack of electrically conductive and an electrically insulating foil.

[0013] Furthermore, it may be advantageous if the first connection partner is designed as a power semiconductor component and the second connection partner is designed as a power electronic connection device comprising a foil stack of electrically conductive foil and an electrically insulating foil arranged therebetween.

[0014] The above-mentioned object is further achieved according to the invention by a method for optically checking the quality of a pressure sintered connection of a first and a second connection partner of a second joining group, designed by means of a device with an above-mentioned first to third sub-device and with a fourth sub-device for optically checking the quality of the sintered connection of the second joining group, wherein the check is carried out by means of the control device for checking an optical property of a control section of the cover film that is aligned with the sintered metal, wherein either the homogeneity of the color spectrum of a surface of the control section is determined by means of a spectrally resolving camera during the check and the quality of a sintered connection is defined as not meeting the target,if the colour spectrum of the control section deviates from a target colour spectrum or from the colour spectrum of a reference section by at least one tolerance value, or if the homogeneity of the contour of the surface of the control section is determined by means of an interferometer during the inspection and the quality of a sintered joint is defined as not meeting the target, if the contour of the control section deviates globally or locally from a target value or from the contour of a reference section by at least one tolerance value.

[0015] Of course, unless this is explicitly or per se excluded or contradicts the idea of ​​the invention, the features mentioned in the singular, for example the second connection partner, can also be present or arranged multiple times in the device according to the invention.

[0016] It is understood that the various embodiments of the invention, regardless of whether they are disclosed in the description of the device or the method, can be implemented individually or in any combination to achieve improvements. In particular, the features mentioned and explained above and below can be used not only in the specified combinations, but also in other combinations or on their own, without departing from the scope of the present invention.

[0017] Further explanations of the invention, advantageous details and features, emerge from the following description of the Fig. 1 to 7 schematically illustrated embodiments of the invention or respective parts thereof. Fig. 1 to 5 each show, in a schematic side sectional view, various partial alternative embodiments of sub-devices of a device according to the invention in various method steps of the method according to the invention. Fig. 6 shows a first embodiment of a second joining group for optical inspection. Fig. 7 shows two second designs of a second joining group for optical inspection.

[0018] Fig. 1 shows a schematic side sectional view of a first and a second sub-device 11, 12. Two first joining groups 100 are shown, the left one in an exploded view. Each first joining group 100 consists, without limitation of generality, of a power electronics substrate, as the first connection partner 102, with a ceramic insulating body and with copper conductor tracks on a surface of this substrate. Two layers of sintering paste 104 are arranged on the conductor tracks, on each of which a power semiconductor component, as the second connection partner 106, is arranged. In principle, the first and second connection partners 102, 106 can be designed as desired. For example, a conventional foil stack as an internal connection device of a power semiconductor module can also form a second connection partner 106.

[0019] The right of the two first joining groups 100 rests with the substrate, i.e. the first connection partner 102, directly, i.e. without an object arranged in between, on a lower tool 20 of the second sub-device 12. Also shown is an upper tool 22 of the second sub-device 12, designed here, without restriction of generality, as a conventional elastic sintering cushion 220 made of silicone with a Shore A hardness of 56, and stabilized by metallic additives such that it can be used at temperatures above 200°C and a pressure above 30 MPa. A frame element surrounding this sintering cushion 220, which is also conventional, has been omitted here. As an alternative to this, the upper tool 22 can also be designed, for example, from one or a plurality of hard punches 222, cf. Fig. 5, whereby here each second connection partner 106, i.e. each of the two power semiconductor components, is assigned its own stamp 222, which only presses on the respective power semiconductor component.

[0020] As an alternative to the above-mentioned arrangement, the left of the two first joining groups 100 is arranged in a workpiece carrier 120, which is designed both to transport the joining group 100 and can also be arranged on the lower tool 20, whereby the first joining group 100 located therein or thereon is then arranged indirectly on the lower tool 20.

[0021] For the arrangement of the first joining groups 100, a first sub-device 11 is also schematically shown, which can be designed as a conveying device, for example as a conveyor belt, or which can also be designed as a conventional handling robot.

[0022] Fig. 2 shows a schematic side sectional view of the previously described second and third sub-devices 12, 13. In this third sub-device 13, the cover film 30 is arranged in a feed device, here on a roll. From this roll, the cover film 30 is arranged over the first joining group 100, i.e., on its side facing the upper tool 22, while this first joining group 100 is already arranged on the lower tool 20. Alternatively, in particular if the first joining group 100 is transported by means of a workpiece carrier 120, the cover film 30 can also be arranged on the first joining group 100 before the first joining group 100 is arranged on the lower tool 20. In this case, it is particularly advantageous if the cover film 30 is divided into sections by means of a cutting tool 50.It may prove advantageous if the cutting tool 50 is designed as an element, in particular as a frame element, of the workpiece carrier 120 itself. Subsequently, the first joining group 100, advantageously arranged in or on a workpiece carrier 120, including a portion of the cover film 30, is arranged on the lower tool 20 by means of the first sub-device 11.

[0023] Fig. 3 shows the arrangement according to Fig. 2 after the pressure sintering connection has been made, whereby the sintering paste 104 is transferred into the sintered metal, and the second joining group 101 is created from the first joining group 100. A materially bonded and electrically conductive connection was formed between the two joining partners 102, 106 using the sintered metal. Due to the high pressure during this process step, the cover film 30 now adheres to the second joining group 101.

[0024] Fig. 4 shows in addition to Fig. 3 also shows a fourth sub-device 14, wherein the upper tool 22 of the second sub-device 12 is omitted. This fourth sub-device 14 is used to visually inspect the quality of the sintered pre-bond of the second joining group 101 by means of a control device 40 for checking an optical property of a control section 300 of the cover film 30 that is aligned with the sintered metal.

[0025] Fig. Figure 6 shows a first embodiment of a second joining group 101, more precisely the second connection partner 106 and a cover film 30 arranged thereon for visual inspection. The cover film 30 has a surface 310 facing away from the second connection partner 106, which here is embodied as a power semiconductor component. The cover film 30 itself is arranged on the sintered metal 114. The first connection partner 102 is not shown here.

[0026] The pressure sintering process reduced the thickness of the cover film 30 above the sintered metal 114, i.e., in the area of ​​the control section 300. This reduction in thickness is accompanied by a color change in the selected, industry-standard cover film 30. To determine the quality of the pressure sintering process, the color spectrum of the control section 300 is now, in the simplest case, determined using a spectrally resolving camera. The quality of a sintered joint is defined as substandard if the color spectrum of the control section 300 deviates from a target color spectrum by at least one tolerance value. If the deviation is smaller, the quality is defined as standard.The implementation of the fourth sub-device 14 thus allows a very simple, quick and non-interruptive way of determining the quality of the pressure sintered joint, of course without damaging or even destroying the second joining group 101.

[0027] In addition, the color spectrum of the control section 300 can also be compared with the color spectrum of a non-pressurized reference section of the same cover film 30.

[0028] As an alternative, height detection using optical methods is preferred, as this can also evaluate the entire control section 300 in a single step, which would not be possible with mechanical scanning, for example. An interferometric method or a fringe projection method would be preferred as a specific method.

[0029] By means of these methods, areas of the control section 300 can be identified which have defects, such as in particular insufficient pressurization during the pressure sintering process.

[0030] Fig. Figure 7 shows a second embodiment of a second joining group 101 for optical inspection. It shows a first connection partner 102, here a power semiconductor component, a sintered metal layer 114, and a second connection partner 106, here a connecting device, which is conventionally designed as a foil stack.

[0031] Also shown is a foreign body in the sintered metal layer 114, which results in the surface 310 of the control section 300 not being flat, but having a raised section 312. Basically, all of the above-mentioned Fig. 6 is also suitable for identifying a pressure sintered joint that is not formed in such a way as to achieve its intended purpose.

Claims

[1] Device (1) for pressure sintering and checking the quality of this pressure sintering of a first and a second connection partner (102,106), with a) a first sub-device (11) for arranging a first joining group (100) comprising the first and second connecting partners (102, 106) with sintering paste (104) arranged therebetween, directly or indirectly on a lower tool (20) of a second sub-device (12); b) the second sub-device (12) with an upper tool (22) which is designed to be movable from the normal direction of the lower tool (20) towards the latter and is provided to exert pressure on the second connection partner (106) in order to convert the sintering paste (104) into a sintered metal (114) and to form a second joining group (101) from the first, in which the connection partners (102, 106) are materially connected to one another by means of a sintered connection; c) a third sub-device (13) for arranging a cover film (30) which covers the first joining group (100) after its arrangement in the second sub-device (12), preferably directly, on the side of the first joining group (100) facing the upper tool (22); d) A fourth sub-device (14) for optically checking the quality of the sintered connection of the second joining group (101) by means of a control device (40) for checking an optical property of a control section (300) of the cover film (30) aligned with the sintered metal (114), wherein the control device (40) is designed as an interferometer. [2] Device according to claim 1, wherein the second sub-device (12) comprises a cutting tool (50) which is designed and provided to cut the cover film (30). [3] Device according to one of the preceding claims, wherein the upper tool (22) is designed as an elastic sintering cushion (220), preferably with a frame element framing it, or as one or more rigid sintering stamps (222). [4] Device according to one of the preceding claims, wherein the cover film (30) is designed as a PTFE film and preferably has a thickness between 10 µm and 200 µm, in particular between 30 µm and 100 µm. [5] Device according to one of the preceding claims, wherein the fourth sub-device (14) is arranged immediately after, but outside, the second sub-device (12). [6] Device according to one of claims 1 to 5, wherein the first connection partner (102) is designed as a power electronic substrate and the second connection partner (106) is designed as a power semiconductor component or as a power electronic connection device comprising a foil stack of electrically conductive and an electrically insulating foil. [7] Device according to one of claims 1 to 5, wherein the first connection partner (102) is designed as a power semiconductor component and the second connection partner (106) is designed as a power electronic connection device comprising a foil stack of electrically conductive foil and an electrically insulating foil arranged therebetween. [8] A method for optically checking the quality of a pressure sintered connection of a first and a second connection partner (102, 106) of a second joining group (101), formed by means of a device (1) with a first to third sub-device (11, 12, 13) according to one of the preceding claims and with a fourth sub-device (14) for optically checking the quality of the sintered connection of the second joining group (101), wherein the check is carried out by means of the control device (40) for checking an optical property of a control section (300) of the cover film (30) that is aligned with the sintered metal (114), wherein either the homogeneity of the color spectrum of a surface (310) of the control section (300) is determined by means of a spectrally resolving camera during the check, and the quality of a sintered connection is defined as not meeting the target,if the color spectrum of the control section (300) deviates from a target color spectrum or from the color spectrum of a reference section by at least one tolerance value, or if the homogeneity of the contour of the surface (310) of the control section (300) is determined by means of an interferometer during the control and the quality of a sintered connection is defined as not meeting the target value, if the contour of the control section (300) deviates globally or locally from a target value or from the contour of a reference section by at least one tolerance value.

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