Circuit carrier with multiple layers of sintered paste molded part

Abstract

Circuit carrier (1) with a sintered paste molded part (18, 19), wherein the sintered paste molded part (18, 19) is printed on the circuit carrier (1), characterized in that the sintered paste molded part (18, 19) is produced by at least two applications of sintered paste (15), in particular by squeegeeing (6) into at least one recess of a stencil (5), wherein each application quantity (8) of the sintered paste (15) is dried to be dimensionally stable (8') before a further application of the sintered paste (15).

Description

State of the art

[0001] The invention relates to a circuit carrier. The circuit carrier has a sintered paste molded part which is printed onto the circuit carrier.

[0002] From DE 101 20 117 A1 a squeegee system with a squeegee holder and a squeegee blade attached to the squeegee holder for applying a printable material to a surface is known, with which very good printing results can be achieved even with small structures with little effort.

[0003] German patent application DE 10 2017 206 925 A1 discloses a method for producing a three-dimensional solder structure on a substrate. In this method, a first layer of solder paste is applied to the substrate by means of a first printing process. Immediately afterwards, in a second printing process, a second layer of solder paste is applied to the still-moist first layer ("wet-on-wet"), whereby the two layers mix to form a homogeneous solder deposit.

[0004] Utility model CN ​​2 07 183 299 U discloses a printing device and a method for applying solder paste, in which two stencils with differently shaped openings are used. By using multiple stencils, it is possible to create solder paste deposits of varying thicknesses at different positions on a printed circuit board in a sequential printing process. The invention aims to control the paste height through the geometry of the respective stencil opening, rather than filling the same opening multiple times.

[0005] US Patent 2019 / 0059162 A1 describes a method for applying conductive paste in which, in a first step, an initial layer of paste is applied and then partially cured or dried. A second layer of paste is then printed onto this partially cured first layer. This procedure is intended to reduce paste adhesion to the squeegee or stencil and improve print quality. The primary goal is to improve the printing process itself, not to deliberately create a specific geometric shape for the paste deposit.

[0006] Japanese patent application JP 2015-153997 A discloses a method for filling a cavity in a substrate with a conductive paste. To compensate for volume shrinkage caused by solvent outgassing, the cavity is initially partially filled with paste. This initial amount of paste is then heated to reduce its volume before additional paste is added to completely fill the cavity. The process thus enables void-free filling of a depression already present in the substrate. Disclosure of the invention

[0007] According to the invention, the sintered paste molded part is produced by applying sintered paste at least twice, in particular by squeegeeing it into at least one recess of a template, wherein each application of sintered paste is dried to a dimensionally stable state before a further application. Advantageously, the sintered molded part produced in this way by intermediate drying can have right-angled edges and flat surfaces. Advantageously, sintered paste molded parts with particularly fine structures can thus be produced on the circuit carrier.

[0008] In a preferred embodiment, the circuit carrier comprises at least one component, particularly an electronic component, especially a semiconductor component, semiconductor chip, leadframe, or cooling element, which is sintered to the circuit carrier by means of the sintered component. For example, the semiconductor component is formed by a semiconductor switch, in particular a field-effect transistor. For example, a power semiconductor, in particular a power semiconductor switch with a gate terminal, can be sintered to the circuit carrier in this way, so that the sintered component for the gate terminal can also be designed with a reliable electrical connection between the circuit carrier and the power semiconductor with the gate terminal.

[0009] In an advantageous embodiment, the component is formed by an assembly comprising an intermediate circuit carrier and at least one component connected to the intermediate circuit carrier. The intermediate circuit carrier has at least one electrical connection on one mounting side, which is designed for sintering with the circuit carrier. Advantageously, a connection arrangement can be formed in which an assembly, for example forming a driver, is sintered with the circuit carrier. The assembly can thus be sintered with the circuit carrier together with a power semiconductor.

[0010] The invention also relates to a method for producing a sintered bond between a component, particularly an electronic component, especially a semiconductor, a semiconductor chip, or a cooling element designed to dissipate waste heat, a sheet metal part, particularly a stamped part, also called a leadframe, and a circuit carrier. In this method, sintering paste is applied to the circuit carrier using a squeegee and a stencil. The sintering paste is pressed into recesses in the stencil by passing the squeegee over the stencil, thus producing at least one sintered part, or several sintered paste parts, on the circuit carrier.

[0011] Preferably, in this method, at least one sintered part is produced by repeatedly, and in particular at least twice, applying the sintering paste into the recesses with a doctor blade. The sintering paste is dried before each application, preferably by introducing heat into the paste, particularly by means of heat radiation or warm air, or by vacuum drying. Advantageously, a sintered paste part with a cubic shape can be produced in this way. It has been observed that when sintering paste is applied simply with a doctor blade and a template, its viscous properties cause the paste to take on a rising shape. This rising shape is created by the forward movement of the sintering paste with the doctor blade while it is being applied to the recess in the template. The applied sintering paste thus exhibits a depression at the entry point and a hump at the exit point of the doctor blade.It was further discovered that after drying or partially drying, the sintering paste can be repeatedly applied using the same stencil, which can remain on the circuit board, and any remaining gaps in the recesses of the stencil can be filled.

[0012] Preferably, in this process, a dimensionally stable boundary layer is formed on the sintering paste by drying, onto which a further quantity of sintering paste can be applied. Advantageously, a dimensionally stable sintered paste molded part can thus be efficiently formed. In a preferred embodiment, the sintering paste is applied at least three or four times, or only three or four times. Advantageously, sufficiently good results regarding the perpendicularity and flatness of the surfaces of the sintered parts have been observed with at least three or four applications of the sintering paste.

[0013] In a preferred embodiment of the method, the sintering paste is applied successively in different directions using a squeegee. Advantageously, this allows for the production of a uniformly shaped sintered part.

[0014] In a preferred embodiment, the circuit carrier is a printed circuit board, in particular a fiber-reinforced one. The printed circuit board is, for example, an FR4 printed circuit board.

[0015] In a preferred embodiment, the circuit carrier is a ceramic circuit carrier, in particular an LTCC circuit carrier, an HTCC circuit carrier, an AMB circuit carrier, or a DCB circuit carrier (DCB = Direct-Copper-Bonded). Advantageously, this allows power semiconductors with particularly small connections, such as control connections, to be reliably sintered onto the ceramic circuit carrier.

[0016] In a preferred embodiment, the sintering paste contains silver and / or copper. Advantageously, the sintered compound can thus exhibit good electrical conductivity.

[0017] Preferably, the sintering paste contains a solvent that is designed to evaporate or outgas from the sintering paste during drying. The solvent is preferably a terpineol, for example, alpha-terpineol. After drying, the sintering paste preferably contains only the metal particles, which are then bonded or baked together, thus forming a solid substrate for further application of the sintering paste.

[0018] Preferably, the sintering paste is heated for drying. Heating can be achieved, for example, by applying heat radiation or warm air. Advantageously, this allows the solvent to be driven out of the sintering paste in a cost-effective manner. The dried sintering paste is preferably low in solvent or solvent-free.

[0019] In another embodiment, the sintering paste is subjected to a vacuum for drying – preferably in addition to heating. Advantageously, the solvent can thus be driven out of the sintering paste quickly at lower temperatures.

[0020] Preferably, the sintering paste is dried to such a dimensionally stable state between reapplications that the sintering paste is not deformed when moist, especially undried, sintering paste is reapplication.

[0021] Preferably, the dried sintering paste exhibits a solvent loss of more than 50 percent, more preferably more than 90 percent, or particularly preferably 100 percent, in each case based on the solvent content before drying. Thus, after drying, the sintering paste retains only a residual proportion of the original solvent content before drying, or is solvent-free. Advantageously, the viscosity of the sintering paste can be generated by the drying process in such a way that the sintering paste does not smear when fresh, solvent-containing, low-viscosity sintering paste is reapplied with a doctor blade.

[0022] In a preferred embodiment of the method, the sintered part has adjacent surfaces arranged at right angles to each other. More preferably, the sintered part has a flat surface designed for the insertion of an electrical contact of a component. Advantageously, this allows for the production of a sintered material with high quality and a low failure rate.

[0023] The invention will now be described below with reference to figures and further exemplary embodiments. Further advantageous embodiments result from a combination of the features described in the dependent claims and in the figures. Fig. Figure 1 shows an embodiment of a method for printing on a circuit carrier, in which sintered paste is applied to a circuit carrier using a squeegee and a stencil; Fig. Figure 2 shows a process step in which the [unclear text] in the Fig. In step 1, the sintered paste shown is dried using heat, especially heat radiation; Fig. Figure 3 shows a process step in which the following is considered - as in Fig. 2 shown - dried sintering paste, a further layer of sintering paste is applied, which at least partially or completely fills the gaps remaining in the template after application in step 1; Fig. Figure 4 shows a circuit carrier with sintered paste molded parts, which are manufactured according to the specifications in the Fig. 1, Fig. 2 to Fig. The 3 steps shown on the circuit board are generated.

[0024] Fig. Figure 1 shows an embodiment of a method for printing a circuit carrier 1 with a sintering paste 15. The sintering paste 1 comprises, for example, silver particles with a diameter between 0.1 and 40 micrometers. The circuit carrier 1 has an electrically insulating layer 4, in particular a ceramic layer. The circuit carrier 1 is, for example, designed as an AMB circuit carrier (AMB = Active-Metal-Brazed). In another embodiment, the circuit carrier 1 can be designed as an LTCC circuit carrier (LTCC = Low-Temperature Cofired Ceramics) or as an HTCC circuit carrier (HTCC = High-Temperature Cofired Ceramics). The circuit carrier 1 also has two electrically conductive layers 2 and 3, each of which is connected to the circuit carrier 1, in particular to the electrically insulating layer 4. The electrically conductive layers 2 and 3 are, for example, designed as copper layers. At the in Fig. In the method shown in Figure 1, a template 5 is placed on the circuit carrier 1 such that recesses in the template 5, which correspond in shape to the electrically conductive layers 2 and 3, form an opening to the electrically conductive layers 2 and 3. The remaining circuit carrier 1 is covered by the template 5. In the procedure shown in Figure 1, the circuit carrier 1 is covered by the template 5. Fig. In the method shown in Figure 1, the sintering paste 15 is removed from the stencil 5 using a squeegee 6, thus creating a sintering paste layer 7 on the electrically conductive layer 2 and a sintering paste layer 8 on the electrically conductive layer 3. The sintering paste layer 8 represents a quantity of the sintering paste applied.

[0025] In this embodiment, the electrically conductive layer 3 is smaller in width—particularly its lateral extent on the circuit carrier 1—than the electrically conductive layer 2. The sintered paste application, formed by the sintered paste layer 8, is uneven in this embodiment and has a recess 9, in particular a defect, where the sintered paste 15 is not completely applied. In the application direction, a bump 10 is formed when the sintered paste 15 is applied, where the level of the sintered paste 15 in the sintered paste layer 8 is higher than in the area of ​​the recess 9. During subsequent sintering with an electrical connection of a semiconductor, particularly a power semiconductor, the sintered paste layer 8 may not be sufficient to form adequate electrical contact with the semiconductor's terminal.

[0026] Fig. Figure 2 shows a further process step in which the Fig. The applied sintering paste layers 7 and 8 are dried by means of heat rays 11. The dried sintering paste layers 7' and 8' produced in this way are sufficiently hard and / or compact after drying by means of the heat rays that further sintering paste can be applied to the recess 9.

[0027] Fig. Figure 3 shows a further process step in which sintering paste 15 is applied to the remaining recesses in the template 5 using the squeegee. Fig. 3 shows the one in Fig. In step 2, the dried sintering paste layer 7' and the dried sintering paste layer 8' are shown, onto which the sintering paste layer applied in the subsequent application step is applied. A sintering paste layer 12 is applied to the dried sintering paste layer 7', so that the recess in the stencil 5, which corresponds to the electrically conductive layer 2, is almost completely or completely filled. A sintering paste layer 13 is applied to the dried sintering paste layer 8', so that the recess in the stencil 5, which corresponds to the electrically conductive layer 3, is almost completely filled. In step 3, unlike in Fig. 3 shown - the squeegee direction of the squeegee 6 is opposite to the squeegee direction with which the sinter paste layers 7 and 8 were applied.

[0028] It was discovered that when applying sintering paste in the direction of the squeegee, a slight bulge forms towards the end of the recess in the stencil. This can be used when applying another layer of sintering paste to almost completely fill a recess in just two application steps, thus using two layers. In this process, the in Fig. The drying step of the sintering paste layers 12 and 13 shown in Figure 2 is repeated, and at least one or two further sintering paste layers are applied. Before each further application of a sintering paste layer, the previously applied sintering paste layer is dried by means of the heat rays 11. In this way, the recess in the template can be filled sufficiently completely so that a top surface 16 facing a component of the last applied sintering paste layer 13 is sufficiently flat. A boundary layer 17 is formed between the sintering paste layers 8' and 13, which extends between the dried sintering paste layer 8' and the still undried, freshly applied sintering paste layer 13. The boundary layer 17 is sufficiently stable so that the sintering paste layer 8' cannot be deformed when the sintering paste layer 13 is reapplied.

[0029] Fig. Figure 4 shows the circuit carrier 1 with sintered paste molded parts 18 and 19, which are arranged according to the specifications in the Fig. 1, Fig. 2 and Fig. The three process steps shown were produced. These process steps include applying, in particular spreading with a spatula, sintered paste onto the circuit carrier 1 in recesses of the Fig. 1, Fig. 2 and Fig. 3 shown template, where the sintering paste is applied between two successive applications - as in Fig. 2 shown - is dried using heat rays 11.

[0030] The sintered paste component 18 is produced on the electrically conductive layer 2 and comprises the dried sintered paste layer 7' and the sintered paste layer 12' applied to the dried sintered paste layer 7' and dried after application. The sintered paste component 19 is produced on the electrically conductive layer 3 and comprises the dried sintered paste layer 8' and the sintered paste layer 13' applied to the dried sintered paste layer 8' and dried after application. The sintered paste component 19 produced on the electrically conductive layer 3 has, for example, a minimum width dimension of between 0.5 and 1 millimeter. A surface 26 of the sintered paste component 19 is advantageously formed flat by the multiple application of sintered paste 15, so that a semiconductor component can make seamless contact with the sintered paste component despite its small dimensions.

[0031] Fig. 5 shows a contact arrangement 20 encompassing the in Fig. Figure 4 shows a circuit carrier 1 and a semiconductor switch 21. The semiconductor switch, in particular a field-effect transistor or IGBT (IGBT = Insulated-Gate Bipolar Transistor), is placed onto the sintered paste molded parts 18 and 10 such that its switching terminal 23, in particular its source terminal, contacts the sintered paste molded part 18 and its control terminal 22, in particular its gate terminal, contacts the sintered paste molded part 19. The semiconductor switch can be sintered together with the circuit carrier 1 under pressure 24 and heat 25, whereby the sintered paste molded parts 18 and 19 form a metallurgical bond between the terminals 22 and 23 of the semiconductor switch and the electrically conductive layers 2 and 3 of the circuit carrier 1.

Claims

[1] Circuit carrier (1) with a sintered paste molded part (18, 19), wherein the sintered paste molded part (18, 19) is printed on the circuit carrier (1), characterized by , that the sintered paste molded part (18, 19) is produced by at least two applications of sintered paste (15), in particular by squeegeeing (6) into at least one recess of a template (5), wherein each application quantity (8) of the sintered paste (15) is dried (8') to be dimensionally stable before a further application of the sintered paste (15). [2] Circuit carrier (1) according to claim 1, characterized by , that the circuit carrier (1) comprises at least one electronic component, in particular a semiconductor component (21), which is sintered to the circuit carrier (1) by means of the sinter paste mold part (18, 19). [3] Method for producing a sintered connection between an electronic component (21), in particular a semiconductor switch, and a circuit carrier (1), in which sintering paste (15) is applied to a circuit carrier (1) by means of a squeegee (6) and a stencil (5), in which the sintering paste (15) is pressed into recesses of the stencil (5) by sweeping over the stencil (5) with the squeegee (6), and thus at least one sintering paste molded part (18, 19) is produced on the circuit carrier (1), characterized by , that that at least one sintered paste molded part (18, 19) is produced by repeatedly, in particular at least twice, applying the sintered paste (15) into the recesses, wherein the sintered paste (15) is dried by applying heat to the sintered paste (15) before each reapplication, in particular by applying the sintered paste (6). [4] Method according to claim 3, characterized by , that the sintering paste (15) is applied successively in different directions. [5] Method according to one of claims 3 or 4, characterized by, that during drying a solvent is driven out of the sintering paste (15), whereby the dried sintering paste (15) is solvent-free. [6] Method according to any one of claims 3 to 5, characterized by , that the circuit carrier (1) is a ceramic circuit carrier. [7] Method according to any one of claims 3 to 6, characterized by , that an electronic component (21), in particular a semiconductor or sheet metal part, is placed on the sintered paste molded part (1) thus produced on the circuit carrier (1) and is sintered with the circuit carrier (1) with the aid of pressure (24) and / or heat (25). [8] Method according to any one of claims 3 to 7, characterized by , that the sintering paste (15) contains silver and / or copper. [9] Method according to any one of claims 3 to 8, characterized by , that the sintered paste molded part (18, 19) has a surface (26) designed for joining with the component (21), which is flat. [10] Method according to any one of claims 3 to 9, characterized by that the sintering paste (15) is applied at least three or four times. Registered office: Stuttgart, Commercial Register: Stuttgart District Court, HRB 14000;

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