CN216389353U - A power module with stepped pads formed on a ceramic substrate - Google Patents

Abstract

The utility model discloses a ceramic substrate element with metal heat conduction bump pads, which is provided with at least one high-heating crystal grain, and comprises: a ceramic substrate body having an upper surface and a lower surface opposite to the upper surface; and at least one metal bump pad comprising a thin bonding layer having a thickness of 10 to 300 μm and bonded to the upper surface, the thin bonding layer having a first coefficient of thermal expansion greater than that of the ceramic substrate body; and a die bonding layer which is combined with the thin bonding layer and used for welding and combining the crystal grains, wherein the die bonding layer has a second thermal expansion coefficient which is larger than that of the ceramic substrate body, so that the thermal stress fracture of the interface of the thin bonding layer and the ceramic substrate is relieved.

Description

A power module with stepped pads formed on a ceramic substrate

technical field

The utility model relates to a power supply module with a ceramic substrate, in particular to a power supply module with stepped pads formed on the ceramic substrate.

Background technique

Compared with traditional printed circuit boards, ceramic substrates have the advantages of good heat dissipation, thin thickness, small size, high temperature resistance and good reliability, and are often used in electronic components such as high-power chips or chips. The most common ceramic substrate materials are direct copper (Dircet Bonded Copper, DBC) substrates made of aluminum oxide (Aluminium Oxide, Al ₂ O ₃ ) or direct aluminum (Dircet Bonded Aluminum, DBA) substrates. The thickness is mostly between 200 and 300 microns. When the thickness of copper or aluminum is greater than 300 microns, it may cause the cracking of the bonding interface due to the temperature change of the substrate caused by the manufacturing process or the installation of high heat-generating components.

With the increasing power of die and chips, the metal pads, lines or conductive layers on the ceramic substrate need to be thicker to meet the needs of high-power components, especially in the case of power modules, which require ceramic substrates for heat dissipation . However, the coefficient of thermal expansion and coefficient of linear expansion of the ceramic substrate and the metal layer are very different from each other. When the temperature is 20 degrees, the thermal expansion coefficients of metal copper and aluminum are 16.5 and 23ppm/K. , while the ceramic materials alumina, aluminum nitride and silicon nitride are about 7, 4.5 and 3.5 ppm/K respectively. When the difference in thermal expansion coefficient between the ceramic substrate and the combined metal layer is too large, the interface between the metal and the ceramic substrate is easy to Problems with cracking, warping or deformation also entail the risk of damage to the contacts due to thermal stress.

Therefore, how to increase the thickness of the metal circuit layer on the one hand, so that the temperature difference can be distributed in the thicker metal layer, reduce the temperature drop per unit height, and make the ceramic substrate suitable for high-power die and chips; The interface of the ceramic substrate is cracked by thermal stress, making the application of high-power electronic components feasible, and at the same time, it can provide various thicknesses of metal pads according to different customer requirements to provide manufacturing flexibility, which is the purpose of the present invention.

Utility model content

In view of the above-mentioned deficiencies of the prior art, according to the embodiments of the present utility model, it is desirable to provide a power module with stepped pads formed on a ceramic substrate, aiming to achieve the following purposes: layer metal structure and reduce the thickness of the thin bonding layer, which greatly reduces the risk of cracking at the interface between the metal circuit layer and the ceramic substrate; (2) the ceramic substrate can be applied to electronic components such as high-power die or chips; The particles or chips can be placed on the ceramic substrate, and the heat can be smoothly conducted out.

According to an embodiment, the present invention provides a power module with step pads formed on a ceramic substrate, comprising: a first ceramic substrate having an upper surface and at least one metal step pad, wherein the metal step The step pad includes: a thin bonding layer bonded to the upper surface and having a thickness of 10 to 300 microns, having a first thermal expansion coefficient, wherein the first thermal expansion coefficient is greater than the thermal expansion coefficient of the first ceramic substrate; and a The die-bonding layer combined with the thin bonding layer has a setting surface away from the direction of the first ceramic substrate, wherein the projected area of the die-bonding layer in the thickness direction is smaller than that of the thin bonding layer, thereby slowing the connection between the thin bonding layer and the first ceramic substrate. The interface of a ceramic substrate is cracked by thermal stress; at least one high-power circuit element has a pair of input and output electrodes respectively located on a top surface and a bottom surface, and the high-power circuit element is electrically connected to the above-mentioned setting surface with the input and output electrodes on the bottom surface; the number Corresponding to the metal spacer unit of the above-mentioned high-power circuit element, each of the foregoing metal spacer units is respectively thermally and electrically conductively disposed on the above-mentioned top surface in-out electrodes of the above-mentioned corresponding high-power circuit components, and is formed in the thickness direction not exceeding the above-mentioned top surface In-out electrodes and a second ceramic substrate parallel to the first ceramic substrate, having a metal corresponding pad, wherein the metal corresponding pad is electrically and thermally bonded to the metal spacer unit opposite to the side of the high-power circuit element.

Compared with the prior art, the power supply module with step pads formed on the ceramic substrate of the present invention uses the metal bump pads of the multi-layer structure to make the interface thickness of the thin bonding layer connected to the ceramic substrate within a certain range. Reduce the probability of thermal stress cracking of the interface, thereby improving the yield rate and prolonging the service life, and using the multi-layer metal structure, the ceramic substrate is combined with a thicker metal bump pad, so that the temperature difference within the unit thickness is reduced. It is reduced, thereby protecting the interface of metal and ceramics, prolonging the service life, and making it more feasible to install high-power circuit components with high heat generation.

Description of drawings

1 is a schematic side view of a first preferred embodiment of a power module with stepped pads formed on a ceramic substrate of the present invention.

2 is a schematic side view of a second preferred embodiment of a power module with stepped pads formed on a ceramic substrate of the present invention.

3 is a schematic side view of a third preferred embodiment of a power module with stepped pads formed on a ceramic substrate of the present invention.

Among them: 1, 1', 1" are the first ceramic substrate; 11 is the upper surface; 2, 2', 2" are metal step pads; 21, 21' are thin bonding layers; 22, 22' are die-bonding 221 is the setting surface; 23" is the wire bonding step pad; 3, 3', 3" are high-power circuit components; 31, 31', 31" are the input and output electrodes; 311 is the bottom surface; 312" is the top surface; 32" is the control electrode; 4, 4', 4" are metal spacer units; 41' is the thin spacer layer; 42' is the spacer solid crystal layer; 5, 5' are the metal corresponding pads; ' is a thin corresponding layer; 52' is a corresponding step layer; 6 and 6' are the second ceramic substrate; 7'' is a wire bonding.

Detailed ways

The present utility model will be further described below in conjunction with the accompanying drawings and specific embodiments. These embodiments should be understood as only for illustrating the present invention and not for limiting the protection scope of the present invention. After reading the contents recorded in the present utility model, those skilled in the art can make various changes or modifications to the present utility model, and these equivalent changes and modifications also fall within the scope defined by the claims of the present utility model.

first preferred embodiment

As shown in FIG. 1 , in a power module provided with step pads formed on a ceramic substrate provided by a first preferred embodiment of the present invention, the first ceramic substrate is an example of a high thermal conductivity ceramic substrate made of aluminum nitride. , has an upper surface 11 and at least one metal step pad 2 , wherein the metal step pad 2 includes a thin bonding layer 21 and a solid crystal layer 22 . In this embodiment, copper is bonded to the upper surface 11 by sputtering, and then thickened to form a thin bonding layer 21 with a thickness of 10 to 300 microns, wherein the thermal expansion coefficient of copper is about 17ppm/K, while a general ceramic substrate The thermal expansion coefficient of materials (such as aluminum oxide, aluminum nitride, and silicon nitride) is about 4-7 ppm/K. By providing a thin bonding layer 21 with a thinner thickness, it can exert better ductility; then use a photoresist After developing and electroplating copper for the second time, a die-bonding layer 22 is further formed on the thin bonding layer 21 for die bonding. The upper surface of the first ceramic substrate 1 in the direction is defined as a setting surface 221 . When the die-bonding layer 22 is thermally expanded, on the one hand, the temperature difference will be distributed in the thicker metal layer, so that the temperature difference per unit thickness is reduced; The bonding interface of the ceramic substrate is not easily broken due to thermal stress.

The high-power circuit element 3 in this embodiment is exemplified as a 1200V automotive-grade SiC power chip from STMicroelectronics, which is soldered and fixed to the setting surface 221 of the die-bonding layer 22 by means of surface mounting, for example. The high-power circuit element 3 in this embodiment includes a bottom surface 311 , an input and output electrode 31 on the bottom surface 311 welded on the setting surface 221 of the die-bonding layer 22 , a top surface 312 , and an input and output electrode 31 on the top surface 312 . Since the current of such high-power circuit components can even reach hundreds of amps, once there is a slight impedance in the transmission path, it will cause great heat. Therefore, in this embodiment, the welding is performed by pressure and heat fusion. achieved.

Next, a metal spacer unit 4 exemplified by copper is welded to the input and output electrodes 31 of the top surface 312 of the high-power circuit element 3 after the surface is subjected to a nano-silver sintering process. On the one hand, the projection of the metal spacer unit 4 in the height direction does not exceed the input and output electrodes 31 of the top surface 312 of the high-power circuit element 3 . Especially in this embodiment, the corners of the metal spacer unit 4 respectively form arc-shaped chamfers, so that whether it is the heating during welding or the temperature rise caused by the passage of a large current during operation, and the repeated temperature difference in temperature reduction. Therefore, the stress between the interfaces caused by thermal expansion and cooling contraction can be effectively dispersed by the arc-shaped chamfer, thereby avoiding the interface peeling caused by thermal stress. Finally, the second ceramic substrate 6 forms metal corresponding pads 5 such as copper metal through the corresponding metal spacer unit 4 , and is welded to the metal spacer unit 4 .

Since the thickness of the thin bonding layer 21 of the metal step pad 2 is relatively thin, in the manufacturing process such as surface mounting or the subsequent operation of the electric vehicle, even if the ambient temperature increases, the degree of thermal expansion between the ceramic substrate and the thin bonding layer 21 is different. If it is larger, the flexibility of the thin bonding layer 21 can still fully absorb the difference in expansion of each other, so as to ensure a good bonding relationship. On the other hand, the thickness of the die-bonding layer 22 can be reduced to reduce the temperature gradient per unit distance and avoid the trouble caused by the temperature difference.

Second Preferred Embodiment

As shown in FIG. 2 , in a power module provided with step pads formed on a ceramic substrate provided by a second preferred embodiment of the present invention, the same parts as those in the previous preferred embodiment will not be repeated here. Elements also use similar names and numbers, and only the differences are explained. The metal spacer units 4' and the metal corresponding pads 5' in this embodiment have similar structures to the metal step pads 2' on the first ceramic substrate 1'. The risk of interface debonding caused by differences in buffer expansion coefficients. The metal corresponding pad 5' includes a thin corresponding layer 51' bonded to the second ceramic substrate 6' and having a thickness of 10 to 300 microns, having a thermal expansion coefficient greater than that of the second ceramic substrate 6', and a The corresponding step layer 52 ′ combined with the thin corresponding layer 51 ′ is electrically and thermally bonded to the metal spacer unit 4 ′ opposite to the side of the high-power circuit element 3 ′, wherein the projected area of the corresponding step layer 52 ′ in the thickness direction is less than The thin corresponding layer 51 ′ is used to reduce the thermal stress cracking of the interface between the thin corresponding layer 51 ′ and the second ceramic substrate 6 ′; and the metal spacing unit 4 ′ includes a The thin spacer layer 41 ′ and a spacer die-bonding layer 42 ′ combined with the thin spacer layer 41 ′ are electrically and thermally bonded to the top surface 312 ′ of the corresponding high-power circuit element 3 ′ and the access electrodes 31 ′, wherein the spacer The projected area in the thickness direction of the die-bonding layer 42 ′ is smaller than the thin spacer layer 41 ′ and the top surface 312 ′ of the corresponding high-power circuit element 3 ′. In this way, the metal spacer unit 4' and the metal corresponding pad 5', like the thin bonding layer 21' and the die-bonding layer 22' of the metal step pad 2', all form a stepped structure. The principle avoids cracking of the bonding interface due to thermal stress.

Third Preferred Embodiment

As shown in FIG. 3 , in a power module provided with step pads formed on a ceramic substrate provided by a third preferred embodiment of the present invention, the same parts as those in the previous preferred embodiment will not be repeated here, and similar components Similar names and labels are also used, and only the differences are explained. The stepped structure of the metal step pads 2" in this embodiment is not only used to carry high-power circuit components 3", but also serves as an independent pad for wire bonding 7". The first ceramic in this embodiment The difference between the metal step pads 2 ″ set on the substrate 1 ″ and the aforementioned preferred embodiment is that the metal step pads 2 ″ further include wire bonding step pads 23 ″, which are connected to the metal step pads 23 ″. The pad 2" has the same stepped structure with the same upper narrow and lower width, wherein the above-mentioned bonding wire 7" is electrically connected from the above-mentioned control electrode 32" corresponding to the above-mentioned high-power circuit element 3" on the above-mentioned top surface 312" to the wire bonding step pad. 23"; the metal spacer unit 4" is the same as the above-mentioned first preferred embodiment, and is arranged on the input and output electrodes 31" of the above-mentioned top surface 312" of the high-power circuit element 3".

To sum up, the power supply module provided with the step pads formed on the ceramic substrate of the present invention can reduce the temperature difference per unit thickness by using the thickness of the solid crystal layer through a plurality of metal step pads with a double-layer structure. , and the use of a structure in which the area of the thin bonding layer exceeds the thickness of the solid crystal layer to show the ductility of the thin bonding layer and alleviate the problem of cracking of the bonding interface between the metal circuit layer and the ceramic substrate, and those with ordinary knowledge in this technical field can request In the space between the metal step pads, the metal corresponding pads or the metal spacer units, that is, the space between the high-power components and the double-sided substrate, it is possible to freely design a double-layer or multi-layer stepped structure without hindering the present invention. Implementation Effect.

Claims (7)

1. A power supply module with step pads formed on a ceramic substrate is characterized in that, comprising: A first ceramic substrate has an upper surface and at least one metal step pad, wherein the metal step pad includes: a thin bonding layer bonded to the upper surface and having a thickness of 10 to 300 microns, having a first thermal expansion coefficient, wherein the first thermal expansion coefficient is greater than the thermal expansion coefficient of the first ceramic substrate; and A die-bonding layer combined with the thin bonding layer has a setting surface away from the direction of the first ceramic substrate, wherein the projected area of the die-bonding layer in the thickness direction is smaller than that of the thin bonding layer, thereby slowing down the connection between the thin bonding layer and the above-mentioned thin bonding layer. The interface of the first ceramic substrate is cracked by thermal stress; At least one high-power circuit element has a pair of input and output electrodes respectively located on a top surface and a bottom surface, and the high-power circuit element is electrically connected to the above-mentioned setting surface by the input and output electrodes on the bottom surface; The number corresponds to the metal spacer units of the above-mentioned high-power circuit element, each of the foregoing metal spacer units is respectively thermally and electrically conductively disposed on the above-mentioned top surface in-out electrodes of the above-mentioned corresponding high-power circuit element, and formed in the thickness direction not more than the above-mentioned top surface in-out electrodes the projection of the electrodes; and A second ceramic substrate parallel to the first ceramic substrate has a metal corresponding pad, wherein the metal corresponding pad is electrically and thermally bonded to the metal spacer unit opposite to the side of the high-power circuit element. 2. The power module of claim 1, wherein the metal corresponding pads comprise: a thin corresponding layer bonded to the second ceramic substrate and having a thickness of 10 to 300 microns, having a second thermal expansion coefficient, wherein the second thermal expansion coefficient is greater than the thermal expansion coefficient of the second ceramic substrate; and A corresponding step layer combined with the thin corresponding layer, electrically and thermally bonded to the metal spacer unit opposite to the side of the high-power circuit element, wherein the thickness direction projected area of the corresponding step layer is smaller than the thin corresponding layer, thereby reducing the above-mentioned The interface between the thin corresponding layer and the second ceramic substrate is cracked by thermal stress. 3. The power module of claim 1, wherein the metal spacer unit comprises: a thin spacer layer bonded to the metal corresponding pads; and A spacer die-bonding layer combined with the thin spacer layer, electrically and thermally bonded to the top surface in-out electrodes of the corresponding high-power circuit element, wherein the projected area of the spacer die-bonding layer in the thickness direction is smaller than the thin spacer layer and the corresponding The above-mentioned top surface of high power circuit components. 4 . The power module of claim 1 , wherein the thin bonding layers of the step pads are made of titanium layer and copper layer. 5 . 5 . The power module of claim 1 , wherein the material of the die-bonding layer of the metal step pads is copper. 6 . 6 . The power module of claim 1 , wherein the metal spacer unit is made of copper plated with silver. 7 . 7 . The power module according to claim 3 , wherein the thin spacer layer of the metal spacer unit is made of titanium layer and copper layer. 8 .

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