Patent Description:
The thermal interface material serves to eliminate large air gaps or other gas-filled voids (which act as thermal insulator) from the interface area between the heat exchange surface and the heat sink so as to maximize the heat transfer. The thermal conductivity of conventional thermal interface material (e.g. from <NUM> W/(m-K) to <NUM> W/(m·K) at a temperature of <NUM>) is greater than the thermal conductivity of the air/gas in the gas-filled spaces, but poor compared to the thermal conductivity of conventional heat sinks. For instance, many conventional heat sinks are produced from aluminum or an aluminum alloy and have, depending on the purity or alloy composition, a thermal conductivity of up to <NUM> W/(m·K). Therefore, it is desirable to keep the layer of thermal interface material as thin as possible.

However, a real heat exchange surface is uneven or becomes uneven during the assembly of the electronic module so that one or more "remote" sections of the heat exchange surface are disposed more distant from the heat sink than other sections. Irrespective of whether or not the space between the heat sink and a remote section is filled with thermal interface material or not, the comparatively large distance between the remote section and the heat sink increases the thermal transition resistance between the heat exchange surface and the heat sink.

<CIT> discloses an electronic power module having an IGBT die and a diode die disposed between and electrically interconnected by two DCB type substrates. Several electrical coupling regions between each die and each substrate and between the substrates are formed by sintering a dried paste that includes an electrically and thermally conductive material like silver.

<CIT> discloses a semiconductor device that includes an insulating substrate, a semiconductor element secured to a top surface of the insulating substrate, a case formed of resin and having a frame portion surrounding the semiconductor element, a metal support located above the insulating substrate and having an end secured to the frame portion, a holding-down portion extending downward from the metal support so as to prevent upwardly convex bending of the insulating substrate, and an adhesive bonding the insulating substrate and the case together. Therein, the insulating substrate can be pressed downward and bent into a downwardly convex shape.

There is a general need for an electronic module assembly that allows for a low thickness of a thermal interface material between an electronic module and a heatsink.

One aspect relates to a method for producing an electronic module assembly. In that method, a curable first mass extending between a substrate assembly and a lid of a module housing is cured while a circuit carrier of the substrate assembly is at a temperature of at least a first temperature, wherein the circuit carrier comprises a dielectric insulation carrier, and a first substrate metallization layer attached to the dielectric insulation carrier, and wherein the substrate assembly further comprises at least one semiconductor chip joined with the first substrate metallization layer. Between a side wall of the module housing and the circuit carrier, an adhesive connection is formed by curing a curable second mass. Subsequent to curing the curable first mass, the circuit carrier is cooled down to below a second temperature lower than the first temperature. The cured first mass is located distant from the edges of the circuit carrier and opposite a heat exchange surface of the circuit carrier, the circuit carrier is heated from an initial state to a heated state in which the temperature of the circuit carrier is at the temperature of at least the first temperature, the circuit carrier bending due to the temperature rise, the curable first mass is cured when the circuit carrier is in the bent state, the curable first mass extending between the module housing and the substrate assembly and bridging a gap between the module housing and the substrate assembly which increases when the circuit carrier bends due to the temperature rise, and the cured first mass fixing said gap so that the circuit carrier remains in the bent state after cooling down.

A further aspect relates to an electronic module assembly. The electronic module assembly includes a substrate assembly, wherein the substrate assembly comprises a circuit carrier, wherein the circuit carrier comprises a dielectric insulation carrier and a first substrate metallization layer attached to the dielectric insulation carrier, and wherein the substrate assembly further comprises at least one semiconductor chip joined with the first substrate metallization layer. The electronic module assembly further includes a module housing connected to the circuit carrier by an adhesive connection formed by a second cured mass between a side wall of the module housing and the circuit carrier, a cured first mass extending between the substrate assembly and a lid of the module housing and bridging a gap between the module housing and the substrate assembly, and a heat exchange surface formed by a surface of the circuit carrier facing away from the cured first mass. The cured first mass is located distant from the edges of the circuit carrier. The circuit carrier is bent away from the module housing and is fixed in the bent state by the cured first mass extending across and fixing said gap between the module housing and the substrate assembly, and at least in a region of the heat exchange surface opposite the cured first mass is convex.

In the following detailed description, reference is made to the accompanying drawings. The drawings show specific examples in which the invention may be practiced. It is to be understood that the features and principles described with respect to the various examples may be combined with each other, unless specifically noted otherwise.

<FIG> schematically illustrates a substrate assembly <NUM> and a module housing <NUM>. The substrate assembly <NUM> includes a circuit carrier <NUM> (also referred to as "substrate") with a first surface 2t and a second surface 2b opposite the first surface 2t. <FIG> illustrates a cross-section of the module housing of <FIG> in a cross-sectional plane E1-E1. The cross-section of the module housing <NUM> of <FIG> is taken in a cross-sectional plane E2-E2. In the completed electronic module assembly, the second surface 2b or a section of the second surface 2b serves as a heat exchange surface at which the electronic module assembly can be attached on a heat sink.

The circuit carrier <NUM> comprises a dielectric insulation carrier <NUM>, a first substrate metallization layer <NUM> disposed on a first surface of the insulation carrier <NUM> and, optionally, a second substrate metallization layer <NUM> disposed on a second surface of the insulation carrier <NUM>. If there is a second substrate metallization layer <NUM>, the first substrate metallization layer <NUM> and the second substrate metallization layer <NUM> may be disposed on opposite sides of the insulation carrier <NUM>.

For instance, a circuit carrier <NUM> may be a printed circuit board (PCB) or an IMS (insulated metal substrate). According to one example, the circuit carrier <NUM> may be a ceramic substrate in which the dielectric insulation carrier <NUM> is a ceramic, for instance a thin ceramic layer. The ceramic may be, for example, composed of or include aluminum oxide (Al2O3), aluminum nitride (AlN), zirconium oxide (ZrO2), silicon nitride, boron nitride, or any other dielectric ceramic. A circuit carrier <NUM> having a ceramic dielectric insulation carrier may be, without being restricted to, a DCB substrate (DCB=Direct Copper Bonding), a DAB substrate (DAB=Direct Aluminum Bonding), an AMB substrate (AMB=Active Metal Brazing) or an IMS substrate (IMS=Insulated Metal Substrate).

At least one of the first substrate metallization layer <NUM> and (if provided) second substrate metallization layer <NUM> may each have, independently of one another, a layer thickness d21 and d22, respectively, in the range of <NUM> to <NUM>, and the insulation carrier <NUM> may have, e.g., a layer thickness d20 in the range of <NUM> to <NUM>. For instance, each of the layer thicknesses of d21 and d22 may be, without being restricted to, from <NUM> to <NUM>, and/or d21 may be equal to d22. The layer thickness d20 of the insulation carrier <NUM> may be, without being restricted to, from <NUM> to <NUM>. However, layer thicknesses that are larger or smaller than those indicated are equally possible.

Metals with good electrical conductivity such as, for example, copper or copper alloys, aluminum or aluminum alloys are suitable as materials for the relevant first substrate metallization layer <NUM> and second substrate metallization layer <NUM>. At least one of the first substrate metallization layer <NUM> and (if provided) second substrate metallization layer <NUM> may be provided in the form of pre-fabricated metal foils and attached to the insulation carrier <NUM>. As illustrated in <FIG>, the first substrate metallization layer <NUM> may be structured to build a circuit pattern.

At least one semiconductor chip <NUM>, which is a constituent part of the substrate assembly <NUM>, is disposed on a first surface 21t of the first substrate metallization layer <NUM>. The first surface 21t of the first substrate metallization layer <NUM> is part of a first surface 2t of the circuit carrier <NUM>. A second surface 22b of the second substrate metallization layer <NUM> (if provided) facing away from the dielectric insulation carrier <NUM> is part of a second surface 2b of the circuit carrier <NUM>. Optionally, the second surface 22b or a section of the second surface 22b may form the heat exchange surface of the completed electronic module assembly.

The semiconductor chip <NUM> may be joined with the first substrate metallization layer <NUM> using a connection layer (not shown), e.g. solder layer, a layer that includes a sintered metal powder, or an adhesive layer. A semiconductor chip <NUM> may include a semiconductor device that has, e.g., a load path formed between a first and a second chip metallization (not shown). The semiconductor device may be, for instance, a diode, or a controllable semiconductor device like a unipolar or bipolar transistor, or a thyristor. In case of a transistor, the controllable semiconductor device may be, for instance, a MOSFET (Metal Oxide Semiconductor Field-Effect Transistor), an IGBT (Insulated Gate Bipolar Transistor), a HEMT (High Electron Mobility Transistor), or any other transistor. In one example, the semiconductor device, e.g. one of the semiconductor devices mentioned above, may optionally be a vertical semiconductor device.

Optionally, the substrate assembly <NUM> may include at least one bonding wire <NUM> directly wire bonded to at least one of a semiconductor chip <NUM> and the first surface 2t of the first substrate metallization layer <NUM>.

The module housing <NUM> includes a side wall which may include a first side wall segment <NUM>, a second side wall segment <NUM>, a third side wall segment <NUM> and a fourth side wall segment <NUM>. The first side wall segment <NUM> and the second side wall segment <NUM> may form opposite outer wall segments of the module housing <NUM>, and the third side wall segment <NUM> and the fourth side wall segment <NUM> may also form opposite outer wall segments of the module housing <NUM>. In this connection, an "outer wall segment" is accessible from outside the module housing <NUM>, i.e. from the environment of the module housing <NUM>. As illustrated in <FIG>, the side wall may be ring-shaped and, e.g., formed as a substantially rectangular ring. However, any ring shape, e.g. a circular ring, would work as well. The module housing <NUM> includes a lid <NUM>. If it is desired to provide for an electrical insulation of the electronic module assembly <NUM> to be produced, the module housing <NUM> may be a dielectric housing, for instance, a plastic housing (e.g. thermosetting housing or a thermoplastic housing), or a ceramic housing.

As illustrated in <FIG>, the module housing <NUM> may include a plunger <NUM> having an end <NUM>. The plunger may be part of the lid <NUM>. The end <NUM> may be a free end. The plunger <NUM> or at least its end <NUM> may be disposed between and distant from the side wall and, therefore, from the side wall segments <NUM>, <NUM>, <NUM>, <NUM>. If the side wall includes a first side wall segment <NUM> and an opposite second side wall segment <NUM>, the plunger <NUM> or at least its end <NUM> may be disposed between and distant from the first side wall segment <NUM> and the second side wall segment <NUM>, and if the side wall includes a third side wall segment <NUM> and an opposite fourth side wall segment <NUM>, the plunger <NUM> or at least its end <NUM> may be disposed between and distant from the third side wall segment <NUM> and the fourth side wall segment <NUM>. If the module housing <NUM> has a lid <NUM>, the plunger <NUM> may be a protrusion of the lid <NUM>. Optionally, the lid <NUM> and the side wall may be made of one piece.

The electronic module assembly includes electrical terminals <NUM> accessible from outside of the electronic module assembly. Such terminals <NUM> may serve to provide electrical power to the module, to connect an electric load to be driven by the module, to provide a control signal for controlling the switching behavior to the module, or to tap any status signal (e.g. a signal indicative of a temperature of a semiconductor chip <NUM>, a signal indicative of an overvoltage condition, a signal indicative of a short circuit detection, etc.). As illustrated in <FIG> and <FIG>, the terminals <NUM> of the completed electronic module assembly may be part of the substrate assembly <NUM> (see <FIG>) and pierce the lid <NUM> (see <FIG>). However, this is only an example. According to a further example, the terminals <NUM> could be joined with the module housing <NUM>, e.g. be injection molded into the module housing <NUM>, and be electrically connected to the substrate assembly <NUM> using bonding wires. However, any other technique for providing terminals <NUM> may be used as well.

During the production of the electronic module assembly, a curable first mass <NUM> and a curable second mass <NUM> are used. The uncured first mass <NUM> (e.g. a droplet) is introduced between the substrate assembly <NUM> and the module housing <NUM> (e.g. the plunger <NUM> or the end <NUM>) so that it extends from the module housing <NUM> (e.g. the plunger or the end <NUM>) to the substrate assembly <NUM>. Optionally, the uncured first mass <NUM> may be applied to the substrate assembly <NUM> prior to placing the module housing <NUM> onto the substrate assembly <NUM>. The uncured second mass <NUM> is an adhesive used for joining the module housing <NUM> and the substrate assembly <NUM>. The uncured second mass <NUM> is introduced between the side wall <NUM>, <NUM>, <NUM>, <NUM> and the substrate assembly <NUM> (the circuit carrier <NUM>) so that it extends from the side wall <NUM>, <NUM>, <NUM>, <NUM> to the substrate assembly <NUM> (the circuit carrier <NUM>). Thereby, the second mass <NUM> may be disposed distant from the first mass <NUM>. This state is illustrated in <FIG>. Suitable curable masses that can be used for at least one of the first mass <NUM> and the second mass <NUM> are, without being restricted to, adhesives, e.g. silicone adhesives, epoxy adhesives or acrylic adhesives. However, the first mass <NUM> may be but is not required to be an adhesive. Optionally, the uncured first mass <NUM> and/or the uncured second mass <NUM> may be thixotropic which facilitates the application of the respective uncured mass <NUM>, <NUM> because it is flexible during application but remains in place after application. The compositions of the curable first mass <NUM> and the curable second mass <NUM> may be identical or different.

Subsequent to introducing the uncured first mass <NUM> between the substrate assembly <NUM> and the module housing <NUM> and, optionally, subsequent to introducing the uncured second mass <NUM> between the side wall <NUM>, <NUM>, <NUM>, <NUM> and the substrate assembly <NUM> (the circuit carrier <NUM>), the first mass <NUM> and, optionally, the second mass <NUM> are cured. The first mass <NUM> and the second mass <NUM> cure in any order. For instance, the first and second masses <NUM>, <NUM> may cure substantially at the same time, or the second mass <NUM> may cure prior to the first mass <NUM>. However, it is also possible that the first mass <NUM> cures prior to the second mass <NUM>.

The circuit carrier <NUM> is heated from an initial state to a heated state so that the circuit carrier <NUM> is in the heated state at least at that moment at which the first mass <NUM> reaches its cured state. The cured state of the first mass <NUM> is reached as soon as the first mass <NUM> everywhere has a modulus of elasticity of at least <NUM> MPa or at least <NUM> MPa or at least <NUM> MPa or even at least <NUM> MPa. In the heated state of the circuit carrier <NUM>, all over the circuit carrier <NUM> (i.e. everywhere on and in the circuit carrier <NUM>), the temperature is at least a first temperature T2<NUM>, and the circuit carrier <NUM> bends, as illustrated in <FIG>, due to the temperature rise so that a gap (a distance) between the lid <NUM> (e.g. between the plunger <NUM>) and a section of the circuit carrier <NUM> that is distant from the side wall <NUM>, <NUM>, <NUM>, <NUM>, appears or increases. In the heated and, therefore, bent state of the circuit carrier <NUM>, the first mass <NUM> is cured while all over the circuit carrier <NUM>, the temperature is kept at at least the first temperature T2<NUM>. The cured first mass <NUM> serves to keep a minimum distance between the substrate assembly <NUM> and the module housing <NUM> (e.g. the plunger <NUM> or the end <NUM>). In order to approximately adjust that minimum distance to a distance which would occur if the electronic module assembly would be operated without the cured first mass <NUM>, curing the first mass <NUM> may take place in a state in which the temperature of the circuit carrier <NUM> is closer to its maximum operating temperature which is significantly higher than room temperature.

Without being restricted to, the duration for which the circuit carrier <NUM> is kept in the heated state, may be at least <NUM> minutes, at least <NUM> minutes, or even at least <NUM> minutes. At the beginning of the heated state, the first mass <NUM> may be paste-like, and, subsequently, be cured. The first mass <NUM> may reach its cured state within that duration. The cured fist mass substantially prevents a bending-back of the circuit carrier <NUM> even when the temperature of the circuit carrier <NUM> subsequently is reduced. If the first mass <NUM> is an adhesive, a first adhesive connection between the lid <NUM> (e.g. between the plunger <NUM>) and the substrate assembly <NUM> is formed by curing the cured first mass <NUM>.

In the initial state, all over the circuit carrier <NUM> (i.e. everywhere on and in the circuit carrier <NUM>), the temperature is less than or equal to an initial temperature T2<NUM> lower than the first temperature T2<NUM>. For instance, the initial temperature T2<NUM> may be, without being restricted to, room temperature, e.g. <NUM>, and the first temperature T2<NUM> may be significantly higher than room temperature, e.g., without being restricted to, <NUM>, or <NUM>, or <NUM>, or even <NUM>. Alternatively or additionally, a difference between the first temperature T2<NUM> and the initial temperature T2<NUM> may be at least <NUM>.

Summarizing the above, <FIG> illustrates the described initial state, in which, all over the circuit carrier <NUM>, the temperature is less than or equal to an initial temperature T2<NUM> lower than the first temperature T2<NUM>. In the initial state, the first mass <NUM> is uncured (i.e. has not yet reached its cured state), and the second mass <NUM> is uncured, and the surface 2b may be plane or substantially plane. However, the surface 2b might also be slightly concave, or even slightly convex. The first mass <NUM> may reach its cured state simultaneously with or after the second mass <NUM> reaches its cured state. The cured state of the second mass <NUM> is reached as soon as the second mass <NUM> everywhere has a modulus of elasticity of at least <NUM> MPa. In the heated and, optionally, also the cooled state of the circuit carrier <NUM>, the circuit carrier <NUM>, over the whole heat exchange surface 2b or at least in a region of the heat exchange surface 2b opposite the cured first mass <NUM>, is convex.

As illustrated in <FIG>, the uncured first mass <NUM> extends (at least) between the lid <NUM> (e.g. between the plunger <NUM>) and the substrate assembly <NUM>. When the circuit carrier <NUM> is heated from the initial state (<FIG>) to the heated state (<FIG>), the circuit carrier <NUM> bends due to the temperature rise. Therefore, the distance between the lid <NUM> (e.g. between the plunger <NUM>) and the circuit carrier <NUM> changes. The bending of the circuit carrier <NUM> may take place such that the distance between the lid (e.g. between the plunger <NUM>) and the circuit carrier <NUM> in the heated state is larger than in the initial state.

In the heated state of the circuit carrier <NUM>, the first mass <NUM> is cured so that the (enlarged) distance between the lid <NUM> (e.g. the plunger <NUM>) and the circuit carrier <NUM> is substantially fixed (apart from a possible elastic deformation of the cured mass <NUM>).

The second mass <NUM>, which is an adhesive, is also cured. Thereby, a (second) adhesive connection is formed between the module housing <NUM> and the circuit carrier <NUM>. That is, the cured second mass <NUM> connects the module housing <NUM> and the circuit carrier <NUM>. In both the uncured and the cured state, the second mass <NUM> extends (at least) between the module housing <NUM> and the substrate assembly <NUM>, i.e. (at least) between the module housing <NUM> and the circuit carrier <NUM>. Optionally, the uncured and the cured second mass <NUM> may be ring-shaped and seal a ring-shaped gap between the module housing <NUM> and the circuit carrier <NUM>. The second mass <NUM> may reach its cured state prior to or simultaneous with the first mass <NUM>.

When the second mass <NUM> reaches its cured state before the first mass <NUM> reaches its cured state, for instance, when the second mass <NUM> reaches its cured state when the circuit carrier <NUM> is still in its initial state (i.e. when all over the circuit carrier <NUM> the temperature is less than or equal to the initial temperature T2<NUM>) or when the circuit carrier <NUM> is between its initial state and its heated state (i.e. when there is at least one location on or inside the circuit carrier <NUM> that has a temperature of more than the initial temperature T2<NUM> and less than the first temperature T2<NUM>), the uncured first mass <NUM> is, to a certain degree, viscous and may be thixotropic so that it does not, on the one hand, flow off and, on the other hand, can follow the bending of the circuit carrier <NUM> in that it extends, at all times between the initial state of the circuit carrier <NUM> and the time at which the first mass <NUM> reaches its cured state (in particular at all times between the initial state of the circuit carrier <NUM> and the time at which the second mass <NUM> reaches its cured state), between the plunger <NUM> (e.g. between the end <NUM>) and the substrate assembly <NUM> (e.g. the circuit carrier <NUM>). Figuratively speaking, the first mass <NUM> "follows" the bending of the circuit carrier <NUM> so that the first mass <NUM> bridges the gap between the lid <NUM> (e.g. between the plunger <NUM>) and the substrate assembly <NUM> at all times.

After the first mass <NUM> has reached its cured state (i.e. after the (enlarged) distance between the lid <NUM> (e.g. between the plunger <NUM>) and the circuit carrier <NUM> has been substantially fixed), and after the second mass <NUM> has reached its cured state (i.e. after the module housing <NUM> and the circuit carrier <NUM> have been joined by the cured second mass <NUM>), the substrate assembly <NUM>, the module housing <NUM>, the cured first mass <NUM> and the cured second mass <NUM> become constituents of an electronic module assembly <NUM>, and the circuit carrier <NUM> may be cooled down so that everywhere on and in the circuit carrier <NUM> the temperature is less than or equal to a second temperature T2<NUM> that is lower than the first temperature T2<NUM>. This state is illustrated in <FIG>. An enlarged section of the electronic module assembly <NUM> of <FIG> is illustrated in <FIG>. According to one option, the difference between the second temperature T2<NUM> and the first temperature T2<NUM> may be, without being restricted to, at least <NUM>. According to one option, the second temperature T2<NUM> may be less than or equal to <NUM>.

The cooled down circuit carrier <NUM> substantially keeps its bent shape because the cured first mass <NUM> prevents (apart from an elastic deformation of the cured first mass <NUM>) a reduction of the distance d15 (see <FIG>) between the lid <NUM> (e.g. between the plunger <NUM>) and the substrate assembly <NUM>, and because the module housing <NUM> is significantly stiffer than the circuit carrier <NUM>. In the cured state of the first mass <NUM>, the distance d15 between the lid <NUM> (e.g. between the plunger <NUM>) and the substrate assembly <NUM> may be, without being restricted to, less than <NUM>.

As further illustrated in <FIG>, a dielectric potting <NUM>, for instance a gel (e.g. a silicone gel) may be disposed inside the module housing <NUM>. The potting <NUM> may adjoin the circuit carrier <NUM>, the side wall <NUM>, <NUM>, <NUM>, <NUM>, the second mass <NUM>, and, optionally, also the first mass <NUM>. Optionally, the potting <NUM> may cover the semiconductor chip <NUM> and, if provided, the bonding wire <NUM>.

Also illustrated in <FIG> is a layer <NUM> of a thermal interface material that may be produced on a heat exchange surface 2b of the circuit carrier <NUM> which is a surface 2b of the circuit carrier <NUM> facing away from the lid <NUM> and, if the module housing <NUM> has a plunger <NUM>, from the plunger <NUM>. That is, the circuit carrier <NUM> is disposed between the plunger <NUM> and the layer <NUM> of a thermal interface material. Instead of this, it would also be possible to produce the layer <NUM> of the thermal interface material on the heat sink <NUM>. In both cases, the thermal interface material may have, at a temperature of <NUM> and without being restricted to, a thermal conductivity in the range from <NUM> W/(m·K) to <NUM> W/(m·K).

If the layer <NUM> applied to the heat exchange surface 2b of the circuit carrier <NUM> or to the heat sink <NUM> is a continuous layer it may have, without being restricted to, a layer thickness d7 of less than or equal to <NUM> so that the down force F required for letting creep a little of the thermal interface material laterally out of the gap between the heat exchange surface 2b and the heat sink <NUM> is very low. For the same reason, if the layer <NUM> applied to the heat exchange surface of the circuit carrier <NUM> or to the heat sink <NUM> includes a plurality of single dots spaced distant from one another, the layer thickness d7 may be, without being restricted to, less than or equal to <NUM>. Thereby, the footprint area of each single dot may be less than or equal to <NUM><NUM>. Optionally, the total amount of the thermal interface material may be chosen such that an average thickness of the layer <NUM> is less than or equal to <NUM>.

Subsequently, the module housing <NUM> and a heat sink <NUM> may be joined so that the layer <NUM> of the thermal interface material adjoins both the circuit carrier <NUM> (i.e. the heat exchange surface 2b) and the heat sink <NUM>, and so that the circuit carrier <NUM> is pressed against the heat sink <NUM>. The result is illustrated in <FIG>. In the example of <FIG>, the module housing <NUM> and the heat sink <NUM> are joined by screws <NUM>. However, any other joining technique, e.g. clamping, riveting, may be used as well. When joining the module housing <NUM> and the heat sink <NUM>, the circuit carrier <NUM> is pressed against the heat sink <NUM> so that the bending of the circuit carrier <NUM> is reduced. Thereby, the module housing <NUM> is pre-tensioned, which causes the lid <NUM> (e.g. the plunger <NUM>) to locally press the substrate assembly <NUM> indirectly (i.e. via the cured first mass <NUM>) against the heat sink <NUM>. This pressing counteracts the formation of air gaps or other gas-filled spaces between the circuit carrier <NUM> (i.e. between the heat exchange surface 2b) and the heat sink <NUM> when the circuit carrier <NUM> is heated during the operation of the electronic module assembly <NUM> by the heat produced from the electronic components <NUM> of the substrate assembly <NUM>. In <FIG>, the downforce F caused by the pretension of the module housing <NUM> is schematically indicated by a bold arrow. In this connection it is to be noted that heating the circuit carrier <NUM> causes the circuit carrier <NUM> to bend towards the lid <NUM> (e.g. towards the plunger <NUM>) and away from the heat sink <NUM> because the edges of the circuit carrier <NUM> are clamped by the module housing <NUM> when this is joined with the heat sink <NUM> so that the only direction the heated and thereby enlarged circuit carrier <NUM> can sufficiently bend in is away from the heat sink <NUM>.

In the previous example, the uncured and cured first mass <NUM> was described to adjoin the substrate assembly <NUM> at the circuit carrier <NUM>, e.g. the first metallization layer <NUM>. However, the principles, methods, designs, dimensions, options, materials etc. of the examples explained above also apply if the uncured and cured first mass <NUM> adjoins the substrate assembly <NUM> at the semiconductor chip <NUM> (see <FIG>), at the insulation carrier <NUM> (see <FIG>) or at a bonding wire <NUM> (e.g. at a region of a maximum loop height of the bonding wire <NUM>) (see <FIG>), or at any other constituent part of the substrate assembly <NUM>.

As further illustrated in <FIG>, a module housing <NUM> may include two or more plungers <NUM>, and between each of the plungers <NUM> and the substrate assembly <NUM> a curable first mass <NUM> may be placed and subsequently cured as described above. If the first mass <NUM> is an adhesive, the cured first mass <NUM> forms a substance-to-substance bond between the respective plunger <NUM> and the substrate assembly <NUM>. The difdifferent uncured and cured first masses <NUM> may optionally be disposed distant from one another and/or, also optionally, distant from both the uncured and cured second mass <NUM>.

In an example electronic module assembly <NUM>, a circuit carrier <NUM> having edge lengths of about <NUM> x <NUM>, an insulation carrier <NUM> of Al<NUM>O<NUM>, a first substrate metallization layer <NUM> and a second substrate metallization layer <NUM> of copper were used. The layer thickness d20 of the insulation carrier <NUM> was <NUM>, and each of the layer thicknesses d21 and d22 of substrate metallization layers <NUM>, <NUM> was <NUM>. The required downforce F was between <NUM> N and <NUM> N, the distance d15 was about <NUM>, the plunger was a straight pin and had a cross section of about <NUM><NUM>, and the modulus of elasticity of the cured first mass <NUM> was, at a temperature of <NUM>, about <NUM> MPa.

As will be explained by way of example with reference to <FIG>, the uncured and cured first mass <NUM> does not necessarily need to be disposed between the substrate assembly <NUM> and a plunger <NUM>. Instead, the uncured first mass <NUM> may be applied between the substrate assembly <NUM> and a section <NUM> of the lid <NUM> where the lid <NUM> has no plunger, and then be cured so that the cured first mass <NUM> is disposed between the substrate assembly <NUM> (e.g. between a bonding wire <NUM> of the substrate assembly <NUM>) and the plunger-free section <NUM> of the lid <NUM>. For instance, the cured first mass <NUM> may extend between the cured first mass <NUM> and the substrate assembly <NUM> (e.g. a bonding wire <NUM>). Apart from the fact that there is no plunger in the section <NUM>, the principles, methods, designs, dimensions, options, materials etc. of the examples explained above also apply.

If a dielectric potting <NUM>, for instance a gel (e.g. a silicone gel) is disposed inside the module housing <NUM> and if the first mass <NUM> extends between a bonding wire <NUM> and the lid <NUM> (e.g. between a bonding wire <NUM> and the plunger <NUM> or the end <NUM>), the bonding wire <NUM> may be completely embedded in the potting <NUM> as illustrated in <FIG> and <FIG>. Alternatively, the bonding wire <NUM> may protrude from the potting <NUM>, and the first mass <NUM> may extend between the protruding part of the bonding wire <NUM> and the lid <NUM>.

As further illustrated in <FIG>, an electronic module assembly <NUM> may include two or more separate substrate assemblies <NUM> disposed distant from one another. Each of the substrate assemblies <NUM> may, irrespective of the structure of the other substrate assemblies <NUM>, have the properties of any of the substrate assemblies <NUM> explained above and be attached to the module housing <NUM> using curable first and second masses <NUM>, <NUM> as explained above. According to one example illustrated in <FIG>, for each of the substrate assemblies <NUM>, the module housing <NUM> may have at least one plunger <NUM>, and a curable first mass <NUM> may be disposed between that plunger <NUM> and the respective substrate assembly <NUM>. According to another example (not shown), for each of at least one of the substrate assemblies <NUM>, the module housing <NUM> may have at least one plunger <NUM>, and a curable first mass <NUM> may be disposed between that plunger <NUM> and the respective substrate assembly <NUM> (as explained with reference to <FIG>), and for each of at least one further substrate assembly <NUM>, a curable first mass <NUM> may be disposed between a plunger-free section <NUM> of the module housing <NUM> and the respective substrate assembly <NUM> (as explained with reference to <FIG>). According to still a further example (not shown), for each of the substrate assemblies <NUM>, a curable first mass <NUM> may be disposed between a plunger-free section <NUM> of the module housing <NUM> and the respective substrate assembly <NUM> (as explained with reference to <FIG>).

As also illustrated in <FIG>, each of the substrate assemblies <NUM> may include a circuit carrier <NUM> having a heat exchange surface 2b. On each of the heat exchange surfaces 2b, a layer <NUM> of a thermal interface material having the properties explained with reference to <FIG> has been produced. The electronic module assembly <NUM> with layers <NUM> of the thermal interface material applied to the heat exchange surfaces 2b may be joined with a heat sink <NUM> as explained in more detail with reference to <FIG>. Instead of this, it would also be possible to produce the layers <NUM> (or one continuous layer <NUM>) of the thermal interface material on the heat sink <NUM>. By joining the module housing <NUM> and the heat sink <NUM>, the circuit carriers <NUM> are pressed against the heat sink <NUM> so that the bending of the circuit carriers <NUM> is reduced. Thereby, the module housing <NUM> is pre-tensioned which causes the lid <NUM> (e.g. the plungers <NUM>) to locally press the substrate assemblies <NUM> indirectly (i.e. via the respective cured first mass <NUM>) against the heat sink <NUM>. In <FIG>, the downforces F caused by the pretension of the module housing <NUM> are schematically indicated by bold arrows.

Irrespective of whether the electronic module assembly <NUM> includes just one or at least two substrate assemblies <NUM>, a downforce F caused by a pre-tension of the module housing <NUM> is transmitted from the module housing <NUM> (e.g. from the lid <NUM>, e.g. from a plunger <NUM> or a plunger-free section <NUM>) via a cured first mass <NUM>. In order to effectively press the respective substrate assembly <NUM> (i.e. the circuit carrier <NUM> thereof) against the heat sink <NUM>, the cured first mass <NUM> may have a high modulus of elasticity which may be higher than the moduli of elasticity of many adhesives used in conventional electronic modules for joining a circuit carrier and a module housing. For instance, the cured first mass <NUM> may, without being restricted to, everywhere comprise, at a temperature of <NUM>, a modulus of elasticity of at least <NUM> MPa or even of at least <NUM> MPa.

In order to prevent large relative movements between the substrate assembly <NUM> and the module housing <NUM>, the cured second mass <NUM> may, without being restricted to, everywhere comprise, at a temperature of <NUM>, a modulus of elasticity of at least <NUM> MPa. Optionally, both the cured first mass <NUM> and the cured second mass <NUM> may everywhere comprise, at a temperature of <NUM>, the same modulus of elasticity, e.g. at least <NUM> MPa. Such identical moduli of elasticity can easily by achieved by producing the cured first and second masses <NUM>, <NUM> from the same type of curable mass.

In order to effectively press the respective substrate assembly <NUM> (i.e. the circuit carrier <NUM> thereof) against the heat sink <NUM>, the cured first mass <NUM> is disposed distant from each edge of the insulation carrier <NUM> of the circuit carrier <NUM> of the substrate assembly <NUM>. <FIG> is a cross-sectional top view of the electronic module assembly <NUM> of <FIG> illustrating just the circuit carrier <NUM>, the cured first mass <NUM> and the plunger <NUM>. For the sake of clarity, the other parts of the electronic module assembly <NUM> are omitted. As shown, the insulation carrier <NUM> of the circuit carrier <NUM> has a number of edges 20e. The shortest among all distances between the cured first mass <NUM> and all edges 20e is designated with d0. For instance, the shortest distance d0 may be, without being restricted to, <NUM>.

As already explained above, <FIG> illustrates an enlarged section of an electronic module assembly <NUM> according to <FIG> that includes a module housing with a lid having a plunger <NUM>, shown after cooling down the circuit carrier <NUM> from the heated state to the cooled-down state, so that everywhere on and in the circuit carrier <NUM> the temperature is less than or equal to the second temperature T2<NUM>. A part of the plunger <NUM> is embedded in the cured first mass <NUM>. As illustrated in <FIG>, there is no layer <NUM> of a thermal interface material applied to the surface 2b (as in <FIG>), and the electronic module assembly <NUM> is not mounted to a heat sink <NUM> (as in <FIG>).

That is, the surface 2b is exposed. In this cooled-down state, the module housing <NUM> is, as described above, pre-tensioned and causes a downforce F. <FIG> is a cross-sectional top view showing just the plunger <NUM> and the cured first mass <NUM> with the cross-section being taken in a cross-sectional plane E4-E4 shown in <FIG>. The cross-sectional plane E4-E4 intersects both the plunger <NUM> and the cured first mass <NUM> perpendicularly to the direction of the downforce F and is taken such that in the cross-sectional plane E4-E4, the cured first mass <NUM> surrounds the plunger <NUM> and adjoins the entire circumference of the plunger <NUM>. In the cross-sectional plane E4-E4, the cross-sectional area of the plunger <NUM> is A55.

The modulus of elasticity of the cured first mass <NUM> is sufficiently high to generate a proper downforce F and to prevent the surface 2b of the cooled-down circuit carrier <NUM> adhered to the module housing <NUM> (see <FIG>) from being concave. A concave surface 2b is undesired because it would cause an accumulation of the thermal interface material when the electronic module assembly <NUM> provided with the layer <NUM> of the thermal interface material is mounted on the heat sink <NUM>. On the contrary, when an electronic module assembly <NUM> with a circuit carrier <NUM> having a convex surface 2b and a layer <NUM> of thermal interface material applied to the convex surface 2b is mounted onto a heat sink <NUM>, a little of the thermal interface material can easily squeezed out of the gap between the heat exchange surface 2b and the heat sink <NUM> so that the layer <NUM> becomes thin and, therefore, has a low thermal resistance.

For a straight plunger <NUM>, a method for estimating a proper downforce F is, as illustrated in <FIG>, to take a sample <NUM>' of the substrate assembly <NUM> (i.e. an identical copy thereof) to be used in the electronic module assembly <NUM>. In each of at least one temperature cycle, the sample substrate assembly <NUM>' is heated to the heated state and subsequently cooled down to the cooled state as described above because it has been shown that, after such temperature cycling, the reproducibility of the thermomechanical behavior of a substrate assembly <NUM>, <NUM>' is significantly improved. After the temperature cycling and in the cooled state, the border of circuit carrier <NUM> is, as illustrated in the measuring arrangement of <FIG>, supported at its border by a stable support <NUM>. Subsequently, the circuit carrier <NUM> resting on the support <NUM> is deflected by locally pressing against the sample substrate assembly <NUM>' so that the position of the force effect is shifted by a pre-defined distance d2, e.g. <NUM> or <NUM>, and the circuit carrier <NUM> becomes convex or more convex at the surface 2b. The local pressing against the sample substrate assembly <NUM>' takes place at the corresponding position at which the first mass <NUM> (illustrated in dashed fashion) is to be placed in the electronic module assembly <NUM> to be produced. In <FIG>, the dotted line illustrates the run of the surface 2b when the desired pre-defined distance d2 is reached. A force measuring device <NUM> is used to measure a force FTEST required to achieve the desired pre-defined distance d2. The force FTEST is taken as the desired (target) down force F explained with reference to <FIG>.

The cross-sectional area A55 of the plunger <NUM>, the distance d15 (see <FIG>) in the cooled down state, the modulus of elasticity E61 of the cured first mass <NUM> are chosen to fulfill the following equation: <MAT>.

Despite the fact that the method for estimating a proper downforce F was explained with reference to the example electronic module assembly <NUM> of <FIG>, the method also may be used in connection with all other electronic modules <NUM> in which a cured first mass <NUM> is (at least) disposed between a substrate assembly <NUM> and a straight plunger <NUM>. The local pressing against the sample substrate assembly <NUM>' takes place at the corresponding position at which the first mass <NUM> is to be placed on the substrate assembly <NUM> of the electronic module assembly <NUM> to be produced, e.g. at the first substrate metallization layer <NUM> (<FIG>), at a semiconductor chip <NUM> (<FIG>), at the insulation carrier <NUM> (<FIG>), or at a bonding wire <NUM> (<FIG>).

In <FIG>, the shapes the heat exchange surface 2b of an electronic module assembly <NUM> takes at two different temperatures of the electronic module assembly <NUM> are illustrated. The shape the heat exchange surface takes when the electronic module assembly <NUM> everywhere has a low temperature Tlow is designated with 2b(Tlow), and the shape the heat exchange surface takes when the electronic module assembly <NUM> everywhere has a high temperature Thigh higher than the low temperature Tlow is designated with 2b(Thigh) and illustrated in dashed fashion. As can be seen by comparing these shapes, the curvature of the heat exchange surface (2b(Thigh)) at the high temperature Thigh of the electronic module assembly <NUM> is greater than the curvature of the heat exchange surface (2b(Tlow)) at the low temperature Tlow. Therefore, a distance between a point P of the heat exchange surface 2b opposite the cured first mass <NUM> and a tangent plane E3-E3 of the module housing <NUM> may depend on the temperature of the electronic module assembly <NUM>. As illustrated in <FIG> which shows the electronic module assembly <NUM> at the low temperature Tlow, a point P of the heat exchange surface 2b is located opposite the cured first mass <NUM> (and, if there is a plunger <NUM>, opposite the plunger <NUM> or the opposite the end <NUM>) at a position Plow. The distance between this point P and the tangential plane E3-E3 at the low temperature Tlow of the electronic module assembly <NUM> is designated with dPlow, and the distance between this point P (i.e. between the position Phigh of the point P) and the tangential plane E3-E3 at the high temperature Thigh of the electronic module assembly <NUM> is designated with dPhigh, As also illustrated in <FIG>, the distances dPhigh and dPlow differ from one another. For instance, if the high temperature Thigh is at least the first temperature T2<NUM> (i.e. the minimum temperature the circuit carrier <NUM> has in its heated state) and the low temperature Tlow is less than or equal to the second temperature T22 (i.e. the maximum temperature the circuit carrier <NUM> has in its cooled state), the absolute value of the difference between the distances dPhigh and dPlow may be, without being restricted to, at least <NUM>. Optionally, the distance dPhigh may be greater than the distance dPlow. The tangent plane E3-E3 may be a (virtual) plane abutting the side of the module housing <NUM> to which the circuit carrier <NUM> mounted.

Alternatively or additionally, a distance between such a point P and the lid <NUM> (if there is a plunger <NUM>, the distance may be the distance between the point P and the plunger <NUM> or the end <NUM>) may change with the temperature of the electronic module assembly <NUM>. This is, analogously to <FIG>, illustrated in <FIG>. As shown in <FIG>, the distance between the point P and the lid <NUM> (which in the example of <FIG> is the distance between the point P and the plunger <NUM> or the end <NUM>) at the low temperature Tlow of the electronic module assembly <NUM> is designated with aPlow, and the distance between this point P and the lid <NUM> at the high temperature Thigh of the electronic module assembly <NUM> is designated with aPhigh, As also illustrated in <FIG>, the distances aPhigh and aPlow differ from one another. For instance, if the high temperature Thigh is at least the first temperature T2<NUM> (i.e. the minimum temperature the circuit carrier <NUM> has in its heated state) and the low temperature Tlow is less than or equal to the second temperature T22 (i.e. the maximum temperature the circuit carrier <NUM> has in its cooled state), the difference aPhigh - aPlow between the distances aPhigh and aPlow may be, without being restricted to, at least <NUM>. Thereby, the distance dPhigh is greater than the distance dPlow.

If the electronic module assembly <NUM> is, e.g. in its cooled state, mounted to a plane surface of a heat sink <NUM> as described with reference to <FIG> and <FIG>, the module housing <NUM> (e.g. the plunger <NUM> or the end <NUM>) exerts a force F on the circuit carrier <NUM> so that the cured first mass <NUM> is compressed. The compression can be expressed in terms of a change Δd15 of the distance d15 (see <FIG>) between a state in which the electronic module assembly <NUM> is in the unmounted state (i.e. when the electronic module assembly <NUM> is not mounted to a heat sink or the like so that the bending of the circuit carrier <NUM> is not limited by external elements) and a state in which the electronic module assembly <NUM> is in a mounted state (i.e. when the electronic module assembly <NUM> is mounted to a plane surface of a heat sink). For instance, if the electronic module assembly <NUM> is in an unmounted state and has an overall temperature of less than or equal to the second temperature T2<NUM>, the distance d15 is as explained with reference to <FIG>. If the electronic module assembly <NUM> is mounted to a plane surface of a heat sink <NUM> as explained with reference to <FIG> and <FIG> and the same overall temperature of less than or equal to the second temperature T2<NUM>, the cured first mass <NUM> is compressed by the force F and the distance d15 is reduced to d15red. That is, Δd15 = d15 - d15red. In order to calculate or at least estimate the required parameters, the following relation may be used: <MAT> Thereby, A55 is the cross-sectional area of the plunger <NUM> as explained with reference to <FIG>, and E61 is the modulus of elasticity E61 of the cured first mass <NUM>.

According to one example, for a cylindrical plunger <NUM> having a diameter of <NUM> (i.e. the cross-sectional area A55 is about <NUM><NUM>), a modulus of elasticity E61 of the cured first mass <NUM> of <NUM> MPa, an initial distance d15 of <NUM>, and a change Δd15 of the distance d15 of <NUM>, the resulting force F is about <NUM> N.

Claim 1:
A method for producing an electronic module assembly, the method comprising:
curing a curable first mass (<NUM>) extending between a substrate assembly (<NUM>) and a lid (<NUM>) of a module housing (<NUM>) while a circuit carrier (<NUM>) of the substrate assembly (<NUM>) is at a temperature of at least a first temperature, wherein the circuit carrier (<NUM>) comprises a dielectric insulation carrier (<NUM>) and a first substrate metallization layer (<NUM>) attached to the dielectric insulation carrier (<NUM>), and wherein the substrate assembly (<NUM>) further comprises at least one semiconductor chip (<NUM>) joined with the first substrate metallization layer (<NUM>);
forming an adhesive connection between a side wall (<NUM>,<NUM>,<NUM>,<NUM>) of the module housing (<NUM>) and the circuit carrier (<NUM>) by curing a curable second mass (<NUM>);
cooling down the circuit carrier (<NUM>) to below a second temperature lower than the first temperature subsequent to curing the curable first mass (<NUM>); wherein
the cured first mass (<NUM>) is located distant from the edges of the circuit carrier (<NUM>) and opposite a heat exchange surface (2b) of the circuit carrier (<NUM>),
the circuit carrier (<NUM>) is heated from an initial state to a heated state in which the temperature of the circuit carrier (<NUM>) is at the temperature of at least the first temperature, the circuit carrier bending due to the temperature rise,
the curable first mass (<NUM>) is cured when the circuit carrier is in the bent state,
the curable first mass (<NUM>) extending between the module housing (<NUM>) and the substrate assembly (<NUM>) and bridging a gap between the module housing (<NUM>) and the substrate assembly (<NUM>) which increases when the circuit carrier (<NUM>) bends due to the temperature rise, and
the cured first mass (<NUM>) fixing said gap so that the circuit carrier (<NUM>) remains in the bent state after cooling down.