Thermal stress compensation bonding layers and power electronics assemblies incorporating the same
A thermal stress compensation layer includes a metal inverse opal (MIO) layer with a plurality of hollow spheres and a predefined porosity disposed between a pair of bonding layers. The thermal stress compensation layer has a melting point above a TLP sintering temperature and the pair of bonding layers each have a melting point below the TLP sintering temperature such that the MIO layer can be transient liquid phase bonded between a metal substrate and a semiconductor device. The pair of bonding layers may comprise a first pair of bonding layers and a second pair of bonding layers with the first pair of bonding layers disposed between the MIO layer and the second pair of bonding layers. The first pair of bonding layers may have a melting point above the TLP sintering temperature and the second pair of bonding layers may have a melting point below the TLP sintering temperature.
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The present specification generally relates to bonding materials, and more particularly, to thermal stress compensation bonding materials for bonding of semiconductor devices to metal substrates during the manufacture of power electronics assemblies.
BACKGROUNDPower electronics devices are often utilized in high-power electrical applications, such as inverter systems for hybrid electric vehicles and electric vehicles. Such power electronics devices include power semiconductor devices, such as power IGBTs and power transistors thermally bonded to a metal substrate. The metal substrate may then be further thermally bonded to a cooling structure, such as a heat sink.
With advances in battery technology and increases in electronics device packaging density, operating temperatures of power electronics devices have increased and are currently approaching 200° C. Accordingly, traditional electronic device soldering techniques no longer provide suitable bonding of semiconductor devices to metal substrates and alternative bonding techniques are needed. One such alternative bonding technique is transient liquid phase (TLP) sintering (also referred to herein as “TLP bonding”). The TLP sintering of a power electronics device utilizes a bonding layer disposed (sandwiched) between a semiconductor device and metal substrate. The bonding layer at least partially melts and isothermally solidifies to form a TLP bond between the semiconductor device and metal substrate at TLP bonding temperatures (also referred to as sintering temperatures) between about 280° C. to about 350° C. The semiconductor devices and metal substrates have different coefficients of thermal expansion (CTE) and large thermally-induced stresses (e.g., cooling stresses) may be generated between a semiconductor device and metal substrate upon cooling from a TLP sintering temperature. The large thermal cooling stresses due to CTE mismatch between the power semiconductor device and metal substrate may result in delamination between the semiconductor device and metal substrate of a power electronics device when currently known bonding layers are used to form the TLP bond.
SUMMARYIn one embodiment, a transient liquid phase (TLP) bonding layer includes a thermal stress compensation layer disposed between a pair of bonding layers. The thermal stress compensation layer comprises a metal inverse opal (MIO) layer with a plurality of hollow spheres and a predefined porosity. The thermal stress compensation layer has a melting point above a TLP sintering temperature and the pair of bonding layers each have a melting point below the TLP sintering temperature. In embodiments, the MIO layer includes a first surface, a second surface and a graded porosity between the first surface and the second surface. In the alternative, or in addition to, the MIO layer comprises a graded stiffness between the first surface and the second surface. The pair of bonding layers may comprise a first pair of bonding layers and a second pair of bonding layers with the first pair of bonding layers disposed between the MIO layer and the second pair of bonding layers. Each of the first pair of bonding layers may have a melting point above the TLP sintering temperature and each of the second pair of bonding layers may have a melting point below the TLP sintering temperature. In embodiments, the MIO layer is a copper inverse opal (CIO) layer, the first pair of bonding layers are formed from nickel, silver or alloys thereof, and the second pair of bonding layers are formed from tin, indium, or alloys thereof.
In another embodiment, a power electronics assembly includes a semiconductor device extending across a metal substrate and a thermal stress compensation layer disposed between and bonded to the semiconductor device and the metal substrate. The thermal stress compensation layer comprises an MIO layer with a plurality of hollow spheres and a predefined porosity. In some embodiments, the thermal stress compensation layer is TLP bonded to the semiconductor device and the metal substrate. In such embodiments, the MIO layer has a melting point above a TLP sintering temperature and the pair of bonding layers each have a melting point below the TLP sintering temperature. In embodiments, the MIO layer includes a first surface, a second surface and a graded porosity between the first surface and the second surface. In the alternative, or in addition to, the MIO layer comprises a graded stiffness between the first surface and the second surface. The pair of bonding layers may include a first pair of bonding layers and a second pair of bonding layers with the first pair of bonding layers disposed between the MIO layer and the second pair of bonding layers. Each of the first pair of bonding layers may have a melting point above the TLP sintering temperature and each of the second pair of bonding layers may have a melting point below the TLP sintering temperature. In embodiments, the MIO layer is a copper inverse opal (CIO) layer, the first pair of bonding layers are formed from nickel, silver or alloys thereof, and the second pair of bonding layers are formed from tin, indium, or alloys thereof.
In yet another embodiment, a process for manufacturing a power electronics assembly includes positioning a thermal stress compensation layer between a metal substrate and a semiconductor device to provide a metal substrate/semiconductor device assembly. The thermal stress compensation layer comprises an MIO layer. In some embodiments, the thermal stress compensation layer includes a pair of bond layers with the MIO layer disposed between the pair of bond layers. In such embodiments, the process may include heating the metal substrate/semiconductor device assembly to a transient liquid phase (TLP) sintering temperature between about 280° C. and 350° C. The pair of bonding layers each have a melting point less than the TLP sintering temperature and the MIO layer has a melting point greater than the TLP sintering temperature such that the pair of bonding layers at least partially melt and form a TLP bond between the metal substrate and the MIO layer, and between the semiconductor device and the MIO layer. The pair of bonding layers may comprise a first pair of bonding layers and a second pair of bonding layers with the first pair of bonding layers disposed between the MIO layer and the second pair of bonding layers. Each of the first part of bonding layers have a melting point above the TLP sintering temperature and each of the second pair of bonding layers each have the melting point below the TLP sintering temperature such that the second pair of bonding layers at least partially melt and form a TLP bond with the first pair of bonding layers, the metal substrate and the semiconductor device. In other embodiments, the process includes placing the metal substrate/semiconductor device assembly in an electrolytic or electroless plating bath and bonding the MIO layer to the metal substrate and the semiconductor device via an electroplating or electroless plating bonding layer.
These and additional features provided by the embodiments described herein will be more fully understood in view of the following detailed description, in conjunction with the drawings.
The embodiments set forth in the drawings are illustrative and exemplary in nature and not intended to limit the subject matter defined by the claims. The following detailed description of the illustrative embodiments can be understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:
Referring initially to
The thicknesses of the metal substrate 110 and the semiconductor devices 120 may depend on the intended use of the power electronics assembly 100. In one embodiment, the metal substrate 110 has a thickness within the range of about 2.0 mm to about 4.0 mm, and the semiconductor device 120 has a thickness within the range of about 0.1 mm to about 0.3 mm. For example and without limitation, the metal substrate may have a thickness of about 3.0 mm and the semiconductor device 120 may have a thickness of about 0.2 mm. It should be understood that other thicknesses may be utilized.
The metal substrate 110 may be formed from a thermally conductive material such that heat from the semiconductor devices 120 is transferred to the cooling structure 140. The metal substrate may be formed copper (Cu), e.g., oxygen free Cu, aluminum (Al), Cu alloys, Al alloys, and the like. The semiconductor devices 120 may be formed from a wide band gap semiconductor material suitable for the manufacture or production of power semiconductor devices such as power IGBTs and power transistors. In embodiments, the semiconductor devices 120 may be formed from wide band gap semiconductor materials including without limitation silicon carbide (SiC), silicon dioxide (SiO2), aluminum nitride (AlN), gallium nitride (GaN), boron nitride (BN), diamond, and the like. In embodiments, the metal substrate 110 and the semiconductor devices 120 may comprise a coating, e.g., nickel (Ni) plating, to assist in the TLP sintering of the semiconductor devices 120 to the metal substrate 110.
As depicted in
The metal substrate 110 is thermally coupled to the cooling structure 140 via a bond layer 138. In one embodiment, the cooling structure 140 comprises an air-cooled heat sink. In an alternative embodiment, the cooling structure 140 comprises a liquid-cooled heat sink, such as a jet impingement or channel-based heat sink device. The metal substrate 110 of the illustrated embodiment is directly bonded to a first surface 142 of the cooling structure 140 via the bond layer 138 without any additional interface layers (e.g., additional metal base plates). The metal substrate 110 may be bonded to the cooling structure 140 using a variety of bonding techniques, such as by TLP sintering, solder, brazing, or diffusion bonding, for example. However, in an alternative embodiment, one or more thermally conductive interface layers may be positioned between the metal substrate 110 and the cooling structure 140.
Still referring to
Within the power electronics assembly 100 may be a first electrical contact 104a and a second electrical contact 104b to provide electrical power connections to the semiconductor devices 120. The first electrical contact 104a may correspond to a first voltage potential and the second electrical contact 104b may correspond to a second voltage potential. In the illustrated embodiment, the first electrical contact 104a is electrically coupled to a first surface of the semiconductor devices 120 via a first electrical wire 121a, and the second electrical contact 104b is electrically coupled to a second surface of the semiconductor devices 120 via a second electrical wire 121b and the metal substrate 110. It should be understood that other electrical and mechanical configurations are possible, and that embodiments are not limited by the arrangement of the components illustrated in the figures.
Referring now to
The pair of bonding layers 134 have a melting point that is less than a melting point of the MIO layer 132. Particularly, the pair of bonding layers 134 have a melting point that is less than a TLP sintering temperature used to TLP bond the semiconductor device 120 to the metal substrate 110, and the MIO layer 132 has a melting temperature that is greater than the TLP sintering temperature. As a non-limiting example, the TLP sintering temperature is between about 280° C. and about 350° C., and the pair of bonding layers 134 have a melting point less than about 280° C. and the MIO layer 132 has melting points greater than 350° C. For example, the pair of bonding layers 134 may be formed from tin (Sn) with a melting point of about 232° C., whereas the MIO layer 132 may be formed any material that can be electrolytic or electroless deposited. Non-limiting examples include materials such as Cu, Ni, Al, silver (Ag), zinc (Zn) and magnesium (Mg) with a melting point of about 1085° C., 660° C., 962° C., 420° C. and 650° C., respectively. Accordingly, the pair of bonding layers 134 at least partially melt and the MIO layer 132 does not melt during TLP sintering of the semiconductor device 120 to the metal substrate 110.
The thermal stress compensation layer 130 described herein compensates thermally-induced stresses, e.g., thermal cooling stresses, resulting from fabrication (e.g., TLP sintering) and operational conditions (e.g., transient electric loads causing high changes in temperature). Because the metal substrate 110 and semiconductor devices 120 of the power electronics assembly 100 are made of differing materials, differences in the CTE for each material may cause large thermally-induced stresses within the metal substrate 110, semiconductor devices 120 and thermal stress compensation layer 130. It should be understood that the large thermally-induced stresses may result in failure of the power electronics assembly 100 due to fracturing of the metal substrate 110 or failure of a traditional TLP bonding material (e.g., delamination) between the metal substrate 110 and one or both of the semiconductor devices 120.
The use of the thermal stress compensation layer 130 to TLP bond the metal substrate 110 to the semiconductor devices 120 alleviates or mitigates such stresses. That is, the thermal stress compensation layer 130 described herein compensates for the thermal expansion and contraction experienced by the metal substrate 110 and semiconductor devices 120. In some embodiments, the thermal stress compensation layer 130 described herein compensates for the thermal expansion and contraction experienced by the metal substrate 110 and semiconductor devices 120 with the MIO layer 132 having a generally constant stiffness between the metal substrate 110 and semiconductor devices 120. In other embodiments, the thermal stress compensation layer 130 described herein compensates for the thermal expansion and contraction experienced by the metal substrate 110 and semiconductor devices 120 with the MIO layer 132 having a graded stiffness across its thickness. That is, a varied hollow sphere size (average diameter) across the thickness of the MIO layer 132 provides a graded porosity and thus a graded stiffness across the thickness of the MIO layer 132. The MIO layer 132, with the constant stiffness or the graded porosity across its thickness, allows the thermal stress compensation layer 130 to plastically deform and not delaminate due to the CTE mismatch between the metal substrate 110 and semiconductor devices 120. Also, the MIO layer 132 provides sufficient stiffness such that the semiconductor devices 120 are adequately secured to the metal substrate 110 for subsequent manufacturing steps performed on the semiconductor devices 120. The thermal stress compensation layer 130 also provides sufficient high temperature bonding strength between the metal substrate 110 and semiconductor devices 120 during operating temperatures approaching and possibly exceeding 200° C.
Generally, the MIO layer 132 comprises a flat thin layer and the pair of bonding layers 134 comprise flat thin films. As non-limiting examples, the thickness of the MIO layer 132 may be between about 25 micrometers (microns) and about 200 microns. In embodiments, the MIO layer 132 has a thickness between about 50 microns and about 150 microns. In other embodiments, the MIO layer 132 has a thickness between about 75 microns and 125 microns, for example a thickness of 100 microns. The thickness of the pair of bonding layers 134 may be between 1 micron and 20 microns. In embodiments, the pair of bonding layers 134 each have a thickness between about 2 microns and about 15 microns.
The thermal stress compensation layer 130 may be formed using conventional multilayer thin film forming techniques illustratively including but not limited to chemical vapor depositing the pair of bonding layers 134 onto the MIO layer 132, physical vapor depositing the pair of bonding layers 134 on the MIO layer 132, electrolytically depositing the pair of bonding layers 134 onto the MIO layer 132, electroless depositing the pair of bonding layers 134 onto the MIO layer 132, and the like.
Referring now to
In embodiments, the MIO layer 132 is formed from copper, i.e., the MIO layer 132 is a copper inverse opal (CIO) layer 132. In such embodiments, the pair of bonding layers 134 may be formed from Sn, the bonding layers 112, 122 may be formed from nickel (Ni), and the TLP bond layers 112a and 122a comprise an intermetallic layer of Cu and Sn. In some embodiments, the TLP bond layers 112a and 122a comprise an intermetallic layer of Cu, Ni and Sn. For example and without limitation, the TLP bond layers 112a and 122a may include the intermetallic Cu6Sn5, the intermetallic (Cu, Ni)6Sn5, the intermetallic Cu3Sn or a combination of the intermetallics Cu6Sn5, (Cu, Ni)6Sn5, and/or Cu3Sn. It should be understood that the bonding layers 134 formed from Sn at least partially melt at the TLP sintering temperature and then isothermally solidify during the formation of the Cu—Sn intermetallic(s) since Cu6Sn5 starts to melt at 415° C. and Cu3Sn starts to melt at about 767° C. That is, a melting temperature of the TLP bond layers 112a, 122a is greater than a melting temperature of the pair of bonding layers 134.
Referring now to
The MIO layer 232 and each of the first pair of bonding layers 234 have melting points greater than a TLP sintering temperature and each of the second pair of bonding layers 236 have a melting point that is less than the TLP sintering temperature used to form a TLP bond between the metal substrate 110 and semiconductor devices 120. As a non-limiting example, the TLP sintering temperature is between about 280° C. and about 350° C. and each of the second pair of bonding layers 236 have a melting point less than about 280° C. and each of the MIO layer 232 and first pair of bonding layers 234 have melting points greater than 350° C. For example, the second pair of bonding layers 236 may be formed from Sn with a melting point of about 232° C., whereas MIO layer 232 and first pair of bonding layers 234 may be formed from materials such as Cu, Al, Ag, Zn, and Mg with a melting point of about 1085° C., 660° C., 962° C., 420° C. and 650° C., respectively. Accordingly, the second pair of bonding layers 236 at least partially melt and the MIO layer 232 and the first pair of bonding layers 234 do not melt during TLP bonding of the semiconductor devices 120 to the metal substrate 110.
The thermal stress compensation layer 230 may be formed using conventional multilayer thin film forming techniques illustratively including but not limited to chemical vapor depositing the first pair of bonding layers 234 and the second pair of bonding layers 236 onto the MIO layer 232, physical vapor depositing the first pair of bonding layers 234 and the second pair of bonding layers 236 onto the MIO layer 232, electrolytically depositing the first pair of bonding layers 234 and the second pair of bonding layers 236 onto the MIO layer 232, electroless depositing the first pair of bonding layers 234 and the second pair of bonding layers 236 onto the MIO layer 232, and the like.
Referring now to
Referring now to
In other embodiments, the thermal stress compensation layer 130 (or thermal stress compensation layer 230) is electroplate bonded or electroless plate bonded between the metal substrate 110 and the semiconductor device 120. In such embodiments, the electronic device assembly is placed in a electroplating bath or an electroless plating bath at step 340 and the MIO layer 132 is electroplate bonded or electroless plate bonded to the metal substrate 110 and the semiconductor device 120 at step 350 via electrolytic or electroless deposition of a bonding layer.
As stated above, the metal substrates and power electronics assemblies described herein may be incorporated into an inverter circuit or system that converts direct current electrical power into alternating current electrical power and vice versa depending on the particular application. For example, in a hybrid electric vehicle application as illustrated in
Power semiconductor devices utilized in such vehicular applications may generate a significant amount of heat during operation, which require bonds between the semiconductor devices and metal substrates that can withstand higher temperatures and thermally-induced stresses due to CTE mismatch. The thermal stress compensation layers described and illustrated herein may compensate for the thermally-induced stresses generated during thermal bonding of the semiconductor devices to the metal substrate and/or operation of the power semiconductor devices with a constant or graded stiffness across the thickness of the thermal stress compensation layers while also providing a compact package design.
It should now be understood that the multilayer composites incorporated into the power electronics assemblies and vehicles described herein may be utilized to compensate thermally-induced stresses due to CTE mismatch without the need for additional interface layers, thereby providing for a more compact package design with reduced thermal resistance.
It is noted that the terms “about” and “generally” may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. This term is also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.
While particular embodiments have been illustrated and described herein, it should be understood that various other changes and modifications may be made without departing from the spirit and scope of the claimed subject matter. Moreover, although various aspects of the claimed subject matter have been described herein, such aspects need not be utilized in combination. It is therefore intended that the appended claims cover all such changes and modifications that are within the scope of the claimed subject matter.
Claims
1. A transient liquid phase (TLP) bonding layer comprising:
- a thermal stress compensation layer disposed between at least one pair of bonding layers, the thermal stress compensation layer comprising a metal inverse opal (MIO) layer with a plurality of hollow spheres and a predefined porosity, wherein the MIO layer comprises a first surface, a second surface and a graded porosity between the first surface and the second surface;
- wherein the thermal stress compensation layer has a melting point above a TLP sintering temperature and the at least one pair of bonding layers each have a melting point below the TLP sintering temperature.
2. The TLP bonding layer of claim 1, wherein the MIO layer comprises a graded stiffness between the first surface and the second surface.
3. The TLP bonding layer of claim 1, wherein:
- the at least one pair of bonding layers comprise a first pair of bonding layers and a second pair of bonding layers, wherein:
- the first pair of bonding layers are disposed between the MIO layer and the second pair of bonding layers;
- each of the first pair of bonding layers have a melting point above the TLP sintering temperature; and
- each of the second pair of bonding layers have a melting point below the TLP sintering temperature.
4. The TLP bonding layer of claim 3, wherein the MIO layer is a copper inverse opal (CIO) layer, the first pair of bonding layers are formed from nickel, silver or alloys thereof, and the second pair of bonding layers are formed from tin, indium or alloys thereof.
5. The TLP bonding layer of claim 1, wherein the MIO layer has a thickness between about 50 microns and about 150 microns.
6. The TLP bonding layer of claim 1, wherein the plurality of hollow spheres have an average diameter between about 5 μm and about 50 μm.
7. The TLP bonding layer of claim 1, wherein the pair of bonding layers each have a thickness between about 2 microns and about 10 microns.
8. A power electronics assembly comprising:
- a metal substrate;
- a semiconductor device;
- a thermal stress compensation layer disposed between at least one pair of bonding layers disposed between and bonded to the semiconductor device and the metal substrate, the thermal stress compensation layer comprising a metal inverse opal (MIO) layer with a plurality of hollow spheres and a predefined porosity, wherein the MIO layer comprises a first surface, a second surface and a graded porosity between the first surface and the second surface; and
- wherein the thermal stress compensation layer has a melting point above a TLP sintering temperature and the at least one pair of bonding layers each have a melting point below the TLP sintering temperature.
9. The power electronics assembly of claim 8, wherein the MIO layer comprises a graded stiffness between the first surface and the second surface.
10. The power electronics assembly of claim 8, wherein the plurality of hollow spheres have an average diameter between about 5 μm and about 50 μm.
11. The power electronics assembly of claim 8, further comprising a pair of bond layers, wherein:
- the MIO layer is disposed between the pair of bond layers and transient liquid phase (TLP) bonded to the metal substrate and the semiconductor device through the at least one pair of bonding layers; and
- each of the pair of bond layers have a melting point above a TLP sintering temperature.
12. The power electronics assembly of claim 8, wherein the MIO layer is electroplate bonded or electroless plate bonded to the metal substrate and the semiconductor device.
13. A process for manufacturing a power electronics assembly comprising:
- positioning a thermal stress compensation layer disposed between at least one pair of bonding layers between a metal substrate and a semiconductor device to provide a metal substrate/semiconductor device assembly, the thermal stress compensation layer comprising a metal inverse opal (MIO) layer with a plurality of hollow spheres and a predefined porosity, wherein the MIO layer comprises a first surface, a second surface and a graded porosity between the first surface and the second surface; wherein the thermal stress compensation layer has a melting point above a TLP sintering temperature and the at least one pair of bonding layers each have a melting point below the TLP sintering temperature; and
- bonding the MIO layer to the metal substrate and the semiconductor device.
14. The process of claim 13, further comprising:
- heating the metal substrate/semiconductor device assembly to a transient liquid phase (TLP) sintering temperature between about 280° C. and 350° C., wherein the at least one pair of bonding layers each have a melting point less than the TLP sintering temperature, and the MIO layer has a melting point greater than the TLP sintering temperature such that the at least one pair of bonding layers at least partially melt and form a TLP bond between the MIO layer and the metal substrate and between the MIO layer and the semiconductor device; and
- cooling the power electronics assembly from the TLP sintering temperature, wherein the thermal compensation layer compensates for thermal contraction mismatch between the semiconductor device and the metal substrate during cooling from the TLP sintering temperature to ambient temperature.
15. The process of claim 14, wherein:
- the at least one pair of bonding layers comprise a first pair of bonding layers and a second pair of bonding layers:
- the first pair of bonding layers are disposed between the MIO layer and the second pair of bonding layers;
- each of the first pair of bonding layers have a melting point above the TLP sintering temperature; and
- each of the second pair of bonding layers have a melting point below the TLP sintering temperature.
16. The process of claim 13, further comprising placing the metal substrate/semiconductor device assembly in an electroplating bath or an electroless plating bath and electroplate bonding or electroless plate bonding the MIO layer to the metal substrate and the semiconductor device.
17. The process of claim 13, wherein the MIO layer comprises a graded stiffness between the first surface and the second surface.
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Type: Grant
Filed: Sep 11, 2017
Date of Patent: Aug 20, 2019
Patent Publication Number: 20190078227
Assignee: TOYOTA MOTOR ENGINEERING & MANUFACTURING NORTH AMERICA, INC. (Plano, TX)
Inventors: Shailesh N. Joshi (Ann Arbor, MI), Ercan Mehmet Dede (Ann Arbor, MI)
Primary Examiner: Kiley S Stoner
Application Number: 15/700,723
International Classification: B23K 31/02 (20060101); C25D 7/12 (20060101); B23K 35/30 (20060101); B23K 1/00 (20060101); C25D 5/50 (20060101); C25D 7/00 (20060101); B23K 101/36 (20060101);