This application claims priority to German Patent Application No. 10 2014 115 201.8 filed on 20 Oct. 2014, the content of said application incorporated herein by reference in its entirety.
The invention relates to the production of a soldered connection between a circuit carrier and a carrier plate, such connections being used for example in the case of electronic modules in which the carrier plate forms a baseplate of the module.
Circuit carriers are usually soldered to the carrier plate. In this case, on the one hand the circuit carriers must be located sufficiently accurately at a predetermined target area of the carrier plate after the soldering operation; on the other hand it is advantageous for the quality of the soldered connection if the circuit carrier floats on the liquid solder during the soldering. The latter may however have the effect that the circuit carrier floats so far as to be outside the target area. This may occur for example if the carrier plate has on the side to which the circuit carrier is to be soldered an unevenness that causes the solder to run away sideways when it melts during the soldering process. In the case of electronic modules, such unevenness often occur whenever the carrier plate is provided with a precurvature before the soldering process, in order to minimize as far as possible later curvatures in the finished assembly, such as occur as a result of different coefficients of thermal expansion of the materials involved. Unwanted floating may for example also occur whenever the side of the carrier plate to which the circuit carrier is to be soldered is in fact planar but is inclined with respect to the horizontal. In the case of electronic modules, the tolerances associated with floating of the circuit carrier may be allowed for in the design of the electrical terminals to be connected to the circuit carrier, but it is nevertheless not permissible for the circuit carriers to float entirely without restriction.
A method is provided for soldering a circuit carrier to a carrier plate with which a circuit carrier can be reliably connected to a carrier plate within a predetermined target area.
According to one embodiment, a carrier plate, a circuit carrier and a solder are provided for the soldering of a circuit carrier to a carrier plate. The carrier plate has an upper side, and also a first adjusting device, and the circuit carrier has an underside, and also a second adjusting device. The circuit carrier is placed onto the carrier plate in such a way that the underside of the circuit carrier is facing the upper side of the carrier plate, the solder is arranged between the carrier plate and the circuit carrier, and the first adjusting device forms a stop for the second adjusting device that limits a displacement of the circuit carrier placed on the carrier plate along the upper side of the carrier plate. After that, the solder is melted and subsequently cooled down, until it solidifies and connects the circuit carrier to the carrier plate in a material-bonding manner at a lower metallization layer.
Those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings.
This and further aspects of the invention are explained below on the basis of exemplary embodiments with reference to the accompanying figures, in which:
The representation in the figures is not to scale. Unless otherwise specified, in the figures the same designations denote elements that are the same or have the same effect.
The circuit carrier 2 also has a dielectric insulation carrier 20, to which an upper metallization layer 21 has been applied, and also an optional lower metallization layer 22, which are located on sides of the insulation carrier 20 opposite from one another. The upper metallization layer 21 may, if required, be structured, so that it has conductor tracks, which can be used for example for electrical interconnection and/or for mounting chips. The dielectric insulation carrier 20 can be used for the purpose of electrically insulating the upper metallization layer 21 and the lower metallization layer 22 from one another.
The circuit carrier 2 may be, for example, a ceramic substrate, in which the insulation carrier 20 is formed as a thin layer which comprises ceramic or consists of ceramic. Metals with good electrical conduction, such as for example copper or copper alloys, aluminum or aluminum alloys, but also any other metals or alloys, are suitable as materials for the upper metallization layer 21 and, if present, the lower metallization layer. If the insulation carrier 20 comprises ceramic or consists of ceramic, the ceramic may for example be alumina (Al2O3) or aluminum nitride (AlN) or zirconia (ZrO2), or a mixed ceramic which, in addition to at least one of the ceramic materials mentioned, also comprises at least one other ceramic material different from it. A circuit carrier 2 may for example be formed as 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). The upper metallization layer 21 and the lower metallization layer 22 may, independently of one another, have in each case a thickness in the range from 0.05 mm to 2.5 mm. The thickness of the insulation carrier 20 may for example lie in the range from 0.1 mm to 2 mm. However, thicknesses greater or smaller than the thicknesses specified are likewise possible. The thicknesses are in this case respectively to be determined in a direction perpendicular to the underside 2b of the circuit carrier 2.
The carrier plate 3 may for example be formed as a metal plate. It may for example consist completely or to at least 90% of copper, aluminum or a copper-aluminum alloy, or of a metal-matrix composite material (MMC=Metal Matrix Composite). Optionally, it may also have on its upper side 3t a thin coating, for example an electrodeposited nickel layer, in order to improve the solderability.
If a circuit carrier 2 is populated with one or more optional semiconductor chips 1, the circuit carrier 2 may be pre-populated with these semiconductor chips 1 and then soldered in the pre-populated state together with the semiconductor chip or chips 1 to the carrier plate 3. Each such semiconductor chip 1 may contain any desired electronic component, for example a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), an IGBT (Insulated Gate Bipolar Transistor), a thyristor, a JFET (Junction Field Effect Transistor), an HEMT (High Electron Mobility Transistor), a diode, etc.; alternatively or additionally, also any one or more other active or passive electronic components.
The upper side 2t of the circuit carrier 2 represents its component side and is provided by the side of the circuit carrier 2 that is facing away from the carrier plate 3, while the side of the circuit carrier 2 that is facing the carrier plate 3 forms its underside 2b. The underside 2b of the circuit carrier 2 serves the purpose of connecting it to the carrier plate 3 in a material-bonding manner.
The carrier plate 3 also has a projection 41, which engages in a cutout 42 in the circuit carrier 2, here a cutout in the lower metallization layer 22. As explained in still more detail below, the projection 41 serves the purpose of limiting floating of the circuit carrier 2 during the liquid state of the solder 5 during the soldering of the circuit carrier 2 to the carrier plate 3.
A method for producing an assembly in which a circuit carrier 2 is soldered onto a carrier plate 3 is explained below on the basis of
The lower metallization layer 22 has a cutout 42, which may optionally extend up to the insulation carrier 20. Alternatively, the cutout 42 may also be formed as a blind hole in the lower metallization layer 22, which extends from the underside 2b into the lower metallization layer 22 in the direction of the insulation carrier 20, but does not reach up to it. Irrespective of whether or not it extends up to the insulation carrier 20, the cutout may in this case be formed as a through-opening in the lower metallization layer 22 that is annularly surrounded by the lower metallization layer 22, but also as a groove that extends laterally into the lower metallization layer 22, which is explained later on the basis of
As also shown in
The use of two or more spaced-apart projections 41 allows not only reliable limitation of linear floating of the circuit carrier 2 floating on the liquid solder 5 but also rotation. In principle, however, rotation can also be achieved with only one projection 41 and only one cutout 42, if their geometries are correspondingly made to match one another. Although the geometries of a projection 41 and a cutout 42 can in principle be chosen as desired, reliable and precise limitation of rotation requires that the projection 41 and the cutout 42 then extend over a great range in the lateral direction. This may, however, be disadvantageous for example if the waste heat that occurs in a semiconductor chip 1 arranged on the upper side 2t of the circuit carrier 2 is to be removed by way of the circuit carrier 2 and the carrier plate 3, because there is no thermal contact, or not particularly good thermal contact, between the circuit carrier 2 and the upper side 41t of the projection 41 (see
By analogy thereto,
The previously explained projections 41 form an adjusting device of the carrier plate 3, and the cutouts 42 form an adjusting device of the circuit carrier 2. By analogy thereto, it would also be possible that an adjusting device of the carrier plate 3 has one or more cutouts, which respectively extend from the upper side 3t of the carrier plate 3 into it, and that an adjusting device of the circuit carrier 2 has one or more projections, which are formed as projections of the lower metallization layer 22 and extend away from the insulation carrier 20 on the side of the lower metallization layer 22 that is facing away from the insulation carrier 20. Each one of these projections can then engage in one of the cutouts in the carrier plate 3 during the soldering of the circuit carrier 2 and limit a linear displacement and/or a rotation of the circuit carrier 2 floating on the solder 5.
Irrespective of whether projections 41 are formed on the lower metallization layer 22 or on the carrier plate 3, they may for example be produced by stamping. Cutouts 42 in the lower metallization layer 22 or the carrier plate 3 may be created for example by drilling or milling.
Furthermore, cutouts 42 in the lower metallization layer 22 may already be created in it before the lower metallization layer 22 is connected to the insulation carrier 20. Thus, for example, one or more cutouts 42 may be stamped into a metal foil and the metal foil then connected to the insulation carrier 20 together with a further metal foil, which later forms the upper metallization layer 21.
If only one projection 41, which is formed either on the lower metallization layer 22 of the circuit carrier 2 or on the carrier plate 3 and engages in a cutout 42 in the carrier plate 3 or the lower metallization layer 22, is used for limiting the floating of a circuit carrier 2, the projection 41 that is formed on the lower metallization layer 22 or the cutout 42 that is formed in the lower metallization layer 22 may for example be located in the region of the middle of the circuit carrier 2, see for example
If, otherwise, two projections 41, which are formed either on the lower metallization layer 22 of the circuit carrier 2 or on the carrier plate 3 and respectively engage in a cutout 41 in the carrier plate 3 or the lower metallization layer 22 are used for limiting the floating of a circuit carrier 2, the projections 41 that are formed on the lower metallization layer 22 or the cutouts 42 that are formed in the lower metallization layer 22 may for example be located on a center parallel m of two opposite side edges 2k of the circuit carrier 2, see for example
In principle, irrespective of whether it is formed on the lower metallization layer 22 or on the carrier plate 3, a projection 41 may have any desired cross section. One possible variant is for example a circular cross section. Furthermore, irrespective of whether it is formed on the lower metallization layer 22 or on the carrier plate 3, a cutout 42 may have any desired cross section. One possible variant is for example a circular cross section, or an approximately U-shaped cross section.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.
Number | Date | Country | Kind |
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102014115201.8 | Oct 2014 | DE | national |