The invention relates to a mold tool for encapsulating a semiconductor power module having top-sided pin connectors as well as a method of manufacturing such a semiconductor power module.
Traditionally, semiconductor power modules being formed by encapsulating the electronics have input and output leads which exit the molded module at the intersection of the two parts of the mold used for forming the encapsulation. This restricts the placements of leads to a plane substantially around the module. For reasons of increasing compactness and creepage distances between adjacent leads, it is disadvantageous to restrict placement of leads just in one plane so that the number of leads is rather restricted that can be arranged for one module. This is contrary to increasing the compactness of such modules. It is known in the art that an external contact on the top of a power module that means to create top-sided contact pins is difficult to mold because there are extreme difficulties to create a seal at the point of exit which influence leaking of mold compound during the molding process. It has to be borne in mind that top-sided contact pins should never be spoiled or contaminated by mold compound during the molding for encapsulating the electronics. One prior art approach is to simply create a metallic surface in plane with the mold surface onto which the contact pins are connected by drilling, welding, gluing, sintering or otherwise after the molding process is complete. However, this is disadvantageous just because it requires an extra manufacturing step.
Therefore, it is the object of the present invention to provide a semiconductor power module formed by encapsulating the electronics and yet leaving top-sided contact pins which can be kept completely clean from the mold compound during molding so that they can provide for a good electric conductivity when connected to other electronic components. A further object is to provide a method of manufacturing such a semiconductor power module having top-sided contact pins which are free of any mold compound even after molding has been completed so that excellent electric conductivity can be provided when the electrical connecting pins are connected to other electronic components.
This object is solved by a mold tool for molding a semiconductor power module with an electrical contact pin is provided which comprises an electrical contact portion for contacting a substrate and a protruding portion being a top-sided pin connector. The mold tool comprises a first and a second mold die which, when brought together for the molding process, form a cavity to be filled with a mold compound. After the mold compound has cured, the electrical components of the semiconductor power module are encapsulated. The first, upper die comprises a recess communicating with the cavity which is being part of the second, lower die. According to the invention, the recess is filled with a cushion-like soft material into which the top-sided pin connector is pushed so as to be completely surrounded by the soft material and to form a sealing device. As the top-sided pin connector is surrounded by the cushion-like soft material and preferably its viscosity is such that compound material being filled, injected or even pressed into the cavity of the lower die the cushion-like soft material stays in place and protects the top-sided pin connector. That means, the cushion-like soft material prevents the mold compound from reaching the electrical contact region of the top-sided pin connector. That means that the cushion-like soft material prevents contamination of the electrical contact portion of the pin connector by the mold compound which is introduced into the cavity. To that extent the cushion-like soft material forms a sealing means.
By means of this cushion-like soft material as the sealing means, the general challenge can be met to avoid any contamination of the contact area of the pins by the mold compound. Generally, such pins might be simple soldered pins, pins of a particular form such as press-fit pins which are meant for insertion into holes in PCBs or pins with holes or threaded holes formed therein for using screw connections. The cushion-like soft material may comprise a natural material such as rubber or a synthetic material such a silicone or a polytetrafluoroethylene (PTFE)-based material. Whatsoever materials are being used, the material should be able to withstand temperatures and pressures used in the molding process. For example, preferably a temperature range of 160° to 220° or even higher and pressures of at least 10 MPa should be easily coped with by the soft material. The soft material is integrated into the recess of the first mold die that means the upper die of the mold tool. The consistency of this soft material should be such that even under the pressure in the cavity when the mold compound is being injected or even pressed into the cavity of the lower die of the mold tool, it should not be compressed or pressed out of the recess, not even under a condition where the electrical contact portion of the electrical contact pin is taken up inside the soft material and completely covered so as to prevent any mold compound from reaching this electrical contact portion of the pin and therefore, any kind of contamination of the contact area of the pin by the mold compound is avoided. The soft material that means the cushion-like soft material should be able to withstand several thousand production cycles before having to be replaced. A mold tool that is used for molding a semiconductor power module with top-sided pin connectors as well as the inventive method of manufacturing a semiconductor power module comprising such top-sided pin connectors have the following advantages: It allows a much greater freedom of placement of contacts, so that increase of compactness is no longer an issue.
It allows contacts to be much more spread-out around the surface of the module and this is often a great advantage because there is a much greater freedom of placement of contacts, let alone the number of contacts which can be increased around the outer surface of the encapsulated electronics, that means the module. The spreading around the surface of the top-sided pin connectors can be used even if there are high-voltages applied between the contacts and in doing so, the distances required to avoid sparking can be maintained despite an increase of the number of pins for the module. So, the corresponding top contact layout enables a reduction of stray inductance which is increasingly significant for new technologies such as the use of silicon carbide semiconductors which allow higher and higher switching speeds. In the context of this application, top-sided contact pins mean that these pins protrude from any surface of the module other than the plane corresponding to the interface plane of the upper die and the lower die of the mold tool. Because of the fact that the top contacts can go straight down to the circuit board, that is, the substrate of the module, space may be saved on the substrate because there is no need for conductors along the surface of the circuit board. This allows circuit boards to become smaller and smaller by means of which the overall size of the module can be reduced. And furthermore, the top contacts allow for shorter control signal paths. Apart therefrom, the top contacts make the design of symmetric control signal paths to the various switching semiconductors much easier. Therefore, the simultaneous control of multiple semiconductors in parallel can be implemented much easier as compared to other layouts.
According to a further embodiment, the recess of the upper die of the mold tool is preferably drilled or machined into the bottom that means from the bottom side of the first die and having a size to take up the complete electrical contact portion of the electrical contact pin. The recess may also be designed such that it broadens out further from the cavity of the lower die towards the upper side, that means from the intersection line of the lower die and the upper die into the upper die in order for the soft material to retain in position within the recess of the upper mold die. For some soft materials, it may be an advantage to increase the pressure within the material simultaneously with transferring mold compound into the mold cavity. This may be done by an external pressurizing device which communicates with the soft material recess through a passage in the wall of the mold. Alternatively, this might be achieved by a careful shaping of the upper portion of the pin itself. For example, the pin can be provided with an area of increased diameter as compared to the upper most portion of the pin which represents the actual contact portion of the pin so that this area of the pin comprises a collar-like shoulder or an area of increased diameter that is pushed slightly into the mold material when the mold is closed and act as a kind of piston to increase the pressure within the soft material to even more guaranteeing a complete coverage of the soft material around the outer surface of the frontmost portion of the pin. Such a pressurizing passage guarantees that the soft material stays in the recess and fulfills its function of preventing mold compound from reaching the contact portion of the pin.
Preferably, the module comprises several pins which are held together by an integral unit of the sealing means. In order to refine the exact force used for inserting the pin into the soft material into the recess of the upper die, the actual length of the pin will have to be chosen carefully. Alternatively, some form of a kind of a spring may be built into the structure of the pin itself which will limit the force applied by the pin to the soft material as it is inserted. This spring-kind of structure can be a relief portion having elastically bendable portions which guarantee a deformation rather than a deformation of the shaft of the pin itself.
According to a second aspect of the invention, a method of manufacturing a semiconductor power module having top-sided contact pins is described. The inventive method comprises the steps of:
These steps guarantee that the electronics can be encapsulated by the mold material because the electronics arranged on a substrate or stacked together with a substrate is set into the cavity where the mold compound is filled in and cures so that the electronics is finally encapsulated. The length of the contact pins is designed such that it protrudes outside the lower die with the height which can be taken up in the recess arranged in the upper die filled with the soft material so that the protruding portion of the pin penetrates into the soft material is completely covered by this material. Thus, the soft material acts as a sealing means which prevents mold compound from flowing into the recess so that after taking out the encapsulated module out of the module tool, the top-sided pins are completely free of any contamination from mold compound and can be directly used for an electrical connection to any other electrical component.
Preferably, the electrical contact portion of the pin is sealed for preventing mold compound from coming into contact with the electrical contact region. This is realized by the electrical insulating surface being arranged perpendicular to the direction of movement of the first and the second die for closing the mold tool for the molding process.
At last, the electrical contact portion of the pin is inserted into the recess at closed mold tool after the recess has been filled with the cushion-like soft material.
A semiconductor power module with top-sided contact pins manufactured according to the described method provides for an encapsulated module with contact portions of pins protruding from the surface of the encapsulated module which are not contaminated by the mold compound used for encapsulating the electronics.
Further details and a general understanding of the invention will become clear with the embodiment described in the drawings for two states, the first one with the top-sided contact pin not yet inserted into the recess of the first, upper die and the second drawing with the top-sided pin contact being completely inserted into the soft material within the upper die, as a matter of course with only the front portion of the pin being penetrated into the soft material within the recess of the upper die.
The recess 7 within the first, upper mold die 6 is filled with a cushion-like soft material 8, the consistency of which, that means its viscosity, is such that it is displaceable when the electrical contact portion 3 is being inserted into this soft material 8 within the recess 7 of the upper mold die 6 of the mold tool 1. The viscosity of the soft material 8 is high enough that it is kept within the recess 7 that means it does not flow out from this recess 7, though soft enough for a protruding portion 5 as the electrical contact portion 3 to penetrate thereinto, displacing it and arranging for the electrical contact portion 3 to be completely surrounded by the soft material 8. By the term “completely surrounded” it is to be understood that the soft material 8 protects the entire surface of the electrical contact portion from the mold compound when the latter one is being inserted into the cavity of the second mold die of the mold tool 1. The soft material is not only displaceable by the electrical contact portion 3 which represents a protruding portion 5 of the pin 2, it is also, at least to a certain extent, compressible in order to further improve the sealing function of the soft material 8. In general, by encircling the complete surface of the protruding portion 5 of the electrical contact pin 2, a sealing means preventing mold compound being injected into the cavity of the lower die from contaminating the electrically conducting surface of the electrical contact portion 3.
In addition thereto, the electrical contact pin 2 comprises at its protruding portion 5 a collar-like section 9 which is designed in the shape of a shoulder and which acts as a piston-like surface when the protruding portion 5 is being inserted or pressed into the soft material 8 in the recess 7 of the upper die 6 of the mold tool 1. This kind of compression of the soft material increases the sealing function of the soft material 8 for the electrical contact portion 3 of the pin 2.
A protective film 18 may be arranged on the bottom side of the first mold die preferably completely extending over the opening of the recess 7 for receiving the contact pin 2. This protective film 18 is designed such that when the contact portion 5 of the pin 2 penetrates into the soft material 8 the protective film 18 engages the entire outer surface of the contact pin so as to prevent any soft material from directly engaging the surface of the electrical contact portion 5. The protective film 18 comprises the property of not adhesively sticking to the surface of the contact portion 5 and yet preventing any direct contact of the soft material 8 with the surface of the electrical contact portion 5 of the pin 2.
Whilst
In the state as represented in
It is important to state that the soft material 8 is made of a synthetic silicone and for this embodiment the protruding portion 5 that means the electrical contact portion 3 of the pin 2 is designed as a press fit pin. As a matter of course the shape and design of the pin 2 can also be different, that means not necessarily be a press fit pin. It is to be understood that the viscosity of the soft material 8 may vary also dependent on the shape of the protruding portion 5 of the pin 2 to be inserted into the soft material 8. When the pin 2 is embedded in the soft material 8, which represents the sealing material, it is prevented from so-called being over molded. The basic advantage of this mold tool 1 as well as the method for making such an electrical component having a protruding portion 5 of the pin 2 which is being electrically clean and need not be cleaned once the molding process for the electrical component to be encapsulated by this molding compound has been completed. It is the soft material 8 that with its sealing function prevents the pin from any contamination by the mold compound. It is not only the viscosity of the soft material that counts, it is also the property to withstand a transfer pressure which is at least 10 MPa and also high temperatures of at least 180° C.
In some embodiments, the module being manufactured may comprises several pins which are held together by an integral unit 14. In order to refine the exact force used for inserting the pin into the soft material 8 into the recess of the first mold die6 , the actual length of the pin will have to be chosen carefully. Alternatively, some form of a kind of a spring may be built into the structure of the pin itself which will limit the force applied by the pin to the soft material 8 as it is inserted. This spring-kind of structure can be a relief portion having elastically bendable portions 105 which guarantee a deformation rather than a deformation of the shaft of the pin itself.
In
In
After the start for carrying out the steps at the point S in the first step 201 a subassembly is supplied that comprises a first mold die 6 and has a recess 7 which is at least partially filled with soft material 8 and which faces to a mold cavity 16 within the second mold die and arranged around a substrate 4 to be encapsulated by a mold compound, the first and the second mold die forming a mold tool.
This first step 201 is followed by the second step 202 for carrying out this inventive method by placing a substrate into the cavity 16 of the second mold die and the pin being fixedly held by a sealing device and placed onto the substrate 4.
In the third step 203 the first 6 and second mold dies are closed together so that the electrical contact portion of the pin is inserted into the soft material 8 within the recess 7.
In the fourth step 204 mold compound is transferred into the cavity 16 of the mold tool. This can be done by simply pressing it thereinto or for example by injection molding. This depends upon the material used for the molding process or the encapsulation required for the module or from other factors known to the persons skilled in the art. After the complete mold of the mold compound has been inserted into the cavity 16, the process of manufacturing the semiconductor power module with an encapsulated casing has been completed.
While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.
Number | Date | Country | Kind |
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10 2018 219 003.8 | Nov 2018 | DE | national |
10 2018 219 005.4 | Nov 2018 | DE | national |
This application is a National Stage application of International Patent Application No. PCT/EP2019/079023, filed on Oct. 24, 2019, which claims priority to German Patent Application No. 102018219003.8 filed on Nov. 7, 2018 and German Patent Application No. 102018219005.4 filed on Nov. 7, 2018, each of which is hereby incorporated by reference in its entirety.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2019/079023 | 10/24/2019 | WO | 00 |