Combining the Features of Modules and Discretes in a New Power Semiconductor Package

A new package for power semiconductors has been developed: Power semiconductor chips are soldered onto a DCB ceramic substrate together with a lead frame with up to ve pins. Subsequently chips and DCB are covered by molding compound. This packaging method combines the technologies of module and discrete assembly. Thus the resulting component provides a combination of the characteristics of both families of devices: The new components are internally isolated from the heatsink they will be clamped onto. The pins are soldered into a printed circuit board; any circuit with an adequate number of pins can be incorporated in the package, using any kind of chip | such as MOSFETs, IGBTs, thyristors, diodes | and any topology. The pinouts are de ned according to the requirements of electrical circuit design | for example avoiding current loops |, which | together with the very compact volume of the package | faciliates a low inductive design of power section. Designing scalable power sections for a broad range of nominal power is easy due to the possibility of connecting devices in parallel. Reliability is expected to be comparable to modules' because of the matched thermal expansion coe cients of silicon chips and DCB ceramic substrate they are soldered onto. These features described in this paper make the new family of components advantageously applicable in a variety of converters, such as for industrial and automotive drives or for power supplies. 1 Packaging Technology The new package will be named Isoplus I4PacTM in the following. Its top and bottom view are shown in gure 1. Basically, it looks similar to conventional discrete components such as TO247; however signi cant di erences become obvious regarding the cross section in gure 2: The chips are not mounted on a solid metal leadframe, but on a DCB substrate [1]. It consists of a ceramic substrate with copper layers bonded onto its top and bottom side. The bottom copper, used to transfer the operational power dissipation to the heatsink, is visible in the package's bottom view gure 1. The ceramic isolates it from the top copper layer, which may be structured corresponding to a printed circuit board as visible in gure 2. The top copper carries the chips, whose upper side is wire bonded towards the DCB pattern and the pins. To provide electrical and mechanical protection, this subassembly is transfer molded, thus creating the typical black plastic package. Two versions of the package with di erent pin distances have been successfully introduced. Their outlines are shown in gure 3. Height and length correspond to TO247, width to TO264 industry standard packages. The experiences gained by IXYS' proprietary DCB production and discrete assembly, together with manufacturing the already introduced TO247 like Isoplus247 package [2], have helped to install the assembly process. The construction as described o ers several bene ts to the user of the components: 2 Combining the Features of Modules and Discretes in a New Power Semiconductor Package Figure 1: top and bottom view of ve pin version Figure 2: cross section of ve pin version Figure 3: dimensional drawing of three pin (left) and ve pin (right) version A large variety of topologies with a all kinds of power semiconductor switches can be incorporated. The pinout can be de ned in an electrically favourable way. The power circuit is internally isolated from the heatsink. A heatsink with an appropriate geometry permits to obtain a creepage distance between pins and ground of more than 6mm without additional measures. Combining the Features of Modules and Discretes in a New Power Semiconductor Package 3 Standard mounting processes can be used: The pins are soldered into a printed circuit board. The package is simply directly clamped onto the heatsink with an industry standard spring [3], generally using some thermal compound to achieve a good heat transfer between the package and the sink. This mounting procedure allows considerable savings, because no external isolator is required. High reliability is achieved due to the corresponding thermal expansion coe cients of silicon chips and DCB substrate. The following section 2 gives more details on several products with reference to the general features previously outlined. Section 3 shows their signi cance in exemplary applications. 2 Topologies, Components This section presents some components in Isoplus I4-Pac package recently developed or currently under development. Of course there is a variety of further possibilities. Numbering of the pins as used in the following is shown in gure 4. Figure 4: pinout of three pin (left) and ve pin (right) version