High reliability module

A module which includes a hermetically sealed housing and a terminal block which is integrated with the hermetically sealed housing to provide electrical connection to external devices.

BACKGROUND OF THE INVENTION

Electronic power modules are generally known for providing electrical power to circuits and devices such as motors, actuators, controllers etc. For applications requiring high reliability and high power, the modules are preferably hermetically sealed to prevent infiltration of moisture, dust or other contaminants into the module interior which can cause impairment or failure.

High power, hermetically sealed modules are usually custom-made and application-specific, and may not conform to industry/commercial standard configurations or outlines. As a result, unlike commercial modules, high reliability power modules are often very expensive. Thus, when a module is required for a high reliability application, the end user must expend a considerable amount of capital for obtaining samples in order to test and qualify the module for its use.

Furthermore, it is customary to make high reliability power modules with a metallic housing that is hermetically sealed. According to the conventional design, the interconnects for electrically connecting the components within the housing to external devices extend through the metallic body of the housing, but are insulated from the same by glass or the like. Kovar is a desirable material for forming interconnects in conventional designs in that Kovar has thermal characteristics similar to glass. However, Kovar's electrical resistivity undesirably increases the overall resistivity of the prior art modules.

BRIEF SUMMARY OF THE INVENTION

A module according to the present invention is adapted for high reliability applications, but includes features that allow it to be scaled for commercial and industrial applications as well.

A module according to the present invention includes a hermetically sealed housing containing components such as power semiconductor devices, and a terminal block which is electrically integrated with the hermetically sealed housing.

According to an aspect of the present invention the terminal block may be designed to fit a commercial or industrial configuration which can be provided to end users for testing and qualification separate from the high reliability, hermetically sealed housing. That is, the terminal block can be provided with a non-hermetic (less expensive) housing to the end user for testing and qualification. As a result, the cost of testing and qualification of the high reliability module for an end user is reduced.

Specifically, a module according to the present invention includes a hermetically sealed housing having a base, sidewalls, a lid, and hermetically sealed interconnects extending from the interior of the housing to the exterior thereof, and a terminal block which includes a lead frame embedded in a molded body. The leads of the lead frame are electrically connected to the interconnects and are adapted for external connection to external devices or electronic circuits.

According to an aspect of the present invention, the hermetically sealed housing can be replaced with a non-hermetic housing, which is less expensive, to reduce the cost of the same.

According to another aspect of the invention the hermetically sealed interconnects are formed from a low electrical resistivity material such as copper.

According to yet another aspect of the present invention each interconnect extends through a stress relief collar that is hermetically attached to a wall of the hermetically sealed housing.

According to a further aspect of the present invention the stress-relief collars are bell-shaped.

According to another aspect of the present invention the stress-relief collars are formed from Kovar.

According to an additional aspect of the invention the sidewalls of the hermetically sealed housing are formed from a material different from the base of the hermetically sealed housing. As a result, the exterior surface of the base of the housing is convex without extra machining steps, thereby reducing the cost of the module. In the preferred embodiment, the housing sidewalls are made from alloy46and the base is a moly base plate.

According to a further aspect of the present invention the lid of the hermetically sealed housing includes at least one rib as a reinforcement which assists in preventing the sidewalls of the housing from curving inwardly, thereby adding strength to the plate and the housing as a whole.

DETAILED DESCRIPTION OF THE EMBODIMENT

Referring toFIG. 1, a module10according to the present invention includes a hermetically sealed housing12, and a terminal block14. Hermetically sealed housing12includes power interconnects16. Power interconnects16serve as power transmission conduits to transmit power to and from the components contained within housing12, and are adapted to be electrically integrated with terminal block14. Specifically, terminal block14includes a molded body15, and a lead frame which is embedded within molded body15. The lead frame includes a plurality of power leads20(FIG. 2) having an end21that includes at least one recess18adapted for receiving, and electrically connecting to a corresponding interconnect16. Each power lead20further includes a free end22which is adapted for electrical connection to an external device (e.g. a motor) and/or a circuit.

In addition to power interconnects16, hermetically sealed housing12further includes control signal interconnects26. Control signal interconnects26are provided to transmit control signals from an external control circuit to corresponding components contained within hermetically sealed housing12. The lead frame embedded within molded body15of terminal block14further includes control leads28. Each control lead28includes an aperture large enough to receive the free end of a corresponding control signal interconnect26, as seen, for example, inFIG. 3. Solder or the like may be used to secure a control signal interconnect26to a corresponding control lead28and a power interconnect16to a corresponding power lead20.

Terminal block14further includes mounting rings30embedded in molded body15thereof. Mounting rings30are preferably comprised of brass or a similar material and are positioned to register with corresponding mounting holes32of hermetically sealed housing12. Thus, terminal block14and hermetically sealed housing12can be together mounted on a heatsink or the like using appropriate mounting hardware such as mounting screws.

It should be noted that molded body15includes compartment32in which control signal interconnects26are received as seen inFIG. 3. Furthermore, molded body15includes slots34each for receiving a corresponding lip portion36of a respective side panel38. Referring toFIG. 4, once each panel38is received by a corresponding pair of slots34, a compartment40is created around power interconnects16and portions of power leads20connected thereto. Potting compound41or the like may be disposed within compartments32,40in order to protect interconnects16,26and leads20,28attached thereto from environmental damage.

It should be noted that to facilitate external connection, molded body15is provided with a plurality of recesses42. Each recess42is adjacent a respective lead20,28and is adapted to receive a respective nut44. Once a nut44is received in a respective recess42, its adjacent lead20, or28is bent over the same to prevent nut44from falling out. As seen, for example, inFIGS. 1-4, each lead20,28is provided with an aperture19which registers with a corresponding nut44and allows access to the same so that a screw or the like may be used to secure a connection to each lead20,28.

Referring now toFIG. 5, hermetically sealed housing12includes a plurality of walls46hermetically attached to base24, and lid48. Walls46are arranged on base24to define a space for receiving electronic components. In the preferred embodiment of the present invention, the electronic components received in the space defined by walls46are power semiconductor devices50such as power MOSFETs, schottky diodes or the like which are electrically connected to one another by wire bonds52or the like to form an appropriate portion of a power circuit. To thermally connect, but electrically insulate, power semiconductor devices50from base24thermally conductive circuit boards54such as direct bonded copper (DBC), or insulated metal substrate (IMS) are attached to base24and power semiconductor devices50are disposed on the same as seen inFIG. 6. Thus, the heat generated by power semiconductor devices50during operation can be transmitted through circuit boards50to base24and dissipated by a heatsink (not shown) attached thereto.

Furthermore, the electronic components contained within housing12are electrically connected to interconnects16,26. Thus, for example, power interconnects16may be electrically connected to the power terminals of the power semiconductor devices50, while control interconnects26may be electrically connected to the control electrodes of the power semiconductor devices50, where appropriate. As seen, for example, inFIG. 6, electrically conductive strips56can be used to electrically connect the components contained within housing12to corresponding power interconnects16. To complete housing12lid48is hermetically attached to walls46.

According to one aspect of the present invention, terminal bock14may be integrated with a less expensive, non-hermetic housing in order to reduce the cost of the same.

Referring now toFIG. 7, according to one aspect of the present invention, lid48includes at least one rib49. Rib49increases the mechanical strength of lid48and thus prevents flexing which may warp the housing.

According to another aspect of the present invention, walls46are formed from NiFe (Alloy 46) while base24is formed from molybdenum. Due to the slight mismatch in the characteristics of these two materials, base24is bent slightly whereby its exterior surface is convexly shaped once housing12is constructed. The convex exterior surface is desirable for making a good thermal contact with a heatsink or the like. In modules according to the prior art such a convex shape is attained by machining the exterior surface of base24, which is costly. In a module according to the present invention the costly machining step is avoided, which is advantageous.

As can be seen, power interconnects16and control signal interconnects26are fed from the hermetically enclosed interior of housing12to the exterior thereof. According to an aspect of the present invention power interconnects16as well as control signal interconnects26are fed through respective stress relief collars58. Each collar58is in turn hermetically attached to a respective seal member60which itself is hermetically attached to a respective wall46. Each seal member60is preferably made from an electrical insulator such as alumina or the like and includes an aperture62which registers with an aperture64in a respective wall46to accommodate at least a portion of a collar58and an interconnect16disposed therethrough.

According to an aspect of the present invention, collars58are bell-shaped. This bell-like shape helps relieve stresses caused by thermal expansion and contraction by bending like a spring. As a result, the reliability of the module is improved.

According to another aspect of the present invention, bell-shaped collars58are made from Kovar, while interconnects16,22are made from copper. Using copper to form power interconnects is particularly advantageous in that copper has low electrical resistivity. In the prior art modules, Kovar is used as an interconnect because of its thermal expansion characteristics. This, however, is a drawback because Kovar's electrical resistivity is relatively high. A module according to the present invention is improved compared to the prior art modules in that its overall electrical resistivity is improved while its mechanical reliability is not compromised.

In a module according to the preferred embodiment, the lead frame embedded in terminal block14is formed from copper to improve the electrically resistivity of the module, while molded body15is formed from a suitable engineering plastic.