Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
1999-07-06
2001-10-16
Picard, Leo P. (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S707000, C361S709000, C361S710000, C361S719000, C257S718000, C257S719000, C174S016300, C165S080300, C165S185000
Reexamination Certificate
active
06304449
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
The present disclosure sets out a power semiconductor mounting apparatus. It involves wedging action to secure a power semiconductor to a heat sink. The heat sink set forth in the present disclosure incorporates at least two fins, one being defined as the base fin and the second being defined as the adjacent and coextensive spring fin. They are arranged with parallel roots along a heat sink base and are constructed with a modest angle between the two. The angle typically is in the range of about 2 to about 8 degrees. As will be defined, the optimum angle is perhaps 5 degrees.
A power semiconductor (hereinafter PSC) is a device required to switch many amperes of current. To handle this, they normally must be provided with a heat sink to dissipate the heat generated with such large currents flowing through the PSC. These devices are normally provided in industry standard packages, and references made to industry standard forms or packages identified as the TO-220, the TO-247 and the TO-264. These are representative devices. They are commonly made with a plastic shell around the semiconductor. On one face, there is normally a flat metal surface which is confined within the edges and is therefore a surface having a metal contact region for dissipation of electrically generated heat.
Good heat transfer is accomplished by making firm contact against the TO-220 or comparable packaging. It is undesirable to pinch the housing at an edge or corner. When this occurs, it will distribute the point loading stress lines in that region and may well cause mechanical failure of the device which will ultimately lead to electrical failure. It is just as undesirable to mount the transistor with the most common mounting mechanisms in use today, which include small machine bolts. They are often used to clamp down the industry standard containers so that the metal face is brought into physical contact with another metal surface for heat dissipation. Where that approach is used, careful alignment must be accomplished to assure that every part is planar in contact. Where contact is not planar, there is the risk of regional stress which will damage the PSC device. There is also the risk that even the most perfect of installations will work free over time when the machine bolt is anchored. The machine bolt typically must be held in place with some sort of lock washer or other split washer which prevents the bolt from backing out with the passage of time. That risk engenders another mode of failure. While installation might be acceptable at the start, vibration and other sources of movement may prompt unthreading. Vibration, unthreading, and difficulty of use are serious problems with bolted down transistor bodies.
The present disclosure is directed to an improved system for anchoring an industry standard PSC. It is placed in the inscribed V between the defined fins, namely, the base fin and the spring fin. They are constructed so that the PSC inserts easily into the gap between the two fins. The PSC is jammed against the fins, but in such a way that no damage arises. Moreover, the present invention contemplates the incorporation of a centralized raised region of specified geometric shape to be attached to the transistor shape. This is in addition to the transistor shape. In that sense, it departs somewhat, but ever so slightly, from the industry standard profile that otherwise is mandated by the semiconductor industry. To take advantage of the high performance characteristics of many PSC's, it is necessary that they be installed in a mode whereby heat is dissipated rapidly. If heat is permitted to build up in the region, then the chips may fail. Such failures are commonly dependent on heat removal. It is possible to underdesign the circuit so that a particular PSC assigned to the circuit is under performing or loafing. When this is done, the PSC will then perform in a desired fashion, but without the maximum performance. It is possible, alternatively, to design the circuit so that the transistor performs to the optimum. This, however, generates so much heat that heat sink construction is commonly critical. The prevailing or normal implementation is use of bolt down techniques. In other words, a finned aluminum heat sink is bolted to the transistor. While this will succeed, there are limitations to it and it is not the optimum way of heat transfer.
The present disclosure has revealed that a heat sink can be intimately contacted against the transistor in a better way. The PSC is clamped against one of the two fins defined above, the two fins being deployed at a small angle, and the transistor and the base fin make good face to face contact so that the temperature of the metal making up the transistor is reduced and heat liberated by this process is easily dissipated.
Another aspect of the present disclosure relates to the ease of installation. The old approach involved machine bolts. Typically, these required hand installation with a small screw driver, and required unusually small fingers to hold the bolt on one side and to hold the lock washer or split ring under the head of a nut to thread these parts together.
In volume, that is very difficult to accomplish. The present system avoids or seeks to avoid use of such screw driver assisted connections. Rather than that, this sets forth a system by which the industry standard PSC is mounted on a printed circuit board (PCB) so that easy mounting and dismounting can be done. More important, the incorporation of a PCB parallel to and commonly under the heat sink enables another feature of the present disclosure to be implemented. The PCB and the heat sink are positioned with respect to each other so that the PSC can be added after other components are fabricated on the board. For this, the PSC is slipped through the board and is inserted across the board at a rectangular slot which is sized to receive the PSC. This leaves the leads protruding on the opposite side of the PCB for easy connection. The body of the PSC is inserted and jammed up into the fins. By adding it after all the other components have been assembled, ease of alignment with the heat sink mechanism can be achieved and ease of alignment of the later installed PSC can be achieved. All of this is desirable from the point of view of improved fabrication quality, speed and improved protection against heat overload.
Heat sinks are necessary to cool power semiconductors (PSC hereinafter). Generally, data processing integrated circuit components handle sufficiently little power that cooling with a heat sink is ordinarily not necessary for them. Indeed, even where the integrated circuit density results in 500,000 or even more than 1,000,000 integrated circuit components in a data processing chip, the amount of heat that is liberated is sufficiently low that power dissipation is easily handled without resort to heavy off board mounted aluminum heat sinks. By contrast, a silicon control rectifier (SCR hereinafter) may be required to switch on and off very large current flows, perhaps 50 amperes or greater. While the voltage across the terminals and the current flow through the SCR or PSC is quite large, there is the risk of generating large heat loads during ordinary operations so that the heat must be dissipated through a heat sink. The heat sink is commonly constructed of aluminum and is normally provided with a number of fins so that the heat in the heat sink is radiated to atmosphere through the enlarged surface region provided by the heat sink. This is essential to avoid burning up the expensive circuit component. Even if the component were not expensive, repair is ordinarily expensive because it requires disassembly of circuit components, often enclosed in a cabinet or housing, and that requires that the circuit be taken out of operation. Such repairs are not welcome events.
A heat sink must be intimately contacted against the SCR or PSC to which it is attached. The heat sink must regularly be brought into firm and solid contact so that heat is transferred from the
Bracewell & Patterson LLP
Chervinsky Boris L.
Picard Leo P.
LandOfFree
Heat sink mounting for power semiconductors does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Heat sink mounting for power semiconductors, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Heat sink mounting for power semiconductors will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2603458