JPH02229456A - Improved cooling assembly for semiconductor vertical power device - Google Patents

Abstract

PURPOSE: To form a lightweight and compact cooled assembly by a method wherein at least one of devices is annexed to the other main surface of the main surfaces of a ceramic pad with a groove and heat generated from the devices is absorbed in a circulating fluid which flows through the groove. CONSTITUTION: A ceramic pad 20 made of a beryllia is annexed to an interposing plate 40, which is made of a copal, under its lower surface so that a closely adhered assembled body, which is annexed to a compact feeding plate 50, in provided by a mounting means 45. Before the pad 20 is brazed or soldered to the plate 140, both surfaces of the pad 20 are metallized. A microscopic channel having such a large aspect ratio as that of a groove 21 is formed on the metallized lower surface of the pad 20. The surface, which has the groove 21, of the pad 20 is brazed to the plate 40 with a Cu/Ag alloy layer 30. The pad 20 and the plate 40 are aligned with each other prior to the brazing in such a way that the groove is extendedly provided to the outer edges of the entrance 41 and the exit 42 of the plate 40.

Description

[Detailed description of the invention] A cooling assembly according to claim 6.

TECHNICAL FIELD This invention relates to semiconductor vertical power devices (high power semiconductor devices) and, more particularly, to an improved cooling assembly and method for cooling such devices during operation.

The current trend toward miniaturization of semiconductor devices has resulted in a significant increase in power generation in semiconductor chips, whether they are discrete devices or large integrated circuits.
Increasing power density increased operating temperature, a factor that negatively affected device lifetime and limited its performance. Traditional cooling methods have not been able to maintain device operating temperatures low enough. rI by Tatzkerman and Bies
EEE Electron Device Letters J (
(1981) showed that forced convection of fluid through microchannels (conducting grooves) formed by etching on the back side of a silicon chip is an effective method for cooling devices. Although their method was attractive, it had many practical problems. In other words, the presence of microchannels in the chip mechanically weakens the chip, making it difficult to package it into a robust package. Furthermore, the bufuses that form microchannels are too fine, which often reduces reliability and yield. There are many applications where it is not possible to form microchannels on the backside of the chip. This is especially true for vertical power devices where the bottom surface of the substrate forms one of the terminals. In such a case, the semiconductor
The semiconductor is electrically isolated from the package case by inserting a ceramic pad, usually beryllia or alumina, between the semiconductor and the package case. The package is then placed on a heat sink. Heat sinks are traditionally heavy and often bulky blocks of copper.

Unfortunately, ceramics are generally poor thermal conductors, thus introducing high thermal resistance between the chip and the heat sink.

The object of the invention is to reduce the above-mentioned drawbacks of the prior art as well as other drawbacks.

Another object of the present invention is to develop a cooling assembly that allows circulating fluid to be brought into close proximity to operating semiconductor devices.

It is an object of the present invention to develop a cooling assembly that reduces the number of interfaces in the path of heat flowing from an installed semiconductor device to the cooling assembly.

Yet another object of the present invention is to develop a cooling assembly that provides very low thermal resistance for semiconductor device packages. Yet another object of the present invention is to develop a cooling assembly for semiconductor devices that does not require any special semiconductor processing. It is also an object of the invention to develop a cooling assembly that is lightweight and compact in size.

The above-mentioned problems are solved in one aspect of the present invention by a new and improved cooling assembly for vertical semiconductor power devices. The cooling assembly includes a ceramic pad with a plurality of small channels or grooves formed on one side having a large aspect ratio, and a semiconductor device is placed on the other side of the pad. In this specification, the terms "microchannel" and "groove" are used interchangeably. A compact feeder plate with multiple spaced inlets/outlets can be attached to the grooved side of the ceramic pad to act as an interface to the circulation means. Circulation means introduce fluid into the inlet of the feed plate, with the fluid being circulated through the groove and discharged through the outlet means. The fluid absorbs heat from the device as it flows through the channels. Although there are many possible geometries for the grooves, the length and configuration of the grooves and inlet/outlet means should maximize heat exchange. In another aspect of the invention, the assembly includes an intervening plate, soldering means and sealing means. An intervening plate is disposed between the feed/discharge plate and the ceramic pad to provide a cohesive assembly in which the inlet/outlet means of the intervening plate are aligned with the corresponding inlet/outlet means of the feed/discharge plate. ．． A brazing means brazes the grooved surface of the ceramic pad to the intervening plate. The sealing means applies an epoxy seal to the outer surface of the ceramic pad to contain the circulating fluid. Figure IA is a schematic side view of a semiconductor device package with an attached cooling assembly according to the present invention. As shown, the cooling assembly consists of ceramic butts 20 mounted on an intervening plate 40. A compact feeding plate 50 is attached to the intervening plate 40. A semiconductor vertical power device 10 is attached to the top surface of the ceramic butt 20. Prior to assembly, microchannels having a large aspect ratio, designated individually or collectively by the reference numeral 21, are formed on one side of the ceramic pad such that the resulting grooves run transversely to the longitudinal direction of the ceramic pad 20. Ru. In another embodiment, the geometric profile of the grooves can be different as long as the profile increases the surface area of the ceramic surface. As mentioned above, the terms groove and microchannel are used interchangeably. A soldering process brazes or solders the grooved surface of the ceramic bud 20 to the intervening plate such that the openings 41 and 42 forming the inlet/outlet are exposed in the groove. A compact feeding/discharging plate 50 is included in the intervening plate 4
0, openings 4l and 42 are provided in alignment with openings 5l and 52, respectively, constituting the inlet/outlet of the feed/discharge bullet 50. Pressurized fluid enters the cooling assembly through inlets 5l and 4l and flows through the ceramic pad grooves before exiting through outlets 42 and 52. Since the flow is laminar and the flow rate is small, the circulation requirements are modest. Figure IB is a detailed enlarged view of the part marked with a circle in Figure IA. As shown in FIG. IB, fluid flows through inlets 41 and 51 and in close proximity to device 10 and through one of the plurality of grooves and microchannels.
This circulation allows the fluid to absorb heat generated by semiconductor device 10 and transferred to the fluid through the ceramic. Fluids with high specific heat, such as water, are used to maximize this heat absorption. Compared to smooth ceramic pads, ceramic pads according to the invention effectively increase the ceramic surface area through which heat is transferred to the fluid. Additionally, the overall thermal resistance of the bag is reduced because the fluid flows closer to the device surface. FIG. 2 is a side cross-sectional view of a single groove across the length of a ceramic pad in accordance with a preferred embodiment of the present invention. Elements of the cooling assembly have reference numerals corresponding to Figures IA and B. Referring to the semiconductor device package in FIG. 2, the ceramic pad 20 manufactured by Perilia is
On its underside, attachment means 45 attach to an intervening plate 40 made of Kovar to provide a tight assembly attached to a compact feed plate 50. Prior to brazing or soldering the beryllia ceramic pad 20 to the intervening plate 40, the pad 20 is metallized on both sides and microchannels with large aspect ratios, such as grooves 21, are formed on the metallized bottom surface. It is formed. Grooved surface is Cu/A
It is soldered to the Kovar intervening plate using g-alloy 30. The beryllia ceramic pad 20 and the Kovar intervening plate 40 are aligned prior to soldering so that the grooves extend around the outer edges of the inlet 4l and outlet 42 of the plate 40. In other embodiments, multiple inlets and outlets may be present, such that maximum heat transfer occurs when the groove also extends to the outer edge of another inlet and outlet. Additionally, other seed ceramics with high thermal conductivity may be used in other embodiments. The assembly is plated with 24kT gold on the top surface of the ceramic pad 20 to which the semiconductor device is eutectic bonded. An epoxy slot seal 25 is coated on the end face of the ceramic pad to contain fluid. A compact feed plate 50 is attached to Kovar interposer plate 40 such that inlet 4l and outlet 42 are aligned with inlet 5l and outlet 52 of feed plate 50, respectively. As shown in FIG. 2 for a single microchannel, fluid enters through inlets 51 and 41 and flows through groove 21 and then exits through outlets 42 and 52. Similar fluid circulation circuits exist for each of the multiple grooves. FIG. 3 shows the ceramic pad 20 and the intervening plate 40.
Fig. 2 is a perspective view with a part of the ceramic pad removed. As indicated by the arrows, fluid enters through the inlet 4l of the interposer plate 40 and passes through the plurality of grooves 21.
The circulating fluid absorbs the heat generated by device 10 and exits the assembly through outlet 42. Although the grooves are present along the entire length of the ceramic bud 20, the grooves are located at the inlet 41 and outlet 4 as suggested in FIG.
It is sufficient to extend it to the outer edge of 2. It is often easier to fabricate it so that it exists along the entire length. An epoxy seal 25 is filled and coated on the groove ends until it reaches the outer edges of the inlet 4l and outlet 42. AND IR AND PRESENTATION As described above, an improved cooling assembly for semiconductor vertical power devices has been provided.

The grooved ceramic pad according to the invention allows for higher heat absorption by the circulating fluid than a flat surfaced ceramic pad. Thermal resistance is also lower because the fluid flows closer to the actuating device. The use of grooved ceramic pads eliminates the need for bulky copper blocks as heat sinks. The cooling method of the present invention is useful when high power densities are present, such as in semiconductor laser and multi-chip applications.
You can use anything. The method also provides that the groove is
Since it is made on the ceramic pad on which the C chip is placed, it does not significantly affect chip reliability or yield.
A vine used to cool IC chips. Furthermore, the method does not require special semiconductor assembly processing processes. Since the use of power devices in outside spaces requires that the device package be lightweight and small, the cooling assembly of the present invention is particularly suited for such applications.

Although preferred embodiments of this invention have been described above, it is to be understood that many changes may be made within the scope of this invention.

[Brief explanation of the drawing]

FIG. 1A is a schematic side view of a cooling assembly for a semiconductor vertical power device according to the present invention. FIG. IB is an enlarged sectional view of the portion marked with a circle in FIG. IA. FIG. 2 is in accordance with the preferred embodiment of the invention of FIG.
FIG. 2 is an enlarged side cross-sectional view of the cooling assembly showing the entire fluid circulation path through a single groove. FIG. 3 is a perspective view of the ceramic pad and intervening plate of the cooling assembly of FIG. IA with a portion of the ceramic pad removed. 30: Brazed metal 10: Vertical power device 20: Ceramic pad 40: Interposed plate 50: Feed/discharge plate 21: Microchannel (groove) 41, 51: Inlet 42, 52: Outlet 25: Seal

Claims (6)

[Claims] (1) A method for improving cooling of a semiconductor vertical power device, which involves forming microgrooves with a large aspect ratio on one of two opposing main surfaces of a ceramic pad, and forming a plurality of grooves on the one surface. attaching to the grooved surface of the ceramic pad an intervening plate having a plurality of inlets/outlets exposed in the grooves; and placing at least one of the devices on the other major surface of the grooved ceramic pad. circulating a fluid through the inlet to flow through the groove and then discharging through the outlet, heat generated by the device by the circulating fluid. (2) attaching to the intervening plate a feed/discharge plate having a plurality of inlets/outlets aligned with the inlets/outlets of the intervening plate; and sealing the outer surface of the ceramic pad to contain the circulating fluid; The method of claim 1 further comprising: 3. The method of claim 1, wherein the step of applying an intervening plate includes brazing the grooved surface of the ceramic pad to the intervening plate. (4) The method according to claim 1, wherein the fluid has a high specific heat. (5) The method according to claim 1, wherein the ceramic pad has high thermal conductivity. (6) A semiconductor vertical power device package with an improved cooling assembly that allows circulating fluid to be brought into close proximity to the device during operation, the semiconductor vertical power device package comprising: a ceramic pad having two opposing major surfaces; hand,
a ceramic pad having a plurality of grooves forming large aspect ratio microgrooves on one major surface of the ceramic pad; and a plurality of inlets/outlets attached to and exposed to the grooved surface of the ceramic pad. at least one of the devices is affixed to the other major surface of the grooved ceramic pad, including an intervening plate and means for circulating fluid through the inlet so as to flow through the groove and then expelling it through the outlet; and the circulating fluid absorbs heat generated by the device. 7) a feed and discharge plate attached to the interposer plate and having a plurality of inlets/outlets aligned with the inlets/outlets of the interposer plate; means for brazing the grooved surface of the ceramic pad to the interposer plate; and circulating fluid. 7. The cooling assembly of claim 6, further comprising means for sealing the outer surface of the ceramic pad to retain the ceramic pad. 8) A cooling assembly according to claim 6, wherein the fluid has a high specific heat. 9) The cooling assembly of claim 6, wherein the ceramic pad has high thermal conductivity.