Claims:
We Claim:

1. A unitary heat sink for electronic devices comprising of a base and a fin array in the form of a unitary piece,
-the base portion of the heat sink made of a rectangular profile having a plurality of variations in height on the first side in order to mate proximately to surfaces of the heat dissipating components on a printed circuit board (PCB);
-and
an array of predetermined number of fins extending outwardly at a predetermined height from the second side the base portion, wherein the fin array has a recessed portion positioned substantially halfway of the fin array, the recessed portion having at least one opening in order to allow a locking member for securing the heat sink to the electronic component on the PCB, wherein each of the fins has projections on either side and is deprived of twisting.

2. The heat sink as claimed in claim1, wherein thickness of the fin is smaller than the spacing between the fins.

3. The heat sink as claimed in claim1, wherein the ratio between the fin heights dimensions to spacing between the adjacent fins is 30:1, thereby providing maximum surface area in a given volume for superior thermal enactment.

4. The heat sink as claimed in claim 1, wherein thickness of the fin is between 0.3mm and 1mm and the gap between the adjacent fins is as narrow as 1mm.
5. The heat sink as claimed in claim 1, wherein the thickness of fins from the base narrow down to height.

6. The heat sink as claimed in claim 1, further comprising:
a thermal interface material (TIM) of very small thermal impedance inserted between the heat producing device (e.g. the PCB) and the heat sink (heat dissipation device) to bring down the overall thermal resistance of the arrangement.

7. A method of forming a unitary heat sink body for dissipating heat from heat generating electronic components placed on the PCB, the body having a base and a plurality of narrowly spaced fins extending from a base, the method comprising the following steps:
-providing a single piece of metal body over which the heat sink is structured;
-machining the metal body on a first side of the base to have variations in height to mate and achieve a thermally conductive contact with the heat generating electronic components on the PCB;
-loading a program onto a machine (EDM machine) for cutting an ideal profile of heat sink fins on the second side of the base;
-tracing the preferred path for cutting fins of desired shape on second side of the base by electrical discharges of the machine (EDM machine), wherein fins are cut perpendicular to the base portion of the metal body and the fin array has a recessed portion positioned substantially halfway of the fin array;
-drilling at least one hole at the recessed portion of the base in order to secure the heat sink on a PCB using studs which extend all the way to the PCB; and
-disposing the structured heat sink over the surface of a PCB and achieving thermal contact with the thermal interface material(TIM) and the PCB.

8. The method of claim 7, wherein the thermal interface material (TIM) of very small thermal resistance is interleaved between the PCB and the heat sink to bring down the overall thermal resistance of the arrangement. , Description:
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)

“A HEAT SINK”
By
BHARAT ELECTRONICS LIMITED
Nationality: Indian
of
M/s. Bharat Electronics Limited, Corporate Office, Outer Ring Road, Nagavara, Bangalore-560045, Karnataka, India

The following specification particularly describes the invention and the manner in which it is to be performed.

Field of the invention
The present invention relates to a heat sink, and more particularly relates to a unitary heat sink for removing heat through forced air-cooling, from electronic components such as a Printed Circuit Board (PCB).

Background of the invention
Most of the boards used in complex electronic systems dissipate a huge amount of heat. A thermally conductive heat sink, which removes high wattages of thermal load by the process of convection, is used in all these applications. These heat sinks essentially have a high density of fins, which provide more surface area to cool these high wattage boards. The traditional heat sinks cannot handle the heat loads of advanced miniaturised circuit boards. The high wattage per unit area in such boards can be removed using only compact high fin-density heat sinks.
The conventional process of milling is not capable of producing such narrowly spaced fins of small cross-sectional area. Therefore to cater the needs of such boards, a bonded fin heat sink is used. Such heat sinks are capable of extracting high heat loads by maximizing the surface area in the given volume. In some cases, the fins are manufactured in the form of corrugated sheet using a die tool and attached to the base plate by a suitable method such as brazing.
The Patent No: EP1156526 explains manufacturing of heat sinks having bonded cooling fins. These cooling fins have a tapering plug, and are seated in the tapered slot machined in the base plate. The thermal conductivity between fins and the base was maximized using an adhesive, and cured when the plug was inserted in the slot with sufficient force.
The other widely used heat sink is an extruded heat sink. In an extruded heat sink, the contour of fins and the base plate are manufactured by a die made exclusively for that purpose. In an extrusion process, preheating of the material stock may be necessary to achieve the desired profile of fins. Moreover, only aluminium heat sinks can be extruded. Copper, albeit having almost twice the thermal conductivity of Aluminium, is less malleable and difficult to extrude. There are limitations for improving parameters, such as the fin height to gap ratio and fin thickness, in an extrusion process. In the case of traditional heat sinks, the fin height to gap ratio is limited to 6:1 owing to the difficulties in manufacturing. Special die molds have been designed to achieve a higher ratio of 10:1 by providing cross-sectional supports.
In the fabrication of a heat sink with thin fins as disclosed in Patent No: EP1156526, an additional process of manufacturing the cooling fins using a coil slitter is required. So, the process of brazing or attaching the fins by other means, to base plate also becomes necessary. This adds up to the manufacturing cost of the heat sink. The parameters like the straightness of cut, linearity of machined slots are critical. Therefore, fins could not be inserted into machined slots, if there was a slight deviation from the set specifications. Special fixtures are required for holding the job during manufacturing and inserting the fins into the base plate. Also, an additional cure time is required for fixing the fins to the base plate using a conductive adhesive. A thermal resistance is added to the path of heat flow at these joints. These joints may deteriorate over time and further increase the contact resistance.

So, there is a need for improved a heat sink for removing and dissipating the heat generated by the electronic components such as PCBs.

Summary of the Invention
An aspect of the present invention is to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below.
Accordingly, in one aspect of the present invention relates to a unitary heat sink for removing heat from electronic components such as Printed Circuit Board (PCB). The heat sink is used for cooling electronic components on a PCB, with fins forming an integral part of base. The unitary heat sink for electronic devices includes a base and a fin array in the form of a unitary piece. The base portion of the heat sink made of a rectangular profile has a plurality of variations in height on the first side in order to mate proximately to surfaces of the heat dissipating components on a printed circuit board (PCB). The second side of the base portion has an array of predetermined number of fins extending outwardly at a predetermined height. The thickness of fin is smaller than the spacing between the fins. In an example embodiment, the thickness of the fin can be 0.3mm to 1mm and the gap between the adjacent fins is as narrow as 1mm. The thickness of the fin can be uniform throughout its height or can vary depending on the thermal performance required for the application. The ratio of the fin height dimension to the spacing between adjacent fins is 30:1. This provides a maximum surface area in the given volume for superior thermal enactment.
Accordingly, another aspect of the present invention is a method of forming a unitary heat sink body. The body has a base with plurality of narrowly spaced fins extending from the base of the heat sink for dissipating heat from heat generating electronic components on the PCB. The method includes providing a single piece of metal body over which the heat sink is structured. The projections on the first side of the metal body base are machined using a conventional milling machine in such a way, as to establish a thermally conductive contact with the heat generating electronic components on the PCB when disposed over it. A program is then loaded onto the wire electrical discharge machine (WEDM), to have heat sink fins structured to a desired shape on the second side of the base. Then, the preferred path is traced using a thin-strand of wire attached to the machine, to achieve the desired shape of fins. The fins are cut perpendicular to the base portion by electrical discharges of the machine. The structured fins form an array of fins on the second side of the base. The array of fins has a recessed portion wedged substantially at halfway of the base. Further, at least one hole is drilled at the recessed portion in order to secure the structured metal heat sink on the PCB using studs which extend all the way to the PCB. Finally, the structured heat sink is disposed over the PCB in order to dissipate the heat generated by the electronic components on the PCB.
Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

Brief description of the drawings
The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:
Figure 1 illustrates a heat sink base and fin bonding technique as it is known in the prior art.
Figure 2 illustrates a process flow chart of conventional bonded heat sink manufacturing process in the prior art.
Figure 3 illustrates a process flow chart of tapered heat sink manufacturing process in the prior art.
Figure 4 illustrates a process flow chart of a heat sink manufacturing, according to one embodiment of the present invention.
Figure 5 illustrates the isometric view of a heat sink used on electronic components, according to one embodiment of the present invention.
Figure 6 illustrates a top view of a heat sink used on electronic components, according to one embodiment of the present invention.
Figure 7 illustrates a side view of a heat sink used on electronic components, according to one embodiment of the present invention.
Figure 8 illustrates a bottom view of a heat sink used on electronic components, according to one embodiment of the present invention.
Figure 9 (a) & (b) illustrates an enlarged view of a heat sink fins structured on metal body, according to one embodiment of the present invention.
Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure.
Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

Description of the invention
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces.
Figure 1-3 illustrates a heat sink base and the fin bonding technique, and the conventional bonded and tapered heat sink manufacturing process known in the prior art.
Figure 4-8 illustrates a process flow chart of a heat sink manufacturing and different views of the heat sink in accordance to the present invention. The present invention relates to a unitary heat sink and relates to the heat sink for removing heat from electronic components such as a Printed Circuit Board (PCB). The heat sink is used for cooling electronic components on a PCB, with fins forming an integral part of the base of the heat sink. The heat sink is used for handling high wattages of thermal load in a forced air-cooled environment. The unitary heat sink for electronic devices includes a base (500) and a fin array (506) in the form of a unitary piece. The base portion of the heat sink made of a rectangular profile has a plurality of variations in height on the first side (502) in order to mate proximately to surfaces of the heat dissipating components on a printed circuit board (PCB). This eliminates the need to have multiple individual heat sinks on each of the heat dissipating components. This also ensures minimal use of thermal paste or selects a gap pad of smaller thickness, thus providing better heat transfer. A thermal interface material (TIM) of very small thermal impedance is inserted between the heat producing device (e.g. the PCB) and the heat sink (heat dissipation device) to bring down the overall thermal resistance of the arrangement. Eliminating the TIM would increase the thermal resistance to a great extent due to minute air gaps between the heat sink and the heat producing device.
The second side (504) of the base (500) has an array of predetermined number of the fins (506) extending outwardly at a predetermined height. The thickness of the fin is smaller than the spacing between the fins. In an example embodiment, the thickness of the fin may be but not limited to 0.3mm to 1mm and the gap between the adjacent fins is as narrow as 1mm. The thickness of the fin can be uniform throughout its height or can vary depending on the thermal performance required for the application. In an example embodiment, the ratio of the fin height dimension to the spacing between the adjacent fins may be but not limited to 30:1. This provides a maximum surface area in the given volume for superior thermal enactment. A high ratio of the fin height to the spacing between adjacent fins is accomplished in the present invention, thereby manufacturing the compact heat sinks with superior thermal performance. The fin array (506) has a recessed portion (508) positioned substantially halfway of the fin array (506) and the recessed portion (508) has at least one opening (510) in order to allow a locking member for securing the heat sink to the electronic component on the PCB. - The projections (512) are provided at the top of the individual fins, on either side to strengthen them, and also to help in easy handling of the heat sink without bending of thin fins. This design also helps in better cooling of electronic components, which are at the farther end of the PCB, away from the source of air supply.
Another aspect of the invention is a method of forming a unitary heat sink body. The metal body base (500) with plurality of narrowly spaced fins (506) extending from the base (500) of the heat sink for dissipating heat from heat generating electronic components on the PCB. The method includes providing a single piece of metal body over which the heat sink is structured. Further, the projections are machined on the first side (502) of the metal body base (500) in such a way, as to establish a thermally conductive contact with the heat generating electronic components on the PCB. Further, a program is loaded onto the wire electrical discharge machine (WEDM), to have heat sink fins structured to a desired shape on the second side (504) of the base (500). The, the preferred path is traced with a thin-strand of wire attached to the machine, to achieve the desired shape of fins. The fins are cut perpendicular to the base portion by electrical discharges of the machine. The structured fins form an array of fins (506) on the second side (504) of the base (500). The array of fins (506) has a recessed portion (508) wedged substantially at halfway of the base. Further, at least one hole (510) is drilled at the recessed portion (508) in order to secure the structured metal heat sink on the PCB using studs which extend all the way to the PCB. Finally, the structured heat sink is disposed over the PCB in order to dissipate the heat generated by the electronic components on the PCB. A thermal interface material (TIM) of very small thermal impedance is interleaved between the PCB and the heat sink to bring down the overall thermal resistance of the arrangement.
Fig 9 (a) & (b) illustrates the array of fins structured on the second side of the metal body base. A program is loaded onto a wire electrical discharge machine (WEDM) to structure the heat sink fins of desired shape on the second side of metal body base. Then, starting from end point B of metal body (as shown in Fig. 9) the preferred path is traced with a thin-strand of wire attached to the machine. From point B, machine traces the path BC with a thin-strand of wire attached to the machine and then moves along CD and then DE; on reaching E, it cuts a small portion of material equal to the wire diameter and reaches point F. Further, the material in the region FGHIJK is removed. One slot is said to be cut when the wire finally moves from K to L. There is difference in height between the base planes of adjacent slots. The difference in height between the planes HI and H’I’ is 0.5mm.Further, the planes HI and H"I" are on the same horizontal level. This difference in height is given to strengthen each of the individual fins so that it does not to peel off from the base over time. The gap EFKL can be slightly greater than the diameter of the wire. The gap allows the wire to pass through it, and remove the material in the region FGHIJK. Further, it creates a passage for releasing the heat trapped which improves the performance of the heat sink in an air-cooled environment. The process is now repeated for the required number of fins, here uniformly spaced with respect to each other as an example embodiment. Skilled person in the art would appreciate that various designs may be possible which have different spacing or arrangement. The extended surfaces of each fin, such as the surface LE’ for 'fin 2', allow easy handling of the heat sink. These surfaces do not allow the fins to bend easily in case of rough handling. It also ensures that a certain amount of air, supplied for cooling, passes through the entire length of the heat sink, thereby removing heat. Figure 9(b) shows varying thickness of fins w.r.t its height as an example embodiment in which thickness of fins may vary with respect to its height. A skilled person in the art can understand that certain designs may also be possible in light of the invention where the fins which are thick at the base and narrow down along its height.
This kind of structure of a heat sink, i.e. the base and the fins cut in the same stock, will have high rate of heat transfer. It also helps in keeping the junction temperature of the processors within the safe operating limits, which is essential for a high performance of the processors.
Figures 1-9 is merely representational and is not drawn to scale. Certain portions thereof may be exaggerated, while others may be minimized. FIGS.1-9 illustrates various embodiments of the invention that can be understood and appropriately carried out by those of ordinary skill in the art. In the foregoing detailed description of embodiments of the invention, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the invention require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the detailed description of embodiments of the invention, with each claim standing on its own as a separate embodiment.
It is understood that the above description is intended to be illustrative, and not restrictive. It is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined in the appended claims. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein,” respectively.

We Claim:

1. A unitary heat sink for electronic devices comprising of a base and a fin array in the form of a unitary piece,
-the base portion of the heat sink made of a rectangular profile having a plurality of variations in height on the first side in order to mate proximately to surfaces of the heat dissipating components on a printed circuit board (PCB);
-and
an array of predetermined number of fins extending outwardly at a predetermined height from the second side the base portion, wherein the fin array has a recessed portion positioned substantially halfway of the fin array, the recessed portion having at least one opening in order to allow a locking member for securing the heat sink to the electronic component on the PCB, wherein each of the fins has projections on either side and is deprived of twisting.

2. The heat sink as claimed in claim1, wherein thickness of the fin is smaller than the spacing between the fins.

3. The heat sink as claimed in claim1, wherein the ratio between the fin heights dimensions to spacing between the adjacent fins is 30:1, thereby providing maximum surface area in a given volume for superior thermal enactment.

4. The heat sink as claimed in claim 1, wherein thickness of the fin is between 0.3mm and 1mm and the gap between the adjacent fins is as narrow as 1mm.
5. The heat sink as claimed in claim 1, wherein the thickness of fins from the base narrow down to height.

6. The heat sink as claimed in claim 1, further comprising:
a thermal interface material (TIM) of very small thermal impedance inserted between the heat producing device (e.g. the PCB) and the heat sink (heat dissipation device) to bring down the overall thermal resistance of the arrangement.

7. A method of forming a unitary heat sink body for dissipating heat from heat generating electronic components placed on the PCB, the body having a base and a plurality of narrowly spaced fins extending from a base, the method comprising the following steps:
-providing a single piece of metal body over which the heat sink is structured;
-machining the metal body on a first side of the base to have variations in height to mate and achieve a thermally conductive contact with the heat generating electronic components on the PCB;
-loading a program onto a machine (EDM machine) for cutting an ideal profile of heat sink fins on the second side of the base;
-tracing the preferred path for cutting fins of desired shape on second side of the base by electrical discharges of the machine (EDM machine), wherein fins are cut perpendicular to the base portion of the metal body and the fin array has a recessed portion positioned substantially halfway of the fin array;
-drilling at least one hole at the recessed portion of the base in order to secure the heat sink on a PCB using studs which extend all the way to the PCB; and
-disposing the structured heat sink over the surface of a PCB and achieving thermal contact with the thermal interface material(TIM) and the PCB.

8. The method of claim 7, wherein the thermal interface material (TIM) of very small thermal resistance is interleaved between the PCB and the heat sink to bring down the overall thermal resistance of the arrangement.

Place: Bangalore S AFSAR
Dated: 30/12/2016 IN/PA-1073
AGENT FOR THE APPLICANT

Abstract
A HEAT SINK
The present invention relates to a unitary construction of a heat sink for removing heat from electronic components such as a Printed Circuit Board (PCB).The unitary heat sink for electronic devices includes a base and a fin array in the form of a unitary piece. The base (500) portion of the heat sink has a rectangular profile and a plurality of variations in height on the first side (502) in order to mate proximately to surfaces of the heat dissipating components on the PCB. The second side (504) of the base portion (500) has an array of predetermined number of fins (506) extending outwardly at a predetermined height. The fin array has a recessed portion (508) positioned substantially halfway of the fin array and the recessed portion having at least one opening (510) in order to allow a locking member for securing the heat sink to the electronic component on the PCB. Each of the fins has projections (512) on either side and is deprived of twisting.

Figure 5 (for Publication)