Claims:I/We Claim:
A vacuum brazing method for joining multiple substrates, comprising:
positioning, in a vacuum furnace, a first substrate (aluminum or copper), a second substrate comprising a pyrolitic graphite sheet, and a third substrate (aluminum or copper), wherein the second substrate is positioned between the first substrate and the third substrate, wherein a first intervening layer and a second intervening layer are formed between (i) the first substrate and the second substrate, and (ii) the second substrate and the third substrate respectively, each of the first intervening layer and the second intervening layer comprise a filler alloy and an additive; configuring, in the vacuum furnace, one or more vacuum levels based on type of the first substrate, the second substrate, and the third substrate; setting temperature of the vacuum furnace to a first pre-heat temperature for a first dwell period such that the temperature of the vacuum furnace is uniformly distributed; adjusting the temperature of the vacuum furnace from the first pre-heat temperature to a second pre-heat temperature such that the temperature of the vacuum furnace is uniformly distributed; setting the second pre-heat temperature to a brazing temperature of the filler alloy for a first pre-determined time interval, wherein temperature in the vacuum furnace attains the brazing temperature that results in melting of the filler alloy and subsequent fusion of the first substrate, the second substrate and the third substrate; cooling the vacuum furnace by setting temperature of the vacuum furnace to a cooling temperature at a second pre-determined time interval such that the fusion of the first substrate, the second substrate and the third substrate results in a solidification of the first substrate, the second substrate and the third substrate; and quenching the vacuum furnace by automatically releasing inert gas at a pre-determine pressure to obtain an encapsulated plate.
The method of claim 1, wherein the first substrate and the third substrate are identical.
The method of claim 1, wherein the first substrate and the third substrate are different from each other.
The method of claim 1, wherein the one or more vacuum levels range between 10-3 millibar – vacuum levels to 10-6 millibar.
A vacuum furnace (100) for joining multiple substrates, wherein the vacuum furnace is configured to:
a fixture (110) that is configured to receive a first substrate (aluminum or copper), a second substrate comprising a pyrolitic graphite sheet, and a third substrate (aluminum or copper), wherein the second substrate is positioned between the first substrate and the third substrate, wherein a first intervening layer and a second intervening layer are formed between (i) the first substrate and the second substrate, and (ii) the second substrate and the third substrate respectively, each of the first intervening layer and the second intervening layer comprise a filler alloy and an additive; a vacuum level adjuster that is configured to adjust one or more vacuum levels in the vacuum furnace based on type of the first substrate, the second substrate, and the third substrate; one or more control thermocouples (104) that are configured to
set temperature of the vacuum furnace to a first pre-heat temperature for a first dwell period such that the temperature of the vacuum furnace is uniformly distributed;
adjust the temperature of the vacuum furnace from the first pre-heat temperature to a second pre-heat temperature such that the temperature of the vacuum furnace is uniformly distributed;
set the second pre-heat temperature to a brazing temperature of the filler alloy for a first pre-determined time interval, wherein temperature in the vacuum furnace attains the brazing temperature that results in melting of the filler alloy and subsequent fusion of the first substrate, the second substrate and the third substrate;
cool the vacuum furnace by setting temperature of the vacuum furnace to a cooling temperature at a second pre-determined time interval such that the fusion of the first substrate, the second substrate and the third substrate results in a solidification of the first substrate, the second substrate and the third substrate; and
quench the vacuum furnace by automatically releasing inert gas at a pre-determine pressure to obtain an encapsulated plate.
The vacuum furnace of claim 5, wherein the first substrate and the third substrate are identical.
The vacuum furnace of claim 5, wherein the first substrate and the third substrate are different from each other.
The vacuum furnace of claim 4, wherein the one or more vacuum levels range between ?10?^(-3) milli Bar to ?10?^(-6) milli Bar.
, Description:VACUUM BRAZING FURNACE AND METHOD FOR JOINING MULTIPLE SUBSTRATES

TECHNICAL FIELD
The present disclosure relates to brazing technique and more particularly brazing techniques for joining two or more substrates using pyrolytic graphite sheet.
BACKGROUND OF THE INVENTION
Electronic devices are becoming increasingly compact and as a result they produce lot of localized heat. In order to achieve better performance on electronics devices, heat that is produced needs to be extracted from such devices or from heat generating sources to maintain steady temperature. Existing solutions include integrating heat sinks, cold plates, heat separators to extract heat from the devices. However heat sinks and cold plates are solid devices and these can operate only up to certain levels. Conventional systems have also utilized thermal straps that are mounted on apparatus such as heat sinks for cooling electronic devices. Thermal straps absorb heat from the heat sinks where electric/electrical operators are mounted on the heat sinks to maintain the required temperature.
SUMMARY
The following presents a simplified summary of some embodiments of the disclosure in order to provide a basic understanding of the embodiments. This summary is not an extensive overview of the embodiments. It is not intended to identify key/critical elements of the embodiments or to delineate the scope of the embodiments. Its sole purpose is to present some embodiments in a simplified form as a prelude to the more detailed description that is presented below. In view of the foregoing, an embodiment herein provides brazing techniques for joining multiple substrates.
In one aspect, there is provided a vacuum brazing method for joining multiple substrates comprising: positioning, in a vacuum furnace, a first substrate (aluminum or copper), a second substrate comprising a pyrolitic graphite sheet, and a third substrate (aluminum or copper), wherein the second substrate is positioned between the first substrate and the third substrate, wherein a first intervening layer and a second intervening layer are formed between (i) the first substrate and the second substrate, and (ii) the second substrate and the third substrate respectively, each of the first intervening layer and the second intervening layer comprise a filler alloy and an additive; configuring, in the vacuum furnace, one or more vacuum levels based on type of the first substrate, the second substrate, and the third substrate; setting temperature of the vacuum furnace to a first pre-heat temperature for a first dwell period such that the temperature of the vacuum furnace is uniformly distributed; adjusting the temperature of the vacuum furnace from the first pre-heat temperature to a second pre-heat temperature such that the temperature of the vacuum furnace is uniformly distributed; setting the second pre-heat temperature to a brazing temperature of the filler alloy for a first pre-determined time interval, wherein temperature in the vacuum furnace attains the brazing temperature that results in melting of the filler alloy and subsequent fusion of the first substrate, the second substrate and the third substrate; cooling the vacuum furnace by setting temperature of the vacuum furnace to a cooling temperature at a second pre-determined time interval such that the fusion of the first substrate, the second substrate and the third substrate results in a solidification of the first substrate, the second substrate and the third substrate; and quenching the vacuum furnace by automatically releasing inert gas at a pre-determine pressure to obtain an encapsulated plate. In an embodiment, the first substrate and the third substrate may be identical. In another embodiment, the first substrate and the third substrate are different from each other. In an embodiment, the one or more vacuum levels range between 10-3 millibar – vacuum levels to 10-6 millibar.
In another aspect, a vacuum brazing furnace for joining multiple substrates is provided. The furnace includes a fixture that is configured to receive a first substrate (aluminum or copper), a second substrate comprising a pyrolitic graphite sheet, and a third substrate (aluminum or copper), wherein the second substrate is positioned between the first substrate and the third substrate, wherein a first intervening layer and a second intervening layer are formed between (i) the first substrate and the second substrate, and (ii) the second substrate and the third substrate respectively, each of the first intervening layer and the second intervening layer comprise a filler alloy and an additive; a vacuum level adjuster that is configured to adjust one or more vacuum levels in the vacuum furnace based on type of the first substrate, the second substrate, and the third substrate; one or more control thermocouples that are configured to set temperature of the vacuum furnace to a first pre-heat temperature for a first dwell period such that the temperature of the vacuum furnace is uniformly distributed; adjust the temperature of the vacuum furnace from the first pre-heat temperature to a second pre-heat temperature such that the temperature of the vacuum furnace is uniformly distributed; set the second pre-heat temperature to a brazing temperature of the filler alloy for a first pre-determined time interval, wherein temperature in the vacuum furnace attains the brazing temperature that results in melting of the filler alloy and subsequent fusion of the first substrate, the second substrate and the third substrate; cool the vacuum furnace by setting temperature of the vacuum furnace to a cooling temperature at a second pre-determined time interval such that the fusion of the first substrate, the second substrate and the third substrate results in a solidification of the first substrate, the second substrate and the third substrate; and quench the vacuum furnace by automatically releasing inert gas at a pre-determine pressure to obtain an encapsulated plate.
In an embodiment, the first substrate and the third substrate may be identical. In another embodiment, the first substrate and the third substrate are different from each other. In an embodiment, the one or more vacuum levels range between 10-3 millibar – vacuum levels to 10-6 millibar.
BRIEF DESCRIPTION OF THE DRAWINGS
The embodiments herein will be better understood from the following detailed description with reference to the drawings, in which:
FIG. 1 is an exemplary block diagram of a vacuum furnace in accordance with an example embodiment of the present disclosure.
FIG. 2 depicts a flow chart illustrating a method for joining multiple substrates using the vacuum furnace of FIG. 1 according to some embodiments of the present disclosure.
FIG. 3 depicts the arrangement and positioning of the substrates (e.g., the first substrate, the second substrate and the third substrate) for performing brazing technique(s) as disclosed in the embodiments of the present disclosure.
FIG. 4 depicts a graphical representation of temperature being varied at various temperature levels for performing brazing technique to join multiple substrates according to some embodiments of the present disclosure.
FIGS. 5A-5B, depict a graphical representation of temperature of various jobs (e.g., substrates) when placed in the vacuum furnace of FIG. 1 in an example embodiment of the present disclosure.
FIG. 6 depicts a graphical representation illustrating variation in pressure in the vacuum furnace of FIG. 1 in an example embodiment of the present disclosure.
FIG. 7 depicts a graphical representation illustrating variation in vacuum levels in the vacuum furnace of FIG. 1 in an example embodiment of the present disclosure.
FIG. 8 depicts a graphical representation illustrating variation in chamber temperature in the vacuum furnace of FIG. 1 in an example embodiment of the present disclosure.

DETAILED DESCRIPTION
The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The words "comprising," "having," "containing," and "including," and other forms thereof, are intended to be equivalent in meaning and be open ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items.
It must also be noted that as used herein and in the appended claims, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Although any systems and methods similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present disclosure, the preferred, systems and methods are now described.
Some embodiments of this disclosure, illustrating all its features, will now be discussed in detail. The disclosed embodiments are merely exemplary of the disclosure, which may be embodied in various forms.
Before setting forth the detailed explanation, it is noted that all of the discussion below, regardless of the particular implementation being described, is exemplary in nature, rather than limiting.
FIG. 1 is an exemplary block diagram of a vacuum furnace 100 in accordance with an example embodiment of the present disclosure. The vacuum furnace 100 (also referred as ‘vacuum brazing furnace’) comprises a heat chamber 102 comprising heating elements (not shown in FIG. 1), one or more control thermocouples 104 for monitoring and controlling temperature within the vacuum furnace 100, one or more job temperature monitoring thermocouples 106 for monitoring temperature of jobs, and an earth rail 108 that is mounted with a fixture 110 on top of the earth rail to hold the jobs (e.g., substrates under consideration for joining). In an embodiment, the vacuum furnace 100 further comprises one or more vacuum level adjusters 112 and one or more controllers (e.g., processor(s) 114, or micro-controller(s)) for processing inputs and generating desired output(s) at desired temperatures respectively.
FIG. 2, with reference to FIG. 1, depicts a flow chart illustrating a method for joining multiple substrates using the vacuum furnace of FIG. 1 according to some embodiments of the present disclosure. The flow chart is now explained with reference to components of the vacuum furnace of FIG. 1. In an embodiment of the present disclosure, at step 202, a first substrate (e.g., aluminum or copper), a second substrate comprising a pyrolitic graphite sheet, and a third substrate (e.g., aluminum or copper) are positioned in the vacuum furnace. In an embodiment, the first substrate, second substrate comprising the pyrolitic sheet and the third substrate are positioned (or placed) in the fixture mounted on the earth rail. More specifically, the second substrate which is the pyrolitic graphite sheet is positioned between the first substrate (e.g., aluminum) and the third substrate (e.g., aluminum). A first intervening layer and a second intervening layer are formed between (i) the first substrate and the second substrate, and (ii) the second substrate and the third substrate respectively, each of the first intervening layer and the second intervening layer comprise a filler alloy and an additive. Based on the base material used filler alloys are selected for any substrate containing Aluminum alloy Grade Al6061 substrate the filler alloy used is Al 4047 Grade , For substrate of copper and steel, Steel and Steel , Copper and Copper, the filler alloy is BVAg-8. Similarly, Titanium Hydrate is used as an additive to create a bonding between metal (e.g., aluminum) and Pyrolytic Graphite sheet.
FIG. 3 depicts the arrangement and positioning of the substrates (e.g., the first substrate, the second substrate and the third substrate) for performing brazing technique(s) as disclosed in the embodiments of the present disclosure.
In an embodiment of the present disclosure, specification of the vacuum furnace 100 is maximum operating temperature: 1250°C, Vacuum level: Up to 5×?10?^(-5) milli Bar, Maximum Quenching Pressure: up to 12 Bar.
In an embodiment of the present disclosure, at step 204, one or more vacuum levels are configured based on type of the first substrate, the second substrate, and the third substrate. The one or more vacuum levels are adjusted using the one or more vacuum level adjuster(s) 112. For instance, assuming that the first substrate and the third substrate is aluminum) and the second substrate is the pyrolitic graphite sheet, the vacuum level that is required for performing brazing technique is 4×?10?^(-4) milli Bar. Similarly, when the first and third substrate are silver, the vacuum level that is required for performing brazing technique is 1×?10?^(-3) milli Bar (e.g., BVAg-8 Silver brazing). In an embodiment of the present disclosure, the one or more vacuum levels range between ?10?^(-3) milli Bar to ?10?^(-6) milli Bar. As can be seen above, that the first substrate and the third substrate are identical (e.g., both being aluminum). In different scenarios, brazing technique can be performed for dissimilar substrates wherein the first substrate and the third substrate can be different from each other.
In an embodiment of the present disclosure, at step 206, temperature of the vacuum furnace 100 is set to a first pre-heat temperature for a first dwell period such that the temperature of the vacuum furnace is uniformly distributed. In the present disclosure the first preheat temperature is set to 400°C for Aluminum brazing and around 550°C for Silver Brazing and soaking is done to reduce delta temperature.
In an embodiment of the present disclosure, at step 208, temperature of the vacuum furnace 100 adjusted from the first pre-heat temperature to a second pre-heat temperature such that the temperature of the vacuum furnace is once again uniformly distributed. This is done at just below the liquid temperature of filler alloy for aluminum brazing. The second pre-heat temperature in this present use case for aluminum brazing is 550°C approximately, wherein dwelling is done to equalize temperature for uniform distribution in the vacuum furnace. Likewise, if the substrates (e.g., first substrate and the third substrate) are a Silver substrate type, the second pre-heat temperature is expected to be 750°C for silver alloy.
In an embodiment of the present disclosure, at step 210, temperature of the vacuum furnace 100 adjusted from the second pre-heat temperature to a brazing temperature of the filler alloy for a first pre-determined time interval, wherein temperature in the vacuum furnace attains the brazing temperature that results in melting of the filler alloy and subsequent fusion of the first substrate, the second substrate and the third substrate. More specifically, in the present disclosure the filler alloy is Al 4047 and the brazing temperature of filler alloy Al 4047 is around 590°C for a predefine time interval (e.g., say for 4 minutes). Similarly, for filler alloy BVAg-8, the brazing temperature is around 820 °C for 10 minutes.
In an embodiment of the present disclosure, at step 212, the vacuum furnace is cooled by setting temperature of the vacuum furnace to a cooling temperature at a second pre-determined time interval such that the fusion of the first substrate, the second substrate and the third substrate results in a solidification of the first substrate, the second substrate and the third substrate. More particularly, after completing of brazing the vacuum furnace cooling is done to solidify the filler alloy for Aluminum brazing wherein the cooling temperature is set up to 540°C. Similarly, for Silver brazing the cooling temperature in the vacuum furnace is around 660°C.
In an embodiment of the present disclosure, at step 212, the vacuum furnace is quenched (by performing quenching technique). The quenching technique includes automatic release of inert gas at a pre-determine pressure to obtain an encapsulated plate. The vacuum furnace may be integrated or deployed with one or more sensors (e.g., temperature sensor) that predict the cooling temperature and cooling operation completion which enables the trigger of quenching technique for automatic release of inert gas.
The above methodology will be better understood by way of example depicted in graphical representation of FIG. 4. More specifically, FIG. 4 depicts a graphical representation of temperature being varied at various temperature levels for performing brazing technique to join multiple substrates.
FIGS. 5A-5B, depict a graphical representation of temperature of various (jobs) substrates placed in the vacuum furnace of FIG. 1 in an example embodiment of the present disclosure. More specifically, in FIGS. 5A-5B, along x-axis is represented with time, and along y-axis are represented temperature values denoted by (T), pressure values denoted by (P) on the left side of the graphical representation, and vacuum levels denoted by (V) on the right side of the graphical representation. FIG. 5A depicts a graphical representation of temperature for substrate 1 (e.g., say job 1) in an example embodiment of the present disclosure. FIG. 5B depicts a graphical representation of temperature for job 2 in an example embodiment of the present disclosure. In an embodiment, job 1 and job 2 may correspond to aluminum substrates that are required to be joined using pyrolytic graphite sheet (also referred as pyrolytic grahite material), in one example embodiment.
Similarly, FIG. 6 depicts a graphical representation illustrating variation in pressure in the vacuum furnace 100 of FIG. 1 in an example embodiment of the present disclosure. FIG. 7 depicts a graphical representation illustrating variation in vacuum levels in the vacuum furnace 100 of FIG. 1 in an example embodiment of the present disclosure. FIG. 8 depicts a graphical representation illustrating variation in chamber temperature in the vacuum furnace 100 of FIG. 1 in an example embodiment of the present disclosure. In the above graphical representations depicted in FIGS. 6, 7 and 8, along x-axis is represented with time, and along y-axis are represented temperature values denoted by (T), pressure values denoted by (P) on the left side of the graphical representation, and vacuum levels denoted by (V) on the right side of the graphical representation respectively.
Although the present disclosure specifically describes brazing technique for joining aluminum substrates, it is to be understood by persona having ordinary skill in the art and person skilled in the art that the present disclosure and embodiments thereof can be implemented for performing brazing technique over other various substrates, for example, wherein the first substrate and the third substrate can be any of the alloy of Aluminum and Copper, Aluminum and Steel, Steel and Copper, Copper and Copper or Steel and Steel, respectively and shall not be construed to be limiting the scope of the present disclosure.