Development of Thermal Products Using the EB Methodby Shinji Takeno * and Yoshikazu Suzuki * 2

In the brazing of aluminum, flux or vacuum brazing have been widely used in thepast. But we have developed exudation brazing (EB) method, a new brazing
process which has no flux in the air. This method is limited to the lap joint, using a special fivelayer brazing sheet, and it is expected to provide brazed bonding with higher quality, lower cost,higher joint strength and higher corrosion resistance. We introduce some examples of thermal
products such as heat sinks and laminated molds using this method.

ABSTRACT1.

INTRODUCTION

Brazing of aluminum is widely utilized in the productionof radiators and coolers for automobiles using a brazing
sheet. In brazing there are currently two methods: the NB
method of non-corrosive flux brazing in an atmosphere ofnitrogen and the VB method of vacuum brazing without
flux. We have developed the EB method a new brazing
process which has no flux in the air 1), and are putting thismethod to practical use. In this paper we introduce someexamples other than those for heat exchangers for automobiles.

2.

EXUDATION BRAZING (EB) METHOD

2.1 EB Sheet
The EB method uses an EB sheet, a special brazingsheet, which is composed of five layers and adds external skin layers to both surfaces of the present three-layer
brazing sheet. The comparison of these compositions isshown in Figure 1. The external skin layer material is purealuminum, the brazing alloys are 4004 and 4104 alloys,
and the core alloys are 3003, 6061 and 6951 alloys.
2.2 Concept of the EB Method
The concept of the EB method, which does not use flux inthe air, is as follows. Generally in brazing, it is necessary
for wetting of the melted brazing alloy to occur. Oxidationof the alloy during heating must be prevented, and theoxidized film must be destroyed. Accordingly current
brazing methods such as the NB method or the VB method are carried out under conditions where flux or vacuum
are used. In the EB method, by contrast, the brazing
alloy is not exposed to the air and thus undergoes nooxidation. In melting, the brazing alloy exudes through* Sky Alumi Products Co., Ltd.
* 2 Technical Research Division, Furukawa-Sky Aluminum Corp.

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Figure 1 Composition of EB sheet.
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Figure 2����� �������

Concept of the exudation of brazing alloy.

the external skin layer and at the moment of exudation,
nonoxidized brazing alloy appears. Thus, wetting can beachieved without flux or vacuum. Figure 2 is a conceptual
representation of exudation in the EB method.
Figure 3 is a schematic showing the change in thickness of the oxidized film on the EB sheet during heatingin air. A close-contact lap joint is required in this method,
so its use in the air is limited to brazed bonding. Figure 4
shows a schematic of the lap joint.
2.3 Features of EB Method
1. High quality brazed bonding: These joints are basedon the exuding of non-oxidized molten metal over thejoint surface. Photo 1 shows the microstructure of abrazed section.
2. Low cost brazing: Although the material cost is higher, total cost is lower because there is no need for ahigh cost furnace with atmosphere control, and noflux is required.

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200536

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Development of Thermal Products Using the EB Method����������� �������������� �������� ���������������� �� �������� ��������� ������������ ���������� �� ���������� �� ���������� �������������� ���������

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Schematic showing behavior of oxidation under
heating in air.

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Tensile strength of EB butt joint.

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Figure 4

TYPICAL APPLICATIONS OF EBMETHOD

3.1 LEB-sink† Heatsinks
3.1.1 Structure
The comb-type LEB-sink heatsink is made by laminating
fins and EB sheets alternatively. Figure 6 shows a schematic figure, and Photo 2 shows the appearance of typical LEB-sinks.

Schematic of lap joint.
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Schematic of LEB-sink.

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Photo 1

Microstructure of brazed section.

3. High corrosion resistance: Because the brazed products are heated to a high temperature (about 600°C)
in the air, the oxidized film is extremely thick.
4. High tensile strength of the joint: Because thismethod is performed with no flux in the air, it enables
residual Mg to enter the brazed alloy, greatly increasing joint strength. In the methods previously used thisresidue could not occur. Figure 5 shows the tensile
strength of the brazed joint using selected base metals. Tensile strength was good for 6061 but not for
5052 and 5083. This is attributed to the effect of Mg
oxide on the Al-Mg alloys of the surface.
† LEB-sink is a registered trademark of Sky Alumi Products Co.,Ltd.

(a) Fin height: 60 mm
Photo 2(b) Fin height: 20 mm

Appearance of middle-size LEB-sink. (base width:60mm, fin pitch: 1.5mm)

3.1.2 Features of LEB-sink
1. The LEB-sink has high-quality heat releasing characteristics. The fin pitch can be reduced, even below
0.5 mm, the narrowest in the world, so that fin area
can be increased. Figure 7 shows the heat releasing
characteristics of LEB-sinks 2), and Figure 8 shows arange of products according to fin pitch. Base widths

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Development of Thermal Products Using the EB Method������������������������������������������������������������������ ���������� ������������������������

Block size: 100 × 100 × 64 mm

Photo 4-1 Appearance of laminated EB mold.
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Figure 7

Heat releasing characteristics of LEB-sink.

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Photo 4-2 Appearance of half section of the mold.
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process.

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Microstructure of LEB-sink section.

ranging from small to large can be made.
2. Because of the high-quality brazed bonding joint
strength is high. Photo 3 shows the microstructure.
3.1.3 Applications
We consider that LEB-sinks are suitable for the following
applications.
• Medium-scale (products for servers using a Peltierelement)• Large-scale (for inverters)
3.2 Laminated Mold
3.2.1 Concept
The laminated mold is a block made from numerous����� ��������

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Photo 3������� �������� ������ ���� ������ ����� ��������� �� ����� ������ ����� �������� ����� � �� �������� ��� ��� ����������������������� ���� ��������� ����Figure 9Hardness distribution in brazed joint.

sheets that have been pre-cut based on CAD data andlaminated. The block also functions as a heat exchanger
with complex inner waterways 3). This makes it possible toproduce blocks that were virtually impossible until now.
The EB method is used in laminated bonding. Currently
development is proceeding jointly with Laminated MoldLaboratory Co., Ltd. Photo 4 shows the appearance ofa trial laminated mold and of its half section. Figure 9shows the hardness distribution in the brazed joint.

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Development of Thermal Products Using the EB Method

3.2.2 Features
1. High-cycle production by blow molding of resinis possible. The shot cycle increase is minimized
because the rise of the temperature of the watercooled mold is reduced.
2. The molds for rubber and foaming which require air
venting are easily produced.
3. Delivery is quicker.

REFERENCES
1) Japanese Patent Application: TOKUKAI 2002-18570
2) Products Catalog of Sky Aluminum. (in Japanese)3) Takaya et al.: Molding Technology, Vol. 18 No. 8, 156-157. (inJapanese)

3.3 Others
Other possible applications for the EB method include
jackets for water-cooled PCs, cooling plates for semiconductors and vacuum vessel, and the like. Figure 10shows the development tree of the EB process. Photo 5
shows the appearance of a water-cooled jacket.

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Photo 5������
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Appearance of water-cooled jacket.

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Figure 10 Development tree of EB process.

4.

CONCLUSION

As was stated above, the EB method has much of uniquefeatures not found in conventional brazing methods, andwe therefore hope to broaden its applications. At present
however there are some limits to its application, namely
1. The joint design in the air is confined to lap joints.
2. Because of the formation of MgO film, Al alloys containing more than 1-% Mg cannot be brazed.
3. Because of the melting point, Al-Cu alloys and casting alloys cannot be brazed.

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