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Brazing Alloys and Fluxes


Brazing Alloys

For the joining of contact materials with carrier substrates, brazing alloys with working temperatures > 600 °C are used exclusively. The working temperature is defined as the lowest surface temperature, by which the brazing material wets the materials to be joined. This temperature is within the melting range and between the solidus (temperature at which melting starts) and liquidus (temperature at complete liquid state) point of the brazing alloy. Silver-based brazing alloys have good electrical conductivity and a sufficient mechanical strength, which allows a bonding process without significant changes in the microstructure of the material to be joined.

For electrical contacts, usually low-melting alloys with a minimum of 20 wt-% silver and additions of cadmium, zinc or tin are used to lower the melting point (Table 1). Because of the toxicity of cadmium, most cadmium containing brazing alloys have been replaced by zinc and tin containing brazing alloys. Alloys containing nickel and manganese are also used for higher corrosion resistance requirements or for easier wetting of stainless steel.. Using any of these brazing alloys in an air environment is only possible with the addition of oxide reducing fluxes.

For high temperature brazing in vacuum or protective atmosphere, vacuum melted silver-copper eutectic brazing alloys are used. These also allow subsequent forming operations due to their higher ductility. For the brazing of contacts with a silver bottom layer to copper backings, phosphorous containing brazing alloys which eliminate the need for a flux application, are widely used. The brazing alloy is typically introduced into the joint area in the form of wire segments, foil, shims or as powder or paste. For larger production volumes it is economically advantageous to pre-coat contact tips with a thin layer (≤ 100 µm) of brazing alloy.

Table 1: Commonly Used Brazing Alloys for Electrical Contacts
Designation
DIN EN 1044 		BrazeTec
Designation 		Designation US
(equivalent or closest similar brazing alloy) 		Designation
DIN EN ISO 3677 		Composition
wt % 		Melting Range (solidus)
[°C] 		Melting Range (liquidus)
[°C] 		Working Temperature
[°C] 		Electrical Conductivity
[MS/m] 		Density
[g/m3] 		Application
AG103 BrazeTec 5507 BAg-7 B-Ag55ZnCuSn
630/660 		Ag54 - 56
Cu20 - 23
Zn20 - 24
Sn1,5 - 2,5 		630 660 650 8,4 9,6 Cu, Cu-Alloys, Ag-materials
Fe, Ni
Ag502 BrazeTec 4900 BAg-22 B-Ag49ZnCuMnNi
680/705 		Ag48 - 50
Zn21 - 25
Cu15 - 17
Mn6,5 - 8,5
Ni4 - 5 		680 705 690 4,0 8,9 W, Mo, carbide steel
Fe, Ni
Ag401 BrazeTec 7200 BAg-8 B-Ag72Cu-780 Ag71 - 73
Cu Rest 		780 780 780 46,1 10,0 Cu, Cu-Alloys, Ag-materials
vacuum brazing
CP 102 BrazeTec S15 BCuP-5 B-Cu80AgP
645/800 		Ag14,5 - 15,5
P4,7 - 5,3
Cu Rest 		645 800 710 7,0 8,4 Cu, Cu-Legierungen, Ag-materials

Fluxes

Brazing fluxes consist of non-metallic materials, mostly salt mixtures of boron and halogen compounds (Table 2). Their purpose is to remove oxides from the brazing surfaces and prevent their new build-up, in order to allow a thorough wetting of these surfaces by the liquefied brazing alloy. Fluxes have to be activated already at a temperature below the working range of the brazing alloy. They are selected mainly according to the working temperature of the brazing alloy and the base material to be joined.

Since the residues of fluxes are hygroscopic and can cause corrosion, they have to be removed completely after the brazing process in very hot or boiling water. Depending on the type and process used, fluxes are being applied in liquid form or as powders or pastes.

Table 2: Fluxes for the Brazing of Heavy Metals

Designation

DIN EN 1045

Designation US (similar)

Active tempe- rature range [°C]

Chemical ingredients

Base materials used for

TYP FH 10

FB 3-A

550 - 800

Boron compounds, Fluorides

All metals and alloys except light metals, alloyed steels, carbide steels

TYP FH 11

FB 4-A

550 - 800

Boron compounds,

Fluorides, Chlorides

Copper,

Aluminum bronze

TYP FH 12

FB 3-C

550 - 850

Boron,

Boron compounds, Fluorides

Special brass,

any steel alloys, carbide steel

TYP FH 21

FB 3-I

750 - 1100

Boron compounds, Chlorides

All metals and alloys

except light metals

References

DIN 8514 Löten metallischer Werkstoffe. Begriffe, Benennungen

DIN EN 1044 Hartlöten, Lötzusätze

DIN EN 1045 Flussmittel zum Hartlöten

ASM Metals, Handbook: Vol 6 Welding, Brazing, and Soldering, ASM, Cleveland, OH, 1993

Dorn, L.: Hartlöten, Grundlagen und Anwendungen. Expert-Verlag, Band 146 (1985)

Krell, A.: Flussmittel und Lötfehler beim Hartlöten. Schweißtechnik, Berlin, 38 (1988)

DVS-Taschenbuch 196: Beuth-Verlag. Berlin, 1997

Müller, W.: Metallische Lotwerkstoffe. Dt. Verlag für Schweißtechnik, Düsseldorf 1990
Physical Properties of the Most Important Metals
The following tables list the physical properties of the most technically significant pure metals as well as carbon. The values given may vary considerably, depending on the degree of purity and sometimes they are also difficult to determine. In compiling the data from the available literature, we selected those that are currently the most probable. Some properties are anisotropic and vary with the crystalline structure of the metal.</onlyinclude> In those cases, we listed the value applicable to the poly-crystalline stage.

Table 3: Mechanical Properties of the Most Important Metals
Element/Metal Density 1

[g/cm³]

Modulus of

Elasticity 1[GPa]

Shear Modulus

[GPa]

Transvers Contraction Coeffic.
Aluminum 2.70 65 27 0.34
Antimony 6.62 56 20.4 0.28
Beryllium 1.85 298 150 0.12
Lead 11.36 14.5 6 0.44
Cadmium 8.65 57.5 29 0.30
Chromium 7.19 160 0.25
Iron 7.89 208 83 0.28
Gallium 5.91 9.6 0.46
Gold 19.32 79 28 0.42
Indium 7.31 11 0.45
Iridium 22.65 538 214 0.26
Cobalt 8.85 216 0.31
Carbon (Graphite) 2.1-2.3 5
Copper 8.95 115 48 0.34
Magnesium 1.74 46 18 0.28
Manganese 7.43 165 77 0.24
Molybdenum 10.21 347 122 0.30
Nickel 8.90 216 83 0.31
Niobium 8.57 113 39 0.38
Osmium 22.61 570 220 0.25
Palladium 12.02 124 51 0.39
Platinum 21.45 173 67 0.39
Mercury 13.55
Rhenium 21.04 480 215 0.26
Rhodium 12.41 386 153 0.26
Ruthenium 12.45 485 172 0.29
Silver 10.49 82 27 0.37
Tantalum 16.60 188 70 0.35
Titanium 4.51 120 43 0.34
Vanadium 6.10 136 52 0.36
Bismuth 9.80 33 13 0.33
Tungsten 19.32 360 158 0.30
Zinc 7.13 96 36 0.29
Tin 7.30 47 18 0.33
Zirconium 6.49 98 36 0.33
1 at 20°C



Table 4: Atomic properties of the most important metals
Element/Metal Chemical
Symbol 		Atomic Number Atomic Weight Crystal Structure 1 Lattic Parameters 1
a or b 2
[1010m] 		Lattic Parameters 1
a or b 2
[10-10m] 		Work Function
[eV] 		Ionization Potential
[eV]
Aluminum Al 13 26,98 foc 4,049 4,08 - 4,3 5,98
Antimony Sb 51 121,75 rhl 4,507 4,1 8,64
Beryllium Be 4 9,01 hcp 2,286 3,584 3,2 - 3,9 9,32
Lead Pb 87 207,19 fcc 4,949 4,0 - 4,1 7,42
Cadmium Cd 48 112,40 hcp 2,979 5,617 3,7 - 4,1 8,99
Chromium Cr 24 52,00 bcc 2,884 4,4 - 4,7 6,76
Iron Fe 26 55,85 bcc 2,866 4,1 - 4,5 7,9
Gallium Ga 31 69,72 ort 4,524 7,661 3,8 - 4,1 6,0
Gold Au 79 196,97 fcc 4,078 4,3 - 5,1 9,22
Indium In 49 114,82 tet 4,594 4,951 4,0 5,79
Iridium Ir 77 192,20 fcc 3,839 4,6 - 5,3 9,1
Cobalt Co 27 58,93 hcp 2,507 4,069 4,4 - 4,6 7,86
Carbon (Graphite) C 6 12,01 hcp-layered lattic3 2,456 6,696 4,8 11,27
Copper Cu 29 63,54 fcc 3,615 4,4 7,72
Magnesium Mg 12 24,31 hcp 3,209 5,210 3,7 7,64
Manganese Mn 25 54,94 complex cubic 8,912 3,8 - 4,1 6,0
Molybdenum Mo 42 95,94 bcc 3,147 4,1 - 4,5 7,18
Nickel Ni 28 58,71 fcc 3,524 5,0 - 5,2 7,63
Niobium Nb 41 92,91 bcc 3,301 4,0 6,77
Osmium Os 76 190,23 hcp 2,734 4,320 4,5 8,7
Palladium Pd 46 106,40 fcc 3,890 4,5 - 5,0 8,34
Platinum Pt 78 195,09 fcc 3,931 4,1 - 5,5 9,0
Mercury Hg 80 200,59 rhl4 3,0614 4,5 10,44
Rhenium Re 75 186,20 hcp 2,760 4,458 4,7 - 5,0 7,8
Rhodium Rh 45 102,91 fcc 3,804 4,6 - 4,9 7,46
Ruthenium Ru 44 101,07 hcp 2,704 4,281 4,5 7,37
Silver Ag 47 107,87 fcc 4,086 4,3 7,57
Tantalum Ta 73 180,95 bcc 3,303 4,0 - 4,2 7,89
Titanium Ti 2 47,90 hcp 2,950 4,683 4,0 - 4,4 6,83
Vanadium V 23 50,94 bcc 3,039 3,8 - 4,2 6,71
Bismuth Bi 83 208,98 rhl 4,746 4,1 - 4,5 8,0
Tungsten W 74 183,85 bcc 3,158 4,3 - 5,0 7,98
Zinc Zn 30 65,37 hcp 2,665 4,947 3,1 - 4,3 9,39
Tin Sn 50 118,69 tet 5,831 3,181 3,6 - 4,1 7,33
Zirconium Zr 40 91,22 hcp 3,231 5,148 3,7 - 4,3 6,92
1 at 20°C
2 for rhombohedral crystals, the rhombohedra angle α is given in angle degrees and minutes; for orthorhombic crystals the parameter β is shown in m x 10-10
3 α-crystal
4 at -50°C

fcc = cubic face cenered // bcc = cubic body centered // hcp = hexagonal dense spherical ort = orthorhombic // tet = tetragonal // rhl = rhombohedral

Table 5: Thermal properties of the most important metals
Element/Metal Specific Heat 1
[kJ/(K*kg)] 		Softening
Temperature
[°C] 		Melting Point
[°C] 		Heat of Fusion
[kJ/kg] 		Vapor Pressure
at Melting Point
[Pa] 		Boiling Point
[°C] 		Heat of Vaporizing
[kJ/g] 		Thermal
Conductivity
[W/(m*K)] 		Linear Expansion
Coefficient2
[10-6m/K] 		Volume Change at
Solidification
[%]
Aluminum 0,900 150 660 398 2,5x10-6 2467 10,47 237 23,6 -6,5
Antimony 0,210 630 163 2,5x10-9 1587 1,97 24,3 10,5 +9,5
Beryllium 1,824 1277 1090 4,3 2477 200 12,3
Lead 0,130 200 327 25 4,21x10-7 1750 24,70 35,3 29,3 -3,5
Cadmium 0,230 321 54 14,8 767 0,88 96,8 41,0 -4,0
Chromium 0,450 1857 314 990 2672 5,86 93,7 6,2
Iron 0,444 500 1537 268 7,05 2750 80,2 12,2 -3,0
Gallium 0,370 29,8 80,4 9,6x10-36 2204 3,90 40,6 18,0 +3,0
Gold 0,128 100 1064 63 2,4x10-3 3080 1,55 317 14,3 -5,1
Indium 0,233 157 28,5 1,5x10-17 2072 1,97 81,6 -2,5
Iridium 0,130 2410 144 1,5 4130 3,31 147 6,5
Cobalt 0,420 1495 260 175 2927 6,66 100 13,8
Carbon (Graphite) 0,720 3825 sublimiert 119 - 165 155
Copper 0,385 190 1084 205 5,2x10-2 2567 4,77 401 16,5 -4,2
Magnesium 1,020 650 373 361 1107 5,44 156 26,0 -4,1
Manganese 0,480 1244 264 121 1962 4,10 7,8 23,0 -1,7
Molybdenum 0,250 900 2623 292 3,6 4639 5,61 138 5,2
Nickel 0,440 520 1453 301 237 2913 6,45 90,7 13,0 -2,5
Niobium 0,272 2477 289 7,9x10-2 4744 7,79 53,7 7,3
Osmium 0,130 3045 141 2,52 5012 3,81 87,6 6,5
Palladium 0,244 1554 143 1,33 2970 3,48 71,8 11,1 -5,5
Platinum 0,130 540 1772 113 3,2x10-2 3827 2,62 71,6 9,0 -6,0
Mercury 0,140 -38,9 11,7 3,1x10-4 357 0,29 8,34 60,8 -3,7
Rhenium 0,137 3186 178 3,24 5596 3,42 72 6,7
Rhodium 0,242 1966 211 6,36x10-1 3695 5,19 150 8,5 -10,8
Ruthenium 0,238 2310 252 1,4 4150 6,62 117 9,5
Silver 0,232 180 961,9 105 3,4x10-1 2212 2,39 429 19,5 -3,8
Tantalum 0,140 850 3017 157 7,86x10-1 5448 4,32 57,5 6,5
Titanium 0,520 1668 403 4,9x10-1 2830 8,80 21,9 10,8
Vanadium 0,490 1902 330 3,06 3287 10,3 30,7 8,3
Bismuth 0,122 271 54 6,5x10-4 1564 1,43 7,87 14,0 -0,33
Tungsten 0,138 1000 3422 193 4,27 5555 3,98 174 4,5
Zinc 0,385 170 420 100 3,06 907 1,76 116 36,0 -4,7
Tin 0,228 100 222 59 6x10-21 2602 1,95 66,6 26,7 -2,8
Zirconium 0,281 1852 224 1,7x10-3 4409 4,6 22,7 5,9
1 at 20°C
2 between 20°C and 100°C



Table 6: Elektrische Eigenschaften der wichtigsten Metalle
Element/Metal Electrical Resistivity 1
[Ω*mm2/m] 		Electrical Conductivity1
[MS/m] 		Temperatur Coeff.
of Electrical
Resistance2
[10-3/K] 		Absolute thermal
e.m.f.3
[µV/K] 		Critical
Superconductor
Temperatur
[K] 		Softening
Voltage
(measured)
[V] 		Melting
Voltage
(measured)
[V] 		Melting
Voltage
(calculated)4
[V] 		Minimum Arc
Voltage
[V] 		Minimum Arc
Current
[A]
Aluminum 2,65 37,7 4,6 -1,6 1,18 0,1 0,3 0,29 11,2 0,4
Antimony 38,6 2,6 5,4 +20,6 - +46,8 0,2 0,28 10,5
Beryllium 4,2 23,8 10,0 -3,3 0,026 0,48
Lead 19,2 5,2 4,2 -1,2 7,196 0,19 0,17 11,5 0,1
Cadmium 7,50 13,30 4,3 -0,1 - +3,6 0,52 0,12 0,17 12 0,4
Chromium 14,95 6,7 3,0 +14,0 3,0 0,67 16 0,45
Iron 9,72 10,3 6,6 +16,0 0,19 0,6 0,54 11,5
Gallium 43,2 2,3 4,0 1,08 0,04 0,35
Gold 2,35 42,6 4,0 +1,7 0,08 0,43 0,42 15
Indium 8,37 11,94 4,9 3,41 0,11
Iridium 5,31 18,83 4,1 +1,5 0,11 0,86 11,5
Cobalt 6,24 16,0 6,6 -18,5 0,54 0,01 - 0,02
Carbon (Graphite) 30,0 3,33 20 0,4
Copper 1,67 59,9 4,3 +1,7 0,12 0,43 0,42 12 - 13
Magnesium 4,42 22,62 4,2 +3,4 0,28
Manganese 185,0 0,54 0,5 0,47 0,75
Molybdenum 5,20 19,2 4,7 +5,9 0,92 0,3 0,75 0,91 12 0,4 -0,5
Nickel 6,85 14,6 6,8 -18,9 0,16 0,65 0,54 14
Niobium 13,1 7,6 3,4 -0,5 9,2 0,778
Osmium 8,12 12,31 4,2 0,66 1,04 0,8 -0,9
Palladium 10,82 9,24 3,8 -0,9 3,3 0,57 0,57 15 - 16 0,8 -1,0
Platinum 10,54 9,58 3,9 -4,4 0,0019 0,25 0,71 0,64 17
Mercury 94,9 1,14 1,0 +8,5 4,15 0,35
Rhenium 19,3 5,2 4,6 1,7 1,09
Rhodium 4,51 22,2 4,4 +1,7 0,000325 0,70 14
Ruthenium 7,62 13,12 4,6 -18,0 0,49 0,81 0,4
Silver 1,59 62,9 4,3 +1,4 0,09 0,37 0,38 12
Tantalum 12,4 8,1 3,5 -2,3 4,47 0,3 1,03 12
Titanium 43,5 2,3 5,5 +7,3 0,4 0,61
Vanadium 26,0 3,8 3,9 +1,0 5,3 0,68
Bismuth 12,1 8,36 4,5 -53 - -110 0,15
Tungsten 5,65 17,7 4,8 +0,8 0,0154 1,1 1,16 1,16 0,8 - 1,2
Zinc 5,92 16,9 4,2 +0,4 - +2,3 0,85 0,17 0,2 0,20 15 - 16 0,1
Tin 11,0 9,09 4,6 -0,6 - -1,5 3,72 0,13 0,14 0,14 11
Zirconium 43,5 2,3 4,4 +9,5 0,55 0,67 0,67 12,5
1 at 20°C
2 near room temperature
3 near room temperature, however values for metals with non-cubic structure can vary widely
4 Calculated according to UMelt = [4L * (T2Melt - T20)]1/2 mit UMelt= Melting Voltage, L = Lorenz Constant (2,45x10-8[V/K], TMelt= Melting Temperature, T0= Temperature at a point distant from the constriction spot


References

Metals Handbook, Desk Edition: Chicago, IL, American Society of Metal, 1985

Landolt-Börnstein: Zahlenwerte und Funktionen. Springer-Verlag, Berlin-Göttingen-Heidelberg, 1959

Handbook of Chemistry and Physics, 70th Edition: CRC Press., Inc. Boca Raton, Florida, 1989 - 1990

Fluck, E.; Heumann, K., G.: Periodensystem der Elemente. Weinheim: VCH-Verlagsgesellschaft, 1986

Kieffer, R.; Jangg, G.; Ettmayer, P.: Sondermetalle. Springer- Verlag, Wien-New York, 1963

Hering, E.; Schulz, W.: Physik für Ingenieure (Periodensystem der Elemente). Düsseldorf: VDI-Verlag, 1988

Degussa AG (Hrsg.): Edelmetall-Taschenbuch. Hüthig-Verlag, Heidelberg, 1995

Slade, P.; G. (editor): Electrical Contacts Principles and Applications. Marcel Dekker, Inc., New York-Basel, 1999

Gerritsen, A.; N.: Metallic Conductivity in: Flügge, S.: Handbuch der Physik, Bd. 19, Springer-Verlag, Berlin-Göttingen-Heidelberg, 1956

Köster, W.; Franz, H.: Poisson,s Ratio for Metals and Alloys. Metallurg. Reviews 6 (1961)

Nesmeyanow, A., N.: Vapor Pressure of the Chemical Elements: Elsevier, Amsterdam-London-New York, 1963

Wyckoff, R., W., G.: Crystal Structures. Vol 1,New York, 1963

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