Outline

Comparing Brazing and Soldering

Both use heat, filler metal and usually flux.
Primary difference is melting temperature of filler metal.
- Brazing filler metals melt above 840°F (liquidus).
Filler metal in both cases melts below melting temperature of base metal.
Sometimes (especialy with brazing) the difference in melting temperaures is small (small process window).
Process window for soldering usually dictated by electronic components
Both rely on capillary action to create a strong joint.
- Joint clearance is critical
- Typical range is .001 to .005 for brazing, .003 to .006 for soldering (inches)
- Joint design may need to compensate for thermal expansion

Brazing

Flux

Prevents, dissolves and/or facilitates removal of oxides and other surface contaminants.
Fluxes are not designed to be cleaners. Joint should be clean before brazing begins.

Six Categories

Type 1, 2, 3A, 3B, 4, 5
Selection is based on base metals.
Contain combinations of fluorides, chlorides, borates (including borax) and wetting agents
Each type has a different working temperature
Available as liquid, paste, powder. Sometimes compounded with filler metal. Braze rod with flux covering or core is available.

Filler Metals

Filler metals are available as

wire
foil
paste
powder
preforms
braze sheet

Brazing Advantages

The joining of dissimilar metals, and materials
Very thin material can be brazed which would otherwise be damaged by welding
Inaccessible joints can more easily be brazed
Brazing is easily and more economically automated than many welding processes
Leaktight joints are easily attained
Multiple joints can be made simultaneously
Less-skilled operators are required
Braze joints are ductile
Braze process is readily automated

Brazable Materials

Most ferrous and non-ferrous metals.
Many carbides and cermet

Brazing Processes

Torch Brazing
Dip Brazing
Induction Brazing
Furnace Brazing

Soldering

Soldering is one of the oldest methods of joining metals. Because filler metals melt at low temperatures there is minimum part distortion and heat damage to sensitive parts.

Soldering Fluxes

Organic
- Contain carbon, corrosive at elevated temperature, noncorrosive at room temp.
  Water soluble
Inorganic
- Very Corrosive, provide better cleaning, do not char or burn easily. Parts must be cleaned after brazing.
Rosin Flux
- Noncorrosive, used for electronics least effective cleaning ability

Solder Filler Metals

Filler materials include combinations of tin-lead, tin-silver-lead, tin-zinc, silver-copper-zinc and zinc-aluminum alloys.
As with brazing filler metals, solders are supplied as wires, foil, sheets, pastes, preforms, or as bars and ingots.

Solderable Materials

Many combinations of metal to metal, ceramic to metal, and glass to metal may be joined.
Soldering is used extensively in the electronics industry where it’s limited mechanical strength is not a major factor.

Soldering Processes

Iron Soldering
Wave Soldering
Reflow Soldering
Torch Soldering
Soldering Sheet (Soldering coppers/irons)

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