Цитата(ZZmey @ Sep 15 2008, 08:40)
Для какого именно золота? Иммерсионное паяется без проблем, все зависит от качества изготовления покрытия.
Любое золото паяется без проблем:-) Дело в том, что если паять золото припоем с оловом - паянное соединение будет не надежным, проблема связана с низкими температурами.
Gold is a noble metal and therefore does not oxidize or
tarnish to any appreciable extent. In electronics this
property makes gold suitable for a number of uses
including contacts for switches and connectors, where
it is plated as a surface finish. Gold is also used as a
solderable surface or as a preserving finish on circuit
boards and other assemblies.
Flux Choice
As gold is a noble metal strong fluxes are not required
to remove any oxides or tarnishes that may form. It is
even possible to solder gold without flux under certain
circumstances. However, if the plated layer is thin, the
gold can become totally assimilated into the solder. In
this situation flux choice is then determined by the
characteristics of the underlying metal.
For reflow temperatures in excess of 330°-350°C forming
gas is effective and may be used instead of flux. An
inert atmosphere will increase flux efficiency and simplify
cleaning issues in high temperature applications
where a flux is still required. For fluxless soldering with
high indium alloys an inert atmosphere is obligatory.
Alloy Choice
Gold is rapidly dissolved by the tin in molten solder. If
sufficient gold is dissolved brittle intermetallic compounds
can be formed in the solder joint. Joint configuration
or alloy choice needs to be done in such a way
as to avoid these formations as they can lead to premature
failure in service. The precise amount of tolerable
gold will depend on joint design and service conditions
but it is possible to make a few guidelines.
For eutectic/near eutectic tin/lead solders, the maximum
permissible amount of gold is generally considered
to be 3% by weight of the solder joint. There is
little danger of this being reached when soldering conventional
Electroless Nickel Immersion Gold coated
PCBs where the gold thickness is typically only 0.03 -
0.07 microns. If the gold thickness is greater than 0.5
microns, the risk of embrittlement is considered significant
and non-tin based alloys, such as those based on
indium, are recommended. Indium dissolves gold at a
much slower rate than tin.
A number of indium-based alloys are available to suit
different requirements. When considering alloy
choice, both the operating temperature of the device
being soldered, and the maximum process temperature,
should be taken into account. A good rule of
thumb is to choose a solder with solidus no less than
50°C above the maximum device operational temperature.
An optimum process temperature will typically
be in the 30°-50°C range over liquidus.
The following indium alloys can be used successfully
against gold without the harmful effects caused when
tin bearing alloys are used:
Indalloy Melting Temperature Composition
Number (Liquidus / Solidus)
# 290 143°C E 97In 3Ag
# 2 154°C / 149°C 80In 15Pb 5Ag
# 4 157°C MP 100In
# 204 175°C / 165°C 70In 30Pb
# 205 181°C / 173°C 60In 40Pb
# 7 210°C / 178°C 50In 50Pb
# 206 231°C / 197°C 60Pb 40In
# 3 237°C / 141°C 90In 10Ag
# 1 266°C / 240°C 75Pb 25In
# 150 275°C / 260°C 81Pb 19In
# 12 310°C / 290°C 90Pb 5In 5Ag
# 164 310°C / 300°C 92.5Pb 5In 2.5Ag
# 11 313°C / 300°C 95Pb 5In
Precautions
Even though indium and indium based solders solve
numerous critical joining applications, certain precautions
must be followed concerning metal compatibility
and corrosion. If device-operating temperatures
exceed 125°C, indium-based solders are not recommended
for use against gold metallizations, as solidstate
diffusion of the gold may occur. In such cases,
gold-tin eutectic or a high lead alloy solder can be
used instead, according to process or commercial
restraints.
Indium can be corroded by halides. Indium based
joints should be protected in service from halide containing
materials or if humidity will exceed 85% in the
presence of halides (a marine environment for example).
This can be accomplished with the use of a conformal
coating.
Fluxes based on halide activators (and any cleaners
containing chlorinated hydrocarbons) should be
avoided when using indium-based alloys. If this precaution
is not followed, corrosion of the solder joint
may occur at a higher rate than for a tin-lead joint.
Сообщение отредактировал ywg - Sep 15 2008, 06:58
пайка карбона и гальванического золота
Aug 27 2008, 07:24
