Vicor VI-J00 Family DC-DC Converters and Configurable Power Supplies - Manual (Page 80)

Design Guide & Applications Manual
For VI-200 and VI-J00 Family DC-DC Converters and Configurable Power Supplies
VI-200 and VI-J00 Family Design Guide Rev 3.5 vicorpower.com
Page 79 of 98
Apps. Eng. 800 927.9474 800 735.6200
22. Recommended Soldering Methods, Lead Free Pins (RoHS)
respect to the PCB to ensure no movement during the
soldering process. The standoffs can be used for this
process. Vicor power modules contain two types of pins:
power pins (which deliver the power to the load and are
typically sized according to the rated output current) and
signal pins (which typically carry very little current and are
of a uniform size across a given product family). The larger
the pin, the more soldering time required to form an
adequate connection. In addition to the sizing of the pin,
the time required to create a robust connection will vary
depending on several parameters:
1. PCB Thickness. The thicker the printed circuit board,
the more heat it is able to dissipate, and will require
more soldering time.
2. Copper Trace Area. Power pins require large copper
traces to minimize resistive power losses in carrying the
power to the load. Since the copper tends to conduct
heat well, the actual sizes of these copper traces
directly affect the amount of time necessary to heat
the PCB socket.
3. Copper Trace Thickness. As above, the thickness of the
copper trace is a function of output current of the
module, and has a direct impact on the amount of
soldering time. Typically, PCB copper thickness is
specified in terms of weight per square foot, typically
2 oz. or 3 oz. copper for current-carrying planes.
4. Soldering Iron Power. A higher power soldering iron
can source more heat and thus take less time to heat a
PCB trace. As a soldering iron is heating a point on the
board, everything that is adjacent to this point is being
heated as well, including the Vicor power module.
A large copper trace, because it conducts heat very
well, will exhibit less of a thermal gradient, and thus a
low-power soldering iron will have to heat the whole
trace to a higher temperature before the area close to
the iron is hot enough to flow solder. Because the
trace and board are both dissipating and conducting
thermal energy, some irons may not have enough
power to heat a trace to the temperature that will
allow proper soldering.
5. Tip Temperature. Typical SAC-type solder melts at
419 – 491°F (215 – 225°C). Pb-free soldering requires
a tip temperature of about 800°F. A higher tip
temperature will bring the barrel and pin above the
melting point of solder faster. However, a higher tip
temperature may cause damage to the pad, printed
circuit board, or module pin.
6. Type of Lead-free Solder. The actual melting point of
the solder varies depending on the type of solder used
and affects the necessary temperature of the pad and
pin for flow. Vicor recommends SAC305 SnAgCu
solder for use on Vicor power modules.
7. Tip Size. A larger tip will be able to heat a larger
surface area, thus lowering soldering time.
Since there are so many factors that influence soldering
time, listing actual times is difficult. In general, it is
recommended that the joint be examined post-process to
insure a quality soldering joint. If necessary, different
parameters can then be varied in order to ensure a solid
process. The soldering times listed in Table 22–1 can be
used as a guideline for establishing more application and
process specific parameters. Below are some recommen-
dations for general practice:
1. Do not run tip temperature above 810°F (430°C). This
will greatly increase the risk of damaging the pads,
traces, printed circuit board, or Vicor power module.
Check with the printed circuit board manufacturer that
the boards are RoHS capable and for any additional
recommendations in regard to temperature.
2. Apply the soldering iron to one side of the pin and pad
and apply the solder to the other, allowing the heat
from the pin and pad to melt the solder. Do not apply
solder to the soldering iron and subsequently attempt
to transfer it to the pad and pin. Melting the solder by
applying it directly to the soldering iron does not
guarantee adequate wetting on the joint and is not
considered good technique.
3. Do not apply excessive pressure with the soldering iron
to the printed circuit board, barrel, or pad. This could
result in breaking a trace, dislodging a barrel, or
damaging the PCB, which becomes noticeably softer
when heated.
4. Do not apply the soldering iron to a connection for an
extended period of time or damage to the module
could result. If the soldering times exceed the upper
limit listed in Table 22–1, consider using a larger tip or
a higher power soldering iron.
5. Make sure PCB pads and holes are clean before to
soldering.
6. Solders with no-clean flux may be used to facilitate
soldering.
7. Keep the tip of the soldering iron clean and free from
resin. Apply a small amount of solder directly to the tip
of the iron. This process is known as tinning.