Elenco Surface Mount Technology Kit - Manual (Page 5)

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CONSTRUCTION
Introduction
The most important factor in assembling your SM-200K
Decision Maker Kit is good soldering techniques. Using
the proper soldering iron is of prime importance. A small
pencil type soldering iron of 10-15 watts is
recommended. A sharply pointed tip is essential when
soldering surface mount components. The tip of the
iron must be kept clean at all times and well tinned.
Solder
For many years leaded solder was the most common
type of solder used by the electronics industry, but it
is now being replaced by lead-free solder for health
reasons. This kit contains lead-free solder, which
contains 99.3% tin, 0.7% copper, and has a rosin-flux
core.
Lead-free solder is different from lead solder: It has a
higher melting point than lead solder, so you need
higher temperature for the solder to flow properly.
Recommended tip temperature is approximately
700
O F; higher temperatures improve solder flow but
accelerate tip decay. An increase in soldering time
may be required to achieve good results. Soldering
iron tips wear out faster since lead-free solders are
more corrosive and the higher soldering temperatures
accelerate corrosion, so proper tip care is important.
The solder joint finish will look slightly duller with lead-
free solders.
Use these procedures to increase the life of your
soldering iron tip when using lead-free solder:
• Keep the iron tinned at all times.
• Use the correct tip size for best heat transfer. The
conical tip is the most commonly used.
• Turn off iron when not in use or reduce
temperature setting when using a soldering
station.
• Tips should be cleaned frequently to remove
oxidation before it becomes impossible to remove.
Use Dry Tip Cleaner (Elenco
® #SH-1025) or Tip
Cleaner (Elenco ® #TTC1). If you use a sponge to
clean your tip, then use distilled water (tap water
has impurities that accelerate corrosion).
Parts Verification
Before beginning the assembly process, familiarize
yourself with the components and this instruction
book. Verify that all parts are present. This is best
done by checking off each item against the parts list.
Care must be taken when handling the chip resistors
and capacitors. They are very small and are easily
lost. Chip resistors are marked with their component
value. The first 2 digits are the first 2 digits of the
resistance in ohms. The last digit gives the number of
zeros following the first 2 digits. The resistor shown at
right is therefore 3,900 ohms.
The values of the chip capacitors are not marked on
the component. The two capacitors, .0039µF and
.015µF, are each in a separate bag with the
component value marked on the bag. To avoid mixing
these parts up, they should not be taken out of their
packages until just before they are soldered to the PC
board. Sometimes these parts are mixed, but can be
identified by different color and quantities.
Safety Procedures
• Always wear safety glasses or safety
goggles to protect your eyes when
working with tools or soldering iron, and
during all phases of testing.
• Be sure there is adequate ventilation when
soldering.
• Locate soldering iron in an area where you do not
have to go around it or reach over it. Keep it in a
safe area away from the reach of children.
• Do not hold solder in your mouth. Solder is a
toxic substance. Wash hands thoroughly after
handling solder.
Assemble Components
In all of the following assembly steps, the components
must be installed on the top side of the PC board
unless otherwise indicated. The top legend shows
where each component goes. The leads pass through
the corresponding holes in the board and are
soldered on the foil side.
Use only rosin core solder.
DO NOT USE ACID CORE SOLDER!