WHY LEAD FREE?
Increasing consumer awareness of the toxicity of lead is prompting the electronics industry to move to lead free
materials in their manufacturing processes. In some countries, the timetable for the elimination of lead from
electronics is being set by governments. However, most companies are motivated primarily by their wish to supply
their customers with products that will not contribute lead to the environment at any stage in their life cycle from
manufacture to eventual disposal.

ADVANTAGES OF SN96CI PF-23 H F M Q
Extensive research by the electronics industry during the 1990s identified the tin-silver-copper eutectic as one of
the best alternatives to lead-containing solders. The three constituent metals are readily available in quantities
sufficient to meet any likely demand for solder by the electronics industry and their non-toxicity is undisputed.
Since they are already used extensively in the electronics industry they do not contribute any new problems to the
recycling of electronic circuitry when it has reached the end of its useful life. The Ames Laboratory of the
University of Iowa, U.S.A. studied the properties of the tin-silver-copper system as they relate to its use as a solder
the uniqueness of which was reflected in the granting of US Patent No 6231691. This patent included methods of
further enhancing the properties of the alloy by trace quaternary additions. Nihon Superior is a licensee of this
patent and has taken full advantage of its scope to develop the SN96 alloy. SN96 solidifies to produce a stable
uniform microstructure over a wide range of cooling rates.

The PF-23flux medium has been developed by Nihon Superior to cope well with the higher reflow temperature of
the tin-silver-copper eutectic while giving good wetting to ensure full fillet formation and maximum coverage. The
F indicates a particle size range of 45-20μm, which ensures good printing down to 0.4mm pitch. The M indicates a
metal content optimized for stencil printing. The Q indicates spherical solder powder. This combination of
specifications ensures that the paste meets all of the requirements of current printing, placement and reflow
processes.

PASTE

Solder Alloy Composition Sn / Ag 3.5 - 4.7 / Cu 1.0 - 0.7
Solder Powder Size 20 - 45μm
Solder Powder Shape Spherical
Metal Content (JIS-Z-3197 6.1) Approximately 89 wt %
Viscosity (Malcom) Approximately 1900PS
Thixotropic Index 0.57
Tackiness Open Time Approximately 8 hr

ALLOY

Melting Point 217ºC
Tensile Strength (10mm/min) 52 Mpa
Elongation (10mm/min) 27%

FLUX MEDIUM

Dryness (JIS-Z-3197 6.2) Pass
Chorine Content (JIS-Z-3197 6.5) 0.1% maximum
Copper Plate Corrosion (JIS-Z-3197 6.6.1) Pass
Water Extract Solution Resistance 1000Ωm minimum
Surface Insulation Resistance (JIS-Z-3197 6.8) Initial value: 1.0×1013 Ω minimumAfter 96hr humidity: 1.0×1011 Ω minimum
Electromigration Test (JIS-Z-3197 6.9) Initial value: 1.0×1013 Ω minimumAfter 96hr humidity: 1.0×1011 Ω minimum
Spreading Test 75% minimum
Non Volatile Content 66 +/- 3% (150ºC for an hour)
APPLICATION

PRINTING
Parameters for optimum printing are dependent on printer and stencil design and ambient temperature but good
results have been obtained under the following conditions.

Squeegee 80 – 90 Durometer Polyurethane
Metal
Squeegee Pressure 2 – 3Kg/cm2
Squeegee Speed 20 – 30mm/sec

Before printing, the solder cream should be stabilized at room temperature for 1 – 2 hours before use. A
temperature-controlled bath can be used to accelerate that process. The PF-23H medium is designed to be ready to
use and may be damaged by excessive mixing. Solder paste packed in jars should be turned over no more than a
few times with a spatula before applying to the stencil.

RECOMMENDED REFLOW PROFILE
SN96CI PF-23 H F M Q solder paste requires only 4 – 5 seconds at a temperature about 10ºC above its melting
point of 217ºC for full reflow and wetting to be achieved. However for a printed circuit board with a variety of
components with a wide range of thermal masses and heat absorption characteristics it may take much longer than
that time to get all joints into this temperature range. How long it will take and the peak temperature that has to be
reached to achieve this for all joints depends on the characteristics of the oven. Because of the smaller difference
between the melting point of the solder and the maximum temperature that the board and components can tolerate
process parameters need to be controlled to a greater tolerance than is necessary in reflowing tin-lead solder. The
peak temperature that has to be reached to ensure that all joints are held in the reflow range for sufficient time
depends on the thermal characteristics of the oven. The peak temperature is minimized if the thermal transfer rates
are high and temperature gradients flat so that the ΔT across the board is minimized. Whether or not a "plateau” is
required in the preheat stage of the reflow profile, and the extent of that "plateau” depends on the ΔT across the
board during ramp up. The "plateau” provides an opportunity for temperature differences across the board to even
out before the final ramp up to reflow temperature. The ΔT is minimized with forced convection heating. A
nitrogen atmosphere is not necessary to get satisfactory reflow but may improve pad coverage on boards with an
OSP finish.

As explained above the thermal profile required to achieve best results in reflow is dependent on the characteristics
of the board and the reflow oven but the following profile has been used successfully to reflow SN96CI PF-23 H F
M Q in a 4 zone forced convection air atmosphere oven. The actual temperature registered in the profile varies
depending on the location of the measuring thermocouple. Test boards should be run to confirm the suitability of
the profile for a particular board and oven combination.