PZT651T1
SOLDER STENCIL GUIDELINES
Prior to placing surface mount components onto a printed
or stainless steel with a typical thickness of 0.008 inches.
The stencil opening size for the SOT–223 package should be
the same as the pad size on the printed circuit board, i.e., a
1:1 registration.
circuit board, solder paste must be applied to the pads. A
solder stencil is required to screen the optimum amount of
solder paste onto the footprint. The stencil is made of brass
SOLDERING PRECAUTIONS
The melting temperature of solder is higher than the rated
temperature of the device. When the entire device is heated
to a high temperature, failure to complete soldering within
a short time could result in device failure. Therefore, the
following items should always be observed in order to
minimize the thermal stress to which the devices are
subjected.
• Always preheat the device.
• The delta temperature between the preheat and
soldering should be 100°C or less.*
• The soldering temperature and time should not exceed
260°C for more than 10 seconds.
• When shifting from preheating to soldering, the
maximum temperature gradient should be 5°C or less.
• After soldering has been completed, the device should
be allowed to cool naturally for at least three minutes.
Gradual cooling should be used as the use of forced
cooling will increase the temperature gradient and
result in latent failure due to mechanical stress.
• Mechanical stress or shock should not be applied
during cooling
* Soldering a device without preheating can cause
excessive thermal shock and stress which can result in
damage to the device.
• When preheating and soldering, the temperature of the
leads and the case must not exceed the maximum
temperature ratings as shown on the data sheet. When
using infrared heating with the reflow soldering
method, the difference should be a maximum of 10°C.
TYPICAL SOLDER HEATING PROFILE
For any given circuit board, there will be a group of
control settings that will give the desired heat pattern. The
operator must set temperatures for several heating zones,
and a figure for belt speed. Taken together, these control
settings make up a heating “profile” for that particular
circuit board. On machines controlled by a computer, the
computer remembers these profiles from one operating
session to the next. Figure 2 shows a typical heating profile
for use when soldering a surface mount device to a printed
circuit board. This profile will vary among soldering
systems but it is a good starting point. Factors that can affect
the profile include the type of soldering system in use,
density and types of components on the board, type of solder
used, and the type of board or substrate material being used.
This profile shows temperature versus time. The line on the
graph shows the actual temperature that might be
experienced on the surface of a test board at or near a central
solder joint. The two profiles are based on a high density and
a
low density board. The Vitronics SMD310
convection/infrared reflow soldering system was used to
generate this profile. The type of solder used was 62/36/2
Tin Lead Silver with a melting point between 177–189°C.
When this type of furnace is used for solder reflow work, the
circuit boards and solder joints tend to heat first. The
components on the board are then heated by conduction. The
circuit board, because it has a large surface area, absorbs the
thermal energy more efficiently, then distributes this energy
to the components. Because of this effect, the main body of
a component may be up to 30 degrees cooler than the
adjacent solder joints.
STEP 5
HEATING
ZONES 4 & 7
SPIKE"
STEP 6 STEP 7
VENT COOLING
STEP 4
HEATING
ZONES 3 & 6
SOAK"
STEP 1
PREHEAT
ZONE 1
RAMP"
STEP 2
VENT
STEP 3
HEATING
SOAK" ZONES 2 & 5
RAMP"
205° TO
219°C
PEAK AT
SOLDER
JOINT
170°C
DESIRED CURVE FOR HIGH
MASS ASSEMBLIES
200°C
150°C
100°C
50°C
160°C
150°C
SOLDER IS LIQUID FOR
40 TO 80 SECONDS
(DEPENDING ON
100°C
140°C
MASS OF ASSEMBLY)
DESIRED CURVE FOR LOW
MASS ASSEMBLIES
http://onsemi.com
4
T
TIME (3 TO 7 MINUTES TOTAL)
MAX
Figure 2. Typical Solder Heating Profile
