Freescale Semiconductor, Inc.
SOLDERING PRECAUTIONS
The melting temperature of solder is higher than the rated
using infrared heating with the reflowsolderingmethod, the
difference should be a maximum of 10°C.
• 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 shall 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 since the use of forced cooling will
increase the temperature gradient and will result in latent
failure due to mechanical stress.
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 mini-
mize 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.*
• For pressure sensor devices, a no–clean solder is
recommended unless the silicone die coat is sealed and
unexposed. Also, prolonged exposure to fumes can
damagethe silicone die coat of the device during the solder
reflow process.
• Mechanical stress or shock should not be applied during
cooling.
• 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
* Soldering a device without preheating can cause excessive
thermal shock and stress which can result in damage to the
device.
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 remem-
bers these profiles from one operating session to the next.
Figure 3 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
STEP 6
VENT
STEP 7
COOLING
STEP 1
STEP 4
STEP 2
VENT
“SOAK”
STEP 3
HEATING
ZONES 4 & 7
“SPIKE”
PREHEAT
ZONE 1
“RAMP”
HEATING
ZONES 3 & 6
“SOAK”
HEATING
ZONES 2 & 5
“RAMP”
205° TO 219°C
PEAK AT
SOLDER JOINT
200°C
150°C
100°C
50°C
170°C
DESIRED CURVE FOR HIGH
MASS ASSEMBLIES
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
TIME (3 TO 7 MINUTES TOTAL)
T
MAX
Figure 3. Typical Solder Heating Profile
1–10
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Motorola Sensor Device Data
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