Motorola Small–Signal Transistors, FETs and Diodes Device Data
1
MSC2295-BT1 MSC2295-CT1
MINIMUM RECOMMENDED FOOTPRINT FOR SURFACE MOUNTED APPLICATIONS
Surface mount board layout is a critical portion of the total
design. The footprint for the semiconductor packages must
be the correct size to insure proper solder connection
0.037
0.95
interface between the board and the package. With the
correct pad geometry, the packages will self align when
subjected to a solder reflow process.
0.037
0.95
0.098–0.118
2.5–3.0
0.094
2.4
0.039
1.0
0.031
0.8
inches
mm
SC–59 POWER DISSIPATION
The power dissipation of the SC–59 is a function of the pad
size. This can vary from the minimum pad size for soldering
to the pad size given for maximum power dissipation. Power
dissipation for a surface mount device is determined by
TJ(max), the maximum rated junction temperature of the die,
R
θJA
, the thermal resistance from the device junction to
ambient; and the operating temperature, TA . Using the
values provided on the data sheet, PD can be calculated as
follows:
PD =
TJ(max) – TA
R
θJA
the equation for an ambient temperature TA of 25°C, one can
calculate the power dissipation of the device which in this
case is 200 milliwatts.
PD =
150°C – 25°C
= 200 milliwatts
625°C/W
The values for the equation are found in the maximum
ratings table on the data sheet. Substituting these values into
The 625°C/W assumes the use of the recommended
footprint on a glass epoxy printed circuit board to achieve a
power dissipation of 200 milliwatts. Another alternative would
be to use a ceramic substrate or an aluminum core board
such as Thermal Clad™. Using a board material such as
Thermal Clad, a power dissipation of 400 milliwatts can be
achieved using the same footprint.
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.*
•
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.
•
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.
2
Motorola Small–Signal Transistors, FETs and Diodes Device Data
MSC2295-BT1 MSC2295-CT1
SOLDER STENCIL GUIDELINES
Prior to placing surface mount components onto a printed
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
or stainless steel with a typical thickness of 0.008 inches.
The stencil opening size for the SC–59 package should be
the same as the pad size on the printed circuit board, i.e., a
1:1 registration.
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 1 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 1
PREHEAT
ZONE 1
“RAMP”
200°C
STEP 2
STEP 3
VENT
HEATING
“SOAK” ZONES 2 & 5
“RAMP”
DESIRED CURVE FOR HIGH
MASS ASSEMBLIES
150°C
STEP 4
STEP 5
STEP 6 STEP 7
HEATING
HEATING
VENT COOLING
ZONES 3 & 6 ZONES 4 & 7
205° TO 219°C
“SOAK”
“SPIKE”
PEAK AT
170°C
SOLDER JOINT
160°C
150°C
100°C
100°C
DESIRED CURVE FOR LOW
MASS ASSEMBLIES
50°C
140°C
SOLDER IS LIQUID FOR
40 TO 80 SECONDS
(DEPENDING ON
MASS OF ASSEMBLY)
TIME (3 TO 7 MINUTES TOTAL)
TMAX
Figure 1. Typical Solder Heating Profile
Motorola Small–Signal Transistors, FETs and Diodes Device Data
3
MSC2295-BT1 MSC2295-CT1
PACKAGE DIMENSIONS
A
L
3
2
1
NOTES:
1. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.
2. CONTROLLING DIMENSION: MILLIMETER.
DIM
A
B
C
D
G
H
J
K
L
S
MILLIMETERS
MIN
MAX
2.70
3.10
1.30
1.70
1.00
1.30
0.35
0.50
1.70
2.10
0.013
0.100
0.10
0.26
0.20
0.60
1.25
1.65
2.50
3.00
INCHES
MIN
MAX
0.1063 0.1220
0.0512 0.0669
0.0394 0.0511
0.0138 0.0196
0.0670 0.0826
0.0005 0.0040
0.0040 0.0102
0.0079 0.0236
0.0493 0.0649
0.0985 0.1181
S
B
D
G
C
H
K
J
STYLE 1:
PIN 1. EMITTER
2. BASE
3. COLLECTOR
CASE 318D–03
ISSUE E
SC–59
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