UMC3 ON Semiconductor, UMC3 Datasheet - Page 11

• Manufacturer Part Number: UMC3
• Description: Dual Common Base-Collector Bias Resistor Transistors
• Manufacturer: ON Semiconductor

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
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 31 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.
Prior to placing surface mount components onto a printed
For any given circuit board, there will be a group of
TYPICAL SOLDER HEATING PROFILE
UMC2NT1, UMC3NT1, UMC5NT1
Figure 31. Typical Solder Heating Profile
SOLDER STENCIL GUIDELINES
http://onsemi.com
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or stainless steel with a typical thickness of 0.008 inches.
The stencil opening size for the surface mounted package
should be the same as the pad size on the printed circuit
board, i.e., a 1:1 registration.
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.