MMFT5P03HD

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10

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 16 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”

STEP 2

VENT

“SOAK”

STEP 3

HEATING

ZONES 2 & 5

“RAMP”

STEP 4

HEATING

ZONES 3 & 6

“SOAK”

STEP 5

HEATING

ZONES 4 & 7

“SPIKE”

STEP 6

VENT

STEP 7

COOLING

200

°C

150

°C

100

°C

5

°C

TIME (3 TO 7 MINUTES TOTAL)

TMAX

SOLDER IS LIQUID FOR

40 TO 80 SECONDS

(DEPENDING ON

MASS OF ASSEMBLY)

205

° TO 219°C

PEAK AT

SOLDER

JOINT

DESIRED CURVE FOR LOW

MASS ASSEMBLIES

DESIRED CURVE FOR HIGH

MASS ASSEMBLIES

100

°C

150

°C

160

°C

170

°C

140

°C

Figure 16. Typical Solder Heating Profile