MMDF5N02Z

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9

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 tempera-

ture 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)

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 15. Typical Solder Heating Profile