MMSF3300

10

Motorola TMOS Power MOSFET Transistor Device Data

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

18 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/in-

frared 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

50

°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

100

°C

150

°C

160

°C

170

°C

140

°C

Figure 18. Typical Solder Heating Profile

DESIRED CURVE FOR HIGH

MASS ASSEMBLIES