9

Figure 17. Surface Mount Assembly Profile.

SMT Assembly

Reliable assembly of surface mount components is a

complex process that involves many material, process,

and equipment factors, including: method of heating

(e.g., IR or vapor phase reflow, wave soldering, etc.)

circuit board material, conductor thickness and pattern,

type of solder alloy, and the thermal conductivity and

thermal mass of components. Components with a low

mass, such as the SOT packages, will reach solder reflow

temperatures faster than those with a greater mass.

Avago’s diodes have been qualified to the time-tem-

perature profile shown in Figure 17. This profile is repre-

sentative of an IR reflow type of surface mount assembly

process.

After ramping up from room temperature, the circuit

board with components attached to it (held in place

with solder paste) passes through one or more preheat

Lead-Free Reflow Profile Recommendation (IPC/JEDEC J-STD-020C)

Reflow Parameter

Lead-Free Assembly

3°C/ second max

Preheat

150°C

200°C

60-180 seconds

Ts(max) to TL Ramp-up Rate

3°C/second max

Time maintained above:

217°C

60-150 seconds

260 +0/-5°C

Time within 5 °C of actual

20-40 seconds

Ramp-down Rate

6°C/second max

Time 25 °C to Peak Temperature

8 minutes max

Note 1: All temperatures refer to topside of the package, measured on the package body surface

25

Time

Tp

tp

t 25

Ramp-up

ts

Ramp-down

Preheat

Critical Zone

zones. The preheat zones increase the temperature of

the board and components to prevent thermal shock

and begin evaporating solvents from the solder paste.

The reflow zone briefly elevates the temperature suffi-

ciently to produce a reflow of the solder.

The rates of change of temperature for the ramp-up and

cool-down zones are chosen to be low enough to not

cause deformation of the board or damage to compo-

nents due to thermal shock. The maximum temperature

These parameters are typical for a surface mount assem-

bly process for Avago diodes. As a general guideline, the

the minimum temperatures and times necessary to achieve

a uniform reflow of solder.