11

Figure 28. Surface Mount Assembly Profile.

SMT Assembly

Reliable assembly of surface mount components is a com‑

plex 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‑tempera‑

ture profile shown in Figure 28. This profile is representa‑

tive of an IR reflow type of surface mount assembly pro‑

cess.

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 zones.

25

Time

Tp

tp

t 25

Ramp-up

ts

Ramp-down

Preheat

Critical Zone

Lead-Free Assembly

Average ramp-up rate (Liquidus Temperature (T

3°C/ second max

Preheat

Temperature Min (T

150°C

Temperature Max (T

200°C

Time (min to max) (t

60-180 seconds

Ts(max) to TL Ramp-up Rate

3°C/second max

Time maintained above:

Temperature (T

217°C

Time (t

60-150 seconds

Peak Temperature (T

260 +0/-5°C

Time within 5 °C of actual

Peak temperature (t

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

Reow Parameter

Lead-Free Reow Prole Recommendation (IPC/JEDEC J-STD-020C)

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 sufficiently to pro‑

duce 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

in the reflow zone (T

These parameters are typical for a surface mount assem‑

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

circuit board and components should be exposed only

to the minimum temperatures and times necessary to

achieve a uniform reflow of solder.