8
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 reow, 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
MiniPak package, will reach solder reow temperatures
faster than those with a greater mass.
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. The
preheat zones increase the temperature of the board and
components to prevent thermal shock and begin evapo-
rating solvents from the solder paste. The reow zone
briey elevates the temperature suciently to produce a
reow 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 components
due to thermal shock. The maximum temperature in the
reow zone (T
MAX
) should not exceed 260°C.
These parameters are typical for a surface mount assembly
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 reow of solder.
Assembly Information
The MiniPak diode is mounted to the PCB or microstrip
board using the pad pattern shown in Figure 17.
2.60
0.40
0.20
0.40 mm via hole
(4 places)
0.8
2.40
Figure 12. PCB Pad Layout, MiniPak (dimensions in mm).
This mounting pad pattern is satisfactory for most ap-
plications. However, there are applications where a high
degree of isolation is required between one diode and the
other is required. For such applications, the mounting pad
pattern of Figure 18 is recommended.
Figure 13. PCB Pad Layout, High Isolation MiniPak (dimensions in mm).
This pattern uses four via holes, connecting the crossed
ground strip pattern to the ground plane of the board.
