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Application note
APT0501
December 2011
www.microsemi.com
Mounting Instructions for SP4 Power Modules
Pierre-Laurent Doumergue
R&D Engineer
Microsemi Power Module Products
26 rue de Campilleau
33 520 Bruges, France
Introduction:
This application note gives the main
recommendations to appropriately connect the
PCB (Printed Circuit Board) to the power
module, and mount the power module onto the
heat sink. It is very important to follow the
mounting instructions to limit both the thermal
and mechanical stresses.
1.
Power Module assembly onto PCB.
The PCB mounted on the SP4 power module can
be screwed onto the plastic post in order to
reduce all mechanical stress and minimize
relative movements on the pins which are
soldered onto the power module.
Plastite screw solderable pins plastite screw
plastic post plastic post
fig 1: PCB mounted on SP4 power module.
First, the PCB must be mounted onto the power
module and screwed onto the plastic posts
(See
fig 1).
We recommend a self-tapering plastite screw
with a nominal diameter of 2.5 mm.
A plastite screw is a type of screw specifically
designed for use with plastic and other low
density materials. (See fig 2). The screw length
depends on the PCB thickness. With a 1.6 mm
(0.063”) thick PCB, use a plastite screw 6 mm
(0.25”) long. The maximum mounting torque is
0.6Nm (5 lbf·in). In any case, the customer must
check the integrity of the plastic post after
screwing.
fig 2: example of plastite screw.
The second step consists of soldering all
electrical pins of the power module to the PCB.
Wave soldering or manual soldering processes
are recommended to solder the signal and power
terminals to the PCB. The standard wave
soldering temperature is 235°C (+/-5°C) for 5
seconds (+/- 1 second).
No-clean solder flux is required to attach the
PCB onto the module since aqueous module
cleaning is not allowed.
The PCB holes for module terminals should
have a diameter of 1.5mm
±0.1
for an easy fit.
Do not reverse these two steps, because if all
pins are soldered first to the PCB, screwing the
PCB onto the plastic posts will create a
deformation of the PCB, leading to some
mechanical stress that can damage the tracks or
break the components on the PCB.
2.
Power module mounting onto heat sink.
Proper mounting of the module base plate onto
the heat sink is essential to guarantee good heat
transfer. The heat sink and the power module
contact surface must be flat (recommended
flatness <50µm for 100mm continuous,
recommended roughness Rz 10) and clean (no
dirt, no corrosion, no damage) in order to avoid
mechanical stress when power module is
mounted, and to avoid an increase in thermal
resistance.
SP4 POWER MODULE