Freescale Semiconductor
Application Note
AN3150
Rev 1.0, 2/2006
Soldering Recommendations for Pressure
Sensor Devices
by: Bill McDonald
INTRODUCTION
Pressure sensor devices require the internal cavity
containing the silicon transducer to be exposed to ambient in
order for the device to function. Exposed cavity packages
require special considerations during board assembly to
prevent damage to the device during soldering and
subsequent cleaning operations.
SURFACE MOUNT COMPONENTS
Components can be mounted using solder paste stencil,
screen printed or dispensed onto the PCB pads prior to
placement of the component. The volume of solder paste
applied to the PCB is normally sufficient to secure the
component during transport to the subsequent reflow
soldering process. Use of adhesives to secure component is
not recommended, but where necessary can be applied
providing the vent at the underside of the package does not
become blocked. This is applicable only to a gauge pressure
sensor device. Absolute pressure sensor devices do not have
a backside vent so vent blocking is not an issue.
Solder pastes are available in variety of metal
compositions, particle size and flux types. The solder paste
consists of metals and flux required for a reliable connection
between the component lead and the PCB pad. Flux aids the
removal of oxides that may be present on PCB pads and
prevents further oxidation from occurring during the solder
process.
The use of a No-Clean (NC) flux is recommended for
exposed cavity components. Using pressure spray or other
methods of cleaning is not recommended. If cleaning of the
pcb is performed Water Soluble (WS) flux can be used, but it
is recommended the component cavity to be protected by
adhesive Kapton tape, vinyl cap or other means prior to the
cleaning process to prevent contamination and foreign
materials from being introduced into device cavity as result of
cleaning processes. Refer to this link for info.
Figure 1. Basic Element
Figure 2. Port Adapter
Ultrasonic cleaning is not recommended as the frequencies
can damage wire bond interconnections.
Reflow soldering is typically used for surface mount
components and accomplished by convection heat from the
sides of the reflow furnace utilizing air circulation to produce
uniform temperature across the PCB. Hot spots and shielding
of the smaller components by adjacent larger components can
be minimized thus achieving more reliable solder connection.
© Freescale Semiconductor, Inc., 2006. All rights reserved.
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