TDA8745 Datasheet, PDF (37/40 Pages) NXP Semiconductors – Satellite sound receiver with I2C-bus control

Philips Semiconductors
Satellite sound receiver with I²C-bus control
Preliminary specification
TDA8745
SOLDERING
Introduction
There is no soldering method that is ideal for all IC
packages. Wave soldering is often preferred when
through-hole and surface mounted components are mixed
on one printed-circuit board. However, wave soldering is
not always suitable for surface mounted ICs, or for
printed-circuits with high population densities. In these
situations reflow soldering is often used.
This text gives a very brief insight to a complex technology.
A more in-depth account of soldering ICs can be found in
our “IC Package Databook” (order code 9398 652 90011).
SDIP
SOLDERING BY DIPPING OR BY WAVE
The maximum permissible temperature of the solder is
260 °C; solder at this temperature must not be in contact
with the joint for more than 5 seconds. The total contact
time of successive solder waves must not exceed
5 seconds.
The device may be mounted up to the seating plane, but
the temperature of the plastic body must not exceed the
specified maximum storage temperature (T_{stg max}). If the
printed-circuit board has been pre-heated, forced cooling
may be necessary immediately after soldering to keep the
temperature within the permissible limit.
REPAIRING SOLDERED JOINTS
Apply a low voltage soldering iron (less than 24 V) to the
lead(s) of the package, below the seating plane or not
more than 2 mm above it. If the temperature of the
soldering iron bit is less than 300 °C it may remain in
contact for up to 10 seconds. If the bit temperature is
between 300 and 400 °C, contact may be up to 5 seconds.
QFP
REFLOW SOLDERING
Reflow soldering techniques are suitable for all QFP
packages.
The choice of heating method may be influenced by larger
plastic QFP packages (44 leads, or more). If infrared or
vapour phase heating is used and the large packages are
not absolutely dry (less than 0.1% moisture content by
weight), vaporization of the small amount of moisture in
them can cause cracking of the plastic body. For more
information, refer to the Drypack chapter in our “Quality
Reference Handbook” (order code 9397 750 00192).
Reflow soldering requires solder paste (a suspension of
fine solder particles, flux and binding agent) to be applied
to the printed-circuit board by screen printing, stencilling or
pressure-syringe dispensing before package placement.
Several techniques exist for reflowing; for example,
thermal conduction by heated belt. Dwell times vary from
50 to 300 seconds depending on heating method. Typical
reflow temperatures range from 215 to 250 °C.
Preheating is necessary to dry the paste and evaporate
the binding agent. Preheat for 45 minutes at 45 °C.
WAVE SOLDERING
Wave soldering is not recommended for QFP packages.
This is because of the likelihood of solder bridging due to
closely-spaced leads and the possibility of incomplete
solder penetration in multi-lead devices.
If wave soldering cannot be avoided, the following
conditions must be observed:
• A double-wave (a turbulent wave with high upward
pressure followed by a smooth laminar wave)
soldering technique should be used.
• The footprint must be at an angle of 45° to the board
direction and must incorporate solder thieves
downstream and at the side corners.
Even with these conditions, do not consider wave
soldering the following packages: QFP52 (SOT379-1),
QFP100 (SOT317-1), QFP100 (SOT317-2),
QFP100 (SOT382-1) or QFP160 (SOT322-1).
During placement and before soldering, the package must
be fixed with a droplet of adhesive. The adhesive can be
applied by screen printing, pin transfer or syringe
dispensing. The package can be soldered after the
adhesive is cured. Maximum permissible solder
temperature is 260 °C, and maximum duration of package
immersion in solder is 10 seconds, if cooled to less than
150 °C within 6 seconds. Typical dwell time is 4 seconds
at 250 °C.
A mildly-activated flux will eliminate the need for removal
of corrosive residues in most applications.
REPAIRING SOLDERED JOINTS
Fix the component by first soldering two diagonally-
opposite end leads. Use only a low voltage soldering iron
(less than 24 V) applied to the flat part of the lead. Contact
time must be limited to 10 seconds at up to 300 °C. When
using a dedicated tool, all other leads can be soldered in
one operation within 2 to 5 seconds between
270 and 320 °C.
1996 Mar 11
37