2003 Mar 20
33
Philips Semiconductors
Objective specification
2
×
25 W class-D power amplifier
TDA8922
18 SOLDERING
18.1
Introduction
This text gives a very brief insight to a complex technology.
A more in-depth account of soldering ICs can be found in
our
“Data Handbook IC26; Integrated Circuit Packages”
(document order number 9398 652 90011).
There is no soldering method that is ideal for all IC
packages. Wave soldering is often preferred when
through-hole and surface mount components are mixed on
one printed-circuit board. Wave soldering can still be used
for certain surface mount ICs, but it is not suitable for fine
pitch SMDs. In these situations reflow soldering is
recommended.
18.2
Through-hole mount packages
18.2.1
S
OLDERING BY DIPPING OR BY SOLDER WAVE
The maximum permissible temperature of the solder is
260
°
C; solder at this temperature must not be in contact
with the joints 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.
18.2.2
M
ANUAL SOLDERING
Apply the soldering iron (24 V or less) to the lead(s) of the
package, either 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.
18.3
Surface mount packages
18.3.1
R
EFLOW SOLDERING
Typical reflow peak temperatures range from
215 to 250
°
C. The top-surface temperature of the
packages should preferably be kept:
•
below 220
°
C for all the BGA packages and packages
with a thickness 2.5mm and packages with a thickness
<2.5 mm and a volume
≥
350 mm
3
so called thick/large
packages
•
below 235
°
C for packages with a thickness <2.5 mm
and a volume <350 mm
3
so called small/thin packages.
18.3.2
W
AVE SOLDERING
Conventional single wave soldering is not recommended
for surface mount devices (SMDs) or printed-circuit boards
with a high component density, as solder bridging and
non-wetting can present major problems.
To overcome these problems the double-wave soldering
method was specifically developed.
If wave soldering is used the following conditions must be
observed for optimal results:
•
Use a double-wave soldering method comprising a
turbulent wave with high upward pressure followed by a
smooth laminar wave.
•
For packages with leads on two sides and a pitch (e):
– larger than or equal to 1.27 mm, the footprint
longitudinal axis is preferred to be parallel to the
transport direction of the printed-circuit board;
– smaller than 1.27 mm, the footprint longitudinal axis
must be parallel to the transport direction of the
printed-circuit board.
The footprint must incorporate solder thieves at the
downstream end.
•
For packages with leads on four sides, the footprint must
be placed at a 45
°
angle to the transport direction of the
printed-circuit board. The footprint must incorporate
solder thieves downstream and at the side corners.
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.
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.
18.3.3
M
ANUAL SOLDERING
Fix the component by first soldering two
diagonally-opposite end leads. Use a low voltage (24 V or
less) soldering iron 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.
