2004 Mar 01
73
Philips Semiconductors
Product specification
Digital video encoder
SAA7102; SAA7103
14 SOLDERING
14.1
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. Driven by legislation and environmental
forces the worldwide use of lead-free solder pastes is
increasing.
14.2
Through-hole mount packages
14.2.1
S
OLDERING BY DIPPING OR BY SOLDER WAVE
Typical dwell time of the leads in the wave ranges from
3 to 4 seconds at 250
°
C or 265
°
C, depending on solder
material applied, SnPb or Pb-free respectively.
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.
14.2.2
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.
14.3
Surface mount packages
14.3.1
R
EFLOW SOLDERING
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 methods exist for reflowing; for example,
convection or convection/infrared heating in a conveyor
type oven.
Throughput times (preheating, soldering and cooling) vary
between 100 and 200 seconds depending on heating
method.
Typical reflow peak temperatures range from
215 to 270
°
C depending on solder paste material. The
top-surface temperature of the packages should
preferably be kept:
•
below 225
°
C (SnPb process) or below 245
°
C (Pb-free
process)
– for all the BGA, HTSSON..T and SSOP-T packages
– for packages with a thickness
≥
2.5 mm
– for packages with a thickness < 2.5 mm and a
volume
≥
350 mm
3
so called thick/large packages.
•
below 240
°
C (SnPb process) or below 260
°
C (Pb-free
process) for packages with a thickness < 2.5 mm and a
volume < 350 mm
3
so called small/thin packages.
Moisture sensitivity precautions, as indicated on packing,
must be respected at all times.
14.3.2
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.
