Philips Semiconductors Product specification
PTN3501Maintenance and control device
2001 Jan 17 13
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).
DIP
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 (Tstg 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.
SO and SSOP
Reflow soldering
Reflow soldering techniques are suitable for all SO and SSOP
packages.
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 between 50 and 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. Preheating duration: 45 minutes at 45°C.
Wave soldering
Wave soldering is not recommended for SSOP 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 longitudinal axis of the package footprint must be
parallel to the solder flow and must incorporate solder
thieves at the downstream end.
Even with these conditions, only consider wave soldering
SSOP packages that have a body width of 4.4 mm, that is
SSOP16 (SOT369–1) or SSOP20 (SOT266–1).
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.