PCF8578 Philips Semiconductors, PCF8578 Datasheet - Page 42

• Manufacturer Part Number: PCF8578
• Description: LCD row/column driver for dot matrix graphic displays
• Manufacturer: Philips Semiconductors

Philips Semiconductors
18 SOLDERING
18.1
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 “Data Handbook IC26; Integrated Circuit Packages”
(order code 9398 652 90011).
18.2
Reflow soldering techniques are suitable for all LQFP and
VSO 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 methods exist for reflowing; for example,
infrared/convection heating in a conveyor type oven.
Throughput times (preheating, soldering and cooling) vary
between 50 and 300 seconds depending on heating
method. Typical reflow peak temperatures range from
215 to 250 C.
18.3
18.3.1
Wave soldering is not recommended for LQFP 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.
1998 Sep 08
Wave soldering is NOT applicable for all LQFP
packages with a pitch (e) equal or less than 0.5 mm.
LCD row/column driver for dot matrix
graphic displays
Introduction
Reflow soldering
Wave soldering
LQFP
CAUTION
42
If wave soldering cannot be avoided, for LQFP
packages with a pitch (e) larger than 0.5 mm, the
following conditions must be observed:
18.3.2
Wave soldering techniques can be used for all VSO
packages if the following conditions are observed:
18.3.3
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.
18.4
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.
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.
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.
The package footprint must incorporate solder thieves at
the downstream end.
Repairing soldered joints
VSO
M
ETHOD
(LQFP
AND
VSO)
Product specification
PCF8578