PCF8573T datasheet(21/24 Pages) PHILIPS

21 / 24 page

1997 Mar 28

Philips Semiconductors

Product speciﬁcation

Clock/calendar with Power Fail Detector

PCF8573

16 SOLDERING

16.1

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).

16.2

DIP

16.2.1

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.

16.2.2

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.

16.3

16.3.1

REFLOW SOLDERING

Reflow soldering techniques are suitable for all SO

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

°C.

16.3.2

WAVE SOLDERING

Wave soldering techniques can be used for all SO

packages if the following conditions are 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.

• The package footprint must incorporate solder thieves at

the downstream end.

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.

16.3.3

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.

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