PCD3745AP datasheet(29/32 Pages) PHILIPS

29 / 32 page

1999 Feb 02

Philips Semiconductors

Product speciﬁcation

8-bit microcontroller with 4.5 kbytes OTP

memory and 32 kHz real-time clock

PCD3745A

21 SOLDERING

21.1

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. However, wave soldering is not

always suitable for surface mount ICs, or for printed-circuit

boards with high population densities. In these situations

reflow soldering is often used.

21.2

Through-hole mount packages

21.2.1

SOLDERING 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 (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.

21.2.2

MANUAL 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.

21.3

Surface mount packages

21.3.1

REFLOW 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,

infrared/convection 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 250

°C. The top-surface temperature of the

packages should preferable be kept below 230

°C.

21.3.2

WAVE 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.

21.3.3

MANUAL 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.

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