Philips Semiconductors

PCF8563

Real-time clock/calendar

Product specification

16 April 1999

25 of 30

9397 750 04855

© Philips Electronics N.V. 1999. All rights reserved.

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. 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.

14.2 Surface mount packages

14.2.1

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.

14.2.2

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:

upward pressure followed by a smooth laminar wave.

– 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.

to the transport direction of the printed-circuit board. The footprint must

incorporate solder thieves downstream and at the side corners.