PCA8574_PCA8574A_2

© NXP B.V. 2007. All rights reserved.

Product data sheet

Rev. 02 — 14 May 2007

23 of 27

NXP Semiconductors

PCA8574/74A

16.3.2 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:

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.

° 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 of the leads in the wave ranges from 3 seconds to 4 seconds at 250

°C

or 265

°C, depending on solder material applied, SnPb or Pb-free respectively.

A mildly-activated flux will eliminate the need for removal of corrosive residues in most

applications.

16.3.3 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 seconds to 5 seconds between 270

°C and 320 °C.

16.4 Package related soldering information

Table 11.

Suitability of IC packages for wave, reflow and dipping soldering methods

Mounting

Soldering method

Wave

Dipping

Through-hole mount

CPGA, HCPGA

suitable

−−

DBS, DIP, HDIP, RDBS, SDIP, SIL

−

suitable

Through-hole-surface

mount

not suitable

not suitable

−