1998 Jul 08

12

Philips Semiconductors

Product specification

Hex D-type flip-flop with reset; positive-edge trigger

74HC/HCT174

SOLDERING

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

“Data Handbook IC26; Integrated Circuit Packages”

(order code 9398 652 90011).

DIP

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

printed-circuit board has been pre-heated, forced cooling

may be necessary immediately after soldering to keep the

temperature within the permissible limit.

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.

SO, SSOP and TSSOP

Reflow soldering techniques are suitable for all SO, SSOP

and TSSOP 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

45

°C.

Wave soldering can be used for all SO packages. Wave

soldering is not recommended for SSOP and TSSOP

packages, because of the likelihood of solder bridging due

to closely-spaced leads and the possibility of incomplete

solder penetration in multi-lead devices.

If wave soldering is used - and cannot be avoided for

SSOP and TSSOP packages - the following conditions

must be 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 and must incorporate solder

thieves at the downstream end.

Even with these conditions:

• Only consider wave soldering SSOP packages that

have a body width of 4.4 mm, that is

SSOP16 (SOT369-1) or SSOP20 (SOT266-1).

• Do not consider wave soldering TSSOP packages

with 48 leads or more, that is TSSOP48 (SOT362-1)

and TSSOP56 (SOT364-1).

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.