P89LPC922FN datasheet(41/45 Pages) PHILIPS

41 / 45 page

Philips Semiconductors

P89LPC920/921/922

8-bit microcontrollers with two-clock 80C51 core

Product data

Rev. 06 — 21 November 2003

41 of 45

9397 750 12285

14. Soldering

14.1 Introduction to soldering surface mount packages

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 can still

be used for certain surface mount ICs, but it is not suitable for ﬁne pitch SMDs. In

these situations reﬂow soldering is recommended. In these situations reﬂow

soldering is recommended.

14.2 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. Driven by legislation and

environmental forces the worldwide use of lead-free solder pastes is increasing.

Several methods exist for reﬂowing; for example, convection or convection/infrared

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 270

°C depending on solder

paste material. The top-surface temperature of the packages should preferably be

kept:

• below 225

°C (SnPb process) or below 245 °C (Pb-free process)

– for all BGA, HTSSON..T and SSOP..T packages

– for packages with a thickness

≥ 2.5 mm

– for packages with a thickness < 2.5 mm and a volume

≥ 350 mm3 so called

thick/large packages.

• below 240

°C (SnPb process) or below 260 °C (Pb-free process) for packages with

a thickness < 2.5 mm and a volume < 350 mm3 so called small/thin packages.

Moisture sensitivity precautions, as indicated on packing, must be respected at all

times.

14.3 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.

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