SC68C752B datasheet(44/49 Pages) PHILIPS

44 / 49 page

SC68C752B_3

Product data sheet

Rev. 03 — 29 November 2005

44 of 49

Philips Semiconductors

SC68C752B

5 V, 3.3 V and 2.5 V dual UART, 5 Mbit/s (max.), with 64-byte FIFOs

13. Soldering

13.1 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 surface mount 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.

13.2 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 seconds and 200 seconds depending on heating method.

Typical reﬂow peak temperatures range from 215

°Cto270 °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.

13.3 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.

• 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;

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