Philips ISP1122 18. Soldering

Philips Semiconductors ISP1122

USB stand-alone hub

Product speciﬁcation Rev. 03 — 29 March 2000 42 of 48

18. Soldering

This text gives a very brief insight to a complex technology. A more in-depth account

of soldering ICs can be found in our

(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.

18.2.1 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 215to 250 °C. The top-surface

temperature of the packages should preferable be kept below 230°C.

18.2.2 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:

•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;

–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.

•For packages with leads on four sides, the footprint must be placed at a 45° angle

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

incorporate solder thieves downstream and at the side corners.