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Philips Semiconductors
ISP1122
USB stand-alone hub
Product specification Rev. 03 — 29 March 2000 42 of 48
9397 750 07002
© Philips Electronics N.V. 2000. All rights reserved.
18. Soldering
18.1 Introduction
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 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 Surface mount packages
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 215 to 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.