ICM7555_2

© NXP B.V. 2009. All rights reserved.

Product data sheet

Rev. 02 — 3 August 2009

16 of 22

NXP Semiconductors

ICM7555

General purpose CMOS timer

13. Soldering of SMD packages

This text provides a very brief insight into a complex technology. A more in-depth account

of soldering ICs can be found in Application Note

AN10365 “Surface mount reflow

soldering description”.

13.1 Introduction to soldering

Soldering is one of the most common methods through which packages are attached to

Printed Circuit Boards (PCBs), to form electrical circuits. The soldered joint provides both

the mechanical and the electrical connection. There is no single soldering method that is

ideal for all IC packages. Wave soldering is often preferred when through-hole and

Surface Mount Devices (SMDs) are mixed on one printed wiring board; however, it is not

suitable for fine pitch SMDs. Reflow soldering is ideal for the small pitches and high

densities that come with increased miniaturization.

13.2 Wave and reflow soldering

Wave soldering is a joining technology in which the joints are made by solder coming from

a standing wave of liquid solder. The wave soldering process is suitable for the following:

Not all SMDs can be wave soldered. Packages with solder balls, and some leadless

packages which have solder lands underneath the body, cannot be wave soldered. Also,

leaded SMDs with leads having a pitch smaller than ~0.6 mm cannot be wave soldered,

due to an increased probability of bridging.

The reflow soldering process involves applying solder paste to a board, followed by

component placement and exposure to a temperature profile. Leaded packages,

packages with solder balls, and leadless packages are all reflow solderable.

Key characteristics in both wave and reflow soldering are:

13.3 Wave soldering

Key characteristics in wave soldering are:

transport, the solder wave parameters, and the time during which components are

exposed to the wave