NXP Semiconductors

PCA9601

Dual bidirectional bus buffer

12 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”.

12.1 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.

12.2 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:

• Through-hole components

• Leaded or leadless SMDs, which are glued to the surface of the printed circuit board

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:

• Board specifications, including the board finish, solder masks and vias

• Package footprints, including solder thieves and orientation

• The moisture sensitivity level of the packages

• Package placement

• Inspection and repair

• Lead-free soldering versus SnPb soldering

12.3 Wave soldering

Key characteristics in wave soldering are:

• Process issues, such as application of adhesive and flux, clinching of leads, board

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

exposed to the wave

• Solder bath specifications, including temperature and impurities

12.4 Reflow soldering

Key characteristics in reflow soldering are:

PCA9601

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Product data sheet

Rev. 3.1 — 4 January 2022

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