PCF85263ATLSLASHA datasheet(86/102 Pages) NXP

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NXP Semiconductors

PCF85263A

Tiny RTC/Calendar with Alarm Function, Battery Switch-Over, Time Stamp Input, and I2C-bus

20 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”.

20.1 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.

20.2 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

20.3 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

20.4 Reflow soldering

Key characteristics in reflow soldering are:

• Lead-free versus SnPb soldering; note that a lead-free reflow process usually leads to higher minimum peak

temperatures (see Figure 51) than a SnPb process, thus reducing the process window

• Solder paste printing issues including smearing, release, and adjusting the process window for a mix of large

and small components on one board

PCF85263A

All information provided in this document is subject to legal disclaimers.

Product data sheet

Rev. 5.4 — 12 December 2025

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