NXP Semiconductors
TFA9872_SDS
High Efficiency Class-D Audio Amplifier with Speaker-as-Microphone
TFA9872_SDS All information provided in this document is subject to legal disclaimers. © NXP B.V. 2017. All rights reserved.
Product short data sheet Rev. 1 — 12 April 2017
COMPANY PUBLIC 26 / 32
14 Soldering of WLCSP packages
14.1 Introduction to soldering WLCSP packages
This text provides a very brief insight into a complex technology. A more in-depth account
of soldering WLCSP (Wafer Level Chip-Size Packages) can be found in application note
AN10439 “Wafer Level Chip Scale Package” and in application note AN10365 “Surface
mount reflow soldering description”.
Wave soldering is not suitable for this package.
All NXP WLCSP packages are lead-free.
14.2 Board mounting
Board mounting of a WLCSP requires several steps:
1. Solder paste printing on the PCB
2. Component placement with a pick and place machine
3. The reflow soldering itself
14.3 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 1) than a SnPb process, thus reducing
the process window
• Solder paste printing issues, such as smearing, release, and adjusting the process
window for a mix of large and small components on one board
• Reflow temperature profile; this profile includes preheat, reflow (in which the board
is heated to the peak temperature), and cooling down. It is imperative that the peak
temperature is high enough for the solder to make reliable solder joints (a solder
paste characteristic) while being low enough that the packages and/or boards are not
damaged. The peak temperature of the package depends on package thickness and
volume and is classified in accordance with Table 11.
Table 11. Lead-free process (from J-STD-020D)
Package reflow temperature (°C)
Volume (mm
3
)
Package thickness (mm)
< 350 350 to 2000 > 2000
< 1.6 260 260 260
1.6 to 1.5 260 250 245
> 2.5 250 245 245
Moisture sensitivity precautions, as indicated on the packing, must be respected at all
times.
Studies have shown that small packages reach higher temperatures during reflow
soldering, see Figure 13.
