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TFA9888UK/N1Z

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16
TFA9888_SDS All information provided in this document is subject to legal disclaimers. © NXP B.V. 2017. All rights reserved.
Product short data sheet Rev. 2 — 14 July 2017 10 of 16
NXP Semiconductors
TFA9888
9.7 V stereo boosted audio system with adaptive sound maximizer and
speaker protection
12. Soldering of WLCSP packages
12.1 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.
12.2 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
12.3 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 5
) 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 5
.
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 5
.
Table 5. Lead-free process (from J-STD-020D)
Package thickness (mm) Package reflow temperature (C)
Volume (mm
3
)
< 350 350 to 2000 > 2000
< 1.6 260 260 260
1.6 to 2.5 260 250 245
> 2.5 250 245 245
TFA9888_SDS All information provided in this document is subject to legal disclaimers. © NXP B.V. 2017. All rights reserved.
Product short data sheet Rev. 2 — 14 July 2017 11 of 16
NXP Semiconductors
TFA9888
9.7 V stereo boosted audio system with adaptive sound maximizer and
speaker protection
For further information on temperature profiles, refer to application note AN10365
“Surface mount reflow soldering description”.
12.3.1 Stand off
The stand off between the substrate and the chip is determined by:
• The amount of printed solder on the substrate
• The size of the solder land on the substrate
• The bump height on the chip
The higher the stand off, the better the stresses are released due to TEC (Thermal
Expansion Coefficient) differences between substrate and chip.
12.3.2 Quality of solder joint
A flip-chip joint is considered to be a good joint when the entire solder land has been
wetted by the solder from the bump. The surface of the joint should be smooth and the
shape symmetrical. The soldered joints on a chip should be uniform. Voids in the bumps
after reflow can occur during the reflow process in bumps with high ratio of bump diameter
to bump height, i.e. low bumps with large diameter. No failures have been found to be
related to these voids. Solder joint inspection after reflow can be done with X-ray to
monitor defects such as bridging, open circuits and voids.
12.3.3 Rework
In general, rework is not recommended. By rework we mean the process of removing the
chip from the substrate and replacing it with a new chip. If a chip is removed from the
substrate, most solder balls of the chip will be damaged. In that case it is recommended
not to re-use the chip again.
MSL: Moisture Sensitivity Level
Fig 5. Temperature profiles for large and small components
001aac844
temperature
time
minimum peak temperature
= minimum soldering temperature
maximum peak temperature
= MSL limit, damage level
peak
temperature
TFA9888_SDS All information provided in this document is subject to legal disclaimers. © NXP B.V. 2017. All rights reserved.
Product short data sheet Rev. 2 — 14 July 2017 12 of 16
NXP Semiconductors
TFA9888
9.7 V stereo boosted audio system with adaptive sound maximizer and
speaker protection
Device removal can be done when the substrate is heated until it is certain that all solder
joints are molten. The chip can then be carefully removed from the substrate without
damaging the tracks and solder lands on the substrate. Removing the device must be
done using plastic tweezers, because metal tweezers can damage the silicon. The
surface of the substrate should be carefully cleaned and all solder and flux residues
and/or underfill removed. When a new chip is placed on the substrate, use the flux
process instead of solder on the solder lands. Apply flux on the bumps at the chip side as
well as on the solder pads on the substrate. Place and align the new chip while viewing
with a microscope. To reflow the solder, use the solder profile shown in application note
AN10365 “Surface mount reflow soldering description”.
12.3.4 Cleaning
Cleaning can be done after reflow soldering.
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TFA9888UK/N1Z

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Audio Amplifiers TFA9888UK/UNCASED//N1/REEL 7 Q1 DP CIRCUIT ELEMEN
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