The TPS65313-Q1 device
is packaged in a 40-pin, VQFN package with a higher coefficient of thermal expansion
(CTE) mold compound to provide less CTE mismatch with the PCB, resulting in improved
board level reliability (BLR) and thermal performance. PCB thickness, copper layer
count, copper layer thickness, and area density are significant factors in solder
joint reliability.
To achieve good performance, follow these precautions:
- Solder joints must have sufficient thickness for better solder joint reliability. TI recommends having at least 50 µm of thickness for the finished solder joint of this device.
- Avoid conformal coating under the device to avoid excessive solder joint stress caused by the expansion and contraction of these material across temperature and aging.
- Avoid use of solder-mask-defined (SMD) land pad designs. Always use non-solder-mask-defined (NSMD) land pad designs for leadless packages.
- Bonding the PCB to the Aluminium housing or back planes to act
as a heat sink to the device can cause significant stress on the solder joint
because of the CTE mismatch between the heat sink and the device mold
compound.
- Avoid bonding heat sinks to top of QFN packages. The load imposed by the heat sink can have a negative effect on the creep performance of the solder joints. If heat sink cannot be avoided because of thermal reasons, a
non-hardening, special thermal gel should be used to minimize the CTE mismatch between the device and the heat sink.
- PCB housing or connectors can cause stress on the device solder joints and solder joints of large package-size components (such as input capacitors, output capacitors, and inductors ).Therefore, effects of housing and
connectors on the PCB should be reduced.
- Temperature cycling test profiles with very a fast temperature ramp rate (for example, greater than 20°C/minute to 25°C/minute) leads to early solder joints failures and are not realistic or useful for
acceleration-factor-based life calculations of solder joints. A temperature ramp rate of approximately 10°C/minute to 15°C/minute is more realistic. For more information, refer to the IPC-SM-785 guidelines.
Note:
Users should evaluate their application conditions and make sure that the device meets their BLR requirements.