Rockchip RK32 Series, Hardware Design Manual

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RK3288 Hardware Design Guide
Fig 9-6
9.2 PCB Layout
Nand Flash and eMMC Flash could be switched through double Layout. Keep-out frame
should be added to pads when pouring copper under eMMC chip, in order to avoid pseudo
soldering due to fast thermal dissipation through GND copper, as shown in Fig 9-7.
All eMMC Flash data traces are required to be surrounded by GND, and eMMC signal traces
should be equal-length with difference between any two limited in 400mil, or else it will
restrain frequency in high-speed mode. Traces length of eMMC should be limited within 12.4
inch. In order to improve stability and compatibility of SDIO, suggest to use the adaptive
algorithms of driven strength and Timing Tuning.
Flash power ripple should be controlled within 80mV, and it power trace should be placed
far away from high-speech signals. Flash data trace can't go through adjacent layers, which is
with large ripple wave and current signal, such as Vbus, Vdc and VCC_SYS etc.
Test point for hardware upgrading mode is recommended to be placed close to Flash, and
should be placed on the layer where components will be placed (not the layer close to LCM),
for better upgrading operation as shown Fig 9-7.
If Layout shown as Fig 9-8 is adopted, no pin traces should be routed through eMMC,
which can reduce the requirement for distance between PCB layers.