Learn about eMMC chips
The eMMC chip is an embedded multimedia card (Embedded MultiMediaCard) chip that integrates a flash memory and a controller. It is mainly used in mobile devices, such as mobile phones and tablet computers, and can be used to store operating systems, applications, data and images, etc. , Whether the eMMC chip supports a specific function depends on the specifications and design of the controller and flash memory chip.
Main features of eMMC chip
Highly integrated
The eMMC chip integrates a controller for managing the flash memory chip, which simplifies the product design process and accelerates product introduction.
unified interface
eMMC adopts the MMC standard interface, which can be matched with a variety of storage devices, including NAND storage devices and MMC devices.
larger capacity
The common capacity of eMMC is 2~256GB, which can meet the user's demand for large-capacity storage.
high speed transmission
eMMC chips support higher data transfer rates, up to 400MB/s or higher, depending on their version and specification.
Strong compatibility
eMMC chips are compatible with a variety of mobile devices and computer systems, including Windows, Mac, Android, and more.
Pins of eMMC chip
The eMMC chip is a solid-state flash memory card, and its pin definition is slightly different from that of a general SIM card or SD card. Therefore, when using it, it needs to be appropriately modified according to the specific hardware device and chip specifications. At the same time, due to the wide application of eMMC chips in mobile devices, understanding their pin definitions and working principles is also helpful for better data communication and operation. Taking KLM8G1GETF as an example, briefly introduce its pins:
VCC/VCCQ
VCC is the pin that supplies power to the flash memory power supply, generally 3.3V; VCCQ is the pin that supplies power to the memory controller.
CLK
Clock input pin, sent by the main processor, enters the eMMC chip.
DATA Strobe
Data strobe pin, the strobe signal sent by eMMC to the main processor, in HS400 mode, read data and CRC response are synchronized with data strobe.
DATA0-DATA7
Data bus, bidirectional data transmission mode "pull-up", eMMC defaults to 1-bit mode, and 4-bit or 8-bit can also be used.
RSTN
The reset pin is active at low level, so generally a resistor will be pulled on the pin, and the default high level will not be reset.
CMD
Bi-directional signal for device initialization and command transmission, commands operate in two modes, open drain for initialization and push-pull for fast command transmission.
PCB design of eMMC chip
The PCB design of the eMMC chip needs to take into account many aspects, including power supply and interface, layout and routing, protection, heat dissipation, testing and debugging, etc., to ensure the performance and reliability of the eMMC and meet the requirements of the device.
power and ground
Make sure to provide stable power and ground lines for the eMMC chip. The power line should be wide enough to withstand the chip's power consumption requirements, and the length and impedance of the power line should be minimized.
Signal line length matching
The length of the signal line of the eMMC chip should match as much as possible to reduce the delay and distortion of signal transmission, and differential pairs can be used to improve the anti-interference ability of the signal.
Signal line routing
Try to avoid signal lines crossing with high-power lines or high-frequency lines to reduce interference. You can use ground planes and power planes to isolate signal lines.
capacitance and inductance
Add appropriate capacitors and inductors to the power and ground of the eMMC chip to provide stable power and ground. The selection of capacitors and inductors should comply with the chip manufacturer’s recommendations.
PCB layout
Place the eMMC chip far away from other high-power or high-frequency components to reduce interference, and at the same time minimize the length of the signal line to improve signal stability.
pin distance outlet method
Because the pin spacing of the eMMC device is relatively small, if the pins inside cannot go out, the following methods can be adopted:
① When the conventional wiring cannot be routed, the tight wiring can be adopted, that is, the minimum line width is used between the pad and the pad;
② If the wiring cannot be traced according to the minimum line width, you can also modify the pad and change the pad to an ellipse to meet the spacing of the minimum line width;
③ When it is really impossible to route the wires, it is possible to drill blind holes on the pads and change the layer routing.
Design for Manufacturability of eMMC Chips
Line width and spacing
The minimum line width and line spacing is generally 3mil, and the design of the minimum line width and line spacing needs to meet the process requirements. If the minimum line width and line spacing exceeds the manufacturing capacity, the PCB board cannot be produced, or the produced board has a low yield rate and a very high cost. .
pad size
The size of the pad affects the welding quality. The pad is too small or even unsolderable. The minimum pad is generally 0.2mm. The production of a pad smaller than 0.2mm may cause the pad to be etched and the board will be scrapped.
plate hole
The hole in the board refers to the hole on the SMT patch pad. The hole in the board generally needs resin plug holes, and copper is plated on the holes to meet the welding requirements. If the holes in the board do not have resin plug holes, the small welding area will lead to poor welding.
Here we recommend a simple and easy-to-use domestic free tool independently developed for PCB+PCBA inspection : Huaqiu DFM software , which is a process software for manufacturability inspection, for PCB manufacturability of eMMC chip package position , can check the minimum line width, line spacing, pad size, solder bridge, etc., and can prevent in advance whether there is a manufacturability problem in the PCB where the eMMC chip is packaged.