1. Core board storage
The core board should be stored in the process of testing, transfer, storage, etc., do not stack it directly, otherwise it will cause the components to be scratched or fall off, and should be stored in an anti-static tray or similar transfer box.
If the core board needs to be stored for more than 7 days, it should be packaged in an anti-static bag and put in a desiccant, and sealed and stored to ensure the dryness of the product. If the stamp hole pads of the core board are exposed to the air for a long time, they are susceptible to moisture oxidation, which affects the soldering quality during SMT. If the core board has been exposed to the air for more than 6 months, and its stamp hole pads have been oxidized, it is recommended to perform SMT after baking. The baking temperature is generally 120°C and the baking time is not less than 6 hours. Adjust according to the actual situation.
Since the tray is made of non-high temperature resistant material, do not put the core board on the tray for direct baking.
2. Backplane PCB design
When designing the bottom board PCB, hollow out the overlap between the component layout area on the back of the core board and the bottom board package. Please refer to the evaluation board for the size of the hollow out.
3 PCBA production
Before touching the core board and the bottom board, discharge the static electricity of the human body through the static discharge column, and wear a corded anti-static wristband, anti-static gloves or anti-static finger cots.
Please use an anti-static workbench, and keep the workbench and the bottom plate clean and tidy. Do not put metal objects near the bottom plate to prevent accidental touch and short circuit. Do not place the bottom plate directly on the workbench. Place it on an anti-static bubble film, foam cotton or other soft non-conductive materials to effectively protect the board.
When installing the core board, please pay attention to the direction mark of the starting position, and locate whether the core board is in place according to the square frame.
There are generally two ways to install the core board to the bottom plate: one is to install by reflow soldering on the machine; the other is to install by manual soldering. It is recommended that the soldering temperature should not exceed 380°C.
When manually disassembling or welding and installing the core board, please use a professional BGA rework station for operation. At the same time, please use a dedicated air outlet. The temperature of the air outlet should generally not be higher than 250°C. When disassembling the core board manually, please keep the core board level to avoid tilting and jitter that may cause the core board components to shift.
For the temperature curve during reflow soldering or manual disassembly, it is recommended that the furnace temperature curve of the conventional lead-free process be used for furnace temperature control.
4 Common causes of damage to the core board
4.1 Reasons for processor damage
4.2 Reasons for processor IO damage
5 Precautions for using the core board
5.1 IO design considerations
(1) When GPIO is used as input, make sure that the highest voltage cannot exceed the maximum input range of the port.
(2) When GPIO is used as input, due to the limited drive capability of IO, the maximum output of design IO does not exceed the maximum output current value specified in the data manual.
(3) For other non-GPIO ports, please refer to the chip manual of the corresponding processor to ensure that the input does not exceed the range specified in the chip manual.
(4) Ports directly connected to other boards, peripherals or debuggers, such as JTAG and USB ports, should be connected in parallel with ESD devices and clamp protection circuits.
(5) For ports connected to other strong interference boards and peripherals, an optocoupler isolation circuit should be designed, and attention should be paid to the isolation design of the isolated power supply and optocoupler.
5.2 Precautions for power supply design
(1) It is recommended to use the reference power supply scheme of the evaluation baseboard for baseboard design, or refer to the maximum power consumption parameters of the core board to select a suitable power supply scheme.
(2) The voltage and ripple test of each power supply of the backplane should be carried out first to ensure that the power supply of the backplane is stable and reliable before installing the core board for debugging.
(3) For the buttons and connectors that can be touched by the human body, it is recommended to add ESD, TVS and other protection designs.
(4) During the product assembly process, pay attention to the safe distance between live devices and avoid touching the core board and the bottom board.
5.3 Precautions for work
(1) Debug in strict accordance with the specifications, and avoid plugging and unplugging external devices when power is on.
(2) When using the meter to measure, pay attention to the insulation of the connecting wire, and try to avoid measuring IO-intensive interfaces, such as FFC connectors.
(3) If the IO from the expansion port is adjacent to a power supply larger than the maximum input range of the port, avoid short-circuiting the IO with the power supply.
(4) During the debugging, testing, and production process, it should be ensured that the operation is carried out in an environment with good electrostatic protection.