Offline Programming
Offline programming, also known as bare-chip programming, involves placing the chip in special adapters for programming, then placing it on the PCB for production. However, the adapter itself is a precision fixture, which is difficult to use across different chip types, increasing costs. Once there are defective products that need to be reprogrammed, it is challenging to remove the chip from the board, reprogram it, and then reattach it. This process requires significant manual labor, resources, and increases costs. During PCBA production, unexpected issues may arise, such as insufficient board temperature resistance, which can cause chip deformation during removal, further increasing the risk of scrap. Offline programming requires extending external circuits and using standard communication interfaces, such as JTAG, DAP, UART, SWD, SPI, and other well-known communication protocols.
Offline programming is typically used in scenarios that demand high security and stability, such as large-scale programming or situations where the data volume is large, and programming time is long. In such cases, offline programming may be more suitable.


Online Programming
Online programming, also known as in-circuit programming, involves programming chips that have already been soldered onto the PCBA after SMT processing. It does not require programming fixtures or other consumables. The programming tool directly programs the chips on the PCB, and after programming, functional testing can be performed. If software errors are found, they can be corrected promptly without the need for complex disassembly or rework steps. This approach reduces costs and is convenient for users who frequently need software iterations. However, its efficiency is lower compared to offline programming.
More importantly, as production lines move towards automation, an increasing number of manufacturers are incorporating ICT, FCT, and other functional testing machines into their production lines. Using automated fixtures combined with online programming allows for reduced manual operations during the programming phase. After placing the board, programming can be done directly, followed by testing on automated machines. This makes the entire production process fully controllable and traceable.


So, which should you choose: online or offline programming? We will analyze it from the following aspects:


Programming Speed
Offline programming uses various adapters to accommodate different chip packages. Through the shortest possible circuit connection, it enables ultra-fast chip programming.
Online programming uses various serial interfaces inherent to the chips, such as USB, SWD, JTAG, UART, etc., through wiring to program the chips. This method is limited by the performance of the serial interface itself.
Whether offline or online, programming speed varies depending on the chip. For example, the fastest programming tool currently on the market, the AP8000, can achieve a programming speed of 50MB/s.


Fixed Investment Costs
Offline programming requires various adapters to support different chip packages. As more chips evolve towards smaller packages like BGA and QFN, these adapters become precision testing fixtures that are more costly.
Online programming uses standard communication buses, such as USB, SWD, JTAG, UART, etc., which have fixed interfaces. These connections require minimal wiring, so the cost is relatively low.


Production Traceability
Offline programming requires precision fixtures for compatibility. If errors are found during the production test, and production traceability is needed for rework, the chip must be removed and reprogrammed according to the established process. By using a powerful PPA (Production Process Automation) development platform and integrating with the MES (Manufacturing Execution System), the mass production programming process can be controlled.
Online programming uses wired connections to program the chips. If errors are found during production testing, the faulty PCBA can be traced and reprogrammed, saving a significant amount of manual labor, resources, and costs, while improving efficiency. In normal production, additional factors, such as PCBA's inability to withstand high temperatures, can cause deformation during chip removal, increasing the risk of scrap.
Generally, for Flash memory chips, especially large-capacity NAND Flash or eMMC chips, which have large storage capacities and long programming times requiring high-speed signals, offline programming is typically used in advance to ensure production efficiency and stability. For MCUs, particularly small package MCUs like BGA or QFN, the small size of the chips makes manual programming challenging, and the precision fixtures required are costly. These chips are more suitable for online programming after placement on the board to reduce production costs.