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After device finish engineering prototypes stage, hardware engineer will need to provide test specification and pass criteria base on the product specification. Production test also could be treated as a simplified regulatlation test, because it has to fulfill standard of worldwide standard (for example: GSM) of local regulation (for example: Wi-Fi).
The target of production test, is deliver quality products. And production test won't go through all engineering details, because factory have time constriant on each station and production line also has cycle time for efficient for production.
Fixture design base on required test item and test point location. At design time, should consider all re-quired test point in the PCB, and must easy accessable during PCBA/PCBA with module/Assembly. If test point and fixture design was bad, it will make product non-mass productionable.
Important test point during GTA production including:
Fixture used for speed up production process, it also has life cycle and need maintance during prodction process. All the connector/test pin/plugs are expendable, and should could be fixed in time during every production process.
Every device has it's own specification and requirement, so the fixture design and requirement should base on device charactics to adjust process. Follwoing just GTA case for your reference.
For example, GTA using following test fixture during production
For development process, all fixture could be integrated into 1 fixture for speed up test software development process. But integrated fixture will cost more and will have more chance get broken during production process, also, integrated fixture need attach every expensive test equipment, and make fixture duplication very non-practical because the cost of expensive test equipment. But singal/integrated test fixture DO very useful during trial run process for software verification.
Factory tend to spilt fixture into simple function and easy maintainable unit, and also could cost saving/balance production line flow process. Base on device charactics and factory process/equipment availability.
GTA uses following equipment during production process:
Surface mount -> Visual inspection -> DM1 download (JTAG) -> GSM firmware download -> GSM test -> DM1 test -> Attach Bluetooth/Wi-Fi/LCM -> DM1.5 (Boot from SD card) -> Housing assembly -> DM2 (Boot from SD card)-> QA -> Packaging -> QA -> Release
DM1 is target for verify main chip component's basic function and surface mount quality. GTA02 integrate DM1 test functions into u-boot, and using the debug board JTAG interface download production u-boot to target board.
GTA02 DM production software could be download from GTA02 DM1 source code
In GTA02, after assembly, will Re-test all DM1.5 function
DM2 specific test including: