Bscan (Boundary Scan) is a technology used for chip testing and debugging, mainly for detecting and diagnosing interconnect faults inside chips or on PCBs (printed circuit boards). It is a part of the JTAG (Joint Test Action Group, IEEE 1149.1) standard, widely used for testing, debugging, and fault analysis of digital circuits.
1. Basic principles of Bscan
Bscan technology creates a controllable data channel by adding Boundary Scan Cells around the I/O pins of the chip. Its workflow is as follows:
(1) Test Access Port (TAP): The chip contains a TAP controller that allows external devices to access the chip through the JTAG interface.
(2) Boundary Scan Register: Each I/O pin corresponds to a register unit used for storing and transmitting test data.
(3) Scan Chain: Multiple Bscan units are connected into a serial link, allowing for gradual transmission and analysis of test data.
(4) Mode selection:
Bypass mode: allows normal signal transmission without affecting chip functionality.
Test Mode: Activate the Bscan unit to capture, store, and forward data for testing.
2. The main applications of Bscan
PCB board testing: detecting connection issues such as poor soldering, short circuits, and open circuits.
Chip level testing: Conduct internal connectivity checks on SoC, FPGA, and other chips.
In System Debugging: Used for debugging in software development, such as debugging CPU, memory, and other peripherals.
IC Burn in Test: Check chip reliability after high temperature or prolonged operation.
3. The role of Bscan in semiconductor testing
During the CP (wafer testing) and FT (finished product testing) stages of the chip, Bscan can be used to discover I/O interconnect issues of the packaged chip and improve test coverage; Combining ATE (Automatic Test Equipment) for structural level testing to improve testing efficiency; As a debugging tool, analyze complex functional failures.
The advantage of Bscan lies in its ability to perform electrical testing without the need for physical probes, making it suitable for modern high-density PCBs and complex chip structures. It plays an important role in chip manufacturing, assembly, and system level testing.
4. Difference between Bscan and Scan
Bscan (Boundary Scan) and Scan (Scan Chain) are two technologies used for chip testing, which differ in application scenarios, implementation methods, and testing purposes.
(1) Definition and Basic Differences

Bscan=External Interconnection Test (I/O Level) → Check if the connection between the chip's external and PCB is normal.
Scan=Internal Logic Test (Gate/Register Level) → Check if the internal logic of the chip is normal.
In the chip testing process, Bscan is mainly used for I/O interconnect testing, while Scan is mainly used for ATPG logic testing. The two can be combined to improve the testing coverage of the chip.

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