CP testing (wafer probe testing) is conducted after the completion of wafer manufacturing and before packaging, to verify electrical performance and functionality by contacting the bare die on the wafer with probes. The content of CP testing varies depending on the chip type (digital, analog, mixed signal, memory, etc.), but usually includes the following categories:
1. DC parameter testing (Direct Current Test): DC testing is used to measure the electrical characteristics of chips under static conditions and is the basis of CP testing. Including power supply current testing; I/O pin parameter testing; Continuity&Leakage Test.
2. Functional Test: Functional testing verifies whether the chip can correctly perform its designed functions. Including digital logic function testing; Memory Test; Simulated functional testing; Interface function testing.
3. Alternating Current Test: AC testing is used to verify the timing performance of the chip under dynamic operating conditions. Including clock frequency testing; Setup Time and Hold Time testing; Propagation Delay Test; Temporal margin testing.
4. Reliability and environmental testing (partially conducted in the CP stage): Although most reliability testing is conducted in the FT (Final Test) stage, some CP testing may also include: Temperature Test: functional and parameter testing is conducted at high temperatures (such as 125 ° C) or low temperatures (such as -40 ° C) to verify the operating temperature range of the chip; Voltage scan test: Change the supply voltage to test the stability of the chip at different Vdds.
In order to efficiently and accurately complete the above testing content, CP testing adopts various technologies and methods, combined with automatic testing equipment (ATE) and probe stations (Prober) to achieve. The main methods include:
1. Probe station and testing machine work together
Probe station: carries the wafer and precisely controls the contact between the probe card and Die to ensure stable electrical connection.
Testing machine: Generate test vectors and collect response data, and apply voltage/current excitation through a high-precision source measurement unit (SMU).
Probe card: Made of materials such as tungsten copper and beryllium copper, small probes (diameter 3-4mil) are fixed with epoxy resin to achieve high-density connection with Die pads.
2. Parallel testing and signal integrity control
Multi Die Parallel Testing: By designing probe cards to support simultaneous testing of multiple Dies (such as 32/16/8/4 simultaneous testing), testing efficiency is improved.
Signal integrity optimization: For high-speed signals (such as Scan testing and Memory testing), it is necessary to control the probe contact resistance and parasitic capacitance to avoid signal distortion (data transmission rate is usually ≤ 50Mbps).
3. Environmental adaptability testing
Temperature cycling test: detect changes in chip performance after high-temperature baking (such as 125 ℃) to ensure its stability.
High current impulse test: Use pulse method to test the on resistance of power devices (such as SiC MOSFET) to avoid the influence of self heating effect on the results.
CP testing will no longer be just a simple judgment of "pass/fail", but will develop towards high-precision parameter testing, failure mode prediction, and data-driven optimization. For chip design companies, foundries, and OSATs, establishing an efficient and reliable CP testing system is a key guarantee for ensuring product competitiveness and market success.

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