After the completion of wafer fabrication by the manufacturer, Wafer must undergo CP chip testing before slicing. On the one hand, it verifies whether the various parameters and functions of the IC meet the design requirements, and on the other hand, it marks the ICs with failed parameters or functions. When binding, there is no need to bind these failed ICs, thus improving the yield rate and saving costs. Mainly for functional testing, DC parameters, and AC parameters. The testing of the latter two parameters is set in the program based on the parameters provided by the IC design company, while the functional testing of the former, as the name suggests, is based on the test vector or functional waveform provided by the design company, adding excitation signals based on this, and then checking whether the data at the output end is correct. ICs with various parameters and functions are considered qualified, otherwise they are considered defective chips.
When a testing project passes all other parameters but fails to pass the function test, the main consideration is: 1. What is the voltage used for the function test? What is the frequency? 2、 Is the input (excitation) signal applied correctly during testing? 3、 Are various signals applied strictly in accordance with the requirements of the test manual? After these points, it can be said that the functional testing task has been completed, and the rest requires the testing engineer to have testing knowledge, such as understanding the concepts of positive and negative voltage multiples; Whether to conduct functional testing using the IC's own clock in addition to the clock; And the issue of selecting Strobe points during testing, and the most important point is the way Clock is applied. Below are several waveform patterns for applying Clock.

For DC parameter testing programming, some parameters do not require precise testing, and we can use the "go on go" testing method to save testing time. But if it is required to classify the magnitude of the current into different levels, it is necessary to test the current using a "Precision Measurement Unit" (PMU) or "DPS", and the range of the "PMU" or "DPS" must be selected correctly, preferably using a range close to the maximum value for measurement - the accuracy of the test data can only be guaranteed.
Testing the driving capability sometimes needs to be combined with functional testing. Only when the output of the tested pin is "High" or "Low", can PMU be used to apply current measurement voltage (VOh, VoL) or voltage measurement current (IOh, IOl). It must be noted that the clock applied by the testing function must be stopped to maintain the IC's current working state unchanged for testing this parameter. Open/Short is used to test whether there is an open or short circuit phenomenon in the protective diode of each pin of the IC. Because a pair of protective diodes are designed for each pin during the design process, usually connected to the power and ground terminals, to provide voltage limiting protection for each pin. If there are many pins, only a few points on the four corners of the layout diagram can be tested. Of course, it is best to test all of them when debugging the program. One thing to note is that during testing, a voltage of 0V is applied to both the power supply VDD and ground VSS, and then a current test voltage is applied through the PMU. The test failure of the chip can be determined by whether the voltage value read is within the qualified range.
For communication parameter testing, the main focus is on frequency testing. The output frequency required for testing general ICs is not high, and all signals are internally divided. Therefore, the tester can directly test the operating frequency of the chip without designing specialized hardware circuits for frequency division. But if it is an IC that operates at high frequencies, testing must consider multiple comprehensive factors: if frequency division is required to test the frequency, a frequency division circuit must be designed and converted before testing; If there is interference, measures must be taken in both hardware and software to eliminate various interferences; If shielding testing can be adopted on hardware, filtering programs can be developed on software.
For some defects caused by slow IC vibration due to design reasons, it is necessary to balance various factors and try to improve the yield of testing as much as possible. Sometimes the testing of DC parameters and AC parameters are interrelated, such as for general meters (three and a half bits, six and a half bits, etc.) and ICs that drive LCDs. When testing their operating current, it is necessary to wait until the chip is fully excited before testing. Only after the chip is fully excited can its current stabilize and reach its minimum. If necessary, the method of repeatedly testing multiple times can be used to improve the yield of testing.

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