ANALYSIS AND

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Analysis Background
In recent years, microchip size is getting smaller, it can realize more functions, and it is applied in the car more widely, the performance of the chip determines the realization of car functions. On November 2, 2020, The General Office of the State Council issued New Energy Vehicle Industry Development Plan (2021-2035), in which it was proposed to strengthen quality and safety assurance [1]. The application failure and reliability of chips have attracted more and more attention.
As we know, there are a variety of chip failure modes. According to literature statistics, IC failure caused by EOS (Electrical over Stress) and ESD (Electro-Static discharge) accounts for about 50% of the total number of field inefficiency devices [2]. This microchip is widely used in automotive headlight system, which is mainly used to control the LED in order to achieve dynamic adaptive lighting. If the microchip fails, the headlights will lose the normal warning function, affecting safety.

Experimental Environment
We studied that one automobile lamp experiment lighted abnormally after a period of use. We disassembled the whole lamp, made the PCBA and component cross validation experiments, and finally locked to a microchip failure. So, this microchip failure caused the entire lamp abnormal.
The experiment date was traced back according to the experimental products, and the data was collected in the dimension of quarter to generate the pie chart, as shown in Figure 1. The experiment date of failure parts mostly occurred in the first and fourth quarter.

Experiments and Analysis
1、 Performance and characterization of the failed part 1.1 IV-curve of the failed part All the pins IV curve (smart-1) of the failed part were measured and compared with good one. Finally, it was found that the IV curve of 19-pin (address bit function) was abnormal and showed short-circuit characteristics, as shown in Figure 2. Through decap, the morphologies of each pin were observed with a microscope (Olympus BX53M). Finally, it was found that 19-pin was ablated and carbonized, as shown in Figure 3. The carbonized position was crossed (TOP-TECH E-F-200), and was observed by SEM (250FEG), as shown in Figure 4. Based on the above two kinds of representation information, it can be seen that the pin failure is caused by EOS. It is speculated that there is a large current or voltage during the produce process or there is excessive static electricity in the produce process. 979-8-3503-4638-1/22/$31.00 ©2022 IEEE  The microchip normal input voltage is 5V(range:≤5.5V). We took one piece of good PCBA, adopting the form of voltage limit, started from 5V, increasing the voltage by 0.1V every time. At the same time, we observed the current changes and made record. We cut off the power supply after recording every time, using multimeter to test the resistance between 19-pin and GND, until the resistance changed a lot suddenly.

Sample 2：Overcurrent simulation on PCBA
We took one piece of good PCBA, adopting the form of current limit, started from 0.06A, increasing the current by 0.01A every time. At the same time, we observed the current changes and made record. We cut off the power supply after recording every time, using multimeter to test the resistance between 19-pin and GND, until the resistance changed a lot suddenly.

IV-curve of sample 1 and sample 2
After soldering chip, we made the IV-curve test of sample 1 and sample 2. It was found that 22-pin (VDD function) has different degrees of short circuit representation, as shown in Figure 6. 19-Pin is normal, as shown in Figure 7. After decap of sample 1 and sample 2, we observed each pin with a microscope. It was found that 19-pin is normal, but 22-pin occurs the carbonization phenomenon, as shown in Figure 8 and Figure 9.

Electrostatic tolerance experiment
According to the microchip specifications, the microchip HBM level is ±2000V. We took 3 lot new microchips to test the electrostatic tolerance level of each pin. Starting from the standard level ±2000V, we increased the voltage 500V every time. It can be seen from the results that all pins meet the standard of ±2000V in the specification, and the anti-static ability of 19-pin is the lowest level of the anti-static ability of all pins. The anti-static ability of 14-pin (VIN function) and 22-pin belong to the upper level of anti-static ability of all pins. The test results are shown in Table 1 as below.

Electrostatic damage simulation
We took good microchips, and made the electrostatic damage with 19-pin, starting with 5000V as the lower limit and 8000V as the upper limit, every time 1000V was superimposed. Four samples were obtained, numbered as sample 3 (5000V), 4 (6000V), 5 (7000V) and 6 (8000V). The 19-pins of four samples were damaged in different degrees.
On-line detection: electrostatic damaged samples 3, 4, 5, and 6 were soldered to PCBA, and made the whole lamp modules performance testing. It was found that the functional detection is normal. Electrostatic damage can not affect the chip to achieve various functions instantly Electrostatic damage microscopic: The substrate of microchip simulated by electrostatic damage was de-layered, and damage is finally found in the substrate layer, which is similar to the microscopic appearance of damage of failed parts, as shown in Figure 10.

PCBA circuit
We check the PCBA design circuit, as shown in Figure 11. 14-pin,19-pin and 22-pin of the microchip are all connected to 5V. 14-pin and 22-pin have 0Ω resistance in front of them, while 19-pin is directly connected to 5V. Figure 11 Circuit of the microchip

3、 Experimental conclusions
In summary, from the experimental date, the failed parts are mostly occurred in the first and fourth quarter, concentrated in winter. The performance and microstructure characterization indicates that the failed part is short caused by EOS; overcurrent and overvoltage simulation on PCBA don't cause failure of 19-pin. The microchip meets the specifications for static electricity. The anti-static ability of 19-pin is relatively weak compared to 14-pin and 22-pin, which are also connected to 5V. At the same time, 14-pin and 22-pin have 0Ω resistance in front of them in the circuit, which can reduce external interference. When the substrate layer is removed from the electrostatic damage simulation microchip, the microstructure is similar to the substrate layer of failed parts. The chip address pin will not immediately cause failure after slight static damage, and does not affect the module to achieve each function.
The static electricity in each station of the experiment was checked, and it was found that the static electricity index in some stations exceeded the standard, so it was corrected immediately. In this case, after the static electricity in each station of the experiment was checked and corrected, no adverse events occurred for a period of time.

Suggestions for Improvement and Discussion
In circuit design, capacitance or other protective devices can be added to improve the ability of electrostatic sensitive circuit to electrostatic discharge [3].
On the other hand, when it comes to the manufacturing of electronic devices, in addition to the formation of ESD protection measures and requirements, the company should form the ESD optimization team with the participation of all departments' members, take the graded protection of components and PCBA, review regularly, optimize and improve continuously, and persistent efforts should be made to reduce the impact of static electricity on products [4].
In this case, there are many places to be improved in the failure process, especially for different electrostatic models and the influence of different electrostatic models on the chip, as well as the aging test of the experimental products after electrostatic damage can be further studied and discussed.