Common IC chips are good or bad and precautions for detection

Date：2022-02-14 17:58:30Views：1552

As the core component of electronic products, the performance of chip tends to be better and better. In order to ensure the quality of chip, people have adopted effective testing technology to test the function of chip. The main function of the chip is to complete the operation and processing tasks. Chip refers to the silicon chip containing integrated circuit. In the current process, in order to ensure the quality of the chip, chip detection is generally carried out in the process from design and molding to mass production.

Chip detection method

1、 Board inspection method:

1. Observation method: whether there is burning, burning, blistering, broken line on the board surface and corrosion of socket.

2. Meter measurement method: whether the resistance of + 5V and GND is too small (below 50 ohms).

3. Power on inspection: for the broken board, slightly increase the voltage by 0.5-1v. After startup, rub the IC on the board by hand to make the faulty chip heat up, so as to perceive it.

4. Check whether there are strong and weak logic input signals of each pen.

5. Identify major work areas: most boards have clear division of labor in areas, such as control area (CPU), clock area (crystal oscillator) (frequency division), background picture area, action area (people, aircraft), sound generation and synthesis area, etc. This is very important for the in-depth maintenance of the computer board.

2、 Troubleshooting method:

1. According to the instructions of the manual, check whether there is a signal (wave type) at the input and output ends of the suspected chip. If there is any input or output, check whether there is a control signal (clock) of the IC. If there is any, the IC is very likely to be broken. If there is no control signal, trace it to its front pole until the damaged IC is found.

2. Do not remove the found from the pole temporarily. The same model can be selected. Or the IC with the same program content is carried on the back. Start up and observe whether it gets better to confirm whether the IC is damaged.

3. Find short routes by tangent and jumper method: find some signal lines and ground wires. + 5V or other pins that should not be connected to multiple ICs are short circuited. Cut off the line and measure again to judge whether it is an IC problem or a board wiring problem, or borrow signals from other ICs and weld them to the IC with wrong wave shape to see whether the phenomenon picture is getting better and judge the quality of the IC.

4. Comparison method: find a good computer board with the same content and compare and measure the pin wave pattern and number of corresponding IC to confirm whether the IC is damaged.

5. Test IC with ictest software in microcomputer universal programmer (all-03 / 07) (expro-80 / 100, etc.).

Precautions for IC chip detection

1. Understand the working principle of integrated circuits and related circuits before testing

Before checking and repairing the integrated circuit, first be familiar with the function, internal circuit, main electrical parameters, the function of each pin, the normal voltage of the pin, the waveform and the working principle of the circuit composed of peripheral components. If the above conditions are met, the analysis and inspection will be much easier.

2. The test shall not cause short circuit between pins

When measuring the voltage or testing the waveform with an oscilloscope probe, the lead or probe shall not cause a short circuit between the pins of the integrated circuit due to sliding, and it is best to measure on the peripheral printed circuit directly connected with the pins. Any instantaneous short circuit is easy to damage the integrated circuit. Be more careful when testing CMOS integrated circuits in flat package.

3. It is strictly prohibited to use grounded test equipment to contact live TV, audio, video and other equipment on the base plate without isolation transformer

It is forbidden to directly test TV, audio, video and other equipment without power isolation transformer with instruments and equipment with grounded shell. Although general tape recorders have power transformers, when contacting special TV or audio equipment, especially those with large output power or little understanding of the nature of the power supply used, it is necessary to first find out whether the chassis of the machine is charged, otherwise it is very easy to cause power short circuit with TV, audio and other equipment charged on the bottom plate, which will affect the integrated circuit and further expand the fault.

4. Pay attention to the insulation performance of electric soldering iron

It is not allowed to use soldering iron for welding with electricity. To confirm that the soldering iron is not charged, it is best to ground the shell of the soldering iron. Be more careful with MOS circuit. It is safer to use low-voltage circuit iron of 6 ~ 8V.

5. Welding quality shall be guaranteed

When welding, it is indeed firmly welded, and the accumulation of solder and pores are easy to cause false welding. The welding time is generally no more than 3 seconds, and the power of the soldering iron is about 25W. The welded integrated circuit should be carefully checked. It is best to use an ohmmeter to measure whether there is a short circuit between the pins, and then turn on the power after confirming that there is no solder adhesion.

6. Don't judge the damage of integrated circuit easily

Do not easily judge that the integrated circuit is damaged. Because the vast majority of integrated circuits are directly coupled, once a circuit is abnormal, it may lead to multiple voltage changes, which are not necessarily caused by the damage of the integrated circuit. In addition, in some cases, when the measured voltage of each pin is consistent with or close to the normal value, it does not necessarily mean that the integrated circuit is good. Because some soft faults will not cause changes in DC voltage.

7. The internal resistance of the test instrument should be large

When measuring the DC voltage of integrated circuit pins, a multimeter with internal resistance greater than 20K Ω / V should be selected, otherwise there will be large measurement error for some pin voltages.

8. Pay attention to the heat dissipation of power integrated circuits

The power integrated circuit shall have good heat dissipation, and it is not allowed to work at high power without radiator.

9. Lead wires should be reasonable

If it is necessary to add peripheral components to replace the damaged parts inside the integrated circuit, small components shall be selected, and the wiring shall be reasonable to avoid unnecessary parasitic coupling, especially the grounding terminal between the audio power amplifier integrated circuit and the preamplifier circuit.