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Nov 6 2018

Substitution And Replacement of Integrated Circuits

Warm hints: This article contains about 3000 words and reading time is about 15 min.

Summary

       This article is divided into two parts: Overhaul Integrated Circuits: Detection Techniques And Disassembly Methods and Methods and techniques of Integrated Circuits substitution. The first part introduces conventional method, inspection method and disassembly method to overhaul integrated circuits; the second part has 13 points to analysis methods and techniques of integrated circuit substitution.


 Overhaul Integrated Circuits: Detection Techniques And Disassembly Methods  

1. Conventional method for overhauling integrated circuits

      The common methods of IC detection are as follow:

① Off-line measurement

      Off-line measurement means that when the integrated circuit is not welded into the circuit, the DC resistance of each pin is measured and compared with that of each pin of the known normal type of integrated circuit, so as to determine whether the IC is normal or not.

② On-line measurement

      On-line measurement is to determine whether the integrated circuit is damaged by measuring the voltage, resistance and current of each pin. 

On-line measurement

③ Substitution method

      The substitution method is to replace the tested integrated circuit with a known IC of same type and specification, which can be used to determine whether the integrated circuit is damaged or not.

2. Inspection method for overhauling integrated circuits

      Usually, there are many integrated circuits in one device. When some integrated circuits in the device are faulty, only the detection can find the fault. Effective detection methods for integrated circuits include:

① Detection of Microprocessor Integrated Circuits

      The key test pins of microprocessor integrated circuit are VDD power supply terminal, RESET reset terminal, XIN crystal oscillator signal input terminal, XOUT crystal oscillator signal output terminal, input terminals and output terminals of other lines. The resistance and voltage values of these key feet to the ground are measured on the road to see if they are the same as the normal values (which can be checked from the circuit diagram of the product or related maintenance materials). The RESET reset voltage of different microprocessors is also different, some of them are low level reset, that is, low level at the moment of startup, and maintain high level after reset; Some are high-level reset, that is, high level at the moment of on-off, maintain low-level after reset.

Microprocessor

② Detection of Integrated Circuits for switching Power supply

      The key voltage of the switching power supply integrated circuit is the power supply terminal (VCC), the pulse output terminal, the voltage detection input terminal, and the current detection input terminal. Measure voltage and resistance of each pin to ground. If the value is far different from the normal value, and the peripheral components are normal, it can be determined that the integrated circuit is damaged. The thick film integrated circuit with built-in high-power switch tube can also determine whether the switch tube is normal by measuring the positive and negative resistance values between the C, B and E poles of the switch tube.

③ Detection of Audio Power Amplifier IC

      When checking the audio power amplifier integrated circuit, first check the voltage value and resistance value to ground of the power supply terminal (positive power supply terminal and negative power supply terminal), audio input terminal, audio output terminal and feedback terminal. If the value of each pin is different from the normal ones, and the peripheral components are normal, the integrated circuit is damaged. For an audio power amplifier integrated circuit that causes a silent fault, when the power supply voltage is normal, it can be checked by interfacing the signal. When measuring, the multimeter should be placed in the R×1, the red test lead should be grounded, and the audio input should be touched with the black test lead. If it is normal, there should be a strong sound like”click” in the speaker.

Audio Power Amplifier IC

④ Detection of Operational Amplifier Integrated Circuits

      A multimeter DC voltage file is used to measure the voltage between the output of t`he operational amplifier and the negative power supply (the voltage value is higher in the static state). The two input terminals of the operational amplifier (with interference signal) are touched by the hand-held metal tweezers in turn. If the needle of the multimeter has a large swing, the operational amplifier is in good condition. If the multimeter needle is not moving, the operational amplifier is damaged.

Operational Amplifier Integrated Circuits

⑤ Detection of time Base Integrated Circuits

      Time-based integrated circuits contain digital circuits and analog circuits. It is difficult to measure them directly by multimeter. The test circuit shown in figure 9-13 can be used to detect time-based integrated circuits. The test circuit consists of resistive and capacitive components, LED,6V DC power supply, power switch and 8-pin IC socket. After inserting the time base circuit (such as NE555) into a IC socket, press the power switch, and if it is normal, the LED will flicker. If the LED is not bright or always bright, the performance of the measured time-based integrated circuit is poor.

3. Disassembly method of overhauling Integrated Circuits

      IC pins are numerous and can be very difficult to disassemble, sometimes it will even damage integrated circuits and circuit boards. But if you know the tips of IC disassembly, you can do it easily. Here are a few useful ways to disassemble integrated circuits: 

① Multi-strand copper wire tin absorption disassembly method

Multi-strand copper

      Remove plastic sheaths from copper wires and use only copper cores. The multi-strand copper core is first infected with rosin alcohol solution. After the electric iron is heated, the multi-strand copper core is placed on the pin of the block to heat up, so that the tin on the pin is absorbed by the copper wire. The copper core covered with tin can be cut off, repeated several times to absorb all the tin on the pin. The braided wire inside the shield wire can also be used to adsorb tin. As long as the tin is adsorbed, with tweezers or screwdriver gently pry the integrated circuit can be removed.

② Tin absorber disassembly method

      Using tin absorbers to remove the integrated block is a commonly professional method. The tool is ordinary double-purpose electric soldering iron, whose power is above 35 W. When removing the integrated block, it is only necessary to place the heated soldering iron on the pin of the integrated block, and the integrated block can be removed when the tin of all the pins is melted and inhaled into the tin absorber. 

Tin absorber

③ Adding solder disassembly method

      This method saves a lot of trouble. Solder on the pin of the integrated block, so that the solder joint of each pin is connected to facilitate heat transfer and easy disassembly. After heating each row of pins by electric soldering iron, pry gently with tweezers until the integrated block is removed. In general, each row of pins can be removed after heating twice. 

④ Medical hollow needle disassembly method

      Take several medical 8 to 12 hollow needles. The inner diameter of the needle is suitable for fitting the pin of the block. Dissolve the pin solder with soldering iron when disassembled, catch the pin with the needle in time, then remove the soldering iron and rotate the needle, pulls out the needle as the solder solidifying. In this way, the pin is completely separate from the printed board. After all pins are done such, the integrated block can be easily removed. 

⑤Electric soldering iron-brush matching disassembly method

      This method is simple and easy, as long as there is a soldering iron and a small brush. When removing the integrated block, Afther heating the electric soldering iron to the temperature that can dissolve tin, melt the solder on the pin and remove it with a brush. In this way, the pin of the integrated block can be separated from the printed board. The integrated block can be removed separately or by row. Finally, use sharp tweezers or screwdriver to pry down the integrated block.

      To sum up, online measurement is commonly used in practice. Measure the pin voltage first, if the voltage is abnormal,  disconnect the pin connection, and the terminal voltage can be measured to determine whether the voltage change is caused by the peripheral component or the inner part of the integrated block. It can also be judged by measuring the DC equivalent resistance (outside R) between the external circuit and the ground. Usually, the measured DC resistance (in-circuit resistance) between a pin and ground is actually the total DC equivalent resistance of outside R in parallel with in-circuit resistance. Sometimes the circuit voltage and the on-resistance deviate from the standard value, not necessarily because the integrated block is damaged, but related to peripheral component damage. Therefore, the R outside is not normal, resulting in an abnormality in the circuit voltage and the on-resistance. Only by measuring the internal DC equivalent resistance of the integrated block can it be judged whether the integrated block is damaged or not.

4.Examples: the disassembly and welding of chip integrated circuits

①Tool selection

  • Choose a 25W internal heat-type long-life pointed soldering iron, which requires no leakage and moderate temperature (power and temperature are preferably controllable).

  • A medical disposable syringe with small needle or a hollow stainless steel needle, and then bends the tail of the small needle into a small hook.

  • A paper knife or a small scalpel.

  • Solder wire with diameter of 0.62~0.8mm. 

②Disassembly

  • Covering the hot electric iron with tin, shake the tin off and wipe it with rags, to ensure its brightness and ease of use.

  • Quickly pick up the pin with needle while melting the solder on the pin of the integrated circuit by electric soldering iron, so that the pin is separated from the circuit, finally remove the integrated circuit.

③Welding   

  • Clean the printing board. Clean with alcohol where the integrated circuit is removed (especially rosin and solder residue).

  • Sanding the new welding surface of the IC pin with fine sandpaper, coating with alcohol rosin liquid and lining with thin tin.

  • In order to avoid the shift of integrated circuit during welding, epoxy resin can be used to attach the components to the corresponding position on the printing board. After curing, brush flux on the pin to facilitate welding

  • During welding, the method of seperation welding can be used. Welding time is controlled within 3 s. After all pins are welded, pull the pin one by one with a small needle to check for virtual welding. Use a magnifying glass to see if there is a short circuit between the pins, handle the problems in time, and then clean the pins with alcohol.

    Substitution And Replacement of Integrated Circuits

④Attention

  • Soldering iron must be light when welding, mainly use gravity to make hot solder flow. It is easy to bend the pin and cause trouble.

  • In addition, the flow of solder is easy to fall on the board. After welding, the residual tin should be carefully cleaned to prevent the loss after electrification.


 Integrated Circuit Substitution: Methods And Techniques  

1. Identification of integrated circuit models

      In order to fully understand the use, function and electrical characteristics of an integrated circuit, it is necessary to know the type and origin of the integrated circuit. The front surface of an integrated circuit is printed with a model or mark. According to the prefix or mark of the model, it can be preliminarily known which factory or company it belongs to, and what kind of circuit function it belongs to is according to its number.

2. Have a comprehensive understanding of integrated circuits before using

      Before using an integrated circuit, you must make a comprehensive analysis and understanding of the integrated circuit's functions, internal structure, electrical characteristics, external packaging, and circuits connected to the integrated circuit. The electrical performance parameters shall not exceed the maximum range permitted by the integrated circuit.

3. Pay attention to the direction when installing integrated circuit

      When installing an IC on a printed circuit board, be careful not to get it wrong, otherwise, the integrated circuit will probably be destroyed when electrified. The general rule is that the pins of integrated circuits are upward,  arranged counter-clockwise with the notches or vertical lines as the criteria.

      In addition to conventional pin alignment, there are some special examples that should be noted. Most belong to the single-row directional-inserted packaging structure, its pins direction are opposite to what described above, with the suffix "R", such as M5115 and M5115RPU HA1339A, A1339A and A1339ARN, HA1366W and HA1366AR, etc. With pin arrangement from right to left, they are mainly some dual-channel audio power amplifiers, which are specially designed for the convenience of the symmetry of the printed board. 

Substitution And Replacement of Integrated Circuits

4. Some empty feet should not be grounded without authorization

      Some pins in internal equivalent circuits and application circuits are not marked and should not be grounded without authorization when the pins are empty. These pins are replacement or reserve pins and sometimes also serve as internal connections.

      All input terminals of digital circuits should be connected with appropriate logic level (Vdd or Vss) according to the actual situation, and must not be suspended, otherwise the working state of the circuit will be uncertain and the power consumption of the circuit will be increased.

      The DC bias of the control terminal should also be considered for the trigger (CMOS circuit). Generally, a 100K Ω resistor can be connected between the control teminal and the Vdd or Vss, and the trigger signal is connected to the pin. To ensure that the circuit state is unique under normal condition,once the trigger signal (pulse) comes, the trigger can flip normally. 

5. Note the stress the pin can withstand and the insulation between the pins

      Do not add too much stress to the pin of the integrated circuit. Be careful when disassembling the integrated circuit to prevent from breaking. For high-voltage integrated circuits, sufficient gaps should be left between the power supply Vcc and the ground wire and other input wires.

6. The following points should be noted for power integrated circuits

      ①  Do not power on at will before installing heat sink.

      ②  Do not weld the ground wire to the heat sink before determining whether the heat sink of the power integrated circuit should be grounded.

      ③  The installation of the heat sink should be smooth, the fastening torque is generally 4 ~ 6 kg / cm, and the area of the heat sink should be large enough.

      ④  Do not mix dust, debris, etc between heat sink and integrated circuits. It is best using silicon grease to reduce thermal resistance. After installed the heat sink, weld the heat sink that needs grounding to the grounding terminal of the printed circuit board by a lead wire. 

7.Integrated circuit pin should be powered on synchronously

      The voltage applied by the pins of the integrated block should be synchronized. When the CMOS circuit is not connected to the power supply, the input signal can never be added to the input end of the CMOS circuit. If the signal source and the CMOS circuit each use a set of power supply, the CMOS power supply should be connected first, then connect that of signal source. When turned off, the power supply of signal source should be cut off first, and then turned off that of CMOS. 

8. Integrated circuits do not allow high current shocks

        High current shocks are most likely to damage the integrated circuits, so current limiting circuits should be attached to power sources in normal use and testing. 

9. Pay attention to the stability of power supply

      If the power supply and the measuring instrument of integrated circuit produce abnormal pulse wave when the power supply is switched on or off, the surge absorption circuit, such as diode, should be added to the circuit.

      The range of power supply voltage of TTL circuit is very narrow, which stipulates that the voltage range of class I and 3 products is 4.75-5.25V ( 5V±5%), and that of class 2 products is 4.5-5.5V (5V ±10%). The typical value is Vcc=5V, and Vcc in use must not be out of scope. The input signal V1 shall not be higher than Vcc or lower than GND.

      The power supply voltage of ECL is generally defined as Vcc=0V, Vee=-5.2V ±10%, and both should not exceed the standard in use. 

10.Avoid exceeding the maximum temperature

Substitution And Replacement of Integrated Circuits

      The maximum temperature that an integrated circuit can withstand is 260 ℃ / 10 s or 350 ℃ / 3 s. The temperature of wave peak welding and immersion welding is generally controlled at 240 ℃ ~ 260 ℃, and the time is about 7 seconds.

      ECL circuits have high speed and high power consumption. For small systems, radiators should be installed on devices; for large and medium-sized systems, air-cooled or liquid-cooled equipment should be installed.

11. Integrated circuit should not be plugged with charge

      Circuits with integrated circuit sockets, circuit connectors and component-type audio equipment should avoid plugging and unplugging integrated blocks or connectors, Cut off the power supply when necessary, and take action after the power supply filter capacitor discharge. 

12. Integrated circuits and their leads should be kept away from pulse high voltage supply

      When setting the position of integrated circuit, we should keep away from pulse high voltage, high frequency and other devices as far as possible. The lead wire and the related wire should be as short as possible, and the over-voltage protection circuit should be added to the inevitable long wire, especially the installation of the car recorder. When connecting the CMOS circuit, the peripheral components should be as close as possible to the connected pin and the leads are as short as possible, and parallel long leads are avoided. Otherwise, it will cause large distributed capacitance and distributed inductance, and form LC oscillations. The solution is to connect the 10 K Ω resistor in series at the input.

       When CMOS is used in high-speed circuits, attention should be paid to circuit structure and PCB design. Long output lead is easy to produce "ring" phenomenon, resulting in waveform distortion.

      Because ECL is a high-speed digital integrated circuit, special problems such as "reflection" on signal lines and "crosstalk" between adjacent signal lines must be considered. Using transmission lines (such as coaxial cables) when necessary, and making ensure the impedance matching of transmission line. In addition, measures for shielding and isolation also needs. When the working frequency exceeds 200Mz, the multi-layer circuit board should be selected to reduce the grounding impedance.

13.Prevention of inductive EMF to breakdown integrated circuits

      When there is an inductive load such as a relay in the circuit, a protection diode should be connected to the relevant pin of the integrated circuit to prevent overvoltage breakdown. When soldering, 20W internal heating type soldering iron should be used, whose shell needs to connect with grounding wire. Or using anti-static soldering iron to prevent damaging integrated circuit due to leakage. Each welding time should be controlled within 3-5 seconds. Sometimes for safety reasons, you can also remove the soldering iron plug and use the residual heat of the soldering iron to solder. Do not solder when the circuit is electrified. 


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