Skill sharing ! How to judge whether the capacitor is good or bad?

As an indispensable part of our daily electrical products, capacitors are widely used in DC blocking, coupling, bypass, filtering, tuning loops, energy conversion, control circuits, etc. Most of the causes of damage to electrical products may be caused by damaged capacitors, so how do we test whether the capacitor is good or bad? Today qihe smt equipment take this opportunity sharing with you some methods of measuring the quality of capacitance!

How to judge whether the capacitor is good or bad?, capacito size table

How to measure the quality of mini capacity capacitor?

Detect small capacitors below 10pF, because the capacity of fixed capacitors below 10pF is too small, if you use a pointer-type multimeter to measure, you can only check qualitatively whether there is leakage, internal short circuit or breakdown.

When measuring, you can choose the R×10k gear of the multimeter, and connect the two pins of the capacitor with the metal measuring rods of the two ammeters, and the resistance value should be infinite. If the measured resistance value (the indicator swings to the right) is zero, it means that the capacitor is damaged by leakage or internal breakdown.

For fixed capacitance above 0.01μF, you can use the R×10k block of the pointer multimeter to directly test whether the capacitor has a charging process and whether there is an internal short circuit or leakage, and the capacity of the capacitor can be estimated according to the amplitude of the pointer swinging to the right.

How to detect whether the electrolytic capacitor is good or bad?

Because the capacity of electrolytic capacitors is much larger than that of ordinary fixed capacitors, when measuring, you should choose a suitable range for different capacities. According to experience, in general, the capacitance between 1 and 47μF can be measured with R×1k gear, and the capacitance larger than 47μF can be measured with R×100 gear.

Connect the metal measuring stick of the red electric meter of the multimeter to the negative pole, and the metal measuring stick of the black electric meter to the positive pole. At the moment of first contact, the pointer of the multimeter will deflect to the right by a large degree (for the same electric resistance, the larger the capacity, the larger the swing ), and then gradually turn to the left until it stops at a certain position.

The resistance at this time is the forward leakage resistance of the electrolytic capacitor, which is slightly larger than the reverse leakage resistance. Practical use experience shows that the leakage resistance of electrolytic capacitors should generally be above several hundred kΩ, otherwise, it will not work normally.

In the test, if there is no charging phenomenon in the forward and reverse directions, that is, the hands of the watch do not move, it means that the capacity has disappeared or the internal circuit is broken; if the measured resistance value is very small or zero, it means that the capacitor has a large leakage or has been broken down. Can no longer be used.

For electrolytic capacitors with unknown positive and negative signs, the above method of measuring leakage resistance can be used to identify them. That is, first randomly measure the leakage resistance, remember its size, and then exchange the metal measuring rod of the ammeter to measure a resistance value.

The one with the larger resistance value in the two measurements is the positive connection method, that is, the metal measuring rod of the black ammeter is connected to the positive pole, and the metal measuring rod of the red ammeter is connected to the negative pole.

Use a multimeter to block electricity, use the method of forward and reverse charging the electrolytic capacitor, and estimate the capacity of the electrolytic capacitor according to the size of the pointer swinging to the right.

Measure the discharge speed of the capacitor

Use a digital multimeter on both ends of the capacitor to charge first, then open the circuit to measure the speed at which the voltage drops. Because the capacitor is an open circuit, the only thing that consumes power is the leakage current. If you measure the curve of the voltage and time, you can reverse the leakage current. Remember to use a better digital multimeter, because the input impedance of the multimeter itself is limited no matter how large it is. If it is a good quality capacitor with low leakage current, then a digital multimeter with a slightly smaller input impedance will not be accurate.

Attention! If you need to measure positive and negative back and forth when measuring a large capacity capacitor, you must short-circuit and discharge the capacitor to avoid damaging the meter head.

According to experience, in high-frequency circuits, switching power supply circuits have many small capacitors that cannot be correctly judged by ordinary multimeters, and some capacitors may increase. It is strongly recommended to measure with a dedicated digital capacitance meter.

Read more: Skill sharing ! How to judge whether the capacitor is good or bad?

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There are mainly three steps in SMT assembly line process flow: solder paste printing, components placement and reflow soldering.

  1. Solder Paste Printing
    Its function in SMT line process is to print the solder-free paste on the pads of the PCB to prepare for the soldering of the components. The equipment used is a screen printing machine, located at the forefront of the SMT production line.
  2. Components Placement
    Its function is to accurately install the surface mount components on the fixed position of the PCB. The equipment used is a placement machine, located behind the screen printing machine in the SMT production line.
  3. Reflow Soldering
    Its function in SMT manufacturing line is to melt the solder paste so that the surface mount components and the PCB board are firmly bonded together. The equipment used is a reflow oven, located behind the placement machine in the fully automatic SMT production line.

WHAT IS SMT pick and place machine?

SMT (Surface Mounted Technology) is a comprehensive system engineering technology, which covers substrates, design, equipment, components, assembly processes, production accessories and management. When it comes to SMT pick and place machines, the automatic SMT production line requires automatic loading and unloading machine, automatic solder paste printing machine, placement machine, reflow soldering machine, AOI inspection equipment, connecting table, etc. For these SMT assembly line equipment, Qihe SMT can offer you machines in prototype SMT line, small SMT production line, mass production SMT line at low SMT line cost. Contact us now if you are interested.


With the development of technology, future electronic products will be lighter, smaller and thinner. Traditional assembly technology can no longer meet the requirements of high-precision and high-density assembly. A new type of PCB assembly technology-SMT (Surface Mount Technology) has emerged. SMT Assembly is the use of automated machines to assemble electronic components on the surface of the circuit board. Its density, high speed, standardization and other characteristics occupies an absolute advantage in the field of circuit assembly technology. In addition, SMT assembly has a wide range of uses.

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