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Ceramic capacitor structure and failure reasons

Introduction: Ceramic capacitors are non-polar components with two terminals. In the early days, the most commonly used ceramic capacitors were disc capacitors, which were earlier than transistors. They were used in many vacuum tube equipment (such as broadcast receivers) from the 1930s to the 1950s. Later, ceramic capacitors were also widely used in transistor equipment. . As of 2007, ceramic capacitors are still widely used in various electronic devices due to their high capacity and low cost compared to other low-capacitance capacitors. Ceramic capacitors are capacitors with ceramics as dielectric. Its structure is composed of two or more alternating ceramic layers and metal layers, and the metal layers are connected to the electrodes of the capacitor.

The composition of ceramic materials determines the electrical characteristics and application range of ceramic capacitors, which can be divided into the following three categories according to their stability:

Category 1: It has high stability and low loss, suitable for the application of resonant circuit.

Category 2: High volumetric efficiency, but poor stability and accuracy, suitable for buffering, decoupling and bypass circuits.

Category 3: The volumetric efficiency is higher, but its stability and accuracy are worse.

The failure causes of multilayer ceramic capacitors are divided into external factors and internal factors

Intrinsic factor one: voids in the ceramic medium-the main factors leading to voids are organic or inorganic pollution in the ceramic powder, improper control of the sintering process, etc. The generation of voids is very easy to cause leakage, and the leakage causes local heating inside the device, which further reduces the insulation performance of the ceramic dielectric and leads to an increase in leakage. This process occurs cyclically and continuously deteriorates, and in severe cases, the multilayer ceramic capacitor may crack, explode, or even burn.

Intrinsic factor 2: sintering cracks-sintering cracks often originate from one end of the electrode and expand in the vertical direction. The main reason is related to the cooling rate during the sintering process, cracks and hazards are similar to voids.

Intrinsic factor three: layering-the sintering of multilayer ceramic capacitors (MLCC) is a co-firing of multilayer materials. The sintering temperature can be as high as 1000°C or more. Weak interlayer bonding, volatilization of internal pollutants during the sintering process, and improper sintering process control may all lead to delamination. Delamination is similar to the hazards of voids and cracks, and is an important inherent defect in multilayer ceramic capacitors.

External factor one: temperature shock cracks-mainly due to the temperature shock of the device during welding, especially wave soldering, improper repair is also an important cause of temperature shock cracks.

External factor two: mechanical stress cracks-Multilayer ceramic capacitors are characterized by being able to withstand greater compressive stress, but their ability to resist bending is relatively poor. Any operation that may produce bending deformation during the device assembly process may cause the device to crack. Common stress sources include: SMT alignment, circuit board operation during the process; human, equipment, gravity and other factors in the circulation process; through-hole component insertion; circuit testing, single board division; circuit board installation; circuit board positioning and riveting ; Screw installation, etc. This type of crack generally originates from the upper and lower metallized ends of the device, and expands into the device along an angle of 45°C. This type of defect is also the most common type of defect.

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