What are the causes of TVS short-circuit burnout? From the electronic solution for you.

The failure modes of TVS tubes include short circuit, open circuit and deterioration of electrical characteristics. Among them, short circuit failure is the most common, and the most serious impact on the circuit. Once a short circuit fault occurs in the TVS tube, the high energy released will often damage the protected electronic equipment. The TVS device is mainly composed of 3 parts: wafer, electrode system and shell. The wafer is the core and is usually formed by diffusion process on monocrystalline silicon wafer. If the TVS tube process is poorly controlled, it may cause inherent defects in the TVS device, reduce the yield and reliability of the TVS, and lead to failure in screening or use.

 

1 、 the hole of chip bonding interface

The most typical cause of TVS short circuit is that the core and the inner lead assembly and the base copper are not sintered properly, and a large area of voids is formed at the sintering interface. Voids may be due to uneven solder or adhesive interface of each layer, the solder oxidation stain stick side, causing welding solder and wafer or metal electrode without causing good welding fusion. When the cavity size is large, the current is gathered near the burning point, and the core of the tube is difficult to heat. It causes the thermoelectric stress concentration and produces partial thermoelectric, which causes thermal rush and burns the device. Empty area islesser can accelerate the thermal fatigue of solder, the solder layer will produce fatigue cracking caused by thermal resistance increases with the increase of exergy, eventually leading to the overheating device.

2. Table defects

The defects caused by defects on the TVS tube surface are often batch. TVS tube in the process of the cause of the wafer table injurymainly, wafer etching in molding for hydrofluoric acid and nitric acid mixed solution formula is too high and too thick or violent reaction, welding after alkali corrosion when cleaning, etching liquid concentration is too high, too high temperature caused by alkali cleaning heavy corrosion.

3 surface strong accumulation layer or strong inversion layer

Even if the TVS device wafer surface is in good condition, the TVS short-circuit fault is also easy to occur on the surface. This is due to the periodic interruption of crystal structure on the surface, and the surface of the semiconductor lattice defects are often many grinding, polishing, sandblasting, slicing and other causes, chemicals, gas or other pollutants adsorption will make the corrosion surface of semiconductor charged. Surface charges are protected by adhesive passivation and adsorb or repel free carriers in semiconductors. The surface space charge layer such as surface accumulation layer, depletion layer or inversion layer is formed on the edge of PN junction. The role of the applied voltage, strong accumulation layer or strong inversion layer of the PN junction edge electric field strength is greater than PN in the node edge will reach the critical electric field than the rated voltage in low breakdown voltage and occurrence of carrier multiplication effect, caused by the concentration of PN junction edge current, power density, high temperature and burning.

4. Wafer crack

Wafer crack is an important intrinsic quality factor for TVS tube short circuit failure. It may be caused by grinding, polishing, sandblasting, slicing the residual deformation and other factors caused by residual stress and after sintering, may also be due to the change of the temperature protection glue and electrode system on chip thermal mismatch stress caused by.

5, impurity diffusion is uneven

The wafer of TVS tube is usually formed by diffusion of boron after a certain diffusion of P or N silicon wafers on a certain resistivity. If the diffusion process appears resistivity axial or radial nonuniform impurity concentration is not uniform throughout the silicon wafers with different breakdown voltages, thereby the device breakdown is the core current uneven distribution of local burn surge after many times.

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