Causes and solutions to defects in ceramic chip capacitors
2024-01-09
In the process of mounting the rugged frame and PCBA, and installing the PCBA and the chassis, the warped PCBA or the warped rugged frame is directly or forcibly installed and the PCBA is installed in the deformed chassis. Mounting stress causes damage and fracture of component leads (especially high-density IC such as BGS and surface-mount components), relay holes of multilayer PCB, and inner connection wires and pads of multilayer PCB
For PCBA or reinforcement frames whose warpage does not meet the requirements, the designer should cooperate with the technician to take or design effective "pad" measures at the part of the bow (torsion) before installation.
Among the chip resistor-capacitance components, the probability of defects in ceramic chip capacitors is the highest, mainly as follows:
1. PCBA bow bending deformation caused by wire harness installation stress.
2. The flatness of PCBA after welding is greater than 0.75%.
3. The design of the pads at both ends of the ceramic chip capacitor is asymmetrical.
4. Common pads, welding time is greater than 2s, welding temperature is higher than 245 °C, and the total welding times exceed the specified value for 6 times.
5. The coefficient of thermal expansion between ceramic chip capacitors and PCB materials is different.
6. During PCB design, the fixing hole is too close to the ceramic chip capacitor, resulting in stress during fastening.
7. Even if the pad size of the ceramic chip capacitor on the PCB is the same, if the amount of solder is too much, the tensile stress on the chip capacitor will increase when the PCB is bent; The correct amount of solder should be 1/2~2/3 of the height of the solder end of the chip capacitor
Solution(s):
Defective ceramic capacitors can be screened by C-type scanning acoustic microscope (C-SAM) and scanning laser acoustic microscope (SLAM) for ceramic chip capacitors.
Defective ceramic capacitors can be screened by C-type scanning acoustic microscope (C-SAM) and scanning laser acoustic microscope (SLAM) for ceramic chip capacitors.
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