Why are surface mount capacitors prone to breakage or terminal detachment?

Analysis of Reasons for Chip Capacitor Fracture and Terminal Detachment
1、 Manufacturing process defects
1. Improper parameter settings of the surface mount machine
Excessive Z-axis pressure: The vertical pressure of the pick and place head of the surface mount machine exceeds the capacity limit of the capacitor, causing the ceramic body to break.
Position deviation of the pick and place head: not aligned with the center area of the capacitor, causing local stress concentration and forming semi-circular or circular cracks.
Mismatch in pick and place head size: The small diameter suction head concentrates pressure, increases pressure, and causes compression cracks.
2. PCB surface issues
Uneven or fragmented: causing uneven stress on capacitors during placement, resulting in microcracks.
Excessive soldering amount: When the solder height exceeds 50%~75% of the ceramic body, the tensile stress increases during PCB bending, leading to cracks.
3. Welding process defects
Thermal shock: Insufficient preheating or high welding temperature can cause a mismatch in the thermal expansion coefficient of the ceramic body, resulting in thermal shock cracks.
Manual soldering: The soldering iron tip directly contacts the ceramic body, causing local overheating cracks.
2、 Material and structural fragility
1. Characteristics of ceramic materials
Low tensile strength: Ceramic matrix has high compressive strength, but low tensile strength, and PCB is prone to fracture due to tensile stress when bent.
Hidden cracks: Internal microcracks caused by thermal shock or mechanical stress, which propagate over time into visible cracks.
2. Terminal coating issue
Alloying failure: Terminal coatings (such as Cu6Sn5) have poor weldability, resulting in virtual soldering during reflow soldering and easy detachment during subsequent assembly.
Insufficient coating thickness: The alloying area is not covered, resulting in weak adhesion between the solder joint and the coating.
3、 Environmental stress during use
1. Mechanical stress
PCB bending: FR-4 substrate has low stiffness, and capacitors are subjected to tensile stress during bending, resulting in the formation of "Y" - shaped or 45 ° oblique cracks near solder joints.
Splitting stress: The capacitor is too close to the edge of the PCB, causing internal fracture due to shear force during splitting.
2. Thermal stress
Temperature cycling: High frequency temperature changes cause a mismatch in thermal expansion coefficients between the ceramic and electrode layers, leading to interlayer delamination.
Hydrogen absorption: High humidity environments cause ceramic bodies to absorb hydrogen, reducing mechanical strength and inducing cracks.
4、 Design and layout issues
1. Unreasonable layout
Capacitors close to large solder joints: During welding, thermal expansion thrust or contraction tension can cause cracks in the capacitors.
Too close to the edge of the PCB: Under stress during board splitting, the lack of slotting design exacerbates the risk of fracture.
2. Design defects in solder pads
Size does not meet specifications: solder pads that are too small result in stress concentration, while pads that are too large result in uneven distribution of solder.
Unoptimized layout: The orientation of the capacitor is not parallel to the opening, and it experiences maximum tensile stress when bent.
5、 Insufficient quality control and testing
1. Limited detection methods
Resistance tester: can only detect obvious cracks, hidden cracks or terminal virtual soldering are difficult to identify.
Lack of non-destructive testing: X-ray, infrared thermal imaging and other methods are not widely used, resulting in early failure not being detected.
2. Lack of process monitoring
Insufficient monitoring of reflow soldering temperature: The temperature at the terminal position did not meet the requirements (such as 245 ℃~250 ℃ for ceramic boards), resulting in poor fusion of the coating.
Poor quality control of solder: The composition or purity of solder does not meet the standard, which affects the reliability of solder joints.
6、 Solution suggestions
1. Optimize manufacturing processes
Adjust the parameters of the SMT machine: Control the Z-axis pressure, ensure that the pick-up and drop heads are aligned with the center of the capacitor, and use suction heads of matching size.
Improve PCB design: Increase slot depth (≥ 1/3 board thickness), arrange capacitors parallel to the edges, and keep them away from large solder joints.
2. Material and structural improvements
Choose high reliability capacitors such as Murata GRM31CC72A475KE11L X7S dielectric capacitors to enhance bending strength.
Optimize terminal coating: Increase the coating thickness to ensure that the solder covers the alloyed area and improve solderability.
3. Environment and layout optimization
Control PCB bending: Use a high stiffness substrate and limit the amount of solder to 50%~75% of the height of the ceramic body.
Thermal management: Avoid rapid temperature changes, control humidity (<60% RH) during storage, and reduce hydrogen absorption.
4. Enhance quality control
Introduction of non-destructive testing: X-ray inspection for internal cracks, infrared thermography for locating hotspots.
Strict process monitoring: Real time monitoring of reflow soldering temperature curve to ensure that the terminal position temperature meets the standard.
Through the above measures, the problems of chip capacitor breakage and terminal detachment can be systematically solved, improving product reliability and service life.