How to prevent capacitor breakage during production?

Comprehensive solution for preventing capacitor breakage during production
1、 Analysis of the Core Causes of Capacitor Fracture
1. Mechanical stress damage
Improper parameters of the surface mount machine: Excessive Z-axis pressure, offset or mismatched size of the pick and place heads can cause the capacitor to be subjected to local high voltage, resulting in compression cracks (such as center circular or semi-circular cracks).
PCB surface defects: Uneven or fragmented surfaces result in uneven stress on capacitors during placement, leading to the formation of microcracks.
PCB bending and splitting stress: Large capacitors experience "Y" - shaped or 45 ° oblique cracks near solder joints due to concentrated tensile stress; When dividing the board, capacitors near the edge are prone to shear force fracture.
2. Thermal stress impact
Welding process defects: Insufficient preheating or high temperature (such as peak welding temperature exceeding 260 ℃), resulting in mismatch of thermal expansion coefficient of ceramic body and thermal shock cracks.
Risk of manual welding repair: The soldering iron tip directly contacts the ceramic body, causing local overheating and cracking.
3. Material and structural fragility
Limitations of ceramic materials: Class II ceramics such as X7R and X5R have low tensile strength and weak bending resistance; Class I ceramics (such as C0G/NP0) have better performance but higher cost.
Terminal coating problem: Failure of alloying or insufficient coating thickness, resulting in weak adhesion between solder joints and coatings, and easy detachment.
4. Process and layout issues
Unreasonable pad design: Too small size leads to stress concentration, while too large size results in uneven distribution of solder.
Improper layout position: The capacitor is close to the edge of the PCB or a large solder joint, and is affected by shear force when splitting the board.
2、 Targeted prevention and control measures
1. Optimize the SMT process
Adjust the parameters of the SMT machine:
Control Z-axis pressure to avoid excessive vertical impact force.
Ensure that the pick and place head is aligned with the center of the capacitor and use a suction head of matching size (such as using a 1.0mm suction head for capacitor 0603).
PCB surface treatment:
Ensure the PCB is flat, remove debris, and avoid uneven stress when placing capacitors.
2. Improve PCB design and layout
Slotting and edge design:
Increase the PCB slot depth (≥ 1/3 of the board thickness), arrange capacitors parallel to the edges, and keep them away from large solder joints.
Pad size optimization:
The width of the solder pad is capacitor width+0.2mm, with a length covering the end electrode and extending 0.5mm to ensure uniform distribution of solder.
3. Control welding parameters
Temperature and time control:
Preheating temperature 120-150 ℃, wave soldering temperature 260 ℃± 5 ℃, welding time ≤ 3 seconds.
Solder quantity management:
The height of the solder should be controlled at 50% -75% of the height of the ceramic body to avoid excessive increase in tensile stress.
4. Choose high reliability materials
Soft terminal MLCC:
By using flexible end electrodes (such as the Micro capacitive Technology soft terminal series) and absorbing stress through a resin layer, the bending resistance is increased to 8mm-10mm.
Ceramic material upgrade:
Priority should be given to using Class I ceramics (C0G/NP0) instead of Class II ceramics, or using high-strength ceramic formulations (such as X7S medium).
5. Environment and Quality Control
Humidity control:
Storage environment humidity should be less than 60% RH to avoid mechanical strength degradation caused by hydrogen absorption in capacitors.
Non destructive testing:
Introduce X-ray inspection for internal cracks and infrared thermal imaging to locate hotspots, ensuring early detection of problems.
6. Process improvement and fixed plan
Epoxy adhesive fixation:
Coat the bottom of the capacitor with epoxy adhesive (such as GD414) to form a ridge like support, reducing the tensile stress caused by vibration.
Process sequence adjustment:
Assemble other components first, then install high capacitors to avoid damage from external forces during turnover.
3、 Industry case studies and data support
Case 1: A certain automotive electronics manufacturer uses soft terminal MLCC, which increases the bending resistance from 1mm to 8mm and reduces the fracture rate by 90%.
Case 2: By optimizing the size of solder pads and controlling the amount of solder, a communication equipment manufacturer reduced the capacitor fracture rate from 0.5% to 0.01%.
Data: The IPC standard requires a capacitance bending strength of ≥ 1mm, and in actual testing, the soft terminal MLCC can reach 8mm-10mm.
4、 Summary
Through process optimization (SMT machine parameters, welding control), design improvement (PCB layout, pad size), material upgrading (soft terminal MLCC, high-strength ceramics), and environmental control (humidity, non-destructive testing), capacitor fracture problems can be systematically prevented and controlled, significantly improving production yield and product reliability.