Fracture failure analysis: fracture causes and solutions of SMT chip components

Date：2021-10-22 14:35:00Views：1635

Fracture refers to the phenomenon that metal or alloy materials or mechanical products are divided into several parts under the action of force. It is a dynamic change process, including crack initiation and propagation. Fracture failure refers to the failure of mechanical equipment products caused by the fracture of mechanical components to complete the functions required by the original design. Fracture failure types are as follows:

① Cleavage fracture failure; ② Dimple fracture failure; ③ Quasi cleavage fracture failure; ④ Fatigue fracture failure; ⑤ Creep fracture failure; ⑥ Stress corrosion fracture failure; ⑦ Intergranular fracture failure; ⑧ Brittle fracture failure of liquid or solid metal; ⑨ Hydrogen embrittlement fracture failure; ⑩ Slip separation failure, etc.

Test purpose: to find out the cause of fracture and analyze the fracture failure, first understand the failure analysis procedure. Because most mechanical components break and fail during operation, whenever a part breaks and damages, it has a very close relationship with other parts, surrounding environment and operators. When finding the cause, find out the main cause of damage from the factors such as design level, material quality, processing status, maintenance, assembly accuracy, working environment, service conditions and operation methods, analyze and judge according to the cause, mechanism, type and stage of damage, and formulate improvement measures.

The fracture process is a dynamic process, so it is difficult to observe and analyze the fracture directly; The fracture is the static response of fracture. If the fracture is carefully observed and analyzed, the cause and mechanism of fracture can be found out. Because the fracture truly reflects the whole process of mechanical component fracture and the initiation and propagation process of mechanical component crack, fracture analysis is an important means of mechanical component fracture failure analysis. In order to obtain better analysis results, this analysis method must be supplemented by a series of other inspection methods, such as nondestructive testing, mechanical property test, metallographic inspection, chemical analysis, X-ray analysis, fracture toughness test, electronic energy spectrum analysis, simulation test, etc. Finally, the above analysis and test results and data are comprehensively analyzed, the improvement measures are put forward, and the failure analysis report is written.

Causes of fracture of SMT chip components:

1. For MLCC capacitors, their structure is composed of multilayer ceramic capacitors, so they have weak structure, low strength, strong heat resistance and mechanical impact, which is particularly obvious in wave soldering.

2. During SMT chip processing, the absorption and placement height of the z-axis of the chip mounter, especially for some chip mounters without z-axis soft landing function, depends on the thickness of the chip element rather than through the pressure sensor, so the tolerance of the component thickness will lead to cracking.

3. After welding, if there is warping stress on PCB, it is easy to cause component cracking.

4. PCB stress in splicing will also damage components.

5. Mechanical stress during ICT test leads to equipment rupture.

6. The stress during assembly will cause damage to the MLCC around the fastening screw.

Solutions for SMT chip components:

1. Carefully adjust the welding process curve, especially the heating speed should not be too fast.

2. During placement, please ensure proper placement of machine pressure, especially for MLCC and other brittle devices installed on thick plates, metal substrates and ceramic substrates.

3. Pay attention to the placement method and shape of the cutter.

4. The warpage of PCB, especially after welding, shall be specially corrected to avoid the influence of stress caused by large deformation on the device.

5. Avoid high stress areas of MLCC and other equipment during PCB design.

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