1.Introduction to BGA

First of all, we need to understand what BGA is. BGA is a surface mount packaging technology. Its main feature is to form a spherical matrix at the bottom of the chip. Through this matrix, the chip can be electrically connected to the circuit board. This packaging method is widely used in high-performance electronic devices due to its advantages such as small size and good heat dissipation. However, BGA also has its inherent drawbacks. Due to its complex structure, once a problem occurs, it is very difficult to repair. The most common problem among them is BGA cracking. So, why does BGA crack? Generally speaking, the main reasons for BGA cracking are as follows:

(1)Excessive temperature: When electronic devices overheat during operation, the solder joints inside the BGA may break due to the inability to withstand high temperatures, causing the BGA to crack.

(2)Excessive mechanical stress: When electronic devices are subjected to intense shock or vibration, BGA may crack due to its inability to withstand mechanical stress.

(3)Welding quality issues: If the welding quality of the BGA is poor, it may also cause the BGA to crack.

Once the BGA cracks, it will seriously affect the normal operation of electronic devices. Therefore, we need to take some measures to prevent BGA from cracking. For instance, we can regularly clean the dust inside electronic devices to maintain their heat dissipation effect. We can also try to avoid subjecting the equipment to strong impacts or vibrations. In addition, we can also choose reliable welding processes to ensure the welding quality of BGA.

2.Several Key Points of Failure Caused by Mechanical Stress in BGA

(1) Appearance analysis:By observing the appearance of the solder joints, ‌ can be used to determine whether the solder joints are twisted inward,‌can help judge whether they have been subjected to external stress,causing the overall brittle fracture of the IMC. ‌

(2) Stress source analysis:stress may originate from multiple aspects, including typical stress processes on production lines such as SMT process, ‌ panel separation process, ‌ICT, ‌FCT, and ‌screw assembly. In particular,if the stress is concentrated on the FPC pad side,may indicate that the stress is conducted from the FPC side.

Solutions to the problem:For BGA failure caused by mechanical stress, ‌ needs to conduct stress detection on the production line,especially in the design environment,such as heavy adhesive heat sinks, deformation of the heat sink blades of ‌heat sinks, screws around ‌, ‌BGA layout on the edge with crimped components or on the edge of the panel, etc.,requires special attention. In summary, the mechanical stress failure analysis of ‌BGA involves the observation of the appearance of solder joints, the analysis of the source of ‌ stress, and the adoption of corresponding solutions, ‌to ensure the stable operation and long-term reliability of electronic equipment.

3.Testing Methods for Mechanical Stress in PCBA Manufacturing Process

The resistive strain force sensor converts mechanical quantities into electrical signals for measurement by utilizing the resistive strain effect and the conversion function of the bridge circuit, ‌. It has a wide range of application fields and high-precision measurement performance. ‌

The working principle of the resistive strain force sensor is mainly based on the resistive strain effect, that is, when a conductor is mechanically stretched or compressed, its resistance value will change. This type of sensor is usually composed of resistance strain gauges (‌ also known as strain gauges) ‌,these strain gauges are adhered to elastic elements. When an external force acts on an elastic element, the ‌element will produce strain, which in turn causes the strain gauge to deform. This deformation will cause a change in the resistance value of the strain gauge. Through the bridge circuit,can convert the change in this resistance value into a change in voltage or current,and then measure it through the measurement amplification circuit, ‌. Finally, based on the pre-calibrated correspondence between voltage or current and force,can determine the magnitude of the force acting on the elastic element.

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