1. Overview The modern electronic assembly process is mainly based on PCBA. Therefore, the research on the reliability of the electronic assembly process is also mainly based on the failure phenomenon that occurs on the PCBA.

The failure phenomena of PCBA can be divided into two categories: those that occur during production and those that occur during user service. (1) Failure phenomena of PCBA (internal or surface) during the manufacturing process: such as bursting, delamination, surface excess, ion migration and chemical corrosion (rust), etc. (2) Various failure modes and failure manifestations on the PCBA during the user's service period: such as virtual welding, solder joint brittleness, microstructure deterioration in solder joints, and reliability deterioration.

Second, the purpose of failure analysis Failure analysis is the process of determining the cause of the failure, collecting and analyzing data, and summarizing the process of eliminating the failure mechanism that causes the failure of a specific device or system.

The main purposes of failure analysis are to:

find out the cause of the failure;

Trace back the unfavorable factors in process design, manufacturing process and user service;

Propose corrective actions to prevent the recurrence of failures. Through the accumulated results of failure analysis, we continuously improve the process design, optimize the product manufacturing process, and improve the usability of the product, so as to achieve the purpose of comprehensively improving the reliability of the product.

3. PCBA failure rate curve
1. The PCBA product failure rate curve includes the following three levels, namely:

Component failure rate curve: as shown in Figure 1(a). Through the forced aging of components before they leave the factory, the failure rate of components during the service period of users can be effectively reduced.

Component supply life curve: as shown in Figure 1(b). It describes the service life of a component after it reaches the user, and it has a significant impact on the reliability of the constituent system.

PCBA assembly failure rate curve: as shown in Figure 1(c). It is jointly influenced by SMD incoming material life, SMD assembly life and solder joint life. At this time, the life of the PCBA basically depends on the life of the solder joints. Therefore, ensuring the welding quality of each solder joint is a key link to ensure the high reliability of the system.

Figure 1 PCBA product failure rate curve

2. Typical transient failure rate curve for a PCBA. The typical instantaneous failure rate of PCBA is referred to as the typical failure rate of PCBA. Instantaneous failure rate is the probability of failure in unit time after PCBA works to time t. The typical instantaneous failure rate curve of PCBA is composed of three areas: premature aging area, product service area and aging area, as shown in Figure 2.

Figure 2 Typical transient failure rate curve of PCBA

4. Levels, principles and methods of PCBA failure analysis
1. The level of failure analysis In the production and application of electronic products, the control and analysis of PCBA and solder joint failure are basically the same as the reliability control and analysis methods of other systems, as shown in Figure 3.

2. Principles of Failure Analysis - The Basis of Mechanistic Reasoning

site information;

Retest (failure mode confirmation) result analysis;

The failure mechanism of the specific process and structure of the object;

failure mechanisms related to specific environments;

The relationship between failure mode and failure mechanism;

Long-term accumulation of relevant knowledge and experience.

Figure 3 Reliability Engineering Control

3. Failure Analysis Method The method adopted in PCBA failure analysis, some experts in the industry have summarized a good analysis model, as shown in Figure 4.

Figure 4 PCBA failure analysis method