PCB News - Reliability failure analysis and appearance inspection of SMT electronic assembly

Reliability failure analysis and appearance inspection of SMT electronic assembly

Failure analysis is an important part of the reliability of the electronic assembly process. To carry out the failure analysis of the electronic process, it is necessary to have certain testing and analysis equipment. All kinds of analysis equipment have their performance characteristics, application range and sensitivity. According to the needs and requirements of failure analysis, it is necessary to comprehensively adopt various analysis techniques and analysis methods to determine the location of the failure, the extent of the failure, the cause and mechanism of the failure, and so on. Therefore, failure analysis is related to the analysis theory of many professional knowledge and various analysis devices. Analysis experience also plays a very important role in failure analysis. Failure analysis of electronic assembly process. Investigation and analysis of the failure of dunk process, identification of failure modes, description of failure characteristics, assumptions and determination of failure modes, as well as corrective measures and prevention of new failures.

The failure analysis of the electronic assembly process is to perform post-inspection and analysis of the failure phenomena related to the assembly process, such as solder joints, vias, and traces that are determined to be failed according to the performance failure criterion. The purpose is to find and determine the failures related to the assembly process. The reasons and mechanisms are fed back to the design, manufacturing and users to prevent failures from recurring and achieve the ultimate goal of improving the process reliability of electronic products.

The functions of failure analysis of electronic assembly process are as follows:

1. Theories and methods for improving hardware design, process design and reliable application are obtained through failure analysis.

2. Find the physical phenomenon that caused the failure through failure analysis, and get the reliability prediction model.

3. Provide theoretical basis and practical analysis methods for reliability test (accelerated life test and screening test) conditions.

4. When the process problems encountered during the treatment process, determine whether it is a batch problem, and provide a basis for whether batch recall and scrapping are required.

5. The corrective measures of failure analysis can improve the yield and reliability of electronic products, reduce the failure of electronic products during operation, and obtain obvious economic benefits.

The techniques and methods of electronic assembly process failure analysis mainly include: appearance inspection, metallographic section analysis, optical microscope analysis technology, infrared microscope analysis technology, acoustic microscope analysis technology, scanning electron microscope technology, electron beam testing technology, X-ray analysis technology and Dyeing and penetration test technology, etc. In the application of failure analysis, it is necessary to comprehensively use one or more of these technologies according to the type, phenomenon and mechanism of the failure problem to complete the failure analysis work.

Visual inspection mainly analyzes and inspects appearance defects. The purpose of visual inspection is to record the physical dimensions, materials, design, structure and markings of PCBs, components and solder joints, confirm appearance damage, and detect abnormalities and defects such as pollution. These problems are all It is evidence of errors, overloads and operating errors caused by process manufacturing or application, and this information is likely to be related to failures.

Visual inspection is usually used for visual inspection, and 1.5 to 10 times magnifying glass or optical microscope can also be used. One of the functions of the visual inspection is to verify the consistency of the PCB, components and solder joints of the process failure with the standards and specifications; the second function of the visual inspection is to find the problem points that may cause the failure. For example, if there are cracks on the shell or the glass insulator, it may be that the external environment gas enters the inside of the component to cause electrical performance changes or corrosion. If there are foreign objects between the outer leads, the foreign objects may cause a short circuit between the leads. Mechanical damage on the PCB surface may cause the PVB trace to break and cause an open circuit.

Since failure analysis may involve destructive analysis work such as slicing and de-encapsulation, the object of visual inspection no longer exists. Therefore, detailed records should be made during visual inspection, and it is best to take some pictures. As a preliminary inspection, you may lose valuable information if you handle the test piece casually before checking the appearance. As part of this visual inspection procedure, firstly, all its information marks should be recorded, that is, the manufacturer name, specification, model, batch, date code and other information of the PCB manufacturer and component manufacturer should be recorded in detail. Secondly, special attention should be paid to the inspection of the following aspects.

1. Mechanical damage: cracks, scratches, and defects from the pins, roots and sealing seams of the electronic components; mechanical damage marks on the solder joints and the surface of the PCB.

2. Device sealing defects: from the joints between the pins of electronic components and glass, ceramics and plastics, as well as the adhesion parts and sealing seams of the roots.

3. Device pin coating defects: uneven coating, bubbles, pinholes and rust from the surface of electronic components.

4. Pollution or adhesions on the PCB surface: mainly from the processing process.

5. Thermal damage or electrical damage of the device.

6. PCB delamination and bursting, etc.

7. The surface treatment layer of PCB is abnormal.

8. Whether the solder joints have remelted or cracked.

In the reliability design, clear control requirements for production, storage, storage, and transportation should be put forward in the process documents. For suspicious parts, further inspections must be performed with measuring instruments that can obtain information. The stereo microscope has a high degree of microscopic observation and a simple low magnification, the magnification between the two (approximately several times to 150 times). The high-magnification metallurgical microscope can be used not only for bright field observation, but also for dark field observation and differential interference observation. The magnification can be from tens of times to about 1500 times. In addition, if it is necessary to make the viewing scene deeper, there is a scanning electron microscope with a magnification of tens to hundreds of thousands of times and a resolution of from a few mm to about 15 nm. It is an indispensable device for observing specimens with fine structures. All important information should be photographed and recorded using the microscope and its photographic accessories.

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