According to customers reflect the PCB before welding is not for baking, so on-line before the PCB board water can not be removed. PCB board moisture and storage environment, exposure to air before welding time, PCB surface mount before baking in addition to the tide and PCB layers of adhesive materials are related to the moisture absorption, due to the inability to obtain the production of PCB board The adhesive materials used in each layer, it is not possible to identify the moisture absorption of adhesive materials, it can not define the cause of excessive water and the specific causes of the stage. Based on the above analysis, it can be seen that the local curing of the PP layer is insufficient to increase the stress of the PCB in the high temperature and strong heat. The bonding force between the outer layer and the PP layer resin is insufficient, and the copper foil and the resin are reduced. , All of which are related to the laminating process of the board and the properties of the bonding material. PCB board moisture absorption and seriously reduce the PCB’s heat resistance, making the PCB in the reflow water vaporization in the rapid, resulting in failure of the delamination phenomenon.
Analysis and treatment
Visual inspection, is the use of visual equipment or a number of simple instruments, such as stereomicroscope, metallographic microscope or magnifying glass and other tools to check the appearance of the PCB to find the location of the failure and related physical evidence, the main role is to determine the failure and the initial failure mode of PCB failure. Visual inspection Mainly inspect the PCB pollution, corrosion, the location of the plate burst, circuit wiring and failure of regularity, such as the batch or individual, is not always concentrated in a certain area and so on. In addition, there are many PCB failure is assembled into PCBA after the discovery, is not the assembly process and the materials used in the process of failure caused by the need to carefully check the characteristics of the failure zone.
For some can not be visually inspected to the site and the PCB through-hole internal and other internal defects, had to use the X-ray fluoroscopy system to check. X-ray system is the use of different thickness of different materials or different density of X-ray absorption or transmittance of different principles to image. This technique is used more often to check for defects inside the PCBA solder joint, internal defects in vias, and defective solder joint locations for BGA or CSP devices in high-density packages. Current industrial X-ray equipment can achieve a resolution of less than one micron and is being transformed from 2D to 3D imaging equipment. Even five-dimensional (5D) devices are used for package inspection, but this 5D X Optical perspective system is very valuable, very few practical applications in the industry.
Slice analysis is the process of obtaining the PCB cross-section structure through sampling, mosaic, slicing, polishing, etching, observation and a series of means and steps. Through slice analysis, we can obtain the abundant information which reflects the microstructure of the PCB (through hole, plating, etc.), which provides a good basis for the next step of quality improvement. However, the method is destructive. Once sliced, Of the damage; the same time, the method of sample preparation requirements, sample preparation time is longer, the need to train a few technical staff to complete. For detailed slicing procedures, refer to IPC standard IPC-TM-6502.1.1 and IPC-MS-
810. & Lt; / RTI & gt;
Scanning acoustic microscope
Currently used for electronic packaging or assembly analysis is mainly C-mode ultrasonic scanning acoustic microscope, which is the use of high-frequency ultrasonic wave reflection at the material discontinuities generated by the amplitude and phase and polarity changes to the image, the scanning method is along The Z-axis scans the X-Y plane for information. Therefore, scanning acoustic microscopy can be used to detect components, materials and PCB and PCBA internal defects, including cracks, delamination, inclusions and voids. If the scanning acoustic frequency width is sufficient, you can also directly detect the internal defects of the solder joint. Typical scanning acoustic images are characterized by a red warning color, due to the large number of plastic encapsulated components used in the SMT process, from lead into lead-free process, a large number of wet backflow sensitive issues arise , That is, the moisture absorption of the plastic components at higher lead-free process temperature when the internal reflow or substrate layer cracking phenomenon in the lead-free process of high temperature ordinary PCB will often burst phenomenon. At this time, scanning acoustic microscope highlights its multi-layer high-density PCB in nondestructive testing of the special advantages. While the general obvious blasting board is only through the visual appearance can be detected.