PCB circuit board quality inspection and the lack of SMT technology
PCB board quality inspection
（1） X-ray search
After assembly, X-ray can be used to see BGA bottom hidden solder bypass, open circuit, insufficient solder, excessive solder, ball drop, loss, popcorn, and the most common void and other deficiencies. The following table shows the occasions and effects of various inspection methods.
（2）Scanning ultrasonic microscopy
The finished panel can be scanned by SAM to check various hidden conditions, and the packaging industry is used to detect various voids and delaminations inside. This SAM method can be divided into three scanning methods: A < spot-like), B < linear) and C < planar).
（3）look at your facial appearance
The method can be used for the lateral visual inspection of optical magnification for small objects in a narrow corner area. BGA ball foot welding can be used to check the situation of the outer ring. This law is to use the prism rotate 90 ° type of lens focus, again tie-in high resolution CCD to transmit images. The multiplier is between 50X and 200X. Visible solder spot conditions are: overall appearance, tin eating, solder shape, solder surface patterns, flux residue and other shortcomings. However, this method is invisible to the inner ball of BGA, which needs to be directly observed through the extremely fine fiber tube endoscope. But good ideas are not practical, expensive and easily broken.
（4）measuring the strength of screwdriver
Using the torsional moment of the special screwdriver, the solder joint is unjacked and torn to see how strong it is. Although this method can find the welding spot floating, interface splitting, or welding body cracking and other defects, but it is not good for the thin plate.
This method not only needs all kinds of facilities for sample preparation, but also needs precise skills and abundant knowledge of interpretation, so as to find out the real problem from the bottom up.
（6）infiltration and dyeing (commonly known as red ink)
The sample was dipped into a dilute solution of a special red dye, and the cracks and holes in the solder were infiltrated by their capillaries and then dried. After each test ball foot is forced open or pry open, can check section on the presence of erythema, and see the integrity of the solder? Dye and Pry, as the method is also known, can be separately prepared with fluorescent dyes, which will be easier to see the truth in ultraviolet light.