In November 1895, the German physicist W.C. Roentgen discovered X-rays by chance. One day he was doing an experiment on cathode rays. He wrapped the discharge tube in black paper and turned it on. At this time, he found that the paper coated with fluorescent substances nearby gave off a fuzzy light. Roentgen replaced the black paper with other things to investigate the transmittance of the unknown rays coming out of the discharge tube (he called those rays X-rays). In front of X-rays, the paper became very transparent, and the fluorescent screen still glowed brightly on the side of the 1,000-page book. Putting tin foil or lead glass in front of the fluorescent screen will cause shadows. Put your hand in front and look at it, and the bones of the hand will appear on the screen. Since it was not known at the time what the ray was composed of, but the ray could sensitize the sealed film and ionize the gas, Roentgen named this mysterious ray X-ray (X-ray).

 

 

        The characteristics and diffraction phenomena of X-ray continue to lay an important foundation with the efforts of Laue, WH Bragg and WL Bragg and other scholars, not only becoming an important inspection tool in medicine and industry, It is also an indispensable research tool in crystallography and solid-state physics.

 

1. X-ray applications

 

1) Medical examination and treatment Use X-ray penetration, photosensitivity, and biological effects for medical examination and treatment. Use the penetrating effect to examine abnormalities in the human body Use the photosensitive effect to make medical films Tumor cells Use biological effects to inhibit or kill tumor cells

 

2) Industrial non-destructive testing Use the penetrability of X-rays to perform non-destructive testing of the quality of industrial products or projects. A certain die-casting part uses penetrability to inspect the internal defects of the die-cast part. A certain engineering welded steel plate uses penetrability to inspect the welding quality

 

3) Security inspection Use the penetrability of X-rays to conduct convenient and quick inspections of articles that endanger the safety of public places or special occasions or related prohibited items. Baggage inspection at a certain bus station Check the source of explosives and other contraband in the baggage

 

4) Micro-focus inspection Use the penetrability of X-rays to analyze the quality of semiconductor manufacturing and packaging, and inspect the quality of soldering in the electronic assembly industry

 

2. 2.5 D X-Ray detects the principle of SMT BGA solder joint Open

 

• If the solder ball is well welded on the top and bottom, the X-ray will produce a double-sided ellipse image due to the thickness difference when it penetrates, as shown in the figure below

• If the solder ball and the solder paste of the PC board are not connected, there will only be an elliptical image on the screen

• This phenomenon needs to be observed with X-RAY transmittance, intensity and control image software

 

3. How does 2.5D X-ray judge BGA open

      As shown in the figure below, it is judged by the shape of the image.

picture

 

        2.5D X-Ray judgment BGA Open case description

        The following 2 pictures can be compared to see the imaging situation of BGA Open.

 

4. Instance description of detected images

 

1) Solder balls normally soldered

 

2) Open tin ball

 

3) Poor welding of BGAPAD

 

Poor welding of BGAPAD

 

PCBPAD poor welding OPEN

 

5. Classic failure cases