How to detect BGA post weld defects?

The use of ball grid array packaging (BGA) electronic components brings a problem to the quality inspection and control department: how to detect the installation quality after welding?

After such devices are welded, it is impossible for the inspectors to see the part under the packaging material, which makes visual inspection of welding quality become empty talk. Other new technologies such as chip on board (OOB) and flip chip installation also face the same problems. And similar to BGA devices, the RF shielding of QFP devices also blocks the line of sight, so that the visual inspector cannot see all the solder joints. In order to meet users' requirements for reliability, the problem of invisible solder joint detection must be solved.

The detection ability of optical and laser systems is similar to that of visual inspection, because they also need the line of sight to determine the detection results. Even if the QFP automatic inspection system AOI is used, the welding quality cannot be determined because the welding points cannot be seen. In order to solve these problems, other detection methods must be sought. At present, the most commonly used production testing technology is X-ray nondestructive testing.

X-ray testing method is the density distribution of welding thickness, shape and quality that can be displayed by X-ray testing results. Thickness and shape are not only indicators of long-term structural quality, but also good indicators in measuring open circuit, short circuit defects and insufficient welding. This technology helps to collect quantitative process parameters and detect defects. In today's era of production competition, these supplementary data help to reduce the cost of new product development and shorten the time to market.

The detection principle of X-ray detection equipment is that X-rays are generated by a micro focus X-ray tube, pass through a glass window in the tube shell, and transmit to the test sample. The X-ray absorptivity or transmittance of the sample depends on the composition and ratio of the material contained in the sample. The X-rays passing through the sample bombard the phosphorus coating on the x-ray sensitive plate and excite photons. These photons are then detected by the flat panel detector, and then the signal is processed and amplified by the computer for further analysis, and the final output is displayed on the screen.

Different sample materials have different penetration of X-rays, so they have different transparency. The processed gray-scale image shows the difference of the density or material thickness of the inspected object.

X-ray testing equipment is a necessary means to detect BGA post weld defects. It can effectively detect internal defects without damaging the package appearance, and provides an effective guarantee for the quality development of electronic manufacturing.