BGA quality inspection method: common welding defects or failures in welding

Date：2021-09-26 11:51:00 Views：3376

As the source power of the rapid development of modern electronic information technology industry, chip has been widely penetrated and integrated into every field of national economic and social development. It is an important support for the digital economy, information consumption and even the long-term development of the country. BGA is an indispensable part of electronic components, but voids often occur in BGA packaging and welding. The generation of voids is mainly due to the bubbles generated by the organic matter in the flux after high-temperature cracking, resulting in the gas being surrounded in the alloy powder to form voids. The generation of voids will affect the use effect of the product to a certain extent, For example, the welding cavity is easy to cause poor contact to electronic components in the later use process and affect the service life. Today, let's introduce several common detection methods for BGA Solder joint defects or failures to help you deeply understand and make better judgment.

Non destructive testing method

1、 Visual inspection of solder joint quality

Visual inspection can be carried out in the whole production process of electronic products. Observe the solder joint through a high-power magnifying glass to preliminarily detect whether there are obvious defects in the solder joint from the appearance.

Objective: To observe the solder joint simply, quickly and directly, whether there is continuous welding on the outside of the solder joint, the condition of the surrounding surface, etc.

However, visual inspection has great limitations and can only be used as a preliminary judgment without inspection equipment. It is impossible to judge whether there are other defects in the solder joint or whether there are holes on the surface of the solder joint.

2、 X-ray inspection of solder joint quality

X-ray detection is a nondestructive physical perspective method, that is, without damaging the chip, X-ray perspective components are used to detect the internal packaging of components, such as bubbles, cracks, binding line abnormalities, etc.

2DX-ray

For the position where the sample cannot be detected visually, the change of light intensity after X-ray penetrating substances with different densities can be recorded to form an image to show the internal structure of the object to be tested, and then the problem area inside the object to be tested can be observed without damaging the object to be tested.

Objective: through X-ray scanning, we can observe quickly and effectively, distinguish BGA welding defects such as empty welding and false welding, analyze the internal displacement of BGA and circuit board, bridge erection and short circuit, etc.

However, 2DX ray has some limitations. It can only observe two-dimensional plane images. The principle is to display the three-dimensional physical samples on the two-dimensional display screen for imaging. For products with complex structure, the information in different depth directions is overlapped, which is very easy to be confused. For example, when there are components on different surfaces at the same position, the shadows formed by solder will overlap, affecting the accuracy of test results. Therefore, it is often used for preliminary and rapid judgment for products with complex structure.

3DX ray (CT scan)

3DX ray well solves the limitations of 2D X-ray, can present three-dimensional images, has high density resolution and high spatial resolution, and can simulate tomography images. The defect problem of BGA Solder joint can be solved perfectly.

Objective: it can clearly and accurately observe the welding quality and structural defects of BGA Solder Joints, and show the shape, position and size of defects in the welding interior.

In the process of detecting solder joint defects by the above non-destructive detection methods, both visual detection and 2DX ray have limitations, while 3DX ray (CT scanning) is the most advanced non-destructive detection technology at present, which can perfectly solve the problem of solder joint defects, but the test cost is expensive. If the product can be damaged, the next destructive detection method can be used for testing.

Destructive testing method

3、 Red ink test to detect the quality of solder joints

Red ink test is applicable to verify the welding of BGA and IC on printed circuit board. By observing and analyzing the solder joint dyeing of PCB and IC components, the welding cracking is determined.

The principle of red ink test is to use the permeability of liquid. Place the solder joint in the red dye, let the dye penetrate into the solder joint crack, forcibly separate the solder joint after drying, and judge whether the solder joint is broken by observing the interface color state at the crack. In short, it is divided into five steps: cutting → infiltration → drying → separation → observation.

Objective: Generally speaking, the soldering phenomenon of all tin balls under a whole BGA can be seen in the red ink test. It is a common analysis method of electronic assembly welding quality, which can investigate whether there are defects such as false welding, false welding and cracks in the welding process of electronic parts.

4、 Slice analysis solder joint quality

Slice analysis is an important technology for PCB / PCBA failure analysis. Slice analysis is more time-consuming than red ink test. The process of slice analysis: sampling → cleaning → vacuum inlay → grinding → polishing → micro etching (if necessary) → analysis. The quality of the slice will directly affect the accuracy of the confirmation of the failure part, so the ability of the inspectors is very high.

Slice analysis

Objective: it can not only be used to check the internal cavity of PCBA solder joint, interface bonding condition, wetting quality evaluation, but also to test the quality of circuit board.

SEM & EDS

On the basis of slice analysis, in order to further understand the causes of solder joint defects, SEM & EDS can be used to analyze the failure causes of solder joints.

Finally, how to improve the BGA welding process in the production of circuit board products? We have provided the following measures for your reference and exchange:

Improvement measures of BGA welding process

① The circuit board and chip shall be preheated to remove moisture. The BGA packaged on the tray shall be baked at 120 ℃ for 4 ~ 6h before welding.

② Clean the pad and remove the flux and solder paste left on the PCB surface.

③ Fresh auxiliary materials must be used to apply solder paste and flux. The solder paste must be stirred evenly. The viscosity and amount of solder paste must be appropriate to ensure no continuous welding during solder melting.

④ During chip placement, each solder ball on BGA chip must be aligned with each corresponding solder joint on PCB.

⑤ During reflow soldering, the heating temperature and time of each zone shall be correctly selected, and the heating speed shall be paid attention to. Generally, before 100 ℃, the maximum heating rate shall not exceed 6 ℃ / s, after 100 ℃, the maximum heating rate shall not exceed 3 ℃ / s, and in the cooling area, the maximum cooling rate shall not exceed 6 ℃ / s. Because too high heating and cooling rate may damage PCB and chip, this damage is sometimes invisible to the naked eye. At the same time, for different chips and solder pastes, different heating temperature and time should be selected; For the non washable solder paste, its activity is lower than that of the non washable solder paste. Therefore, the welding temperature should not be too high and the welding time should not be too long to prevent the oxidation of solder particles.

⑥ During PCB design, the pads of all solder joints of BGA on PCB should be designed to be the same size. If some vias must be designed below the pads, appropriate PCB manufacturers should also be found to ensure that all pads are the same size and have the same amount of solder on the pads and the same height.

The above is the related content of "BGA quality detection method" brought by the core detection. Through this article, I hope it can be helpful to you. If you like this article, you might as well continue to pay attention to our website, and we will bring more wonderful content later. If you have any needs related to the inspection and testing of electronic products, please call Chuangxin testing, and we will serve you wholeheartedly.