Method and principle of BGA welding inspection

January 30, 2023

The extensive application of BGA encapsulated chips forces us to consider the reliability testing of BGA welding. BGA package types include PBGA (plastic BGA), CBGA (ceramic BGA) and TBGA (carrier BGA). The main characteristics required during the packaging process are: reliability of the packaging components; Thermal matching performance with PCB; Coplanar welding ball; Sensitivity to heat and moisture is: alignment through packaging edges, and handling economic performance. It should be noted that the solder ball on the BGA substrate is formed by a high temperature solder ball (90Pb / 10Sn) or by an injection process on the ball. The solder ball may be missing or missing, or over-formed, too small or occurring. Solder ball is even, defect. Therefore, it is necessary to test and control some indexes of BGA quality after welding.

At present, the commonly used BGA detection techniques include electrical testing, boundary scanning and X - ray detection

1) Electrical test. Traditional electrical testing is the main method to find open circuit and short circuit defects. The purpose is to make the actual electrical connections at the prefabricated points of the circuit board so that the interfaces that allow signals to flow into the test board and into the ATE can be assembled. If the printed circuit board has enough space to set up test points, the system can quickly find open, short, and faulty components in,. The system can also check the function of the components. Test instruments are usually controlled by microcomputers. When testing different PCBS, the corresponding needle bed and software are required. For different test functions, the instrument can provide corresponding test work units. For example, test diode and transistor with DC level unit; Test capacitor and inductor with AC unit; Low - value capacitors and inductors and high - resistance resistors are tested by high - frequency signal units

2) Boundary scan detection. Boundary scanning technology solves some search problems related to complex components and package density. Using boundary scanning technology, each IC component is designed with a series of registers that separate the functional lines from the sensing lines and record the detected data through the component. Test path Check the open and short circuit of each solder joint on the IC component. A boundary scan design based on the detection port, where each edge is set with a path through the edge connector, eliminates the need for a complete node lookup. Electrical testing and boundary scan testing are mainly used to test electrical properties, but not good weld quality. In order to improve and guarantee the quality of the production process, other methods must be found to detect the quality of welds, especially invisible welds. 3) X-ray test. X-ray inspection is an effective method to detect the quality of invisible solder joints. The test method is based on the idea that X-rays cannot pass through solder as well as materials such as copper and silicon. In other words, the X-ray perspective shows the density distribution of weld thickness, shape and mass. Thickness and shape are not only indicators of long-term structural quality, but also good indicators for measuring open circuit and short circuit defects and welding deficiencies. This technology helps to collect quantitative process parameters, reduce the cost of new product development and shorten the time to market. An automated X-ray layering system uses 3D analysis. The system can detect single - or double-sided surface mount panels without the limitations of conventional X-ray systems. The system uses software to define the area and height of the solder joints to be inspected, and cuts the solder joints into different sections to create a complete cross-sectional view of all the inspections.

The above test methods are commonly used for plant discharge operations, but they are not used for general BGA remediation. Only maintenance personnel can observe the boundaries of the chip around the chip and rely on experience and feeling to operate.

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