Method and Principle of BGA Welding Inspection

March 22, 2023

A large number of applications of BGA package chips force us to consider BGA solder reliability test.BGA package types are: PBGA (plastic BGA), CBGA (ceramic BGA), and TBGA (carrier BGA).The main characteristics required in the packaging process are: reliability of the packaging assembly and thermal matching performance of the PCB, coplanarity of the solder balls, sensitivity to thermal humidity, alignment through the edges of the package, and handling economy.It should be noted that the solder balls on the BGA substrate are formed by high temperature solder balls (90 Pb/10 Sn) or by an injection on ball process.Solder balls may be missing or missing, or over-formed, too small, or occur.Solder balls and even defects.Therefore, it is necessary to test and control some indicators of BGA quality after soldering.At present, the commonly used BGA inspection technologies are electrical testing, boundary scan and X-ray inspection.

1) Electrical test.Traditional electrical testing is the main method to find open circuit and short circuit defects.The purpose of the is to make the actual electrical connections at prefabricated points on the board so that the interfaces that allow signals to flow into the test board and into the ATE can be combined.If the printed circuit board has enough space to set up test points, the system can quickly find open circuits, short circuits, and faulty components.The system can also check the functionality of the component.The test instrument is usually controlled by a microcomputer.When inspecting different PCBs, corresponding needle beds and software are required.For different test functions, the instrument can provide corresponding test work units.For example, diodes are tested with DC level cells, transistors are tested with AC cells, capacitors, inductors, and low value capacitors and inductors, high resistance resistors with high frequency signal cells 2) Boundary Scan Detection.Boundary-scan technology solves some of the search problems associated with complex components and packing density.Using boundary scan technology, each IC component is designed with a series of registers that separate the function lines from the sense lines and record the detected data through the component.The test path checks for open and short circuits at each solder joint on the IC assembly.Based on the boundary scan design of the detection port, each edge is provided with a path through the edge connector, thereby eliminating the need for a full node lookup.Electrical testing and boundary scan testing are primarily used to test electrical performance, but not good solder quality.In order to improve and guarantee the quality of the production process, it is necessary to find other methods to detect the quality of the weld, especially the invisible weld.3) X-ray test.The effective way to detect the quality of invisible solder joints is X-ray inspection.The test method is based on the idea that X-rays cannot pass through solder in the same way as copper, silicon and other materials.In other words, the X-ray perspective shows the density distribution of the weld thickness, shape, and mass.Thickness and shape are not only indicators of long-term structural quality, but also good indicators for measuring open, short defects and insufficient welding.This technology helps to collect quantitative process parameters, which helps to reduce the cost of new product development and shorten the time to market.The automated X-ray layering system uses 3D analysis.The system can inspect single-sided or double-sided surface-mount boards without the limitations of conventional X-ray systems.The system defines the area and height of the weld to be inspected by the software and cuts the weld into different sections to establish a complete cross-sectional view of all inspections.The above test methods are common test methods for plant emissions operations, but for BGA repairs in general, these test techniques are not used.Only maintenance personnel can observe the boundary of the chip around the chip and rely on experience and feeling to operate.


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