BGA(Ball GridAray) has a variety of structures, such as laminated BGA(p-bga), inverted BGA(f-bga), loaded BGA(t-bga) and ceramic BGA(c-bga).The process features are as follows:
1) the BGA pin (welding ball) is located under the package body, and the welding condition cannot be directly observed by naked eyes, so X-ray equipment must be used for inspection.
2)BGA is a humidity sensitive device. If it absorbs moisture, it is prone to deformation and aggravation, "popcorn" and other defects. Therefore, it must confirm whether it meets the process requirements before pasting.
3) BGA is also a stress sensitive device. The stress concentration of the four-corner solder joint makes it easy to be broken under the action of mechanical stress. Therefore, when designing PCB, it should be placed away from the edge of the panel and the mounting screws as far as possible.
Overall, BGA welding craft is very good, but there are a lot of special welding problems, mainly related to BGA encapsulation structure, especially for thin FCBGA and PBGA, due to the layered structure of the packaging, will happen in the process of welding deformation, the general called this occur in the welding deformation in the process of dynamic deformation, it is the main cause of BGA assembly of bad.
Dynamic deformation occurs in the fc-bga heating process because BGA is a layered structure and the CTE of each layer of materials is quite different.
BGA welding is significant in setting the temperature curve of reflow welding.Due to the large size and heat capacity of BGA, it is generally used as the key monitoring object for setting the reflow welding temperature curve.
BGA welding defect spectrum is closely related to package structure and size. Common defects can be roughly summarized as follows:
(1) for BGA (or CSP) with ball spacing < 1.0mm, the main welding defects are ball and socket, non-wetting open welding and bridge connection, which have been introduced in section 4.3.
(2) due to its dynamic deformation characteristics, PBGA and FBGA with > and 1.0mm spacing between the welding balls are prone to the unique low-probability welding defects such as non-wetting open welding, non-wetting cracking and shrinkage tin fracture.These welding defects are not easy to be found by conventional inspection, easy to flow to the market, with a great reliability risk.
(3) BGA with a size greater than 25mmx 25mm is likely to cause stress fracture and pitting crack of solder joints due to its large size.