Spherical contact display, one of surface mount packages. Spherical bumps are made on the back of the printed substrate instead of pins, LSI chips are assembled on the front of the printed substrate, and then sealed with molding resin or potting. Also known as bump display carrier (PAC). There can be more than 200 pins, which is the package of multi-pin LSI. The package can also be made smaller than QFP (quad pin flat package). For example, a 360-lead BGA with a pin center distance of 1.5mm is only 3 1mm square; A 304-pin QFP with a center-to-center distance of 0.5 mm is 40 mm2. And BGA doesn't have to worry about pin deformation like QFP. Developed by Motorola, the software package was first used in portable phones and other devices, and may be popularized in personal computers in the United States in the future. At first, the center distance between the pins (bumps) of BGA was 1.5mm, and the number of pins was 225. Now some LSI manufacturers are developing 500-pin BGA. The problem of BGA is visual inspection after reflow soldering. It is not clear whether this is an effective visual inspection method. Some people think that because of the great distance between welding centers, the connection can be regarded as stable and can only be handled through functional inspection. Motorola Company of the United States calls the package sealed with molding resin OMPAC and the package sealed with potting method GPAC (see OMPAC and GPAC).