Fine pitch high pin count AlN LGA package

This work studied ways to reduce a flip chip assembling cost. It was hypothesized that low cost assembling would be achieved by lowering the bump height on a chip and by eliminating an underfilling work which is incorporated to assure solder joint reliability. Among several candidates for package materials such as plastic, metals, and ceramics, aluminum nitride (AlN) was examined to reduce a flip chip assembling cost. In this report, an AlN LGA (land grid array) package was manufactured and evaluated on its flatness of a chip attaching area and on electrical characteristics. Flatness was found to be low (5.5 mu m). The package showed possibility to use a chip with low bumps. AlN also showed high solder joint reliability with a low bump of 27 mu m m. This is because coefficient of thermal expansion (CTE) of AlN is close to that of silicon (Si). It was found that an AlN package was a possible candidate for establishing a lower bump flip chip assembly compared with a package made of plastic or alumina. The plating technology used in this AlN package was proved to be applicable for a fine pitch flip chip assembly.