Disclosed is a method that uses a restrainer clip with an optimized force to help reduce package co-planarity during the underfill epoxy cure process. Benefits include a solution that can be modified for a variety of packages.

Background

Currently, excessive outgoing co-planarity causes open contact or high resistance between the substrate and the socket. Intensive design of experiments have concluded that the epoxy underfill process in the flip chip technology is responsible for the higher substrate co-planarity, due to high curing temperatures.

General Description

The disclosed method controls and improves package co-planarity by using a restraining clip during the underfill epoxy cure process. The disclosed method improves package co-planarity without affecting the substrate quality or reliability.

Figure 1 shows the restrainer process beginning once the epoxy dispenser module finishes. The standard Integrated Heat Spreader (IHS) link attaches the restrainer clip onto the metal carrier. All substrates are restrained for co-planarity before moving into the epoxy cure oven. Lastly, restrainer clips are removed using the standard IHS removal link before moving to the end of the line process (such as test and ball attach). Figure 2 shows the restrainer clip design, which consists of the restrainer bridge with a leaf spring pressured onto the restrainer clip. Figures 3 and 4 show two different restrainer cl...