Non-Surface Contact Approach for Device Flip

Abstract

What approaches are available for the flip of devices prior to die bond when the top wafer surface cannot be touched? Conventional 180 degree flip on a chip by chip basis during the die sort process requires rubber vacuum pick-up tools to touch both the top and bottom surfaces of device during the required transfers from one pick-up tool to another. However, for a growing number of applications ranging from medical devices, imaging sensors, MEMS, and bumped die used in flip chip applications, touching the sensitive top surface of a device is not desirable, while the need to flip the device remains. Factors to be evaluated in seeking a successful invert process without top surface contact include throughput, wear resistance of tooling, device and tooling material properties, and risk for top surface damage (yield). A pick and place process using an edge gripper instead of vacuum pick-up tip allowed for no contact of device surface but did not provide a robust device flip process due to imprecise device positioning. However, a non-surface contact approach to protect surface features was able to be achieved by using a radius/channel style pick-up tool to pick the die from the wafer and deposit onto a die inverter arm with vacuum surface contact pick-up tool to hold the device in place from the bottom with vacuum. This arm then rotated 180 degrees to place the device into a second radius/channel style pick-up tool, with the tool touching two of the top edges only. Based on the radius design of the channel style tools, the die protruded past the face of the tool, allowing it to be repicked by the main pick-up tool and then subsequently placed to the output. This non-contact approach was found to successfully protect the device surface during the flip. Future research will focus on improving precision of edge grippers so they may also be a potential solution, as well as the testing of the radius/channel pick-up tip approach for applicability with thin devices.