Uniqarta, Inc. (www.uniqarta.com) has developed a process for flip-chip assembling ultra-thin (<50 µm) dies. This patent-pending process involves a material preparation step and a die placement step.
Uniqarta’s material preparation step involves thinning a commercial off-the-shelf device wafer to the desired thickness, bonding a support wafer (“handle wafer”) to the device wafer, and dicing the device/handle wafer combination to create individual die/handle stacks mounted on standard UV dicing tape. Each die/handle stack has a thickness comparable to a standard die and can therefore be handled and placed using standard die bonder equipment. Each die handle is flip-chip assembled by a die bonder onto a substrate. Since the handle is bonded to the die using a heat-sensitive adhesive, it is released during the die bonder’s thermal cure cycle when the die is bonded to the substrate. The handle is subsequently removed leaving behind only the ultra-thin die. a heat release adhesive.
In this example the thin die is 2.6 mm X 2.6 mm X 100 microns thick silicon attached to a 280 micron thick handle. Die as thin as 15-20 microns or less have been bonded using this method. . The dicing tape is Nitto DU300 UV tape. The die bonder is a Semiconductor Equipment Corp Model 860. The overall process is based on Uniqarta’s “FlexChipTM” technology.
The video shows the bonding process beginning with transfer stamping conductive adhesive from a manually doctored tray to the substrate. The bonder is equipped with a dual tool head. One tool is for transfer stamping. The second tool which is heated is for bonding the die. The 860 automatically brings the appropriate tool into position. After stamping conductive adhesive onto the substrate the die stack is aligned and lowered to a specific bond load.
Once the die stack is at bond load the epoxy will be cured and the temporary bond will be released. The bond tool is slowly retracted taking the handle away for disposal and leaving the bonded die on the substrate. All bonder settings including sequence, cycle time, bond load, temperatures and tool velocity are defined in the Model 860 macro program. The images in the video were captured by the optional 860 side view camera.
The demonstrated process shows a method by which SEC’s die bonder can be used to place and adhesively bond ultra-thin die using Uniqarta’s FlexChip process.
The SEC Model 860 Die bonder used in this application was equipped with the following options:
· High resolution dual imager vision system
· Dual tool
· Manual dipping station
· 2” rapid heatstage
· Dual goniometer stage leveling
· Side view camera