FlexChip Ultra-Thin Die Assembly


The size, thickness, and flexibility of today’s electronics devices is limited by thick and rigid ICs. This constrains manufacturers’ ability to miniaturize such devices and more intimately integrate them with real-world items that are often thin, curved, or flexible. The electronics industry has been progressing to ever thinner ICs. However, they have now hit a limit below which existing handling, placement, and interconnection solutions don’t work. An alternate method of accommodating ultra-thin ICs is required. Uniqarta's FlexChip technology transforms off-the-shelf semiconductor dies or wafers into ultra-thin ICs assembled onto rigid or flexible substrates.

This transformation involves the manufacturing steps shown at right. Uniqarta has developed solutions for each of these steps and combined them into a complete ultra-thin die assembly solution.

FlexChip can be used with any type of semiconductor wafer or die without any modification to the semiconductor fabrication process. In addition, with its pick-and-place option, FlexChip can be implemented using industry-standard pick-and-place equipment.

Uniqarta is making FlexChip available for licensing by manufacturers. In most cases, it is desirable to implement the die/wafer preparation steps separately from the die assembly steps. Uniqarta accommodates this by offering preparation services in support of users seeking to perform thinned-die assembly in their own facilities.

Die Placement Options
FlexChip supports two placement options: pick-and-place or laser transfer. Pick-and-place is most suitable for use with existing equipment, assemblies that are sparsely populated, or assemblies that involve ICs of different types.​ Laser transfer is most suitable for high-speed assembly lines with closely-spaced identical ICs such as with RFID inlays. 

Pick-and-Place Die Transfer
The starting point for pick-and-place transfer is a set of thinned dies mounted on a conventional wafer tape, each having a temporary handle attached. The combined die/handle thickness falls within the normal operating range of conventional pick-and-place equipment and can therefore be easily accommodated. The dies are placed and interconnected using a conventional flip-chip method by which each die is placed face down on the substrate and is electrically connected to the substrate conductors by an anisotropic conductive paste or film. The handle is removed after die placement via a release mechanism that detaches the handle from the die.

Laser Die Transfer
The starting point for laser die transfer is a set of thinned dies mounted on a transparent glass carrier, each having a temporary handle attached. The interface between the die/handle stacks and the transparent carrier is a dynamic release layer that is responsive to laser energy.

This assembly is placed face-down above the substrate that is to receive the dies. It is envisioned that this method will be used in a roll-to-roll manufacturing process by which the substrate material is indexed continuously underneath the prepared wafer. 

Die transfers are performed by focusing a laser through the top side of the transparent carrier at a selected die. The dynamic release layer at that die location expands in response to the laser energy and pushes the die down onto the substrate where it is to be connected. The process is completed identically as with the pick-and-place method in terms of interconnection and handle removal.

With laser transfer, the repeated back-and-forth motion of pick-and-place is eliminated since the laser is electronically scanned to each die position. As a result, extremely high assembly throughput can be achieved.