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Why is Stratus the optimum electroplating configuration for flip chip and 3D packaging?
Copper, nickel, and solder layers used in flip chip, WLCSP, and 3D processes are thick; even at high deposition rates, the deposition times are well over 10 minutes per wafer. To achieve high throughput, many wafers must be plating simultaneously. The Status system architecture allows for a line configuration that is readily matched to the multi-process requirements. For example, in a solder bump process, four copper and 16 solder wafers can be depositing simultaneously.
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Isn't paddle-agitated deposition an unusual technique?
No. Vertical paddle agitation deposition was developed by IBM in the 1970's for critical electroplating processes used in the thin film heads industry where fountain process cells could not deliver the required results. A paddle moving rapidly back and forth in front of the wafer surface creates much better fluid mixing than occurs in horizontal fountain cells, providing a variety of process advantages. Horizontal fountain cell plating has been used because, prior to Stratus, equipment vendors had not developed a cost-effective and reliable perimeter fluid seal and electrical contact suitable for vertical orientation. The Stratus ShearPlate electrodeposition process cell is an economical and reliable means of achieving a thin, uniform boundary layer.
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How has NEXX made thin, uniform boundary layer deposition cost effective?
The critical success factor for reliable thin boundary layer deposition equipment is a completely leak-free sealed contact to the wafer edge. Our patented integrated contact/seal and fail-safe wafer holder provide a compliant seal and continuous electrical contact around the wafer perimeter. This design enables paddle agitation just 1.5 mm from the wafer surface, facilitating superior fluid mixing. These innovations are the foundation of a process cell with the process advantages of thin boundary layer deposition in a configuration that is reliable and cost-effective.
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What are the advantages of thin boundary layer deposition from a process perspective?
Better uniformity results because the ShearPlate agitation decouples the fluid flow and electric field at the wafer surface, providing more range for field uniformity optimization. In fountain cells, the fluid boundary layer thickness varies with radial position on the wafer surface; with ShearPlate agitation, the boundary layer is thin and uniform. The Stratus ensures complete filling of deep photoresist patterns and void-free solder bumps and TSVs.
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Why is NEXX's Stratus the best Electrodeposition system?
Stratus systems offer several patent-pending advantages.
- The Stratus system architecture enables 20 wafers to be plating simultaneously.
- The Stratus offers bridge system capability: 200 and 300 mm wafers can be processed at the same time.
- Superior process performance yields void-free solder (including lead-free) bumps and TSVs.
- A patented, back-to-back wafer holder virtually eliminates repetitive wafer handling and doubles the effective throughput of each process cell.
- The Stratus was specifically designed for high throughput/high yield processing; Coupled with lower operating costs, this results in the best cost of ownership for electrodeposition in the packaging industry.
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Is automation of a vertical system more expensive than for a fountain system?
No. It is less costly, and it is simpler to maintain. Wafers are handled only once, by the standard front-end wafer handling robot, which loads and unloads them from the wafer holders. There is no need for the expensive robotic precision necessary to reliably move wafers between process chambers because, in Stratus, the movement occurs while wafers are securely held in the fail-safe wafer-holder. This feature also makes Stratus an ideal platform for electrodeposition on substrates as thin as 1.75µm up to as thick as 2 mm. Wafer breakage is reduced and automation costs are less.