Wafer Bump AMTX™ Stencil
Just recently, printing solder paste on wafers has come into focus as a cost-effective wafer bumping alternative to the conventional sputtering and plating methods. Overprinting of the wafer pads is normally utilized to supply additional solder paste to achieve maximum solder bump height. Wafer Bumping Electroformed AMTX stencils are used to print solder paste directly onto the pads of the wafer. After reflow, solder bumps (truncated spheres) are formed on the wafer, and the wafer is cut and diced into die. The die can then be attached to a substrate using Flip Chip assembly.
Advantages
- Hard tooling for evaporation masks required in the sputtering process is eliminated.
- Expensive sputtering chambers are eliminated.
- Time to tool a Wafer Bumping Stencil is short (less than a week).
The Wafer Bumping AMTX E-FAB Stencil usually has anywhere from 25,000 to over 2,000,000 apertures.
Typical designs for a Wafer Bumping Stencil
| Wafer Die Array Type | Pitch | Pad Size | Aperture Size | Stencil Thickness | Area Ratio | Predicted Bump Height |
|---|---|---|---|---|---|---|
| Full | 12 | 6 | 9 square | 3 | 0.75 | 3.3 |
| Full | 10 | 5 | 7.5 square | 2.5 | 0.75 | 3> |
| Full | 8 | 4 | 6 square | 2 | 0.75 | 3 |
| Peripheral | 12 | 6 | 9x18 rectangle | 3 | 1 | 6 |
| Peripheral | 10 | 5 | 7x16 rectangle | 3 | 0.81 | 5.2 |
| Peripheral | 8 | 4 | 5.5x14 rectangle | 3 | 0.65 | 4.8 |
| Note: All dimensions are in mils (0.001") | ||||||
