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Application Notes

Semiconductor Printing Applications Process Solutions

The increased use of electronics in our daily lives has led many companies to look for innovative ways to apply material to wafers or individual die in their manufacturing process. One such cost-effective method is to print the material using a computer controlled print head. The following are some solutions to applying material to substrates for cost effective manufacturing.

• Applying adhesive to the backside of wafers. - The process solution is to use either a stencil or screen based on the thickness of adhesive required. For thinner deposits a screen is required and the final wet thickness will range from 0.00071" to 0.0055" with screen mesh 400 to 600 respectively. The print stroke is generally a print flood and the pattern on the screen is the wafer diameter with a base coat on the screen. For thicker deposits a stencil is used with a stiff squeegee blade. The stencil opening is 0.060 less than the wafer diameter and the reason for the stiff squeegee blade is to prevent scooping of the material as the blade goes over the large aperture.
• Printing gold fritt to bond pads of individual die. The process solution is to make a dedicated workholder that the die fits into with a depth 0.003 less than the die thickness. The print alignment system is the SPM High RES To align the substrate either the standard mylar system may be used A more accurate method of alignment is to print on a blank substrate with the table locked, then move the cameras using diagonal corner pads for alignment and draw boxes around the printed material. The die is then placed in the workholder and the corner pads are aligned to the boxes.
• Printing a B-stagable silastic stand off material to individual die on wafers. This was a difficult application as the print height requirements and a printable material that gave good definition did not exist. By working with the customer to modify the print area, the screen supplier to try various mesh size and orientations and several material formulators a solution was developed over a two-month period. The components from the new process were sent out for ACCELerated life and the manufacturer is now manufacturing product with this new process.
• Printing glass fritt dams to die on wafers for subsequent capping to protect from environmental exposure. This was another case where the screen printable material did not exist and the compounders recommended print parameters did not give the required definition of the device manufacturer. To meet the dam definition of the manufacturer the screen mesh was changed from 280 to 400 with a 22.5-degree bias of the mesh.

Several formulations of the glass fritt were tested as the initial trial was with a dispensable material that would dry out on the screen due to the solvent base of the material. The component manufacturer is ramping up with production trials has a cycle time of less than a minute including alignment and a print flood print stroke.