As die sizes are becoming increasingly smaller, yield losses are increasing with the use of traditional mechanical methods of singulation. A new process called laser assisted plasma singulation (LAPS) has been developed. This new process, otherwise referred to a plasma dicing, is a non-mechanical passive method for singulation of the die. The basic process consists of five (5) steps:
- Application of a mask coating to the wafer
- Clearing areas on the mask layer with a laser
- Plasma dicing process
- DI water rinse to remove the mask coating layer
- Die pick up
Plasma dicing process steps
In many cases, the wafers have high surface topography in the form of pillars or solder bumps. In order to be effective for this process, the coating must be applied “conformally” to these surface structures. USI’s nozzle-less ultra-Thin Coating Application Technology applies a thin, uniform conformal coating of these water-washable mask layer coatings. This technique is much more effective than traditional spin coating for producing a uniform and conformal layer on the wafer surface.
In order to demonstrate the ability to apply the masking layer on a wafer with high surface topography, a study was conducted using tCAT and coating materials by Daetec, LLC.
A multi-layer coating process is utilized to conformally apply the coating to the wafer. The wafer is placed on a heated vacuum plate to dry the coating between applicaiton layers. In order to ensure that a uniform coating is applied conformally to he surface topography on the wafer a defined coating sequence is required. This four (4) layer coating sequence operates as follows. A 5-position rotate and tilt mechanism is used to position the ultrasonic spray head during the coating process; the spray head has two (2) rotational positions (0 & 90 degrees) and two (2) tilt positions (forward and reverse up to 45 degrees) providing four (4) possible approach angles for the coating process. The tilt and rotate position of the spray head is defined for each layer so that every exposed surface of the components is coated. This four (4) layer process is repeated until the desired coating thickness is achieved.
The following are part of the results of this study that demonstrate the conformal coating capability of tCAT for surfaces with topography.
This image shows the solder bumps before coating (top) and after coating (bottom).
This is a depiction of the measured coating thickness of a single solder bump. This shows that the coating is applied conformally with coverage on all surfaces.
This image shows a coated single solder bump with high topography.
This is a depiction of the measured coating thickness on a high topography solder bump. This demonstrates the conformal coating capability of the tCAT technique.
Advantages of Plasma Dicing
This chart summarizes the key advantages of the plasma dicing process as: increased throughput, increased real estate utility (smaller kerf widths theoretically <10µm), die smoothing and strength, and no chip out, scratches, or cracks due to no mechanical contact.
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