Wafer dicing is the process by which individual silicon chips (die) are separated from each other on the wafer. The dicing process is accomplished by mechanically sawing the wafer in the extra areas between the die (often referred to as either dicing streets or scribe lines).
To facilitate the sawing of the wafer, backside support is provided by first mounting the wafer onto tape. This dicing tape is typically 3 mils in thickness with adhesive on one side to hold the wafer to a frame. Using a wafer mounting tool, a wafer is mounted utilizing the following steps:
1) the frame and wafer are centered on the mounting chuck of the tool, the wafer is positioned face down on the chuck;
2) application of dicing tape to the wafer and wafer frame at which point wafer tape is stretched over the back of the wafer and a roller is used to evenly distribute the tape on the wafer;
3) cutting of the excess tape; and
4) unloading of the mounted wafer.
During wafer mounting, Pac Tech uses great care to prevent wafer cracking or breakage, bubble trapping on the adhesive side of the tape, scratches on the active side of the wafer, and non-uniform tape tension which can result in tape wrinkles.
After mounting, the wafers are loaded into cassettes and into the dicing tool. This step is where the wafer is actually cut into individual die. The wafer saw process consists of the following steps:
1) the frame-mounted wafer is vacuum mounted onto another chuck and aligned to the dicing streets in both the X and Y axes of the wafer.
2) the wafer is then cut through its thickness and 1 to 2 mils into the dicing tape according to the programmed die dimensions using a nickel plated diamond wheel rotating at a very high rpm (other blade types are used depending on the material and cut dimensions) PacTech has the capabilities to double cut the wafers using its tool set.
3) the wafer goes through a cleaning process using high pressure DI water sprayed on the rotating platform and then dried by an infra-red light in order to remove dust and water from the sawing process.
DI Water is also dispensed on the wafer during the saw process to wash away particles (Si dust) and to provide lubrication and cooling during the dicing process.
The following parameters are monitored to ensure a high quality cut:
1) feed speed (speed at which the wafer passed through the blade),
2) spindle revolution speed,
3) blade height, and
4) cutting water flow.
Important parameters for the washing step include the following:
1) wash time & rpms,
2) DI water pressure,
3) dry time & rpms
4) temperature, and
5) air flow rate.
|Wafer||Material:||Si, GaAs, SiGe, InP, LiTaO3, Ceramics, Glass, Quartz|
|Size:||100 mm||125 mm||150 mm||200 mm||300 mm|
|Die||Dicing Streets:||> 60µm|
1) Test features in the streets that are plated with nickel and gold require a double cut.
2) Die can be left on the mounting tape and frame
3) Saw blades are specific to the material and cut dimensions of the wafer