In recent years, the demand for ultra-thin die for use in mobile phones, stacked packages, and a myriad of other applications has been increasing. But a decrease in die thickness has also resulted in decreased die strength and increased die warpage. Stress relief improves die strength for greater viability while reducing die warpage for greater usability in stacks and thin packages. The chart below outlines the four main types of stress relief, including dry polishing, a proprietary DISCO process.
CMP (Chemical Mechanical Polishing)
Figure 1: Major stress relief processes
Dry polishing effectively removes the damage layer that inevitably remains after fine grinding. The result is a mirror finish on the wafer backside, increased die strength, and reduced die warpage.
The following graph shows die strength (as measured with the ball press test) at increasing amounts of material removal. DISCO research has demonstrated that 2 micrometers of removal provides optimum stress relief results.
Figure 2: Variation in die strength with DP removal depth
DISCO's polishers handle a wide variety of applications and are in-line configurable with DISCO grinders for greater wafer handling safety. In addition, DGP8760 offers grinding and polishing in one complete unit.
DISCO's specially-developed wheel for stress relief has
the following features:
• Contains a non-diamond grit.
• Provides a mirror finish without saw marks.
• Uses no chemicals, slurry or water for reduced environmental impact.
• Improves cost of ownership through reduced water costs, etc.