New die-separation process increases throughput

By Pieter Bruggraaf
WaferNews Technical Editor

It is hard to imagine disruption of conventional wafer-to-tape mounting carriers used with wafer dicing in semiconductor assembly, but a newly patented wafer mounting technique (US patent 6,383,606, May 7, 2002) from Diamond Touch Technology Inc. (DTTI), Prescott Valley, AZ, brings a whole new set of capabilities and productivity to dicing and scribing.

Dubbed DiaFrame, the new frame greatly eliminates die edge chipping problems associated with conventional processes, prevents tape sagging – which is an increasing problem with large wafers – and enables a new high throughput sequence of scribing and die separation.

Briefly described, DiaFrame is a tape mounting ring designed with a novel “S” shaped strain relief diaphragm around its inner circumference.

DTTI CEO Michelle Broyles tells WaferNews, “In its natural state with mounting tape attached to the diaphragm, but without a wafer, the tape follows the shape of a plane cutting a chord across a sphere, with a chord depth of approximately 500-micron.”

As with conventional frames, the tape is coated with a high tack, heat, or UV-release adhesive to which wafers are attached using conventional mounting tools.

“Attaching the wafer to the sticky tape, the DiaFrame is forced flat by the strength of the wafer, with the compression absorbed by the S-shaped relief structure on the diaphragm,” says Broyles. The mounted wafer is now ready for sawing or scribing by any conventional means.

What isn’t conventional, however, is that once the DiaFrame mounted and diced wafer is released from the vacuum chuck of a saw or scriber, the tape and attached die dome up, separating each die by 18- to 50-micron depending on the specific wafer and DiaFrame.

Engineers at DTTI have incorporated the DiaFrame into a proprietary Scribe & Fracture process that is capable of singulating wafers (up to 300mm) faster than existing technologies, with improved yields. A DiaFrame mounted wafer is scribed on a DTTI DS system. The optimum scribing speed for silicon is ~3 in/sec, done with a position accuracy of 0.025-micron with no cumulative errors produced during the scribing of multiple streets. The individual scribe lines are ~3-micron wide and 1-micron deep. Once scribing is completed all the streets are fractured simultaneously – in milliseconds – by forcing a metered supersonic puff of air through the chuck.

“While experiencing no losses in yields, this fracturing speed is over 200% faster than current scribe and break processes that require mechanically linked breaker bars striking the wafer or positioning and moving a mechanical roller on the top of the wafer above a static breaker bar,” explains Broyles.

She continues, “Our testing has demonstrated this new method eliminates the need for heat and stretching steps and associated equipment, and produces no measurable dust or liquid hazardous waste when used with GaAs or silicon wafers.”



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