New die-separation process increases throughput
07/01/2002
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 substantially eliminates die edge chipping problems associated with conventional processes, prevents tape sagging (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's proprietary Scribe & Fracture process |
DTTI CEO Michelle Broyles said, "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 microns." As with conventional frames, the tape is coated with a high-tack heat- or UV-released 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," Broyles explained. The mounted wafer is now ready for sawing or scribing by any conventional means.
What is not 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 18-50μm, depending on the specific wafer and DiaFrame. Engineers at DTTI have incorporated the DiaFrame into a proprietary Scribe & Fracture process that they say is capable of singulating wafers (up to 300mm) faster than existing technologies, with improved yields.
 A DiaFrame mounted wafer, naturally domed-up to separate die after dicing |
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 0.025μm with no cumulative errors produced during the scribing of multiple streets. The individual scribe lines are ~3μm wide and 1μm 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," Broyles said. "Our testing has demonstrated that 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." —P.B.