In Search of the Perfect Cut

Longer blade life, sawing accuracy and high throughput are major concerns in the selection and use of next-generation singulation systems.

Figure 1. The Towa Intercon SBS-8800 system, equipped with a Disco saw, consists of 10 processes linked by a robotic handling system.

A CSP singulation system is, at its most basic, a saw-not unlike that used for wafer dicing-connected to or incorporated into several systems and submodules, including vision, input, output, display and computer control.

Unlike older methods of singulation, i.e., punching and routing, equipment targeted at the CSP market now universally employs a saw as the core mechanism.

It is, of course, how the saw interacts with the total system that will ultimately provide either a near-perfect cut or a cut that's lacking in accuracy or produces package chipping. Throughput and accuracy are key issues, most experts agree. Accuracy with CSPs has become highly problematic, because the packages tend to be placed quite close together on the substrate, forcing the saw to address a very narrow pitch.

Totally new concepts in singulation are the order of the day, according to Edward G. Combs, senior vice president of ASAT Inc., Fremont, Calif. "Many of the new CSPs and near-CSPs are built in arrays, requiring saw singulation rather than the older methods."

In the past, saw-singulated parts used standard wafer saws and wafer-mounting equipment. The newer singulation equipment, Combs points out, uses nests with vacuum chuck systems to eliminate tape mounting. "New saws are being developed with larger blades and spindles to handle multiple package cutting and to extend blade life," he adds.

Figure 2. The MTI LPS-350 is geared toward large panel singulation and utilizes a dual supported gang blade arbor. Applications include BGAs, PC boards, copper panels, discrete components and ceramics.

"Of paramount interest to users," says Combs, "is the offload system, which is typically the bottleneck of the operation, as well as the wash/clean and vacuum handling systems."

Lee Smith, a product marketing manager at Amkor Technology Inc., Chandler, Ariz., says singulation machinery should offer improved loading options, from simple tray loading to tube feeders and tape and reel, and should also support package tests before loading.

Singulation systems also should optimize blade materials and process variables to deal with several different package material types, including tape, glass, ceramic and copper, Smith adds.

"All the major suppliers have concentrated entirely on BT laminate-based substrates. Different material types will require different saw types, such as single spindle/single blade systems vs. dual spindle/multiple blade systems. Some material properties," Smith adds, "will limit the singulation processing speed-and the most effective way to improve process throughput is by increasing the number of blades/spindles."

The issues that tend to recur in singulation, says Mark Brown, product manager for Disco USA, Santa Clara, Calif., are "throughput and accuracy." Disco is a major supplier of saws to OEMs that produce singulation systems, but it makes no complete systems itself.

"As with any manufacturing process, the end user wants to produce more and more product. To enable these requests, the manufacturer of the cutting engine has two choices: cut at faster feed rates, or employ multiple blades," says Brown.

If faster feed rates win, says Brown, then the issues "that come into play will include shortened blade life, chipping of the molding, copper smearing, etc., although the one result that is easier to obtain is overall parts accuracy when using a single blade and cutting at higher feed rates."

Figure 3. The MTI NSX-250DS is a dual spindle system for substrates up to 250mm square or a 300 mm x 250 mm strip.

On the other hand, higher throughput is easier to get with the use of multiple blades. The user, however, will sacrifice the accuracy of the overall part, observes Brown. "This lower accuracy is not primarily due to stacking inaccuracies, but rather due to the overall accuracy of the strip, caused by warpage or other anomalies."

Other issues, in addition to accuracy of the cut and throughput, are product changeover time and package cleanliness.

Vada W. Dean, director of sales and marketing for Towa America, Morgan Hill, Calif., feels that the way to overcome these obstacles is through a unified process rather than with linked components. Towa's Intercon SBS-8800 singulation system (Figure 1) overcomes these challenges by approaching saw, clean, and pick-and-place as a unified process.

The Towa system's high-speed saw (supplied by Disco) is enabled by proprietary reusable tooling that maintains accurate strip positioning without using tape. The tooling carries the singulated devices through wash and dry, then accurately presents them to pick and place. The system is offered with flexible single blades in high-throughput gang blade configurations.

Figure 4. The Meco system is a fully-automated, self-adjusting machine for CSPs and similar packages.

Another key issue-and it's always an issue-is IC assembly's recurring cost, which must be kept low, emphasizes Mitch Marvosh, business development and marketing manager for MTI, Ventura, Calif. MTI provides several application-specific systems (Figures 2 and 3).

Motorola Manufacturing Systems, Phoenix, entered the singulation market in 1994, when MMS began selling its products commercially. In 1998, about 75 percent of MMS products were sold to Motorola, with the remainder sold to commercial accounts, according to Dan Viza, general manager for sales and marketing.

This year, Viza said, Motorola is aiming to sell 60 percent of its equipment on the world market. The company's HDS-1000 singulation system employs a commercially available dicing saw integrated into a high-volume package handling work cell for panels and substrates.

As wafer-level CSPs gain a foothold as mainstream products, the line between wafer dicing-a front-end process-and singulation will continue to blur as accuracy and throughput demands increase.

*Except where noted, all information has been furnished by the equipment manufacturer. For more information, please contact the companies directly.

We asked the makers of singulation equipment to describe the theory of operation for their products. Their answers, edited, but in their own words, follow.

The Han-Mi SPS-510 uses saw singulation and can handle either ball-up or ball-down substrates at a customer's option and can additionally handle any kind of saw. For reliability purposes, packages do not touch any part of the machine, and only vacuum air is employed to hold or transport packages. The machine can sort good units and reject bad ones using a vision inspection system, and will provide over 4,000 UPH.

MTI systems singulate with blades/saws similar in operation to basic dicing and slicing machines. A diamond wheel or carbide saw is rotated via a precision spindle. As the blade is fed into the part, it grinds or cuts away material and slices the substrate.

Utilizing MTI's gang blade technology, multiple gang-quality blades are assembled on an arbor or hub assembly. These are spaced at the desired pitch with precision spacers to the desired pitch. Once the streets (or rows) are cut, the parts are quickly rotated; then the avenues (or columns) are cut. The substrate is now fully singulated, often with a single pass in each direction. Using Windows-based CNS power for unlimited motion commands and our fully programmable MTIsion, NT II process optimizations, alignments and inspections are easily programmed.

The strip to be singulated is fixed below a head from a four-axis manipulator. The connection employs suction cups, one per product, to maximize forgiveness for warpage.

This means that the product can move with complete freedom of position and direction in all horizontal planes in a vertical area.

All positioning information, such as how the strip is to be positioned on the head, position of the saw, position of the cut, etc., is measured, and the calculations are sent to the manipulator. As a result, the system aligns itself and the substrate prior to sawing.

The system takes units from a cassette input and places the substrates onto a vacuum fixture. Vacuum is applied to the bottom and vision alignment is performed. During this sequence, the machine preloads another substrate for placement onto the vacuum chuck. After vision alignment, the parts are diced in one axis, then the second axis.

Once dicing is complete, a second tool acquires the diced parts and the first tool loads the second substrate. Diced parts are cleaned via high-pressure DI wash, followed by top and bottom dry. Parts are then inspected prior to loading into an accumulator. Reject parts are discarded. The accumulator queues parts awaiting final pick and place. Parts are picked in multiples and are spread to the appropriate tray pitch. Parts are then placed in trays.

The Towa America Intercon SBS-8800 tapeless singulation system consists of 10 processes linked by a robotic handling system and proprietary tooling. The system receives magazines, then pushes the strips from the magazines into the system proper. The substrate is then aligned and loaded onto a nest. The saw uses both mechanical guides and pattern recognition systems to properly position the substrate.

After a successful alignment, the saw singulates the device on the nest. To constrain the devices within the nest during wash, a cover is placed over the singulated devices and their nest. The devices are washed and dried and the cover is removed. Finally, the devices are picked from the nest and offloaded into JEDED trays or tubes, or onto tape and reel carriers.