SCRIBING AND breaking semiconductor wafers is a lot like cutting glassonly on a much, much smaller scale. Modernization in the compound semiconductor market usually is associated with fine-tuning scribing and breaking processes. However, as far back as 30 years ago, scribe dicing of wafers yielded irregular quantities because the tools werent manufactured properly and/or those tools werent accurately positioned in the system. To address these issues, staff at Loomis Industries, St. Helena, Calif., collaborated with its suppliers and customers, shared trial and error, and took risks to develop a scribe alignment and accuracy process, which the company claims is unmatched by its competitors.
Some of our older equipment has been on production lines with very little maintenance for more than a decade, says Jim Cook, production manager for Loomis. By using quality, proven components on our new LSD-150 scribe and break system, we hope to continue this level of reliability and productivity.
ALLOYS FOR WAFERS
Loomis wafer building process consists of dicing wafers made of gallium arsenide, indium phosphide, and other semiconductor compounds less than 300 µm thick. Wafers are covered with thousands of copies of a device that a manufacturer wants to assemble. These copies of the chip are separated from each other via Loomis scribe-and-break system. The devices are laid out on the wafer in a grid. The space between the devices is referred to as a street. Streets are typically 50 µm wide and act as the pathway for the scribing process.
ETHERNET AIDS MOTION CONTROL
In its most recent quality improvement effort, Loomis decided to use Galil Motion Controls motion and I/O components as the core of its new LSD-150 scribe-and-break system (See Figure 1 below). Galils motion controller, a two-layer module containing the motion controller and the amplifier, and its I/O board provided two communication options: serial or Ethernet. Ethernet was the cleaner solution, explains Cook. Many PCs sold today arent designed with serial ports. They often come with only USB, but most PCs have Ethernet built-in.
|FIGURE 1: HIGH WAFER YIELD|
Loomis Industries reports its LSD-150 scribe dicing machine is bringing about a new standard in yield, throughput, and cost-effectiveness by achieving +99.5% yields and industry-leading throughput times in 24/7 production environments.
In addition, Loomis already had a 24 VDC switching power supply inside its LSD-150 machine. With this Ethernet switch we were able to use up to 36 VDC with simple screw plugs to easily connect power from our switching power supply, he says.
The BAS switch size also was a factor in Loomis decision to use it. As small as possible, thats what we needed, adds Cook. When we decided to use the Galil system, we were short on space. The Galil components are much larger than what we had used. A switch designed for home or office wasnt an option.
Measuring 3.3x0.9x3.5 in., the DIN-rail mount switch provides five 10/100 Mbps shielded RJ-45 ports. Each port opts for the auto-negotiation protocol to select data rate, duplex and flow control. All five ports are Auto-MDIX compliant, so any port can operate as an uplink port to another switch, eliminating the need for crossover cables. It also offers low-voltage, wide-range AC or DC power sources, as well as LEDs for activity/link, data rate and power indication. Built-in broadcast storm control prevents excessive broadcasts from degrading network performance.
NETWORKING THE MACHINE
Loomis says it took much time and effort to make certain an Ethernet-based network and infrastructure was correct for its scribe-and-break process. The system includes a PC and the LSD-150 unit, which is used inside environmentally controlled clean rooms.
This PC is positioned near the LSD-150 because interaction sometimes is required from the operator via the mouse and the keyboard. A typical, 2-m, unshielded (UTP) CAT5 Ethernet cable connects the PC to the LSD-150. The PC functions as the supervisory controller. All the motors, digital I/O, and analog I/O are controlled and monitored by the Galil components to do the real-time servoing. These components interface with the PC through the BAS switch (See Figure 2 below). Meanwhile, an I/O controller eliminates the need for an external PLC. It includes a 32-bit microcomputer with memory and multitasking for programming various I/O events.
|FIGURE 2: SERVO, CONTROL INTERFACING|
All of the LSD-150 machines motors, digital I/O and analog I/O for its scribing and dicing process are controlled and monitored by Galils components to do real-time servoing, and are interfaced with the units supervisory controller PC through its Ethernet switch.