Semiconductor manufacturing can require the use of many different materials including gallium (Ga) base materials. Due to the sensitive nature of some of these materials, unique assembly methods may be required to prevent chipping or fracturing from the assembly process. In addition, the dark mirrored surfaces must be manufactured in clean room environments to minimize airborne contamination.
Typically, devices are introduced into the micro-assembly machines through the use of special polished stainless steel boats with the mirrored surfaces facing up. There can be no contact within the images on the mirrored surface. The delicate edges of the parts are extremely brittle and can be damaged easily. In the past, mechanical gripper nozzles (Fig. 1) were used to pick up and place devices onto the wafer for bonding. While the gripping force is light, pressure is applied to the side of the chip. There is also the issue of uniform placement pressure while the bonding occurs (spot curing). In either case, whether due to the localize gripper arm or the different forces in the placement, breakage and chipping can occur.
In some cases, there can be a “safe” area around the perimeter of the semiconductor device where no image is present. For this application, perimeter contact tools (PCT) were designed for safely picking up and placing chips (Fig. 2). A raised 10 mil (0.010”) polished perimeter edge gently makes contact with the outside edge of the chip’s surface leaving the delicate, interior surface un-touched. Also, a uniform contact area means much more precise bonding and pressure control. A consistent bond line is critical for most sensor manufacturing.
In addition to picking and placing of the devices, some components may require flipping to achieve the proper orientation of the dies to be bonded. Therefore, receiving tools or landing pads (LP’s) were created to capture the flipped devices now mirror side down (Fig. 3). Both the pick tool and flipper components incorporate an independent vacuum channel to secure the dies while in motion.
The vacuum system is typically a venturi based design where there is instant on and instant off capabilities. This reduces any chance of movement during motion events.
If the semiconductor chips cannot allow for perimeter contact areas, the use of inverted pyramid tools (IPT) can be utilized (Fig. 2). These tools allow for minimal contact of the die while a gentle vacuum flow holds the components without damage to the edges. IPT’s also provide a very uniform placement and bonding control.
Non-Contact
Future development will call for non-contact means for component handling particularly in the component flipper area. A system that incorporates a universal holding station would eliminate several custom tooling pieces and reduce cost. A design using the Bernoulli Principle could be integrated into the machine to allow for a non-contact part transfer of the delicate materials. This principle can be used to create a dynamic lifting force using standard air pressure to hold or move objects around. One concern is the manufacturing size of the non-contact lifting units. Current suppliers have sizes ranging from 20 to 60 mm diameters. For the semiconductor industry, however, these sizes will need to be reduced. As a mechanical device, there would be no physical reason a smaller unit could not be created. Another interesting possibility is the concept of ultrasonic levitation where a thin gas film is produced offering enough repelling forces to move the part without friction. Further studies are required to assess the feasibility of integration into the robot peripherals.
Flatness
Another critical area of concern is component and wafer flatness. To ensure proper bond lines, accurate control of perpendicularity of the robot heads to the working surfaces must be maintained. While tight mechanical specifications are held to provide good robot accuracy, the use of touch probes offers an excellent solution for both adjusting and monitoring machine flatness (Fig. 4). Depending on the touch probes used, an overall flatness within 2 microns can be achieved. A simple predetermined program can be activated where three positions are selected around the perimeter of the boats or wafer to verify true position. Once the measurement is taken at the 3 locations and the offset determined, a series of fine spring-loaded setscrews are adjusted to correct the flatness. These custom setscrews have a calibration feature where one turn equals approximately 5 microns.
Micro Force
While the need for high bonding pressures (2000 – 4000 grams) may be required in some applications, there is also a need for feather-touch force placement. Micro-force load tables can utilize up to 4 load cells and provide a delicate pick and place possibility down to just a few grams. As with all sensitive materials, such as LED’s, it will be important to offer both a firm yet gentle bond control to prevent component fractures.
Conclusion
Delicate component handling will be very important to produce higher yields with minimal loss. Sensor and semiconductor manufacturing will continue to utilize sensitive materials such as Ga and, with the increase in security and surveillance, this need will only continue to grow. Machines will need to be able to adapt quickly to changing technologies and specific applications. Dark mirrored surfaces offer a unique challenge to laser distance sensors as an example. Robot platforms should offer quick-change tool designs (Fig. 5) so manufacturers can move from process to process for the lowest possible cost. Companies should ask robot suppliers about their internal manufacturing and software development capabilities to determine their ability to address customer needs quickly. Having the ability to pool in-house resources at a moments notice will be vital to meet the customer demands and timelines. The issues of handling sensitive materials will challenge suppliers to invent new capabilities. In many cases, the smaller custom robot supplier will be able to respond much more rapidly to difficult application requirements.
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