How SCARA, Six-Axis, and Cartesian Pick-And-Place Robotics Optimize and Streamline Electronics
than that of other robotic types. However, accuracy is exceptional … especially when controls use feedback and generate commands for millisecond responsiveness. Such motion is key for automated board manufacturing; trimming and surface polishing; and extensive assembly routines. Cartesian robotics stations are also the top choice for large-format electronics such as flat-panel displays and solar panels. Specific cartesian robotics application example Consider cartesian robotics in maximally automated printed circuit board (PCB) manufacture and assembly. Cartesian robotics either maneuver end effectors over the boards or take the form of cartesian tables that move PCBs through the reach of fixed processing equipment. For example, such tables might move boards through lithography equipment to print copper circuits onto a nonconductive silicon substrate. Then after the initial PCB print process, copper not part of the design circuitry is chemically etched off. Nonconductive solder masks isolate adjacent traces and components. In many PCB assembly operations, cartesian robotics accept electronic subcomponents on reel tapes or box tapes fed into the workcell. (The robotics’ pick- and-place head is designed to
more. Absolute encoders at each joint and Ethernet-based networking provide motion feedback and connectivity for PLC, PC, or dedicated robot controls and adaptive software to both command and improve processes over time. These controls include the integration of sophisticated end effectors — for example, grippers to safely handle small and fragile electronics components. Six-axis robots excel at machine tending and the packaging of electronics products. Beyond the assembly of the boards themselves, the robots can fasten electronics into end products’ metal or plastic housings and make the necessary electrical connections as well. Some six-axis robots can also execute finished electronics products kitting, case packing, and palletizing.
Cartesian robotics in electronics manufacturing Cartesian robots — those based on modular stacks of linear axes — help operations satisfy the semiconductor industry’s need to maintain cleanroom conditions for many processes. Nearly unlimited scalability means travel can cover anything from a few centimeters to more than 30 meters. Cartesian robot repeatability can stay within ±10 μm on linear DOFs with comparable angular repeatability from end effectors as well as rotary-to-linear and direct-drive options for especially smooth transport of wafers. Speeds to six meters per second are common. Cartesian machinery typically executes dedicated automation tasks, as its kinematics tend to be less flexible and reconfigurable
consume less power and less of the premium cleanroom real estate. Variations abound to deliver the speed and accuracy needed for high-throughput handling and assembly. The servomotors to drive the robots’ joints are similar to those found in other robot types, but six-axis robots are far more likely to pair these motors with strain-wave or cycloidal gearing. Like SCARAs, six-axis robots also pair well with conveyors used in semiconductor processing stations. The main strength of six-axis robots is their dexterity and large working volume for a given linkage- set size — whether installed on a floor base or inverted from a ceiling. To illustrate, a six-axis arm that’s 600 mm tall when folded might reach 650 mm in all directions with the ability to quickly and concurrently sweep each joint 120° to 360° for nimble movement of electronic payloads of a few grams to several kilograms or Figure 7: SCARA robots execute pick-and-place wafer handling and processing tasks quickly and precisely. (Image source: Dreamstime)
Figure 9: Cartesian robots execute fully automated semiconductor manufacturing tasks. Note the linear motors that provide high-precision direct driving on the critical axis. (Image source: Dreamstime)
the SMT component connections. Wave soldering is more common for through-hole components; this involves passing the board across a standing wave formed on the surface of a pan of molten solder. Such machines are costly and best suited to very high-volume manufacturing. Typical motors and drives for cartesian robotics Cartesian robotics use many of the same types of servomotors, precision gearing, and electromechanical drives as other robotics solutions. One caveat is that the stepper motors in some cartesian designs that transport semiconductors during production shouldn’t be confused with so- called step-and-repeat cameras — sometimes simply called steppers. The latter are essential to photolithography processes during chipmaking.
grasp and place a variety of these subcomponents.) The robotics verify each subcomponent value and polarity and then set and solder the subcomponents via through-hole or surface-mount technology (SMT) attachments. Through-hole subcomponent leads insert into board holes, get trimmed and clinched, and then get soldered to the board backside for top mechanical strength (though necessitating more complicated assembly routines). In contrast, SMT subcomponents accept maximally automated high-volume set and solder routines … so they now dominate many board designs. That said, through-hole mounting is still most common for attaching large capacitors, transformers, and connectors to boards. For SMT components, solder paste is pre-applied to the PCB before component assembly. Reflow soldering then uses hot air to melt the solder paste to form
Figure 8: This six-axis articulated robot is available in ISO 5 (class 100) cleanroom models. (Image source: Denso Robotics )
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