# Ideal Motors for Semiconductor Manufacturing Equipment

In today’s market, the demand for semiconductors is growing. Equipment used to manufacture and handle the silicon wafers for semiconductors need increased throughput to keep up with demand. The prime movers of this equipment are electric brushless DC motors (BLDC). They are used for positioning and holding tasks when processes get performed on a wafer to produce the conductor structures required.

Wafers are moved and repositioned within each stage of production. To increase overall throughput, time to execute a given motion needs to be decreased, while maintaining exceptional precision, accuracy, and position repeatability. Using gears and other transmission components decreases position repeatability, motion smoothness and serviceability. Genesis direct drive motors can push the boundaries of throughput.

A direct drive motor with high motor constant is the ideal for increasing throughput in semiconductor manufacturing. A higher motor constant means that more torque is produced for a given amount of heat generation. More torque, enables higher acceleration, which in turn enables faster motion.

Given two motors of the same size, a great way to judge their difference in performance is to compare their motor constants. The motor constant (Km) is the ratio of a motor’s torque to heat generation with units of $$Nm/√W$$. It is defined as follows:

$$K_m=\ \frac{K_t}{\sqrt R}=\ \frac{T}{I\sqrt R}=\ \frac{T}{\sqrt{I^2R}}$$

 Km = motor constant Kt = torque constant R = terminal resistance T = torque I = current

From the above formula it can be seen that for a given amount of heat generation, $$\sqrt{\left(I^2R\right)}$$, the motor with a higher Km will be able to produce more torque. If given the choice between two or motors of the same size, selecting the one with higher Km will provide more torque for the same amount of space claim inside a machine.

To orient and position wafers, lasers, mirrors and other optical instruments, motions in semiconductor manufacturing are often characterized by short travels and stops. In these cases, the motor driving the axis of motion only rotates a short amount before it stops. Short travel motion is mainly comprised of acceleration and deceleration components (high torque), with little or no time spent at constant velocity (low torque). Because acceleration and deceleration are high torque (and high current) time periods, a motor with a high Km value is ideal because of its low heat dissipation.

With higher torque from a higher Km value, the acceleration and deceleration components can be executed faster. The following time series charts provide time saved information when performing the same motion between two motors of the same size, that have different Km values.

 Motor with a lower Km value Motor with a higher Km value

Higher acceleration is key to reducing motion time and increasing throughput, but a motion is not complete until the motor stops and settles. Direct drive motors are connected to the load which means there is no backlash and extremely low compliance. Positioning is determined by the resolution and accuracy of the encoder. These factors enable repeatable positioning and fast settling. In fact, when the motor is not directly coupled to the load, but rather coupled through a flexible coupling or gearbox, it can lead to inertia mismatch issues.

Direct drive motors are ideal for optimizing rotary positioning. Those with high Km values can also make a further contribution to situations where the highest precision and accuracy are needed. A motor with a higher Km value could be used to replace a motor of the same size (that has a lower a Km value) and deliver the same torque with less heat dissipation. Less heat will reduce overall machine temperatures, ease thermal expansion issues, and enable other precision instruments sensitive to high temperatures to perform more optimally.

Another benefit of motors with high Km values is that a smaller motor can replace a larger one while providing the same torque. A smaller motor will contribute to space and mass savings, this allows for additional design features to equipment or additional units of equipment within in the same footprint. This increases capacity and is another way to improve throughput.

As the world moves forward, the need for devices containing semiconductors will increase. For companies that make semiconductors, producing them quickly is key to their success. Direct drive motors with high Km values will be vital to ensure that future production equipment will be equal to the task.

Genesis produces the most torque dense direct drive motors with the highest Km values. Want to increase your equipment performance? Contact us with your application requirements.

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