Meeting conflicting machine control demands
Precision at high speeds can be challenging for machine designers because of network speeds. Towa Corp., a manufacturer of semiconductor equipment, had to deal with several challenges while developing a molding machine. It needed to be precise while operating at high speeds so it could be used in the semiconductor production process. The molding machine was designed to be compatible with the fan-out wafer level packaging (FOWLP) technique by using a compression molding method. This technique provides a higher integration level and more external contacts. It also is designed to provide thermal and electrical protection along with input/output (I/O).
Many semiconductor chips are sealed simultaneously with resin onto the surface of 300 mm diameter wafers or 320 mm square panels. Using compression rather than transfer molding is a more efficient method and it reduces the amount of resin used to seal the semiconductor chips.
Overcoming control issues
During development, the biggest challenge for Towa’s molding machine was the control system’s design. A major issue was effective control of the mechanical system. The company needed to design a way to control the dispenser table that supplies resin to the mold. To convey resin to the mold, the dispenser applies it in advance onto the resin table. The resin table and dispenser must be guided along specific trajectories using advanced calculations to dispense the resin evenly. The movement also needed to be optimized to match the type of resin being used.
"To handle multiple demands at once, the control system function and performance both needed major enhancement," said Hitoshi Kita, department manager for equipment development at Towa. "Therefore, we decided to review the design of the control system from scratch."
The solution was to use an Ethernet-based industrial open network standard, which provided separate control and information communication data bandwidths. This allowed transmission of large volumes of data without affecting control.
Within the molding machine, the Ethernet network is used to connect multiple servo amplifiers and controllers that drive mechanical systems as well as for safety system control.
"In the context of designing a system that processes the greatly increased intra-equipment data which accompanies multifunctionality, it offered a good solution," said Takanobu Nakajima, manager of equipment development, Towa.
The Ethernet network’s attributes allow the molding machine to meet the conflicting demands placed upon it—high functionality with a simple and rational control system.
Another issue that needed to be overcome was controlling the pressure when the wafer or panel is pushed into the resin in the cavity. Compression molding requires pressure management to be controlled precisely. To meet these requirements, the speed of the feedback circuit for the press mechanism pressure sensor output needs to be increased.
The development team decided to reform the feedback circuit. A new control system in which the analog signals from the press mechanism pressure sensor are directly inputted to the servo amplifier that is driving the press mechanism sensor. The result was faster system feedback.
"Feedback, which was conventionally 2 ms at best, has been dramatically shortened with the new control system design," said Ryota Okamoto, supervisor of equipment development, Towa.
The effort taken to redesign the pressure control and the overall control system design resulted in a molding machine that is designed to increase productivity using FOWLP manufacturing equipment for semiconductor chips.
Robert Miller, director, CLPA-Americas. This article originally appeared in the 2017 Control Engineering Europe supplement. Edited by Chris Vavra, production editor, Control Engineering, CFE Media, firstname.lastname@example.org.
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- A molding machine for making semiconducting wafers was designed to operate at high speeds and be precise.
- An Ethernet network was used to ensure that all the parts in the molding machine functioned properly.
- A feedback circuit was reformed to help improved feedback speeds.
What other advances could be made to improve molding machines?