Machine Design

Plastic pads give silicon wafers TLC

Piper Plastics Inc., Chandler, Ariz., wanted to injection mold end-effector pads for use in semiconductor manufacturing.

Though exposed to organic chemicals and high temperatures, end-effector pads molded from Victrex T-Series polymers retain their properties. The proprietary PEEK/PBI blend reportedly resists a range of extreme environments that degrade most plastics.

Piper Plastics Inc., Chandler, Ariz., wanted to injection mold end-effector pads for use in semiconductor manufacturing. A proprietary blend of polyetheretherketone (PEEK) and polybenzimidazole (PBI) fit the bill. Typically made of metal, end effectors are the "hands" of a robotic arm that picks up silicon wafers and carry them from one operation to the next. Pads on the tips of the end effectors act as "fingers" that grip wafers as they move through the semicon fab.

The pad material had to have ultrahigh purity and the ability to withstand temperatures typically in the range of 572°F (300°C). Advantages of PEEK, a high-performance semicrystalline thermoplastic from Victrex Inc., Greensville, S.C., include a continuous-service temperature (UL746B method) of up to 500°F (260°C), excellent wear properties, good chemical resistance, and outstanding toughness and strength. Likewise, Celazole PBI, a thermally stable amorphous thermoplastic polymer, from PBI Performance Products Inc., Charlotte, N.C., is stable at high temperatures, strong, resists chemicals, and is nonflammabile.

Together, the melt-processible combination called Victrex T-Series reportedly outperforms other advanced polymers in demanding high-temperature applications that need superior strength, good wear and hardness, improved creep, and good thermal properties.

Victrex T-Series polymer is said to be the most thermally stable thermoplastic available. It works at temperatures up to 572°F. Piper Plastics also chose the T-Series because it molds with lubricious and smooth surface finishes. Additionally, it is a low sloughing material and resists abrasion. Since it began using the polymer blend, Piper Plastics reports that life spans of end-effector pads have more than doubled.

According to Dave Wilkinson, materials engineering manager at Piper Plastics, "Victrex T-Series has one of the best overall property profiles of any high performance material, including superior high-temperature resistance, unparalleled compressive strength, excellent tensile and flexural strength and low fatigue properties — all with the cost effectiveness of a melt-processible polymer."

PBI Performance Products Inc., (704) 554-3378,
Piper Plastics inc., (800) 526-2960,
Victrex USA Inc. div. of Victrex plc, (800) 842-8739,

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