Convey Technology Inc

Description

A particle loosely bound to a surface may later be transferred to a sensitive area of a product or process, creating a defect or a reliability risk. This mechanism defines a class of particulate contaminates: bits of the surface that are easily removed. We turn this mechanism into an inspection technique. If a small piece of a surface is peeled off by moderate normal force then that piece is identified as a particulate contaminant. Our basic approach is analogous to offset printing, where a supply of colored particles and the paper are offset or separated by a print roller with special surface properties. In offset printing, parts of the print roller surface are hydrophilic and parts are hydrophobic, so that only parts of the roller pick up and transfer colored particles. In offset inspection, the surface of the roller is also engineered for the specific task of gathering particles and presenting them to an inspection system. Roller for Offset-Inspection A roller can have many configurations. Here we show a manual applicator, which is a disposable sampler loaded onto a rotating core on a handle. The handle and sampler are convenient for a wide variety of configurations and services. The rotating core is on a double sealed cleanroom bearing. The sampler is the heart of the technique. It is a thin flexible tube coated with a tough, zero-residue, removable pressure sensitive adhesive (PSA). The PSA is a proprietary urethane containing no silicones or plasticizers. A sampler can be repeatedly rolled and inspected, substantially reducing the inspection cost. Samplers are delivered in sealed containers; these can also serve as archival containers for the used samplers. Sampling Operation for Arbitrary Surfaces Obtaining the right balance of adhesion to particles and lack of adhesion to particles and lack of adhesion to surfaces requires a combination of sampler surface chemistry, physical compliance, and normal application force. Since manual rolling of the sampler gives uncontrolled normal forces, the sampler and core are designed to supply most of the required application force, using the peel force of removing the sampler from the surface. The surface chemistry of the sampler can be modified for different amounts of adhesive force. Most metal's surfaces will generate a somewhat lower peel force, and plastic surfaces can be significantly lower. A release stripe without PSA is provided on the sampler. The sampler can be easily removed from a surface if the release stripe is contacting the surface. The sampler may be physically distorted as it is rolled. Each time the sampler is scanned, these distortions are measured and applied to the detected particle coordinates.

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