Using Polycapillary Optics for Coatings Analysis

As electronic components and electronics as a whole continue to get smaller in size and more complicated, metal finishes on such components have to be plated on smaller features (for example, thinner layers) and regulated to tighter tolerances. In case the platings are very thin, then the product will not be able to satisfy the performance specifications and could deteriorate beforehand, leading to reputation damage and warranty claims. Very thick platings result in the wastage of money and materials, and could possibly even result in difficulties with mechanical fit that might lead to rework or expensive scrap.

Image Credit: FM Callahan

X-ray fluorescence (XRF) method is widely applied for measuring coating thickness and composition as it is simple, fast, and non-destructive to use. In order to measure coatings on smaller features, mechanical collimation is used by conventional XRF instruments to reduce X-ray tube’s beam size to fractions of 1 mm. To achieve this, a metal block drilled with a small hole is placed in front of the tube, which allows only the X-rays in alignment with the hole to pass through and strike the sample. The huge majority of the output from the X-ray tube cannot be used for analysis because it is blocked by the collimator block.

Using a polycapillary optic is the latest strategy to measure fine features. A polycapillary optic is a type of focusing optic formed of arrays of small glass tubes that are tapered and curved. Similar to the guiding of light in fiber optic technology, X-rays are made to pass through the tubes by reflection. The polycapillary optic is matched with a micro-spot X-ray tube to gather a major portion of the tube output. This makes it focus on smaller areas that have flux many orders of magnitude higher than that of a mechanically collimated system. There are many benefits of using polycapillary optics in XRF coatings analyzers.

Smaller Features Measurement

A less than 20 µm beam size of the polycapillary optics enables the measurement of ultra-fine features on wafers, lead frames, connectors, advanced circuit boards, and microelectronics. This enables measurement of areas that cannot be measured by using mechanical collimators.

Thinner Coatings Measurement

An XRF analyzer integrated with a polycapillary optic focuses more X-ray tube output onto the sample, thereby measuring nanometer-scale coatings.

Increased Testing Throughput with Higher Confidence

The generation of higher intensity by the optic leads to higher count rates. In the case of XRF, higher count rates relate to rapid results and enhanced precision. This enables more measurements to be carried within a given period of time and guarantees better results, resulting in tighter production and better quality control.

Easier Conformity to Specifications

The application of XRF in measuring and regulating the finish thickness is enabled by performance specifications IPC-4556 for ENIG (electroless nickel/immersion gold) and for ENEPIG (electroless nickel/electroless palladium/immersion gold) analysis. These tests have to exhibit performance levels within a definitive tolerance. The application of a capillary optic renders it easier to accomplish this performance level.

Hitachi High-Tech Analytical Science Coating Analyzers

In the FT150 series of coatings analyzers manufactured by Hitachi High-Tech Analytical Science, a polycapillary optic is combined with a high-definition camera, a high-precision stage, a high-resolution Vortex® detector, and intelligent software for the absolute analysis of ultra-fine coatings on ultra-fine features.

Hitachi High-Tech has 40 years of expertise in coatings analysis and has developed more than 1000 applications with a series of products including handheld XRF, benchtop, and microspot instruments, as well as handheld and benchtop electromagnetic gauges.

This information has been sourced, reviewed and adapted from materials provided by Hitachi High-Tech Analytical Science.

For more information on this source, please visit Hitachi High-Tech Analytical Science.


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