Using Polycapillary Optics for Coatings Analysis

With electronics and electronic components getting smaller and more complex, it is required that metal finishes on these components be plated on smaller features, as thinner layers, and controlled to tighter tolerances. In case the finishes are too thin, the product will not be able to fulfill performance specifications and could fail prematurely, risking warranty claims and reputation damage. Similarly, if platings are too thick, money and materials are wasted, and mechanical fit is also associated with potential problems that could lead to costly scrap or rework.

X-ray fluorescence (XRF) is a non-destructive, rapid, and user-friendly technique, and hence it is extensively used for measuring the thickness and composition of coatings. In order to measure coatings on small features, conventional XRF instruments use mechanical collimation to lower the beam size of the X-ray tube to fractions of a millimeter. This is realized by placing a metal block, with a small hole drilled through it, in front of the tube, allowing only the X-rays aligned with the hole to traverse and reach the sample. Most of the X-ray tube output cannot be used for analysis, because it is blocked by the collimator block.

A polycapillary optic provides a more novel method to measure fine features. It is a focusing optic consisting of arrays of tiny glass tubes that are curved and tapered. Similar to the way light is guided in fiber optic technology, X-rays are guided through the tubes by reflection. The polycapillary optic is matched to a micro-spot X-ray tube in order to collect more of the tube output. This focuses it onto smaller areas with flux that is orders of magnitude greater than that of a mechanically collimated system. The use of polycapillary optics in XRF coatings analyzers has many benefits.

Image Credit: Courtesy of F.M. Callahan

Image Credit: Courtesy of F.M. Callahan

1 Smaller Features Measurement

The beam sizes of Polycapillary optics are less than 20 µm, which makes it possible to measure ultra-fine features on connectors, microelectronics, wafers, lead frames, and sophisticated circuit boards. This enables measurement of areas that are impossible to achieve with mechanical collimators.

2 Thinner Coatings Measurement

An XRF analyzer equipped with a polycapillary optic can measure nanometer-scale coatings by focusing more X-ray tube output onto the sample.

3 Increased Testing Throughput with Higher Confidence

The greater intensity produced by the optic leads to higher count rates. In XRF, higher count rates denote enhanced precision and faster results. This enables more measurements in any given time period and higher assurance in the results, resulting in superior quality control and tighter production.

4 Easier Conformity to Specifications

The use of XRF in establishing and controlling finish thickness is enabled by performance specifications IPC-4556 for ENEPIG for (electroless nickel/electroless palladium/immersion gold) and ENIG (electroless nickel / immersion gold) analyses. These tests must exhibit performance levels within a definite tolerance. This performance level can be achieved more easily with the use of a capillary optic.

Hitachi High-Tech Analytical Science offers the FT150 series of coatings that integrates a high-resolution Vortex® detector with a polycapillary optic, a high-definition camera, a high-precision stage, and a smart software for the ultimate analysis of ultra-fine coatings on ultra-fine features.

With more than four decades of coatings analysis expertise, Hitachi High-Tech has developed more than 1,000 applications with a range of products such as handheld, benchtop and microspot XRF instruments, in addition to 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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