Coating Thickness Measurement and Materials Analysis

New X-Ray Technique De-Skills Coating Thickness Measurement and Simplifies Coatings Analysis

Until now, sample analysis of unknown bulk material alloys or unidentified coatings has required certain knowledge of what to expect before accurate quantitative results could be obtained.  A new X-Ray technique developed by the Helmut Fischer Institute pre-empts this need and has far ranging applications from lead soldering issues affecting the electronics industry and aerospace and military, through to practicalities on the plating shop floor, where plating shop operators can quickly make accurate coating thickness measurements without selecting specific programmes.

The key to this advanced analysis software lie in automatic ‘Class Determination', whereby groups of specific applications are stored in a library and when a sample is presented to the instrument, this library is scanned an the application with the closest fit selected.  This saves operator time, negates the need for a skilled operative and removes any possible operator errors.

Plating Shops

In the case of a normal plating shop, there are often many lines are running, each with a different process.  Regular measurement of samples requires the operator, in many cases not skilled in the operation of X-ray systems, to select the correct application before making the measurement.  This has previously been simplified by setting tasks, so that all is required is to select the one correct button, but it still relies on getting the correct button.  The new software takes even this source of error away.  An unknown sample can be placed into the instrument and its class will be automatically determined, the correct application selected and measurement made.

Electronics Applications

Until now, sample analysis of unknown bulk material alloys or unidentified coatings has required certain knowledge of what to expect before accurate quantitative results could be obtained.  This may involve drawing some initial conclusions from studying the spectrum.

The identification of new solder material, both in bulk form and on manufactured circuit boards is an important application for producers and users and the advances in X-ray analysis software by Fischer have simplified this task.  The new software uses a function called Class of Materials, which groups sets of specific applications in a library and when a sample is presented to the instrument this library is scanned and the application with the closest fit selected.  Fig. 2 shows a range of complex solders but clear distinctions can be seen in the different coloured spectra.

Fig.2  The green spectrum is pure tin, while the red is of SAC305 (SnCu0.5Ag3).  The yellow is SnPb3, used in high reliability soldering.  The blue is from a SnBi solder with 1% Bi.  Clear differences can be seen by the small peaks of the accompanying elements Cu, Ag, Pb and Bi being clearly visible.

The analysis is a very complex mathematical task as elemental radiation is affected by other components in the alloy and in the case of coatings the underlayer radiation is partially absorbed by layers on top.  The thickness of each layer also complicates the situation, as the model must accommodate a whole range of various layer thicknesses.  Fig. 3 shows the analysis of thin solder coatings; bromine in the PCB material can now be compensated to provide better accuracy.

Fig 3. Thin solder coatings (pure tin,SnBi and SnPb3) on PCB material, in the presence of Cu-brominated epoxy PCB.

For the producer of electronic circuit boards the selection of the correct bulk solder material is as simple as placing a sample in the instrument.  The importer can scan populated circuit boards to ensure they are lead free or importantly, that there is lead present for high reliability applications.  If a repair has been carried out on a board, it is essential the correct solder is used in order to comply with regulations, ensure high reliability and to avoid failures, as a mismatch with the original solder can lead to dry joints as the melting temperatures are different.

The distinct families of solder material are shown in Table 1, where the difficulty of the task can be appreciated, some families have multi element alloys, but they can be distinguished within a few seconds and the precise application selected for a detailed measurement.

Table 1. Solder types shown with the main automatic class groups.  The classes can be for bulk alloys (such as solder reels) or coatings on printed circuit boards, wires or components.  It can be seen that very complex alloys can be screened automatically

To talk directly to an XRay Systems expert, contact 01590 684100 or email Xray@fischergb.co.uk