Helmut Fischer Institute developed new X-ray technique for coating thickness analysis

Citation

(2009), "Helmut Fischer Institute developed new X-ray technique for coating thickness analysis", Circuit World, Vol. 35 No. 3. https://doi.org/10.1108/cw.2009.21735cad.001

Helmut Fischer Institute developed new X-ray technique for coating thickness analysis

Article Type: New products From: Circuit World, Volume 35, Issue 3

Introduction

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 preempts this need and Ray Scruby of Fischer Instrumentation (GB) Ltd discusses its diverse applications and how the technique can benefit the UK electroplating industry.

The key to advances in this analysis software lie in automatic “Class Determination”, which saves operator time, negates the need for a skilled operative and removes any possible operator errors. How it works is best demonstrated from studying applications ranging from lead soldering issues affecting the electronics industry, aerospace and military, through to practicalities on the plating shop floor, where plating shop operators can quickly make accurate measurements without selecting specific programmes.

Bulk solder materials and tin solder coatings

For many years, the replacement of leaded solder with alternative alloys or pure metals has been a constant issue for electronic industries as well as suppliers, operators and consumers. During this time well in excess of a 100 replacements have been proposed and evaluated but only a few have been accepted. Importantly, there are still applications where a minimum proportion of lead is still required. These are so-called “high reliability' applications, including the aerospace and military sectors. Lead is demanded in these applications due to the unfortunate and uncontrollable property of pure tin to grow fine hair like whiskers out from solder joints. These can span quite large distances to connect with other joints and cause short circuits. They can be clearly seen in Figure 1. Here, tin whiskers can literally be fatal and tin-lead alloys must be used as the lead prevents this unfortunate metallurgical property of pure tin. Lead is now banned in most commercial products, so the growth of whiskers will inevitably increase.

Figure 1

Identification of solder materials

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. Figure 2 shows a range of complex solders but clear distinctions can be seen in the different coloured spectra.

Figure 2

Analysis of solder composition

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. Figure 3 shows the analysis of thin solder coatings; bromine in the printed circuit board (PCB) material can now be compensated to provide better accuracy.

Figure 3

Selecting solders for electronic circuit boards

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.

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

The distinct families of solder material are shown in Table I, 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.

Precious metal analysis

The complexities of solder materials are mirrored in the precious metal industries. Assay offices, for example, have to certify a whole range of gold, platinum, palladium and silver alloys. Like solder, the problem is complicated by the requirement to measure thin coatings as well (thick coatings are even more of a problem as counterfeiters try to pass items off as solid gold).

Modern jewellery coatings

Modern jewellery coatings are now complex and may contain elements such as Au, Ag, Cu, Zn, Co, Pd, Fe, Mn, Cd, Pt and Ni. Nickel is now not allowed in jewellery as some people have an allergic reaction to it, but it is often used as an underplate, as in Ag/Ni/sterling silver. It is also not allowed as an underplate and must be identified in the analysis process.

General electroplating

In a normal plating shop 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.

Outlook

The development of this new technique will alter the way in which X-ray systems are used in the future. Analysis of samples has always required certain knowledge of the possible outcome, studying the spectrum for example, before setting up an application for the precise measurement. The automatic class determination removes this step and any possible operator errors. It will become even more useful for coating thickness measurement, as this will be completely de-skilled, the operator merely having to place a sample into the instrument. It offers savings in time and improves accuracy, removing operator error from an important everyday task.

For more information please visit: Fischer Instrumentation (GB) Ltd www.fischer-material-analysis.co.uk