Pictures of the Future    Fall 2007

Catching Contaminants

A bare and windowless corridor leads past a succession of dark doors. Behind these are labs where chemists and physicists from Siemens Corporate Technology (CT) in Munich track things that are barely tangible. They search for toxic substances in telephone casings and power cables, they unearth the causes of component failures, and they investigate why light switches in cars fail. Thanks to their ultra-expensive, ultra-sensitive collection of analytical equipment, the scientists are able to detect chemical and physical impurities diffusing through nanometer layers of computer chips—and even, if necessary, individual ions and molecules.

It is their laboratory that gets a call whenever a Siemens Group has a real problem—when inexplicable failures occur and a product suddenly ceases to work for no apparent reason at all. "What we do is to apply forensic methods to technology fields," explains Dr. Klaus Budde, a specialist in analytical chemistry at CT. At the same time, the labs also get to examine new Siemens products for toxic substances before they go to market. Naturally, the presence of any prohibited chemicals in a new line can kill its chances before it has even begun to bud. A few years ago, for example, a Japanese consumer electronics company had to withdraw a new game console worldwide just before Christmas because there were traces of cadmium in the console’s power cable. By the time the problem had been remedied the lucrative Christmas market was long gone.

Such stories are legend at CT. Some time ago Budde and his colleagues examined a batch of telephones for outlawed chemicals. Although most of the components came through the tests, they discovered that the tiny screws used to secure the housing were coated with traces of a toxic chrome VI anti-corrosion compound. Chrome VI has long been recognized as a carcinogen and prohibited worldwide. But a screw supplier from the Far East had ignored the ban. Thanks to Budde’s efforts the breach of contract was discovered and the agreement with the supplier terminated.

Knowledge Counts. The work performed by Budde and his team is perhaps best compared to a daily hunt for the proverbial needle in a haystack—not least because many electronics products contain hundreds of tiny components. How do team members find the one component that actually contains toxic substances? "It boils down to experience, familiarity with substances, and the ability to identify which chemicals might be used in what places," explains Budde. "The average age in the analytical department is close to 50," he adds with a laugh. "That must be unique!" Alongside their high-tech equipment, the team’s key to success lies in the accumulated expertise of 27 specialists.

It’s not that the team is exclusively on the lookout for toxic substances. Its lab work can benefit the environment in other ways. This is because analyses often reveal causes of failure in advance. Moreover, early analyses can sometimes avoid expensive product recalls with all of their associated logistical headaches. Dr. Hans Cerva is a specialist in such "nonconformance" jobs. One tool at his disposal is a so-called time-of-flight secondary ion mass spectrometer—or TOF-SIMS, for short. This piece of equipment is every bit as exciting as its name suggests. It comprises a shiny cube of stainless steel a little larger than a washing-machine drum. Metal cylinders and cables project out from the sides of the cube.

The TOF-SIMS is one of the most sophisticated pieces of equipment that analytical chemistry has to offer. Inside the stainless steel cube an ion beam is fired at the sample under investigation with an accuracy of a few micrometers. This in turn strips ions—so-called secondary ions—from the sample. These then race along a short track before they are deflected into a time measurement chamber. The TOF-SIMS is able to calculate the ion’s mass on the basis of its time of flight and thus determine the chemical element in question.

The determination of flight duration is so precise that the machine can identify not only simple chemical elements but also more complex molecules made up of different elements. The ion beam of the TOF-SIMS bores its way into samples like a fine needle and analyzes the layers and the substances they contain.

Cerva recently fired this ion beam at the surface of an ASIC—one of the small chips used to control safety systems in cars. Before production launch of a new model automobile, manufacturers generally test drive a batch of a few hundred vehicles in what is known as the qualifying round. In this particular case the manufacturer was becoming increasingly concerned about the newly developed ASICS. The problem was that they kept failing, and nobody could work out why. With his knowledge of the physical properties of semiconductors and his many years of experience, Cerva had a hunch that the chips might contain more than just standard semiconductor materials such as silicon. He therefore decided to carry out a TOF-SIMS analysis. This revealed a suspiciously high concentration of sodium, a light metal that is fatal to semiconductor components, since its ions get everywhere and interfere with the chip and its transistors.

Equipped with this crucial tip the manufacturer proceeded to check its ASIC production line and discovered a fault in process control. For some reason the production system was switching itself on and off in a fraction of a second, which caused sodium from the immediate surroundings to land inside the ASIC. A simple program debug was enough to spare the manufacturer thousands of complaints as well as the problem of having to dispose of tons of electronic scrap. "This was a typical case," says Cerva. "What we almost always discover is a fault in the production process, the wrong choice of material, or damage to the material. But to locate the cause takes real detective work, and that’s where the fun comes in."

The labs is crammed with sophisticated equipment such as an infrared spectrometer, a gas chromatography mass spectrometer, and a huge transmission electron microscope (TEM). Humming away in one room there is even a massive particle accelerator made up of large pipes the size of those used to transport natural gas. Within it, high-energy helium ions rebound from a sample with varying energies that reveal the exact chemical composition of the sample surface. Likewise, the TEM uses an electron beam to illuminate extremely thin samples of material, thus enabling researchers to analyze layers that are only a few nanometers (a millionth of a millimeter) thick—a degree of precision crucial for determining the functionality and quality of semiconductor components such as light-emitting diodes and diode lasers.

"Our nanoscale analysis capability means that we have the very latest analytical methods the market has to offer. These are accompanied by a body of expertise that is in demand during the development of almost every new material or technology at the Siemens Groups," says Dr. Helmut Oppolzer, head of the analytical team. Oppolzer and his colleagues mainly work for Siemens, since no other analytical laboratory is as available or trustworthy when it comes to dealing with confidential information. "If they come to us it usually means they are up against an acute problem that they can’t solve," says Oppolzer, "and one that needs to be resolved very quickly." In addition, his team also works for former Siemens spin-offs such as Epcos and Infineon.

Setting Standards Worldwide. The team’s expertise—especially in the analysis of contaminant substances—is also in demand from external clients. Here, areas of interest include the application of the EU’s environmental directive on the Restriction of Hazardous Substances in Electrical and Electronic Equipment (RoHS). RoHS stipulates that from 2006 onward such products may contain at most only traces of the heavy metals lead, cadmium and mercury as well as the brominated flame retardants. Initially, however, there was a lack of information on how the limits should be met and products tested. Understandably, manufacturers were very unsure about how to proceed according to the directive. After all, there was a real danger that products containing hidden traces of harmful substances would have to be withdrawn from the market. "It was a real time bomb for the manufacturers," says Budde. Whereas a homogenous solder paste is relatively easy to test for toxic substances, a printed circuit board full of tiny components such as resistors, capacitors, and processors is by no means as straightforward.

The International Electronics Commission (IEC) in Geneva, Switzerland, set up a task force with expert panels to establish international analytical standards. Their job was to lay down practical, reliable test methods and to work out sensible ways of examining the diversity of electronic components. The German Commission on Electrical Engineering appointed Budde to the international task force. With his wealth of experience in analytical methods he was able to make a number of telling contributions, including an astoundingly simple drop test for chrome IV compounds: if drops of a specific corrosive fluid are spotted onto the surface of a sample, it immediately turns a violet color in the presence of chrome IV. Although such a test is astoundingly simple, compared to the TOF-SIMS it is in fact extremely sensitive and reacts with chrome VI concentrations of only a few nanograms, which is certainly responsive enough for the limits prescribed by RoHS.

Budde was able to remind the IEC of the virtues of the drop test. Instead of running everything through incredibly expensive analytical equipment, he argued, it makes more sense to do a cheap and simple drop test to separate the wheat from the chaff. Today it has become a standard test worldwide. "Our analytical laboratory has been in existence for 30 years," says Oppolzer. "It was therefore relatively easy for us to come up with the tests required to check our products for RoHS conformance."

It says everything for the quality of its work that the laboratory’s expertise has become a world standard in the field of materials analysis and contaminant identification. What’s more, its success rate in clearing up cases of nonconformance is extremely high. As Klaus Budde explains, "We track down just about anything that departs from the norm."
                                                                                                                   Tim Schröder