Exploring the Elemental Information in Credit Card Chips without Sample Prep

As credit cards have become a staple in daily life, security measures have evolved. Despite the rise of touchless RFID payments, chip-based transactions remain a trusted and secure option. These chips, and many other common consumer products, contain sophisticated microelectronics that are generally hidden for aesthetic reasons. This is often accomplished using a layer of plastics or coatings, which must be then removed if analysis is desired. However, with the information depth potential of micro-XRF (X-Ray Fluorescence), these components may be analyzed without the need for sample preparation or destruction.

In this study, a common credit card chip was investigated for its elemental composition information via SEM EDS, using QUANTAX EDS for SEM, and micro-XRF on SEM, using QUANTAX Micro-XRF with an XTrace 2 micro-XRF source. To augment the specificity and efficiency of our analysis, both the standard SEM stage and the specialized Rapid Stage were used. This dual-stage and dual excitation source setup in the SEM facilitated a comprehensive and swift examination, leading to improved insights into the chip’s characteristics.

Figure 1: Comparing EDS and micro-XRF spectra. The electron beam spectrum (in blue) gives surface information, the light elements (here Si, Cl, C) are generated on the surface of the credit card chip. Micro-XRF (in red) have a much higher depth in penetration, it can clearly resolve sample structures underneath the sample surface. Nickel (Ni) is incorporated into the contacts, where the Gold (Au) signal represents the bonding wires and the signal from the contact pins.

Figure 2: Elemental mapping distribution by EDS (left) and micro-XRF on SEM (right) shows that the sub-surface Au, Ni and Cu signals can only be detected via micro-XRF due to its superior depth penetration.

The elemental composition of credit card chips typically comprises silicon as the predominant semiconductor material, accompanied by copper and gold. Silicon serves as the primary substrate material owing to its semiconductor properties, while copper is favored for its conductivity and utility in interconnections within the chip architecture. Gold is commonly employed for its excellent electrical conductivity and resistance to corrosion, primarily in bonding pads and wire bonding applications. Additionally, trace amounts of other elements, such as aluminum and nickel, may be present, their presence influenced by the intricacies of the chip's design and fabrication processes.

In this chip analysis as shown in Fig. 1 and Fig. 2, the detection of silicon (Si) from the sample surface can be achieved using both EDS and micro-XRF on SEM, while the silicon in the substrate can only be detected by micro-XRF. In addition, the copper (Cu) and gold (Au), which are both located underneath the sample surface, can only be identified by micro-XRF thanks to its superior depth penetration capability which reaches centimeter levels.

Leveraging high-energy X-ray beams, micro-XRF on SEM provides heightened spectral intensity and improved detection of high-energy lines. In addition, micro-XRF has significantly reduced background noise when compared to EDS, thereby facilitating the detection of trace elements due to an elevated peak-to-background ratio.

Rapid Stage enables the acquisition of seamless mapping, as shown in Fig. 3. Unlike traditional SEM stages, the Rapid Stage offers clear imaging without any stitching effects that could obscure details. It is a modular piezo-based apparatus, meticulously engineered to be mounted atop existing SEM stages and to achieve large-area high-speed elemental X-ray mapping of up to 4 mm/s.

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Figure 3: With Rapid Stage, smooth mapping data can be achieved with higher speed. Top: EDS map with Rapid Stage, Bottom: EDS map with SEM Stage.

Dig Deeper: Exploring the Elemental Information in Credit Card Chips without Sample Preparation