By Debbie Sniderman

Contactless methods are next in the evolution of consumer payment options. Physical contact was needed to integrate payment cards with point-of-sale terminals using magnetic stripes or chips. The faster tap-and-go contactless interactions using Radio Frequency (RF) communication and inductive coupling with a card reader are becoming more widespread. They’re more convenient, more secure, and can link to many different types of payment systems such as subways to help reduce the need for cash.

Typical payment cards with both contact and contactless interfaces have two types of antennas, one on the back of the card’s communication chip (IC) and a separate booster antenna on the card spanning its entire body. This larger antenna helps the passive system harvest enough power from the electromagnetic field when it is within the working range (~4 cm) of the card reader.

Traditionally antennas on plastic cards are created with wire windings or lithography and batch chemical etches when produced in high volumes. But, Alan Conneely, Centre Manager at the National Centre for Laser Applications (NCLA) at the National University of Ireland Galway, says high resolution UV nanosecond laser ablation techniques and new antenna designs have allowed the creation of IC antennas without booster antennas.

UV nanosecond laser ablating antennas from ½ oz copper printed circuit board materials

UV nanosecond laser ablating antennas from ½ oz copper printed circuit board materials

His group’s new techniques offer many production advantages, but also increased card reliability. “The coil on module technology eliminates the need for the interconnection to the chip as it uses a second RF induction loop. When it is bent in a wallet, it doesn’t break as easily. It is more self-contained,” says Conneely.

Schematic showing how a card reader (left) inductively couples with a coil on module contactless payment card (right) through its secondary antenna module for power harvesting and communication

Schematic showing how a card reader (left) inductively couples with a coil on module contactless payment card (right) through its secondary antenna module for power harvesting and communication

Ablation Processing
Together with industry partner AmaTech Group Ltd, and the Antenna & High Frequency Research Centre at the Dublin Institute of Technology, Conneely’s team created IC antennas with optimized designs and laser ablation processing suitable for use without booster antennas. They performed RF modeling and simulation, antenna design, laser ablation processing trials on copper PCBs and testing to optimize the following process and quality goals:

  • Complete electrical isolation with minimal debris within ablated kerf
  • Narrow kerf to enable increased resolution
  • Minimal heat affected zone to avoid damaging electrical track
  • Minimal damage to FR4 substrate to ensure long-term antenna robustness and prevent copper layer delamination

Process parameters such as power, repetition rate, pulse energy, scan speed, number of passes, antenna tool path length and cycle time were varied. Devices were produced and tested to check performance and processing relationships.

Smaller Antenna Resolutions Possible than Chemical Etch
Conneely says the resulting devices demonstrated robust isolation and minimal substrate damage. In addition, one key advantage to laser ablation processes in the copper thickness tested is it created higher resolution structures compared to other production methods. At 17 µm copper thickness, the smallest chemical etching feature separations are around 75 µm.

The laser ablation studies in this research produced kerf widths in the range of 15-25 µm with an optimal combination of isolation, resolution and throughput. With better resolution machining capabilities, IC antenna designs can have more coil turns per given area.

Laser ablated prototype antenna module with soldered RF transponder chip

Laser ablated prototype antenna module with soldered RF transponder chip

Wearable Payment Devices
Europay, MasterCard and Visa (EMV) industry standards exist for contactless cards and payment systems, and they currently are under development for wearable objects. Wearable devices are aiming for an activation distance of 4 cm from the reader for ease of use. In this work, laser ablated antenna modules on flexible substrates were inserted into a wearable wristband with new antenna designs and were able to meet the 4 cm activation distance and other EMV industry standards.

“One challenge lasers have always had to overcome when compared to mass batch production are techniques for high volume production. Improving the antenna designs and using traditional techniques for improving throughput, such as multiple lasers, beam splitting and thinner copper will speed up the process and make the laser ablation process more effective,” says Conneely.

LED representation of the working envelope of where the card would operate in space when over and close to the card reader. Outside of this envelope operation ceases

LED representation of the working envelope of where the card would operate in space when over and close to the card reader. Outside of this envelope operation ceases

LED representation of the working envelope of where contactless payment card would operate in space when close to the card reader shown in overlay. Outside of this envelope operation ceases

LED representation of the working envelope of where contactless payment card would operate in space when close to the card reader shown in overlay. Outside of this envelope operation ceases

More Flexible Designs Possible
The industry trend is moving away from cards towards bracelets, key fobs, jewelry and other wearable devices. “As producers move more towards customized wearable designs with smaller batch runs, laser ablation processes will be competitive and very helpful. Laser machining processes are flexible and able to change more quickly than chemical batch etching when antenna design configurations change for any kind of object,” says Conneely.

In addition to designs on plastic substrates, Conneely’s group also has designs for metal substrates which attenuate RF signals that demonstrate better performance. “Metal cards offer greater aesthetic appeal and card feel resulting in higher value payment devices. Higher-end payment cards and wearables such as jewelry would ideally use metal substrates. The laser machining process allows for larger antenna design spaces, more design iterations faster, and overall more opportunities for antenna design,” he says.

“Contactless payment systems are currently a very competitive market. Our technology is still in development, heading towards manufacturing, which involves working not only with the card issuers, but all of the stakeholders in the financial space,” Conneely says. He will present more on this topic at ICALEO, Oct. 16-20, 2016 in San Diego, CA in his talk M501 in the Laser Microprocessing Conference LMF Session 5 on Tuesday.

Debbie Sniderman is a freelance writer for LIA.