Note: This is one in a series of blogs about fingerprint on card technology.
Miniaturization, in the form of increasingly small electronic components, has made it possible to put remarkably sophisticated features into very compact spaces. Fingerprint on card technology, which lets you authenticate a payment using your fingerprint, is an excellent example of miniaturization, since it places several complex components, including an image sensor, a secure element and a low-power microcontroller onto a standard smartcard.
To create a “fingerprint” card, you start with a standard payment card, which already has integrated circuits for digital authentication and the payment transaction, and then you add the necessary components and connections for biometric authentication.
Design for Manufacturability
Today’s payment cards are produced using manufacturing techniques that enable very high volumes, with minimal yield loss and at a reasonable cost. This kind of scalability is key to meeting strong market demand while keeping payment cards affordable.
Since fingerprint cards involve more circuitry than conventional payment cards, they will always be more expensive to manufacture than their conventional counterparts. But there are ways to minimize the extra expense. The goal is to design a fingerprint card that’s compatible with existing manufacturing techniques so there are fewer changes to be made to the manufacturing line before starting production. By making a few important choices in the design phase, developers can create fingerprint cards that can be manufactured using a standard production line and standard production processes.
Prepare for Hot Lamination
The manufacturing process is likely to use one of two lamination processes, hot or cold. Hot lamination uses heat to merge the PVC layers as they pass through the laminator. Hot lamination is the less expensive approach and the one most commonly used for manufacturing payment cards, but it’s only an option if the components used in the card can withstand the heat and pressure of the lamination machine. Cold lamination uses a pressure-sensitive adhesive that doesn’t need to be heated, so it’s safer for use with a wider set of electronic components, but it’s a more expensive process.
Some fingerprint on card solutions use components that aren’t compatible with hot lamination. As discussed in our previous blog, some designs add batteries or super capacitors to increase the amount of power available for biometric authentication, but these extra components are often too delicate for hot lamination. To reduce the chance of damage to sensitive batteries and super capacitors, manufacturers are likely to recommend using the more expensive cold lamination process. The other components used for biometric authentication are usually compatible with hot lamination, so choosing a solution that doesn’t require extra batteries or super capacitors is likely to be a better option.
Optimization for Integration
Another reason to eliminate extra components, such as batteries and super capacitors, is to simplify the design and reduce complexity in the manufacturing process. Using fewer components means there are fewer items to keep track of, fewer connections to make on the card, and fewer opportunities to break or damage something on the card during production, stress tests or when the card’s put to real-world use.
In particular, choosing a fingerprint on card solution that houses all the necessary components in a single module can lower production costs quite a bit since the module can be delivered in a production-ready format and there’s only one item to place on the card.
Eliminate the Flex PCB
A flexible printed circuit board, or Flex PCB, is a popular choice for assembling a biometric design during development and prototyping, but keeping the Flex PCB format when transitioning to mass production can cause problems.
To begin with, the Flex PCB format most frequently used with biometrics, a polymer reinforced with glass fiber, isn’t usually used with standard payment card manufacturing and is likely to require special handling, especially since it can be damaged by hot lamination. Even cold lamination can be tricky, though, since the PVC typically used with cold lamination doesn’t always make a good connection with a Flex PCB. Using Flex PCB may also create difficulties passing the usual stress tests since the bending and twisting actions performed in these tests can be more than the card can handle.
This is another instance where integration can help. Replacing the Flex PCB with a single module, which combines all the necessary components in one element, creates a more robust design. The module requires a very small PCB including all components which are protected by a mold cap. Protection via mold cap has been widely used with contactless cards for several years now and has helped make smartcards of all kinds more robust, since it does a better job of withstanding the mechanical challenges of production and everyday use.
NXP has designed a single-module solution for fingerprint cards that’s designed for high-volume manufacturing. Our solution delivers fast biometric performance using only the power provided by the payment terminal, so it doesn’t need a battery or super capacitors. Also, it withstands the higher temperatures used with hot lamination, requires placement of only one component, doesn’t use a big PCB set up and performs well in stress tests for everyday smartcard use. The result is a streamlined, cost-effective solution that is both robust and scalable.
Next Up: Sensors
The next topic in this series is sensor technology. We’ll look at the design and performance requirements for the fingerprint card’s onboard image sensor, which captures the fingerprint image used for biometric authentication.