Producing card bodies without integrated coils
Card bodies for smart cards that do not have integrated coils can be mass-produced using three different basic processes. These processes differ in terms of the durability of the card, surface features and allowed card components. Many card manufacturers often offer only one type of process, rather than the full range of options. Laypersons often regard the manufacturing of card bodies as an uncomplicated, easily mastered technology that essentially only amounts to punching out a few pieces of plastic foil and gluing them together. However, this is by no means true. The mass production of high-quality card bodies involves a multitude of complex manufacturing steps, and it demands outstanding mastery of the chemical processes needed to produce and use the plastic materials and associated inks. The technically most elaborate process is to construct the card body from several layers of plastic that are thermally bonded. This is called a multilayer construction, and the process of bonding the layers using heat and high pressure is called lamination. The thickness of the plastic foils used for the inner part of the card (the core foils) ranges from 100 μm to 600 μm, while the thickness of the outer or cover foils (overlay foils) ranges from 25 μm to 300 μm. A card body constructed in this manner allows a great degree of freedom in the form and layout of the card components, is very stable and also allows security features to be placed between the layers. For example, this technique is used in the MM process for German Eurocheque cards. Monolayer construction of the card body, using a single piece of 800-μm plastic sheet (monofoil), is a simplified version of multilayer construction. This process is less expensive, but the cards are less stable than multilayer cards. Above all, they allow significantly fewer options for the design and layout of the card components. For instance, with monolayer construction it is not possible to have a transparent cover layer to protect the printed elements against scratching and rubbing.

The third process that can be used to produce a plastic card body is injection molding. This essentially results in a monolayer card body, with all of its advantages and disadvantages. However, there is one small but significant difference.Athin printed foil (approximately 80 μm thick) can be placed in the mold, which allows injection-molded cards to be produced with printing right from the mold. This process, which is called in-mold labeling, has its limitations compared with offset printing or silk-screening in terms of layout and the inks that can be used. However, it has the advantage that it is not necessary to run the cards through a single-card printing machine after they have been molded. An additional feature of the injection molding process is that the cavity for the chip module can be formed in the molding process, so it does not have to be milled out afterwards. There are also processes newly available in which the chip module is placed in the mold, so that it is anchored to the card body when the card is molded. This method also makes it unnecessary to perform many of the steps described below. Standard injection molding machines have a capacity of approximately 2000 card bodies per hour. Although injection molding may appear to be inexpensive, it is usually more expensive than stamping single-layer card bodies from a large sheet of plastic if very many cards have to be produced (more than one million). This is primarily due to the time-consuming handling of individual cards, which is one of the primary cost factors.

Printing the foils
With regard to printing the card body, there is usually no difference between multilayer and monolayer cards. In the sheet printing process, large sheets of plastic are printed on multiplecopy sheets, and the individual cards are then punched from the sheets. The sheets are normally big enough to allow 24 to 48 images (cards) to be printed on each sheet, which is fed one or more times through the individual inking stations of an offset or silk-screen printing press. The front and rear sides of the card bodies must be printed separately. A basic distinction is made between offset printing and silk-screen printing with regard to processes used for printing cards. Finer details can be printed on the card with offset printing than with silk-screen printing. In addition, the inks used for offset printing are hardened using ultraviolet light. This occurs immediately following printing, which has the advantage that the printed cards can be stacked right away. However, it is not possible to apply holograms or magnetic stripes on top of UV-hardened coatings using the hot-stamp process,6 since they are not thermoplastic. A similar consideration applies to internal foils for laminated card bodies, since the lamination process requires the foils to be thermoplastic. Consequently, the silkscreen printing process is used, in which the inks harden by the evaporation of a solvent and remain thermoplastic. Additional card elements can easily be added on top of surfaces printed in this manner.

In practice, the two printing processes are often used in combination. For example, large single-color areas and the background for the magnetic stripe and hologram can be printed using silk-screening, while the fine details can be applied in a second step using offset printing. Silk-screen printing cannot achieve such a high level of detail. In summary, offset printing is ideal for colored subjects with high resolutions and large piece quantities. However, if additional functional elements (such as holograms) must be permanently applied to the surface of the card, either the entire card or at least the backgrounds for these elements must be printed with thermoplastic inks using the silk-screen process. Inks for offset printing cannot be used for this purpose, since they are hardened using ultraviolet light and are not thermoplastic. A third process that is sometimes used is thermal-transfer printing, in which a piece of colored foil is released by heating and transferred to a white card body. The colored foil bonds to the surface of the card. This process is frequently used as a purely black-and-white printing process to apply serial numbers to cards, but in principle, it can be used to reproduce all colors and shadings. However, it is slow and expensive, so it is primarily used for small quantities of cards in desktop personalization machines. It has a resolution of up to 300 dpi. An additional disadvantage of this process is that the applied colors are only bonded to the surface of the card, so they can be scratched off. The disadvantages of colors that are only bonded to the surface of the card can be avoided by using thermal dye-sublimation printing. In this process, a print head heated to nearly 200˚ C presses hot dye into the top plastic layer of the card body. The maximum penetration is 5 μm, which is sufficient to make the printing scratchproof. Thermal dye-sublimation printing otherwise has essentially the same characteristics as thermal transfer printing, including high costs, so it is also suitable only for relatively small quantities of cards. Even then, both processes can generally only be used to print on suitably prepared card surfaces, which limits their use. Nevertheless, they represent an entirely worthwhile complement to just-in-time printing for small and medium-sized quantities of cards.

Laminating the foils
With a multilayer card body, after the foils have been printed they are laminated at a temperature of 100–150˚ C and the required features are integrated. The printed foils are protected against scratching and wear by supplementary transparent overlay foils laminated onto the front and rear surfaces, which are often called overlay foils. Depending on customer requirements, signature panels, magnetic stripes and security features are also embedded in multilayer cards or laminated on top of the cards at this stage. It is certainly possible to use foils with different thicknesses for the front and rear sides of the card. In general, though, it is better to use a symmetrical construction for mechanical reasons. This means that foils with the same thickness are used for the front and back of the card. This avoids possible problems with a ‘bimetallic’ effect that causes the card to warp.

Punching the foils
Once the individual foils have been laminated, they must be brought to the desired card format. This is achieved using a punching process. The machines used for this have an hourly throughput of 4000–8000 cards. The burr that can be seen or felt at the edges of some cards is due to a worn punch and die set.

Milling the module cavity
A necessary part of the process of producing a card body is milling a cavity to receive the module. There are also processes in which the foils are punched out in advance to produce an opening to receive the module when the card body is laminated. The cavity is also already present in the card body if it is produced by injection molding. Since the underside of the module has a bump where the encapsulated die is located, a matching cavity must be formed in the card body by milling out a recess. A single-level cavity is generally unsatisfactory for modern types of modules, so it is common practice to mill a cavity with two or even three levels. This provides a larger contact surface between the card body and the module, which allows the module to be durably attached to the card body. In addition, it is mechanically significantly better if only the rim of the module is firmly attached to the card body, with no physical contact between the die on the rear side of the module and the card body. In a manner of speaking, the module is fitted into the card so that it ‘floats’ in the card body. The first step in making the cavity is to mill a recess that is as large as the contact assembly of the module and just as deep as the contact assembly is thick. Following this, an additional recess is milled in middle of the first recess to provide room for the encapsulated die. This yields a cavity with two steps. The milling must be performed very precisely, since the thickness of the remaining card material at the deepest part of the cavity is only 0.15 mm. If the milling machine vibrates or rocks, the card body could be milled all the way through and thus be rendered useless. If the cavity is not deep enough, the module will stand proud of the surface of the card, which is only allowed within very narrow limits. This tricky production step is performed by fully automated machines, with the card bodies fed in from one bin and passed out to another bin. The throughput of a single machine is around 1000 cards per hour.

Printing the card body
A second type of printing process, in addition to sheet printing, is individual card printing. With this process, the cards are printed after they have been separated. When cards are printed individually, this always takes place before the cavity is milled. The throughput of machines for printing individual cards ranges up to 12,000 cards per hour. A variation of individual card printing is thermal transfer or thermal dye-sublimation printing in desktop personalization equipment. The throughput of such equipment is significantly lower, and is around 300 cards per hour at most.

Applying card components to the card body
After the card bodies have been trimmed to size, various components such as holograms and magnetic stripes are applied to them. Holograms, which are supplied in rolls, are permanently bonded to the card body using a thermal bonding technique (hot stamping or hot rolling). After this, any attempt to remove this security feature will destroy it. Magnetic stripes are applied to the card bodies using lamination or hot stamping.