Laser marking of ID documents is increasing. Mandated in European Union driving licences, selected by governments on every continent to personalise over one fifth of all 2013 passports, and proliferating in national ID projects around the globe, it is a technology that has seen a significant and relatively recent rise in implementation. Latest figures (September 2013) reveal 250 million documents per year are personalised by laser, representing 45% of national ID, 35% of driving licences, and over 20% of passports. In this article the authors use the QSDC best practice methodology to examine what is causing this growth.

Quality, Security, Durability and Cost (QSDC, see figures 1 and 2) are the cornerstones of any successful identity document (ID) program. These criteria have trade-offs and compromises, and the relative value of each must be considered when designing the most appropriate ID. The QSDC criteria are summarised below.

figure 1

Quality
A high-quality document will be consistent in appearance and closely match all other documents issued in the same ID program. The security features – in particular, the cardholder’s image – will be crisp and clearly defined to allow easy authentication. Overall, a high-quality identity document will look and feel authentic.

Security
The security of an ID is a measure of how well it resists deliberate attack; by simulation to produce a counterfeit, or by tampering to alter the information. The security of the document also depends on the ease with which it may be verified as being genuine.

Durability
The durability of an ID defines its resistance to environmental change. A document encounters a variety of hazards during its life, including accidental attack – such as laundry – or deliberate misuse. An ID needs appropriate durability to survive the required validity period without significant visual change, and without compromising its performance. A useful approach to achieving ID card durability is set out in ISO/IEC 24789, where the use and storage of a card are considered, as well as the required lifetime.

figure 2

Cost
The cost of the document refers to the cost to produce it. This will include the fixed and variable costs associated with enrolment, components, manufacture, personalisation, issuance, shipping, and the many administrative functions necessary to manage and secure these activities. Understanding the total cost of ownership, and the issuance cost per card over the validity period, is an important yet often challenging task.
  The QSDC requirements of an ID document can be used to assess the relative merits of personalisation technologies. Laser marking has traditionally been associated with high security and high durability, but at high cost. Quality is seen as excellent, though some have felt a monochrome image seems somehow ‘old technology’.
Before considering each characteristic, it is worthwhile considering the fundamental principles of laser marking. Personalisation by laser occurs when energy is focused within the body of a suitable substrate to produce a permanent darkening of material. As this involves reaction within the body of the material, the marking quality is affected by the construction of the layers, as well as their chemistry. Other components, such as preprint, adhesives and optically variable devices (OVDs) must also be considered.

Quality
The quality of laser marking essentially depends upon the control and optimisation of three factors: 
• Substrate: the material being marked, including any surface printings.
• Hardware: the laser and ancillary components of the system.
• Firmware: the instructions that drive the marking process.

First the substrate to be marked is considered; the material, its chemistry, construction, any additional components, and the preprint design.

Substrate
Polycarbonate (PC) material that is suitable for laser marking is available from several sources. However, it is very important to note that not all PC is the same and not all sources of PC result in good quality personalisation. Although a material may be referred to as ‘polycarbonate’, and its principle chemistry might be that of polycarbonate, this is no guarantee that it will react to marking laser energy in the same way as a different PC substrate. Indeed some new PC grades are available which offer shorter marking times, and thus a higher throughput of documents. It is important that the system is correctly tuned for the grade of polycarbonate selected.
  New markable materials that are not based on PC are beginning to show some very promising results. These materials are typically based on doped polyester (polyethylene terephthalate or PET), and may offer an interesting alternative to traditional PC for ID documents.
There is no substitute for thorough testing. All materials needed to make the product such as the preprint, adhesives, embedded holographic components, lens structures and contactless chip inlays should be tested to verify suitability. Also, it is recommended that both white stock, as well as preprinted stock, is tested to ensure the product will meet end-use requirements.

figure 3
 

Construction
There are guidelines and rules regarding the sequence, thickness and chemistry of layers required to optimise the quality of laser marking. These are particularly important when specific features are required, such as MLI/CLI or tactility, or when embedded holograms are used. Other components may also need to be considered, such as security preprint and the use of

figure 4

contactless chip inlays (see figures 3 and 4). For example, several important guidelines exist for preprint design, including the carbon content of the ink, its density, and the layer within the substrate on which it is printed. Details of construction best practices are outside the scope of this paper, but are available.

In practice, issuing offices may be faced with the challenge of laser personalising multiple documents that vary in their chemistry, construction and preprint design. Modern high-speed laser personalisation systems are configurable to handle different batches and utilise optimum laser parameters specific to each document. For example, the system can be set up to optimise laser marking quality on alternate batches of PVC and PC, with different preprint and layouts. This can be done simply to speed set up, or at a more detailed level as required.

Hardware
Generally, materials have been designed to be marked with laser wavelengths of 1064nm. Best practice consideration of hardware selection includes:
• The marking speed of the system.
• Flexibility of features available.
• Precision and accuracy of the location of an ID document in the marking module.
• Control and accuracy of the laser beam position and focus.

New laser hardware is emerging, which could permit higher speed or lower cost, and may also enable new security features. There is much R&D activity in this area.

Firmware
Firmware can be thought of as the instructions given to the laser, and its importance in achieving optimum quality should not be underestimated. The critical requirements for quality marking are the precise positioning and characteristics of the laser beam, and to achieve these, control of the following is required:
• Power, pulse rate, scan speed and resolution. There may be trade-offs between quality and throughput, for example delays may be required to improve the edge quality and sharpness of the laser mark;
• Size and shape of the marking field.
• Distortion correction, for example as caused by lenses in the beam train; there may be as many as twenty firmware parameters available to correct for distortion.

figure 5

As well as the impact on visual quality and aesthetics, poor laser marking can render machine readable features such as barcodes unreadable, impacting security. Experience provides a solid foundation for knowledge, with R&D and real programs contributing to a better understanding of cause and effect. The practical benefit of this know-how is seen in the implementation of best practices that include design rules and guidelines for substrate, hardware and firmware. Optimisation of firmware is not only critical for quality, it is also a key factor in achieving the security features produced during personalization.

Security
Laser marked polycarbonate offers great potential for security features that are easy to verify, and defend against both counterfeiting and alteration. That does not mean that an ID that includes a laser marked polycarbonate is automatically secure, it has to be designed that way.
  Put another way, most counterfeits of laser marked polycarbonate are neither laser marked nor polycarbonate. Instead, criminals more likely use digital black graphics and PVC to simulate – or alter – an ID. Strong defence against this comes in the form of security features that utilise key characteristics of laser marking: writing beneath a surface, exceptionally high resolution, true greyscale and tactility, to name just a few. In addition, laser marking can be seen under low magnification (for example a simple x10 loupe) to exhibit certain characteristics that indicate a laser has been used. Artefacts of the marking process that might be regarded by some as a fault can be used by a document examiner as evidence that the genuine personalisation technology was used.

Flexibility
An advantage of laser is the flexibility of marking parameters it offers. The wide range of energies and other laser settings enable a single piece of hardware to interact with the substrate in multiple ways, to produce many different security features, at overt, covert and forensic levels. This flexibility also enables laser systems to accommodate a variety of materials, variety of elements, and combinations of both to obtain the desired quality and throughput.

Security at Time of Personalisation
Security features are especially strong if they include personal variable data. Security at Time of Personalisation– where security is added to a blank document – creates security that is both anti-tamper and anti-counterfeit, encourages strong first line verification, and helps defend against mass counterfeiting and even component theft (figures 6 and 7).

 

figure 6

Examples of strong overt laser personalisation features include CLI/MLI lenticular devices, tactile elements and perforation. More recently, cards and passports have been constructed with PC containing clear and/or foiled windows, which are laser personalised using marking or ablation processes.
More sophisticated lenticular features are also appearing, which are marked by laser to exhibit very strong 3D optical effects. Extreme tactile features have also begun to emerge. Covert and forensic personalisation features are also available using laser systems, including the incorporation of personal data hidden within the portrait. A study and comparison of these features is beyond the scope of this article.

Another benefit of laser as a secure personalisation technology is its relatively limited availability. By developing features that are challenging to simulate or alter unless a laser is used, the difficulty in sourcing a laser helps protect the ID from attack. Even if a laser was obtained, the know-how and expertise required to create good simulations of genuine features would still challenge the counterfeiter.

 

figure 7

Durability
Durability of IDs is generally measured using test methods that examine such properties as resistance to flex, abrasion, chemicals, daylight and extremes of temperature and humidity. When compared with most common polymer substrates, polycarbonate performs extremely well in most, if not all, of these tests. Together with certain grades of polyester, polycarbonate is widely considered to offer the longest lasting and best protection to the personal data held on an ID document, whether that data is printed, laser marked or in electronic form.

Laser marking is in itself inherently durable. The mark formed by the personalisation process is typically carbon, which is chemically inert and does not fade, discolour or migrate. Protection against harsh environments is achieved by creating the mark deep inside the layers of PC. This helps defend against criminal attempts to alter the document. Important durability standards for ID documents are ISO/IEC 24789 (for cards) and ICAO’s ‘Durability of Machine Readable Passports’1. The durability performance of both material and personalisation are considered in these documents.

As for security, the durability of a document is not automatically assured by the use of laser marked PC. Construction design and processing conditions must also be correctly defined and diligently followed to ensure the required lifetime is achieved.

Cost
The advantages considered previously in this article go some way to explain the recent increased interest in laser marking, however cost reduction is perhaps the biggest reason for its global popularity.
The costs of the hardware and substrate material have both fallen substantially over the last five years. What used to be considered a solution that only some governments could afford is no longer beyond the budgets of most, particularly when factoring in the longer validity periods enabled by higher durability.

Costs have been driven down by higher production volumes, as well as more competition and technological innovation. Competition from other laser markable substrates, including PET polyester and PVC, is helping to keep polycarbonate prices lower, whilst cost reduction due to innovation applies to both substrate and laser marking systems.
Another driver for PC is the high cost associated with including a microchip in the document. If this expensive device is to survive in circulation, a robust physical ‘package’ is preferred and well-designed and constructed PC has shown itself to give suitable protection.

Summary
Effective laser marking of secure ID documents is perhaps more complex than might first appear, with numerous opportunities to get it wrong. By utilising the QSDC best practice methodology and know-how built up over years of research and implementation, experienced technology providers work together to design, manufacture and personalise cost-effective ID documents that are able to deliver outstanding quality, security and durability performance.

Reference
1 ICAO Technical Report Durability of Machine Readable Passports, August 2006, Version 3.2. http://www.icao.int/Security/mrtd/Downloads/Technical%20Reports/TR%20-%20Durability%20of%20Machine%20Readable%20Travel%20Documents%20V3%202.pdf

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Nick Nugent
Nick Nugent has a degree in Applied Chemistry (Hons.) from Lanchester Polytechnic, Coventry, England and has spent more than 30 years in the secure document industry. He has worked in product development, project management and marketing, in the design, manufacture and implementation of security features and personalisation systems. Nick uses his extensive experience of the document security market to advise governments on the selection and implementation of cost-effective security for ID documents, and is a regular contributor to this Journal. At the time of writing this article, Nick was employed with Entrust Datacard.