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Facts About Data Matrix Codes for Product Identification

A data matrix code, or in short simply “DMC”, is a 2D code. In many industries DMCs have become the preferred way of encoding data, e.g. in automotive and medical industries. Machine readable data matrix codes are marked reliably, efficiently, permanently and abrasion-resistant with laser marking machines. But what do I need to know if I would like to mark products with data matrix codes?

Content

What are the advantages of data matrix codes?

What is the Error Correcting Code (ECC)?

How can the size of a data matrix code be defined?

What is behind the symbol size of a DMC?

Are there also rectangular data matrix codes?

Does the surface structure have an impact on the readability of DMCs?

How can you avoid that DMCs are incorrectly marked?

How can you optimize the DMC to increase its readability?

How can you decrease the marking time for a DMC?

Marking and reading of data matrix/2D codes in the automotive industry

Summary: 5 facts about data matrix codes

What are the advantages of data matrix codes?

One of the biggest advantages: They need little space to store information. Furthermore, since data is redundantly encoded in the DMC, reading the information back from the DMC is possible, even when the DMC is partially impacted. That also contributes to the popularity and wide application of DMCs.

What is the Error Correcting Code (ECC)?

There are different error detection and error corrections methods related to DMCs, called error correct code (ECC). Nowadays the most common one is the ECC200. So typically, when you talk about DMCs, most people with some DMC knowledge will assume that you mean the DMCs with ECC200. Nevertheless, it makes sense to explicitly point out which DMC with which ECC you mean, especially prior to application tests, in order to avoid any misunderstandings with other people, because the selected ECC results in different looking DMCs. Look at the following illustration.

Despite the same content, the DMC looks different, depending on the ECC:

How can the size of a data matrix code be defined?

Another source of possible confusion is the size of the DMC, when there is no metric or clear reference mentioned nearby. You might hear from a colleague that he or she needs a 16×16 DMC on the product. Without any further explanation, that leaves room for interpretation, because the mentioned dimension “16×16” could refer to the requested area size (typically in mm) or symbol size (number of rows x number of columns) of the DMC. Does that make a difference?

Oh yes, it does. The following example shows how a DMC with symbol size 16×16 is marked on an area smaller than 16mm x 16mm (the right DMC below), while the other DMC on the left side with only a 14×14 symbol size covers an area of 16mm x 16mm.

(beware: both DMCs enlarged for better visibility, i.e. original area size of the left DMC was 16x16mm²; the proportional relationship between the two DMCs remained the same).

What is behind the symbol size of a DMC?

The symbol size determines the data capacity of a DMC. The larger the symbol size is, the more alphanumerical characters or numerical digits can be stored in the DMC. Beware that it also makes a difference for the symbol size, if you want to encode only digits or alphanumerical characters, i.e. a mix of letters and digits. In fact, you can encode more digits than alphanumerical characters in a DMC with the same symbol size.
The following two DMC examples illustrate that more data drives up the symbol size.

And the following table lists the most typically used symbol sizes and the related data capacity of the DMC.

Are there also rectangular data matrix codes?

When looking at the table, you might have asked yourself: “Wait a sec, a rectangle symbol size?” Yes, indeed. You can also create DMCs with a rectangle shape. In situations when you have limited vertical space for your DMCs, a rectangle DMC can the suitable approach to deal with that space restriction, as you can see below.

Does the surface structure have an impact on the readability of DMCs?

Complex surface structures are challenging regarding the readability of data matrix codes. Especially automobile parts often have rough surfaces with contours or changing dark shades. These are not the best conditions for a perfect machine-readable mark. That is where ultra high contrast black/white marking comes into play: This laser marking solution provides high readability of marked codes even on rough surfaces.

Laser marked data matrix codes on a brake caliper. On the left with optimized black/white marking, on the right without optimization.

How can you avoid that DMCs are incorrectly marked?

Complete traceability is more than having a DMC with a high contrast. It is also important that the right data are marked on the right product on the right position. With a laser-integrated vision system the marking can be read and validated. Furthermore, an integrated vision system that provides a closed-loop marking process like HELP (Holistic Enhanced Laser Process) offers validation steps prior to laser marking to avoid that parts are incorrectly marked.

How can you optimize the DMC to increase its readability?

There are several factors that influence the readability of laser marked DMCs, especially the contrast between the “black” and “white” cells of the DMC. This contrast can appear particularly low, where the surface of the marking area of the DMC is rough. In such cases, the marked DMC often looks a little bit fuzzy, not as crisp as it should be for good readability with a scanner or camera.

In such situation, one remedy could be smoothening the background first and then mark the DMC on the flat surface. Alternatively, and more time efficient is the ultra high contrast or “black/white” marking with fiber laser: First, the black cells are marked as usual, and then an inverted DMC is marked on the same place with laser parameters, which result in a “white” marking. That typically gives you a DMC with a nice cell contrast, as you can see below (the left code), entailing much better machine readability. The optimized ultra high contrast marking provides optimal readability, even on complex surface structures.

How can you decrease the marking time for a DMC?

Sometimes your available production cycle time forces you to look for possibilities to decrease the marking time for your DMC as much as possible. The natural first approach would be to look for other laser parameter combinations (i.e. the mix of marking speed, frequency repetition and power) that allow to mark the requested DMC with still acceptable appearance.

However, if that still does not lead to the required marking time, you might want to think of using a DMC which consists of dots instead of squares. The following illustration shows two DMCs with the same content, yet the left one with “standard” squares, while the right one comes with dots.

Marking and reading of data matrix/2D codes in the automotive industry

The automotive industry is particularly committed to mark safety-relevant components permanently and perfectly readable to meet the requirements of product and process safety, traceability and quality management. Marked codes also have to be extremely resistant to abrasion, temperature, light and lubricants.

Laser markers are optimally suited to mark safety-relevant components and other automotive parts with codes because they mark permanently and highly-precise. Only precisely marked codes are reliably readable.

An efficient and practical solution for marking automotive parts are laser marking systems with integrated vision system which do not only mark but also validate the code and are capable of optical character verification (OCV). This vision-based marking process helps automotive manufacturers to achieve reliable traceability, highest product quality and process reliability all while lowering production cost per part.

Summary: 5 facts about data matrix codes

You can have the DMC as a square or rectangle.
The area size and symbol size of a DMC are two different things.
The symbol size determines the data capacity of a DMC, or phrased the other way around, the amount of data to be encoded determines the symbol size of a DMC.
The possible maximum amount of data in a DMC depends whether the data consists only of digits or of alphanumerical characters.
Laser marking machines are optimally suited for marking data matrix codes on nearly every material, even on complex surface structures.