Laser Marking
the Laser Marker in smd production
In SMD production, a Laser Marker is used to “engrave” codes or markings into the PCB (DPM, direct part marking). The codes usually contain a unique serial number or other information used for identifying the PCB and are thus an essential component of continuous traceability.
Ideally, the laser marker should be positioned at the beginning of the production line to ensure traceability throughout every production step. Direct part marking can be seen as prerequisite for long-lived traceability, as it offers many advantages over the application of labels in terms of durability and flexibility.
The right laser source
There are numerous laser sources, each with their own areas of application.
The distinction between the types of lasers is made by the laser medium used; among other things, a distinction is made between gas and solid-state lasers.
In a solid-state laser (such as a YVO4 laser), the active medium is a crystal, whereas in a gas laser the active medium is a gas (such as a CO2 laser).
For the marking of printed circuit boards, the CO2
laser has established itself as the standard, since with a wavelength of approx. 10.6µm it is particularly well suited for processing organic materials such as wood or paper, but also plastics.
How Laser Marking works
Material procesing with a laser follows a simple principle: The laser transfers energy into the material that is to be processed, which triggers a reaction based on the material. Therefore, a laser can ablate, engrave and oxidize metal, while plastics can be ablated, carbonized and foamed. A color shift is also possible. Because a color shift only needs a little energy, this method is most commonly used for marking PCBs.
Color shift in solder resist
In this process, the color pigments in the solder resist are deliberately destroyed by the laser, which becomes visible on the surface as discoloration (marking).
The color of the marking cannot be controlled by the intensity of the laser; the contrast between the marking and the background therefore varies with the color of the solder resist. In general, markings on green or blue PCBs result in a very good contrast, while markings on red PCBs have a lower contrast.
LASERABLE CODE TYPES
Usually, laser markers can laser all common types of codes as well as characters. With a YJ LINK laser marker, 2D codes like QR-codes and data matrix codes, 1D codes (barcodes) and characters, logos and images can be realized as markings on the PCB.
Which information can be coded?
To ensure continous traceability, the marking should contain information with which the PCB can be clearly identified. A unique ID, i.e. a unique serial number, is usually used for this purpose. In addition to the unique ID, other information such as the current date or the job number can also be encoded. The YJ LINK laser marker divides the information to be coded into two groups:
Rigidly defined information
The code contents stored here are lasered on each PCB. Information that is valid for each PCB, such as the name of the manufacturer or the name of the end product in a batch, can be stored here.
Variables
Variable Code contents like the current date or the unique ID can be realised as well with the YJ LINK laser marker. Individually definable variables such as various counters, e.g. a continuous PCB counter or one counter per program, can also be implemented.
How small can the code be lasered?
With the ongoing miniaturization, PCBs are becoming smaller and increasingly more crowded –space for markings is thus getting scarce and the question "How small can I laser my codes?" arises.
Since a Data Matrix code requires less space than a QR code to display the same information, the Data Matrix code is predominantly used for marking printed circuit boards. However, how large or small the marking ultimately is depends on the structure of the code and the information encoded in it.
A Data Matrix Code basically consists of individual dots:
The dot is the basic element of the Data Matrix code
In order to be readable by standard scanners, a dot should not be smaller than 0.2 to 0.25mm. Since each Data Matrix code consists of at least 10 x 10 digits (dots), the recommended minimum size is 2mm x 2mm - even if smaller formats can be implemented with a laser marker.
10 x10 dots are the minimun size of a data matrix code
The final code size depends directly on the amount of coded information: A maximum of six-digit numbers or three alphanumeric characters can be stored in a 10 x 10 matrix. The more information to be contained, the larger the barcode.
More information can be stored in a larger code.
YJ LINK's "Ghost Marking" function, a pre-projection of the code onto the PCB, allows you to check if there is enough space on the PCB before inserting the code.
Barcode Grading - Classification according to ISO IEC TR 29158
The quality of 2D codes directly embedded in the printed circuit board is regulated by the ISO IEC TR 29158 standard, also known as "AIM DPM". The standard specifies various evaluation criteria that can be used to classify the quality of a code on a scale from "A" (very good) to "F" (very poor).
The criteria specified by the standard include pattern errors, contrast ratios, distortions and aspect ratio errors. With the YJ LINK laser marker, all codes are automatically checked and evaluated according to the criteria of the ISO IEC TR 29158 standard.
Do I need a Laser saftety officer to operate a Laser Marker?
Whether or not a laser safety officer is required to operate a laser marker depends on the design of the system.
Since YJ LINK's laser marker is completely enclosed and equipped with additional safety measures such as a door interlock, the system has a laser class 1 rating. A laser safety officer is therefore not required to operate YJ LINK's laser marker.
