Barcode on printed circuit board
In the production of pcbs machine-readable markings, like barcodes, could improve the production process. Especial considering the product liability multiplex variable data have to be acquired and where appropriate to be marked at the pcb. A laser marking is because of the flexibility, the simple integration and the forgeries secure marking for such applications held over to other processes.
The marking of printed circuit boards with barcodes will be more important for the future production process. Variable data could only be marked during the production. Such markings could not be done directly at the basis material. Thermal effects cause a carbonising of the material and the contrast for such markings is worse. Other marking processes like ink jet marking does not have this disadvantages, but they have not the same durability and the line resolution, especial for barcodes, is to low.
Barcodes reach high density of information
Barcodes are machine-readable codes, which allow a high density of information at low space. The most usable barcodes are 2/5 interleaved, code 39 and code 128. While the code 2/5 interleaved could only mark numerical characters, the other two codes could mark alphanumerical characters. The code 39 and the code 128 include all 128 ASCII-characters. The code 128 includes lower and capital letters as a standard as well as user defined additional signs. In addition the density of information is higher for the numerical characters as for the code 39 and for more the 14 numerical characters higher as for the 2/5 interleaved.
An additional alternative is the two-dimensional Datamatrix code. This code gives a high flexibility in size and density, depending on his structure. This code needs lower features to the contrast and the print tolerances. This code is able to mark alphanumerical characters in all languages and the representation of binary data is possible.
Especial with a laser barcodes could be marked reliable and fast with a high line resolution. This gives the user the advantages of the laser technology for the marking of printed circuit boards. Such markings reach short cycle times at high line resolutions and the brilliant contrast. LS Laser Systems GmbH, Munich, is able to offer different methods to mark barcodes on printed circuit boards. All methods are verified at the application lab during numerous tests.
Barcode marking with variable possibilities
The simplest method is the production of labels. The laser removes a top layer and the subordinate layer with another colour produces a good contrast to the top layer. Depending on the layer construction black/white and other colour combinations could be produced. The laser markable labels are available prefabricated or on endless rolls. The marking occur n time and with endless rolls the label format will be cut by the laser. The disadvantage of this method is the additional process step to stick the label on the printed circuit board before or after the laser marking. When the label will be mounted after the marking, the user has the additional problem to stick the right label to the right board.
If a homogeny area is printed for the marking or assembly print, this area could be used for the barcode. During the print process an additional area with white colour must be printed. As well as before the laser removes the screen-printed colour partial and the contrast between the basis material and the screen print colour allows the variable marking with a barcode. This is the most suitable method for printed circuit boards that have already a marking, because the print of the additional area causes no change in the layout and the assignment from barcode to board is always guaranteed.
Is no marking layer available on the board, the alternative is the solder resist mask. A CO2-laser allows the direct marking of the resist, without any remove. Even some basis materials could be marked with the CO2-laser without any carbonising. The user does not need any additional process steps and the reliable assignment of the barcode to the board is always given. In addition to the variable choose of the marking position (no need of a cooper area) the CO2-laser has low investment and a simple integration.
A Nd:YAG-laser is able to mark a barcode on printed circuit boards by removing the solder resist. A good contrast will be reached, if below the solder ersist a cooper area exists. The good contrast between cooper an solder resist gives a good readable barcode marking. A disadvertage of this method is the additional cooper area, which has to be designed in the layout of the printed circuit board.
But each of this four methods have advantages and the user has to decide, which method is the best for his process.
The laser - integrated or stand-alone
For such barcode markings CO2- or Nd:YAG- lasers are used. LS Laser Systems GmbH uses lasers from their own production. These marking systems could be integrated in existing production lines without any problems. The intelligent, user-friendly software controls the marking, communicates with the periphery and/or a host computer and checks the barcode marking. For the check a barcode will be used, which controls and matches the marking and intervenes the marking process by error routines. If the laser should not be integrated into the production line, the LS-technicians could also build up stand-alone systems with or without handling.
The know-how and the experience of the laser experts of LS Laser Systems by the construction of in-line systems guarantee an advanced system, that marks barcodes on printed circuit boards reliable and fast. Such systems give the user new possibilities to mark their boards.
Author of the paper is Dipl.-Phys. Peter Lenk
More informations:
LS
LS Laser Systems GmbH
Gollierstr. 70
80339 Munich
Tel.: ++49 / (0) 89 / 502 002 - 0
Fax.: ++49 / (0) 89 / 502 002 - 30
Email:
3/3