Opening solder-resists

Printed circuit boards generally have to be covered with solder-resists to improve mechanical soldering. The mask is usually applied using classic screen printing or modern photo techniques and is an important factor in preventing the formation of solder bridges and associated short circuiting.

The handling of screens is, however, complex. In addition, the positioning accuracy of the solder-resist printing with respect to the circuit layout is low at ±100 μm due to the elasticity of the screen and problems in adjusting the screen image to the circuit layout. For the creation of finer structures solder-resist is exposed using photo techniques. Exposure gives an accuracy of approx. 50 μm.

Laser processing is suitable for the most ambitious solder-resists in the HDI range <50 μm. The solder-resist is ablated in the area of the openings to leave a residue-free copper surface. Laser processing enables openings to be created with diameters down to 30 μm. Moreover, online scaling makes it possible for distortions as well as positioning errors to be corrected during processing. Laser processing therefore guarantees maximum positioning accuracy and throughput rates.


Read further under Opening Cover Foils