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Laser Direct Imaging (LDI)

by Matt Stevenson

One of the most amazing advances in PCB manufacturing technology has been the advent and usage of LDI technology. This technology is able to transfer the digital design data directly to the manufacturing panel without the use of an intermediary. The result is sharper and more precise features, better registration and the ability to resolve smaller features more effectively.

Imaging is a key step to transfer your PCB design from its original digital format onto the physical manufacturing panel. This step will eventually define all of the copper features on a given layer; pads, traces, plane areas, etc. Having the ability to produce an image as close to the digital data as possible makes the product much higher quality and better reproducibility. Much like the traditional imaging processes (figure 1.) , LDI does use a photoimagable polymer (photoresist) to transfer the image to the panel, however it does not require a photo tool as an intermediary (figure 2.) during the exposure step.
Eliminating these two layers (photo tool and the mylar (or glass) layer from the process allows the light source to more directly expose the photoresist with less interference and less opportunity for air gaps to be created in either of these two extra layers. Air gaps cause issues with the quality of the exposure usually causing unwanted exposure in areas causing defects. Getting closer and eliminating air gaps effectively creates the majority of the benefits from the LDI process. Sharper, truer representations of the data are transferred and less introduction of error potential.

The other benefit of the LDI system is that the image can be better aligned to the panel that with traditional methods. Because LDI is digital it can use aligning targets (fiducials) and is able to calculate any movement that has occurred in the panel and correct for it digitally. Any stretch, shrinkage or skew that has occurred during the previous manufacturing steps can be calculated and adjusted, making the copper image align nearly perfectly with the drilled holes. This can be a very tedious if not impossible situation in traditional imaging.

Sunstone Circuits uses LDI imaging technology on every copper layer on every PCB to give you the best possible quality and reliability for your PCB projects.

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