Blog  /  Laser Direct Imaging: LDI in PCB Manufacturing

Laser Direct Imaging: LDI in PCB Manufacturing

Etching and printing the pattern on the copper-clad laminates is one of the crucial steps in manufacturing circuit boards. The imaging procedure is fundamental in developing the PCB design as it outlines the circuit traces. Although the typical imaging procedures require UV light and phototool fill when transmitting images, Laser Direct Imaging employs computerized laser irradiation. As a result, it can now outline the circuit lanes straight to the board.

In this article, we will learn everything about the LDI. Let's get started!

 

Emerging Capabilities of Electronic Devices

Manufacturers of electronic devices persist in developing products that excel in areas like durability, portability, low weight, and compact size. This pattern will persist as long as there is a need for compact electronics in the market. As a result, manufacturers are more careful when creating compact ICs (integrated circuits) casings. CSP (Chip Scale Package) is a multi-output circuit that is an alternative design. Through its design, it is possible to reduce electromagnetic noise, provide a lag in signal transmission, and lessen induction.

Electronic devices trends in this area include:

  • Use flip-chip technology to integrate a disclosed semiconductor assembly openly to the PCB
  • Circling wire outputs towards the circular links
  • Constructing Circling wire using electrically powered outputs, positioned on all four sides using a relatively minor raster of approximately 0.5mm
  • Circling the covering with yields on the perimeter into outputs towards the entire bottommost with a trivial raster.

 

PCB Printed Circuit Board close up with short Depth Of Field

PCB Printed Circuit Board close up with short Depth Of Field

 

Imaging Challenges That Circuit Pattern Encounters

PCB board designers develop HDI boards in response to rising consumer demand for smaller, powerful, and more versatile electronic devices and components. In addition, it puts PCB fabricators to build fine-pitch, ensuring all the electrical structure runs off all more minor chips. Nevertheless, manufacturing HDI PCB is difficult because of all these demands, particularly in circuit pattern imaging. As a result, the printed circuit boards need Laser Direct Image (LDI) for patterning to produce the desired imaging results. Then, PCBs will have both ultra- and fine-line printing.

What Does Laser Direct Imaging Mean?

The LDI only employs a highly concentrated and computer-controlled laser beam to define the circuit patterns directly on the board. The laser imaging procedure used during the production of circuit board patterns is what distinguishes the circuit traces. Transferring pictures via the conventional imaging technique necessitates using UV light and a phototool.

 

CNC Laser cutting of metal, modern industrial technology Making Industrial Details

CNC Laser cutting of metal, modern industrial technology Making Industrial Details

 

Improved Process Capabilities Of Laser Direct Imaging (LDI)

When it comes to the development of PCB photolithography, Laser Direct Imaging is the next logical step. LDI, in contrast to photo exposure, omits a phototool. It exposes the digital pattern to the photoresist. The laser beam traverses the substrate in a raster image pattern, exposing the photoresist in discrete increments. Such consistent images resemble those made by the array of lines on a CRT screen. Laser printing, like photolithography, may benefit from resist production. Also, LDI needs a photoresist. However, LDI-resist is more efficient than standard photoresist. Furthermore, LDI comes in liquid and dry films, while the resist application procedures are similar to photolithography.

 

Large printer format inkjet working images

Large printer format inkjet working images

 

The following are the stages taken during an LDI process:

Scrubbing

To remove any oxide layers, scrub the board surface with abrasion pads and anti-oxidant using a machine-driven scrubber. In addition, manufacturers may use isopropyl alcohol to eliminate oil and organic material from the entire board surface.

Laminating Photoresist

Coat the PCB board with a photosensitive layer.

Packing CAM libraries

Then, load the laser with the CAM libraries.

Printing the Laser

Afterward, the CNC laser prints the circuit layout onto the board.

Engraving

Next, using the acid, engraving out the parts of photoresist material that aren't exposed to the laser beam. As a result, it leaves all the anticipated circuit traces/paths.

Photoresist Strip

The method entails removing the photosensitive substance.

Drying

After removing the photo substance, the final process is drying the CCL/core.

 

 

Laser cutting of metal sheets, 3D rendering images

Laser cutting of metal sheets, 3D rendering images

 

LDI’s Benefits Compared to Those of Photolithography

PCB manufacturers opt for LDI for various reasons, primarily for HDI circuit assembly. Besides, the conventional photo processes will require several steps when creating the phototool that generates images on the PCB. As a result, it creates some challenges for PCB fabricators over time. Here are some explanations why PCB fabricators opt for LDI instead of photolithography.

  • The photo procedure to provide accurate image transfer to the boards requires an environment with proper humidity and temperature control. Changes in humidity and temperature hurt photography equipment and may even corrupt the original. LDI eradicates the light refraction effect and minimizes the environmental impact on imperfect images using photo-processing techniques.
  • Light deflection impacts the phototool even under perfect weather conditions. The preservation, tracking, and storage attract some costs. Also, there are still expenses related to LDI despite removing the need for continued phototool inspection.
  • Damage to the film/phototool from contaminants such as scratches, fibers, and dirt makes it less effective in producing the vital circuit layout.
  • With the substrate, the phototool arrangement has more extensive limitations. Once subjected to processing, the flexible circuit outer layer might experience structural variations. In such instances, manufacturers can use static phototool to attain the most delicate structure. You can account for the changes to the structure by fine-tuning the LDI picture pattern in the computer. It's crucial to include additional features during via and trace printing. This method is also essential for the creation of multilayer circuits.

When quick turn-around and short runs are crucial, LDI fabrication provides precise benefits. They make artwork creation and phototool methods setup impractical. Besides, when there is a need for fast registration and close tolerances, LDI plays an important role.

Fundamental Differences Between Positive and Negative Images

 

Composite image between a photography and a 3D background

Composite image between a photography and a 3D background

 

Negative Image

With the negative image, the UV light has a formation that hits the material in the areas where you need to remove unwanted copper. The exposed part to the UV light becomes hard and polymerizes, enabling the developer solution clean the obscure photoresist parts. As a result, it leaves behind a converse duplicate of the shape.

Positive Image

With the positive image, the formation of UV light hits the parts where you need to remove the copper laminate. The photoresist is soluble in the photoresist designer solution by exposing the positive image to UV light. As a result, it leaves a matching copy of the design behind.

 

Digitization scanning of photographic film negatives on the scanner

Digitization scanning of photographic film negatives on the scanner

 

When to Opt for LDI Technology?

The inability to develop a workable solution with existing technology hurts PCB manufacturing efficiency. Complex multilayer PCBs have a regular PCB image trace width of (3mil) 0.075mm. Furthermore, the photolithography imaging development got to its parameters due to the creation of high compactness connects on PCB. Therefore, it can't' create PCB below 5/5mil (0.0127/0.127mm) of trace spaces and widths. Therefore, when a circuit board's trace spacing and widths are less than 5/5mil (0.0127/0.127mm), it should be the most imaging quality choice.

Initially, producers of HDI boards used LDI photo technology. However, PCB manufacturers use LDI technology to produce ultra-fine-line and fine-line firm-flex PCBs. Besides, the conductive circuits'' widths and spaces are 3/3mil (0.075/0.075) or 2/2mil (0.05/0.05mm). Hence, LDI is the most comprehensive imaging pattern for suitable trace spacing and widths.

In the PCB manufacturing industry, multilayered PCBs are the newest trend. They enable simplicity of the motherboard's design for all connections. Hence, it's' the best solution for better CSP technologies and interconnectivity thicknesses.

Summary

Today's customers are looking for PCBs with high densities that are still lightweight and compact. Laser Direct Imaging technology is the next step in advancing PCB printing. Its cost advantage over the traditional photolithography imaging process is irreplaceable in producing prototype boards and high-precision PCBs. There are no indications of a slowdown in the use of LDI in PCB production, which is already seeing a rapid expansion.

That's all for this article. If you have any questions, please feel free to contact us!