- Mask●less Li●tho●gra●phy
Maskless lithography is a type of lithography common in printed circuit boards (PCB) and other precision manufacturing applications. It uses DLP® technology to project UV or LED light onto photoresist films and other photosensitive materials, including silicon wafers. Unlike traditional lithography, however, maskless projects the light directly onto the material without the need for a custom mask layer to selectively limit and disperse the light appropriately.
A closer look at lithography
Lithography, formerly known as “photolithography,” has been essential in making microchips and other tiny parts used in our most common consumer products. To truly understand how maskless stands out, you have to first understand the two types of lithography: traditional and maskless.
Lithography is basically a projection system where a map or blueprint is placed in front of the light that will be used to create a pattern on a photosensitive silicon wafer or other material. This blueprint only allows some of the light through (the light that will reach the photosensitive layer) and asks as a mask or “reticle.”
This same mask can be used again and again to create identical creations out of the light and can work on a very small scale for the tiniest of patterns and designs. For each new design used, a new mask must be created or purchased. A mask aligner or stepper is also required.
This process is best for high-volume manufacturing of materials on the sub-micron scale.
There’s another solution that transfers a design directly to the wafer, without the use of a mask. Maskless photolithography draws the pattern with a spatial light modulator (SLM), which replaces the mask by arranging the light so it hits the photosensitive wafer or resist-covered substrate in the exact design needed. The design is written on and skips the expensive and lengthy process of having to create or buy a mask and stepper.
Because you don’t have to wait for a mask, it’s possible to recreate new patterns immediately, over and over, and perfect the design as you go. This process is best for low-volume projects where high precision and flexibility is preferred.
Why make the move to maskless?
Maskless is the newer of the lithography technologies, but it is quickly gaining traction as a way to make lithography for all purposes much more accessible.
The benefits of maskless are many but include a lower overall production cost. Not only is it possible to do lower volume batches affordably, since a new mask doesn’t have to be made for each project, but the replacement cost for components is negligible.
Currently, traditional lithography methods using lasers require many more parts, including the laser itself, which must be replaced as often as annually and can cost upwards of $80,000 or more. Since the DLP light sources have an incredibly long lifespan, this cost won’t have to be a consideration at all. In fact, the DLP technology is incredibly simple in its design, requiring little more than an optical channel (LED light source), a high-speed digital micromirror device (DMD), and a projection lens.
Beyond that, no cumbersome or expensive equipment must be replaced or maintained. Between equipment savings and the savings on mask materials, it's a more affordable option for small-batch and large producers alike.
Another advantage of maskless lithography is its throughput. Experts put production speeds for something like a circuit board at up to 10 times more expedient than traditional lithography. Turnaround on even a one-off circuit board is now possible with less preparation and material cost, and the process is ideal for fast-turnaround jobs or those requiring multiple iterations. With no mask to deal with, it’s feasible to make design changes as needed. This wasn’t practical with the rigid production parameters of traditional lithography and its multiple, costly photomasks. It also works well for products that require double exposure.
With accuracy available at the micron level (or a precision of 2µm), maskless lithography is the future for PCB, flat panel displays, chip scale packages (CSP), ball grid arrays (BGA), real-time barcode marking, direct computer-to-plate printing, and even silicon wafers.
It also supports extended wavelengths of 355 – 2500 nm and works with a variety of photosensitive coatings and materials, giving developers more space to explore and create than ever before.
With no high-cost masks to contend with, this new type of lithography may even power new research and development areas in small or independently-funded labs that were once held back by the parameters of traditional lithography.
The future of maskless
Before maskless lithography, it was costly and time-consuming to adjust CAD designs, as a new mask had to be made each time. Now, with the flexibility to adjust patterns on the fly, creators and developers have the freedom to try new things and experiment as they go. The level of detail and precision is the same, but the cost and time restrictions associated with traditional lithography are a thing of the past. As more advancements are made, the promise of maskless lithography for only low-volume projects can be expanded to be used in even high-volume, factory and bulk manufacturing settings.