with 3D printing

The scale of sizes that 3D printing machines can handle is impressive, from huge wind turbine blades to parts that are small, such as two microns. John Kawola, CEO of Boston Micro Fabrication discusses the microscale side of 3D printing.

Microscale 3D printing is the concept of making parts at millimeter scale or even sub millimeter scale. It’s a technology that has been available for five, maybe even 10 years. What’s new is that this technology is being commercialized for industrial use.

Boston Micro Fabrication (BMF) uses a microscale technology that is a variant of stereolithography. It is called projection micro stereolithography, or PµSL. A Boston MIT professor, Nick Fang, developed the idea. Fang had been working on micro fabrication techniques over the years.

A lot of those micro fabrication techniques are not 3D printing. These techniques include embossing, and etching and photolithography. But for 3D printed micro parts, applications include the semiconductor and the MIM space.

Fang’s idea was to try to move into the 3D printing/additive manufacturing space. The concept was to use the PµSL approach, which is similar to other DLP 3D printers in the market. The approach consists of a resin bath, with light to cure the resin. In BMF systems, the light source is focused down to a very fine resolution and the movement is controlled to ensure precision. Microscale 3D printing fits a market segment of high-value industries that do product development, manufacturing, and production, but with resolution and dimensional accuracy requirements in the millimeter, and perhaps micron area in tolerances, such as electronic connectors.

Other small size production technologies exist, including photon lithography. One criticism of photon lithography is that it takes a long time to make a very small part. For example, a 20-millimeter size part might take a week to build.

The connector market, worldwide, is valued at $100 billion dollars. And connectors are getting smaller all the time. New markets, such as AR/VR for glasses are emerging that suit this technology. Design efforts continue to try to miniaturize in the optics and photonics market. In the medical device market, things are getting smaller, whether they’re sensors or drug delivery devices, or implantable devices. There’s a trend around industries wanting to get smaller.

Challenges when designing for the microscale market

Design challenges with microscale parts are not much different than those for macro parts. If it’s a connector, it needs to have certain features to be a connector, same with chip packaging. It needs to have certain characteristics to hold a chip, or a lens holder, but there are always considerations about how are you going to make it, including how to mold, machine, and/or stamp the part. One of the realities is the manufacturing processes for these smaller parts are more difficult and much more expensive.

For example, if you’re molding something like a computer mouse, that’s not that hard to do. The injection mold for that mouse is maybe tens of thousands of dollars, maybe $25,000. But if you’re making something really small, that injection mold may no longer be $25,000. It might be $250,000 because you need to machine that mold to get all the tolerances that you need, and you need to be able to build in the ports and all the dynamics that go into an injection mold, but at a very small scale.

Uses of micro 3D printing systems

Most users of these micro 3D printing machines are using them for prototyping. Until about two years ago, affordable micro 3D printers were not available for this application. Users could not get the resolution and detail they wanted one for one.

Today, about a third of users are doing some production. Users are testing materials, their design and then looking into production quantities. Some are finding out it’s less expensive to let the 3D printer handle the mold than to machine or stamp them. The mold materials are predominantly resin-based, with some ceramic materials.

What goes into the development of a macro 3D printer

BMF’s chief technology officer, Chunguang Xia, came from the semiconductor industry. One of the challenges was ensuring high tolerance, to create a platform when people are looking to get tolerances in the plus or minus five-micron area. At this level, measurements are done using technologies similar to a CT scanner.

“We needed to have a platform that could image onto the resin and create the part,” says Kawola. “If you’re making a larger part, our platform actually moves to be able to image in certain sections. All of that had to stack up. You’re also dealing with material shrinkage, so you’ve got all these variables that you’re trying to get to a place where you’re plus or minus whatever that tolerance is. I think it’s just a lot of good engineering by our team here to recognize that’s the target.”

For the DLP system, high precision optics were needed. “We’re really focusing down to a certain pixel size,” Kawola continued. “When we talk about, let’s say 10-micron optical resolution, that’s actually the size of the pixel that’s being imaged onto the liquid. Most DLP systems in the market are upside down, so they’re coming out of the liquid. That has a lot of advantages. We are top down. We do that for a couple reasons. One is we need to control layer thickness. The thicknesses of our layers are in the 10-to-20-micron range, so we need to be able to highly control that. Two, all DLP systems, all resin-based systems, when that light comes down and polymerizes the resin, that’s a reaction and there’s heat. Most 3D printing systems, there’s heat being generated and that’s one of the challenges, actually, for a lot of DLP platforms.

“A company in Chicago, Azul, has some new breakthroughs in how to control that heat and try to cool that process as it goes, but it’s a challenge and heat is bad for trying to maintain dimensional accuracy. That’s another reason why we are top down because when you’re bottom up, you only have a thin layer of resin. There’s heat there and that can build up. When the system is top down and you have a vat, it acts as a heat sink, so you don’t really have that buildup of heat that affects most other technologies.”

A materials ecosystem

An ecosystem for materials has been evolving for about five years. BMF is an open platform. “For prototyping, arguably the materials don’t matter that much. They need to be close enough and most people can be pretty happy, but when you get into manufacturing, they need to be really close or exact. I think the collective wisdom of more companies coming into the 3D printing material space, in my opinion, has significantly moved the industry forward over the last five years, at least.