SMTA UHDI Symposium 2025, Part 2: State of the Art

Estimated reading time: 7 minutes

Editor’s note: Click here to read Part 1 in this two-part series.

Comfortably seated below the stadium of the Peoria Sports Complex, home of training grounds for the San Diego Padres and Seattle Mariners, a group of about 50 attended the second annual SMTA Ultra High Density Interconnect Symposium on Jan. 23, 2025. After a morning of technical presentations on challenges and solutions regarding UHDI technology, we gathered for a delicious Mexican buffet lunch and some networking before reconvening for an afternoon of more technical topics.

We were refreshed and ready as the conference moved deeply into UHDI assembly with a presentation by Greg Smith of BlueRing Stencils, a company that develops advanced fiber laser cutting systems that create very precise SMT stencils. I found it interesting, though unsurprising, that we are reaching the limits of what we can achieve in stencils with standard laser technology and electroform (E-form) technology. He discussed monolithic laser ablation (MLAB), a new technology that provides a less harsh “cut,” produces a smoother sidewall, and actually changes the surface being ablated from a solid straight to a gas, eliminating some of the challenges that its liquid form presented. The standard tolerance on apertures is ±0.2 mil.

Greg was followed by Tony Lentz, a field application engineer at FCT Assembly, who discussed printing, stencils, and solder powder sizes for UHDI. Tony compared the performance of different SAC305 T6 solder pastes when it comes to very fine aperture sizes and made note to remember that different solder paste chemistries will have different print and reflow performance regardless of having the same solder powder size. He also suggested that it is time for a revision of the IPC standard for stencil design, “I think this standard needs to be updated,” he said. “I don’t think the five ball rule (for printing solder paste) works.”

Next up was Jim Rathburn of Precision Circuit Technologies, whose presentation was titled “LCP (Liquid Crystal Polymer) and 10 Micron Feature Sizes.” Jim said his company can obtain precision control of trace geometries and via structures at 25–50 microns and has a path toward achieving 6–9 microns.

He showed several examples of UHDI boards for different product applications as well as highlighting some interesting connector technologies, including a plug-in/pull-out solder ball used in smartphone manufacturing that then requires no actual soldering. His presentation focused entirely on additive technologies. PCT has developed its own ink-jet printing product and “thinner alternatives to PTFE products that are easier to manufacture,” specifically a non-Teflon, ultra-low loss dielectric material with a dissipation factor (Df) of .0004 and that can still be laser ablated. He also announced that his firm is building a newer facility in the Minneapolis area.

What’s a good symposium without a chocolate chip cookie and coffee break? We did more quick networking and then settled in for the final presentations of the afternoon. First up were Jason Schipp and Andrew Alvarez of NSWC Crane. Jason pointed out that the terminology for UHDI was actually VHDI first, but they are one and the same. NSWC is involved in PCB fabrication with the DoD Executive Agent for printed circuit board and interconnect technology and is unique as just one of two DoD fabrication facilities. One aim is to enable the Defense Industrial Base (DIB) with advanced microelectronic technology, i.e., keeping their finger on the pulse of domestic PCB fabrication and helping develop “leap ahead” semi-additive processes to help produce UHDI printed circuits and substrate like printed circuit boards.

NSWC partners with LQDX, Boise State University, and AFRI to “figure it out” and make it a drop-in process for other board shops. LQDX (formerly Averatek) is a developer of liquid metal ink LMI. They described the process as dipping your material into palladium using LMI technology to create your seed layer. It’s a project with four phases that will result in half-mil traces on a six-layer board. As Andrew said, “We are not necessarily bleeding edge, being part of the government, but we are focused on making things repeatable and reliable, getting those 50-micron and 25-micron features down.” As was illustrated in several other presentations during the day, their cross-sections showed amazingly clean and straight sidewalls even at 1 mil and half-mil traces. Jason went through the lineup of alternative UHDI build-up materials they are just starting to work with—Zaristo, AGC fastRise™, Panasonic RF10, NAMICS ADFLEMA, Arlon 1017 and 1027—and reminded the group that only domestic sources may be used, somewhat limiting their choices.

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