Elephantech Unveils HDI Microvia Formation Process Using Copper Nanoparticle Ink
– A Novel Solution for High-Density Board Manufacturing –

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As AI servers and other advanced electronic systems evolve rapidly, demand for high-speed, high-density circuit boards is intensifying. However, the formation of blind via holes (BVH), which connect layers of the board, has become a major bottleneck. It is reported that 40% of HDI board defects are attributed to microvia cracks or plating voids [1], making improvement to via-formation process an urgent priority.

Conventional BVH formation via electroless copper plating presents several shortcomings: Graphite-based direct plating technology has also been commercialized as a palladium-free and outgas-free alternative. However, it still faces challenges such as high electrical resistance, as the seed layer is not composed of a copper layer.
In order to address these challenges, Elephantech has developed a novel direct plating process using its proprietary advanced copper nanoparticle ink.

Technology Overview

This technology enables copper seed layer formation in BVHs by combining the application of copper nanoparticle ink with aqueous reduction treatment.

After desmear processing of the vias, a copper nanoparticle ink coating is applied. As the newly developed copper nanoparticles are engineered to adsorb onto the via sidewalls, upon drying, the nanoparticles align on the inner walls of the vias.

Subsequently, immersion in a reducing solution removes the oxide film on the nanoparticle surface, allowing them to form a continuous, uniform copper layer.

With this process, the reducing solution serves as an alternative to chemical plating, enabling a significantly simplified flow while offering enhanced process stability and greater design flexibility. By employing a reducing solution that does not generate hydrogen, it eliminates outgas from the underlayer. As a result, the risk of gas-induced voids is fundamentally eradicated to achieve palladium-free and formaldehyde-free engineering.

By replacing electroless plating with “copper nanoparticle ink coating + reduction” solution, the technology is applicable to a wide range of manufacturing methods across SAP, MSAP, subtractive and full additive. Additionally, the ink, as an inkjet-printable material, supports both selective and full-surface deposition.

The mechanism of the process is that copper nanoparticle ink penetrates deeply into the micro-scale surface irregularities of the via sidewalls and adheres firmly to them. Owing to their miniaturized particle size of 15 nm, the nanoparticles carry high surface energy. The force that reduces surface energy by driving the nanoparticles onto the via walls, and the force that pulls nanoparticles toward each other maintain a well balance, sustaining a state where the nanoparticles adsorb to the via walls without aggregation. Such behavior is realized on both glass and epoxy substrates.
While other processes require a seed layer removal step, Elephantech’s approach manages to eliminate it due to the homogeneous copper-copper interface formed between the inner-layer copper nanoparticles and the subsequently plated copper. Through a straightforward reduction and plating process, a robust electrical connection is created, ensuring reliable conductivity.

Evaluation Results

Vias fabricated using this process have successfully passed the following thermal cycling test.

Test pattern
4-layer HDI (1-2-1 build-up)
Hole diameter (Top): φ0.1mm, Insulation layer (dielectric) thickness: 0.06 mm
Target plating thickness: 20μm
L1-L2 Via: 36 chains, L3-L4 Via: 32 chains

Temperature
1 cycle: -65°C (15 min.) / 125°C (15 min.)
Number of cycles: 700
Criteria: Resistance variation within ± 10%
Result: PASSED

After 700 cycles, the resistance variation remained minimal within the ±10% threshold. No abnormalities, including disconnections or cracks, were observed. All test requirements were successfully satisfied.

Outlook

Moving forward, Elephantech will advance commercialization of this BVH technology by supplying printing equipment and functional inks to PCB manufacturers.

With a stable mass-production process for the copper nanoparticle ink in place, samples are currently available to support customer evaluation. The technology is designed for integration into existing production lines, enabling manufacturers to assess its applicability for new via formation process.

[1]: https://www.ltcircuit.com/news/how-to-identify-and-fix-hdi-pcb-design-versus-manufacturing-issues-241046.html