Laser Drilling And Metallization Process of Aluminum Nitride Ceramics under Controlled Atmosphere

 01 Introduction

Aluminum nitride (AlN) ceramics have become ideal candidates for next-generation heat dissipation substrates and electronic packaging due to their excellent thermal conductivity, reliable electrical insulation, low dielectric constant, low dielectric loss, and a thermal expansion coefficient matched with silicon. In the preparation of AlN ceramic electrical connections, a key requirement is to process a large number of through-holes with diameters ranging from 30 to 500 μm on substrates typically 0.1-1 mm thick. As electronic devices tend toward miniaturization, processing interconnect through-holes with diameters as low as 100 μm is becoming increasingly important.

However, the extremely high brittleness of AlN ceramics greatly limits their machinability. Traditional processing techniques are inefficient and difficult to meet precision requirements, while laser drilling is considered the preferred method for processing high-hardness and brittle ceramics like AlN due to its ability to overcome material types and aperture size limitations. Nevertheless, traditional laser processing often faces problems such as slag accumulation, micro-cracks, and heat-affected zones. Additionally, as a strong covalent bond compound, AlN has poor wettability with metals such as copper and aluminum, making reliable metallization connections a challenge. This study systematically investigated the influence of processing atmospheres on through-hole quality and subsequent metallization effects by developing a hybrid method integrating nanosecond laser direct drilling and electroless copper plating.

 02 Overview

The experiment used a nanosecond pulse laser system (wavelength 1064 nm, pulse width 100 ns, repetition frequency 20-200 kHz) to perform drilling experiments on 0.5 mm thick AlN substrates. The research focused on comparing the effects of three different atmosphere environments—air, water, and argon—on the micro-hole entrance/exit morphology, sidewall roughness, heat-affected zone, and remelted layer formation. To achieve high-precision micro-hole processing, the study adopted a scanning strategy based on concentric circle filling. The laser beam rotates and scans from the outside to the inside along a predefined concentric circle path at a specific speed. In this process, the ratio of the scanning interval to the beam waist radius is a key indicator determining the uniformity of energy distribution and processing quality. The results show that micro-holes manufactured in an Ar atmosphere exhibit the best geometry, with almost no molten debris or micro-cracks at the hole edges, the thinnest remelted layer, and the smoothest surface, providing ideal substrate conditions for subsequent metallization. In contrast, holes drilled in air and water show significant oxidation and contamination. After electroless copper plating, the coating of micro-holes treated in an Ar atmosphere showed excellent density, uniformity, and strong adhesion to the AlN substrate. Finally, a micro-hole resistance as low as 7.35 mΩ was achieved in an Argon atmosphere, fully demonstrating the great advantages of controlled atmosphere in improving the reliability of electronic packaging interconnects.

 03 Graphic Analysis

Figure 1 details the six-step strategy for micro-hole processing and metallization. First, the laser scanning trajectory is set through a concentric circle filling path, where precise control of laser power, scanning speed, and filling interval is crucial for energy deposition. Step 5 highlights the core variable of this study—the atmosphere control system, which maintains the purity of the Ar atmosphere through a dedicated gas chamber or performs underwater processing by maintaining a 0.5 mm thick water layer. Finally, the laser-activated sample is placed in a 55°C chemical bath for electroless copper plating.

Figure 1. Schematic of drilling process and electroless copper plating.

Figure 2 reveals the time evolution characteristics of laser-induced plasma through numerical simulation and high-speed photography. In an air environment, the plasma plume expands violently and irregularly. In underwater processing, the pressure and density of the plasma are significantly increased due to the mechanical confinement effect of the liquid phase medium, forming a regular hemispherical profile. This confinement effect helps generate high-intensity mixed plasma, thereby suppressing excessive expansion of the plasma plume while enhancing physical removal and cooling effects on the material.

Figure 2. Analysis of laser drilling of AlN ceramics in air and water environments.

Figure 3 shows the chemical composition analysis of the hole wall after multi-atmosphere laser processing. X-ray photoelectron spectroscopy analysis shows that the original AlN surface is relatively smooth, while the hole wall treated with air has micro-cracks accompanied by significant oxidation, forming an aluminum oxide recast layer. In contrast, treatment in an Ar atmosphere can balance the laser-induced decomposition process, effectively producing metallic aluminum while suppressing excessive oxidation. In an Ar atmosphere, the metallic Al content on the hole wall surface is as high as 97.47%. This highly activated surface acts as a catalytic center for subsequent electroless copper plating, ensuring the continuity and conductivity of the coating.

Figure 3. Chemical composition analysis of the hole wall after multi-atmosphere laser processing.

Figure 4 shows the final metallization results after optimizing process parameters. When the filling interval is 13, the energy distribution is uneven due to the low overlap of the laser beam, leading to periodic fluctuations and un-melted areas on the hole wall, resulting in discontinuous or even peeling coatings. When the filling interval is 8 and the number of scans is 8, the beam overlap rate is significantly increased, producing uniform energy distribution and continuous material removal. Under these conditions, the micro-holes obtained a dense and uniform copper layer with strong adhesion, resistance as low as 7.35 mΩ, and a taper angle controlled at 9°, perfectly meeting the strict requirements of high-density electronic packaging.

Figure 4. SEM images of the cross-section of electroless copper plated micro-holes processed in an Ar atmosphere under different scan numbers and filling circle intervals.

 04 Summary

This study demonstrates that controlled atmospheres, particularly argon, significantly improve the quality of laser-drilled microvias in Aluminum Nitride (AlN) ceramics. Argon atmosphere suppresses oxidation and promotes the formation of a highly metallic Al surface (97.47%), which effectively catalyzes subsequent electroless copper plating. The optimized process yields dense, uniform metallization with low resistance (7.35 mΩ) and controlled taper, offering a robust solution for high-density electronic packaging and advanced heat dissipation applications.

Original Link:

https://doi.org/10.1016/j.ceramint.2026.01.331

**--Cite the article published by 高能束加工技术 on April 29th, 2026, in the WeChat public account "High-Energy Beam Processing Technology and Applications."