The exponential growth of AI computing power is pushing thermal management for high-frequency PCBs to its limits. NVIDIA’s Rubin GPU chip has reached a single-chip power consumption of 2.3 kW—2.3 times that of the B200 chip—and future Feynman GPUs are expected to scale up to 4,400 W.
In high-density HDI PCBs, vias serve as the “blood vessels” connecting multi-layer circuits. However, traditional resin-filled vias have become a “blockage” in the thermal dissipation chain—poor thermal and electrical conductivity make them a performance bottleneck in high-power applications. Copper paste filling technology has emerged as a solution, transforming vias from “thermal insulation layers” into “heat-conducting pathways” and “electrical conduits” by filling via holes with conductive copper paste and electroplating a cap. This article systematically analyzes the high-frequency PCB copper paste via filling technology from perspectives including technical principles, process key points, and application scenarios.
1 The “ceiling” of resin hole sealing – Why is copper paste needed?
1.1 Limitations of Resin Hole Sealing
Resin hole filling is currently the most commonly used method for hole processing in high-frequency PCBs. It involves filling the holes with epoxy resin, smoothing them, and then electroplating copper caps to achieve the Via-in-Pad design. The core value of resin hole filling lies in:
Prevent the solder paste from flowing into the holes during welding to avoid false soldering. Improve surface flatness to meet the high-precision assembly requirements of BGA. Seal the holes to prevent the residue of soldering flux and contaminants from entering.
However, in high-power scenarios, the shortcomings of resin through-hole technology become obvious: the thermal conductivity of epoxy resin is only about 0.5 – 1 W/m·K, and its electrical conductivity is zero. In high-power AI acceleration cards, heat cannot be vertically discharged through the through-holes; it can only rely on the horizontal copper layer for heat dissipation, resulting in a significant reduction in efficiency.
1.2 The “dimensional enhancement” advantage of copper paste hole drilling
The copper paste holes were sealed with conductive copper paste instead of epoxy resin, achieving two key breakthroughs:
| Performance dimension | resin plug hole | Copper filled vias | Improvement extent |
| heat conductivity coefficient | 0.5-1 W/m·K | 124 W/m·K | Increase by more than a hundred times |
| electrical conductivity | isolator | 5-8×10⁻⁵ Ω·cm | From “breakpoint” to “pathway” |
| Reflow soldering reliability | Prone to cracking under thermal stress | 12 reflow soldering processes, 0 voids, 0 cracks | Reliability degradation |
This means that the conductive holes formed after the copper paste is filled become vertical heat conduction channels and electrical pathways, opening up a new dimension for the thermal management of high-power devices.
2 The manufacturing process of copper paste hole filling
2.1 Standard Process Path
The manufacturing process of copper paste hole filling is more complex compared to that of resin hole filling:
1. Drilling and metalization of holes: Complete the drilling of through holes, perform copper plating and electroplating, and the thickness of the copper in the holes usually needs to reach 80-120 μm (depending on the hole diameter)
2. Graphic transfer: Perform graphic transfer based on the aperture size. For diameters less than 0.6mm, it can be transferred in a single operation. For diameters ranging from 0.6mm to 1.4mm, a two-step transfer is required.
3. Copper paste hole filling: Using the screen printing method, the conductive copper paste is filled into the vias.
4. Baking and curing: The copper paste needs to be cured at 170-180°C for approximately 1 hour.
5. Polishing: Grinding to remove the excess copper paste that has overflowed from the board surface.
6. Electroplated cap: The surface is electroplated with copper to cover the through-hole area, creating a flat solderable pad.
2.2 Challenges in Drilling Holes for Copper Paste on PTFE High-Frequency Boards
For PTFE-based high-frequency sheet materials (such as Rogers RO3000 series and RT5880), the difficulty of making copper paste holes has significantly increased. The thermal expansion coefficients of PTFE and copper paste are quite different, and the traditional process is prone to defects such as incomplete hole filling, bubbles, and rough surfaces. The patented solution of Xi’an Microelectronics Technology Research Institute addresses the issue through the following measures:
Perform differentiated graphic transfer based on the aperture (single transfer for diameters ≤ 0.6mm, and secondary transfer for diameters ranging from 0.6mm to 1.4mm)。 The copper thickness is increased to 80-120 μm, serving the functions of isolation and fixation. Combined with plasma activation treatment, improve the surface wettability of PTFE
2.3 Key Process Parameters for Copper Paste Hole Sealing
| Parameter | Typical Value | Explanation |
| curing temperature | 170-180°C | Low-temperature curing, reducing the thermal stress of the substrate |
| curing time | ~ 1 hour | Low-temperature rapid curing, enhancing efficiency |
| volume resistivity | 5-8×10⁻⁵ Ω·cm | Close to the conductivity of pure copper |
| heat conductivity | 124 W/m·K | Better than the majority of thermal conductive materials |
| Orifice depression | ≤0.075mm | Ensure the surface is level |
3 Application scenario: Who needs copper paste hole-making?
3.1 AI Server and High-Power Acceleration Cards
The OAM acceleration card of the AI server and the bottom of the UBB adopt 20-30 layers of HDI PCB, with extremely high power density. The copper paste through-holes can provide vertical heat conduction channels for the heat-generating core, allowing the heat to be directly discharged from the top layer to the bottom heat sink.
The test result showing that the Jufeng Sealing Copper Paste still maintained no voids and no cracks after 12 reflow soldering cycles proves its reliability under harsh thermal cycles.
3.2 QFN/Power Device Ground Pad Heat Dissipation
The GND pad at the bottom of the QFN package serves both as an electrical ground and the main heat dissipation path. In traditional designs, if the vias beneath the GND pad are filled with resin, the thermal resistance is high and the heat dissipation is poor. By using copper paste to fill the vias, the heat can be vertically conducted out through the metal-filled vias, significantly improving the heat dissipation efficiency.
3.3 Optimization of Grounding Path for High-Frequency Module
In the high-frequency microwave module, the copper paste through-holes can serve as a low-impedance grounding path, reducing the inductance of the grounding circuit and improving the EMI performance of the high-frequency signal.
4 Cost and Selection Suggestions
The copper paste hole-making process is highly complex and has high material costs. It should not be uniformly applied. The selection suggestions are as follows:
| application scenarios | recommended solution | Reasons |
| High-power AI acceleration card / power amplifier module | Copper filled vias | Dual demands for heat conduction and electrical conductivity, with benefits far exceeding costs. |
| QFN/Power Device Grounding Heat Dissipation Hole | Copper filled vias | Optimization of heat dissipation path leads to significant improvement in reliability. |
| Regular BGA via in pad | Resin hole filling + Electroplated cap | Cost is controllable and meets the requirements for welding and sealing. |
| Low-power radio frequency module | Resin hole filling | The heat dissipation pressure is not high, and the resin solution is sufficient. |
Dinamike Solution, a professional practitioner of the copper paste hole-making process
Dinamike Solution has over 15 years of experience in the research and manufacturing of high-frequency PCBs. It has established a complete technical system in the copper paste through-hole manufacturing process.
✅ Copper paste hole drilling capability
Support copper plating holes for high-frequency boards (Rogers, Taconic, F4B)
The hole depression is ≤ 0.075mm, and the surface flatness meets the requirements for BGA welding.
Combined with the electroplated cap, it enables the design of holes in the plate.
✅ Supporting manufacturing capabilities
Plasma activation treatment, suitable for PTFE-type high-frequency sheet materials
LDI laser direct writing, high-precision graphic transfer
100% hole resistance testing to ensure reliable conduction performance
✅ Application Scenarios Coverage
High-power PCB for AI server
77GHz millimeter-wave radar
Satellite communication high-frequency module
5G base station power amplifier PCBs
The copper paste hole filling technology upgrades the through-holes of high-frequency PCBs from “passive filling” to “active thermal and electrical conductivity”. Against the backdrop of the continuous increase in power density driven by AI computing power, this process is evolving from an “optional solution” to a “mandatory option”. From resin hole filling to copper paste hole filling, it is not only a material substitution but also a paradigm shift in the thermal management logic of high-frequency PCBs.