Wiwynn Machined Microchannels into Single-Crystal Diamond. What Did It Measure?

On October 14, Wiwynn presented thermal-test results at the OCP Future Technologies Symposium. The team bonded laser-machined single-crystal diamond (SCD) with microchannels to a silicon thermal test vehicle. At 360 W/cm², junction-to-coolant-inlet thermal resistance was 38.2% lower than with a copper cold plate and phase-change-material (PCM) thermal interface material. The earlier simulation had predicted a 59.5% reduction. Wiwynn suggested that the gap may be due to the bonding interface; “may” matters here.

The public trail has four milestones. On May 26, ahead of Computex 2026, Wiwynn announced two cooling technologies, including a diamond-composite microchannel cold plate and its potential for future IC-package-level cooling. On June 4, it published the white paper Advanced Microchannel Material – Diamond Composite Thermal Solutions; its public abstract mentioned single-crystal diamond and diamond microchannel heat sinks. At the August 11–12 OCP APAC Summit, the team showed concepts, simulations and a test plan. The measured results followed on October 14.

One caveat when reading these materials: Wiwynn’s public wording for the material has not been consistent. The May and June materials use “diamond composite,” although the June abstract already mentions SCD. The October talk calls SCD a starting point and compares it with diamond-copper and diamond-silicon-carbide. A separate October 12 show announcement returns to “diamond-based composite materials.” The October 14 presentation is therefore the basis here for identifying the tested specimen as SCD.

1. Why Focus on Thermal Resistance, Not Just Conductivity?

Heat travels from the chip junction to the coolant through the chip itself, the thermal interface material (TIM) and the cold plate. Wiwynn’s illustrative breakdown assigns 40–45% of total resistance to the cold plate, 25–40% to the TIM and 15–25% to the chip. Together, the cold plate and TIM account for roughly 65–85%. The slide does not identify the specific system behind these percentages.

That suggests two approaches: use a more conductive material to lower cold-plate resistance, and direct bonding to reduce TIM resistance.

Figure 1. The presentation’s illustrative resistance breakdown and heat-flux context. It does not identify a specific system for the percentages.

The heat-flux figures also need context. The slide’s schematic marks about 100 W/cm² in 2022 and 200 W/cm² in 2026, and says advanced packaging “may” push chip-level heat flux above 500 W/cm². The white-paper abstract says local heat flux has already exceeded 500 W/cm². Any use of that number should distinguish a trend from a local hotspot. The test’s maximum of 360 W/cm² is calculated by dividing heater power by heating area.

2. Why Start with Single-Crystal Diamond?

	Single-crystal diamond	Diamond-copper	Diamond-silicon carbide	Copper
Thermal conductivity, W/(m·K)	>2,000	600–900	500–800	~400
CTE, ppm/K	~1.0	6.0–9.0	2.0–4.5	~17
Density, g/cm³	~3.5	5.0–6.0	3.30–3.45	~8.96

The slide’s stated rationale is straightforward: SCD has the highest thermal conductivity, so it was chosen as the starting point. The CTE of diamond-based materials is generally closer to silicon (about 2.6 ppm/K) than copper’s, which may make direct bonding more practical.

Figure 2. Material-property comparison from the presentation.

The table deserves a closer look: the CTE range for diamond-silicon carbide includes silicon’s 2.6 ppm/K, making it a closer match than SCD at about 1.0. SCD’s advantage here is thermal conductivity, not a uniquely favorable CTE. The speaker also called SCD a research starting point and said the team would explore other diamond-based materials and package-level cooling approaches.

3. What Was Machined into the Diamond?

Item	Disclosed parameter
Microchannel field	32.2 × 25.7 mm²
Fin width and gap	0.1 mm each
Fin height	1 mm
Base thickness	0.5 mm
Process	Laser machining

The 0.1 mm fin width is 100 μm. A 1 mm fin height gives an aspect ratio of roughly 10:1. At a 0.2 mm pitch, a rough estimate gives 130–160 fin/channel pitches in one direction; the slide does not specify channel orientation, so this is my estimate. Fin plus base thickness is about 1.5 mm, an inference. The speaker said verbally that the diamond piece was the same size as the silicon die to make bonding practical. In any case, the single crystal must cover at least the 32.2 × 25.7 mm² microchannel field.

Figure 3. Disclosed microchannel dimensions and process sequence. Fin width, gap and base thickness are parameters given in the talk.

The presentation did not disclose how this SCD was grown, its grade, source or cost. Large, thick single crystals are a first materials challenge, but that part of the story remains blank.

The process sequence is clear: laser-machine the microchannels first, then bond the diamond. This question had come up at OCP APAC, so the October talk explicitly put machining first.

The slides provide no data on sidewall taper, roughness or the heat-affected layer after laser machining. An audience question raised graphitization in the context of coolant particles clogging channels and creating hotspots. The speaker said graphitization had occurred in the experiment, but that the team observed only a thin surface layer; he added that it might be one reason the measured improvement fell short of simulation. The answer did not establish whether graphitization occurred during machining or operation, and no measurements were provided.

4. Bonding Diamond to Silicon

The team deposited Ti/Ni/Au on both the diamond and silicon surfaces, then reflowed indium solder under controlled temperature and pressure. Titanium promotes adhesion, nickel acts as a diffusion barrier, and gold improves wetting and helps prevent oxidation.

Figure 4. Integrated cross-section and interfacial stack from the presentation. “Direct-bonded” describes the engineering integration; metallization and indium remain between diamond and silicon.

“Direct-bonded” describes the engineering integration; metallization and indium remain between the diamond and silicon. In the final assembly step, an O-ring and screws secure the top lid to the silicon carrier. The manifold has three inlets and two outlets. Coolant impinges on the diamond microchannels and returns through the channels; by design, it does not contact the bonding layer or silicon.

The talk left several questions unanswered: What is the thermal resistance of the indium interface? Will it survive repeated thermal cycles? Does machining affect surface quality? Can the channels and manifold sustain stable flow over time?

5. Reading the 38.2% Test Result

Power (heat flux)	Copper + PCM junction temp.	Diamond microchannel junction temp.	Temp. reduction	Resistance, baseline → diamond	Reduction (calculated)
2,000 W (240 W/cm²)	84.3°C	64.9°C	19.4°C	0.0272 → 0.0175 °C/W	35.7%
2,500 W (300 W/cm²)	95.0°C	70.8°C	24.2°C	0.0260 → 0.0163 °C/W	37.3%
3,000 W (360 W/cm²)	106.2°C	77.1°C	29.1°C	0.0254 → 0.0157 °C/W	38.2%

Test conditions: PG25, 30°C inlet, flow rate of 2 L/min per kW, and nine junction-temperature measurement points on a silicon thermal test vehicle. I calculated the reductions for the first two rows from the thermal-resistance values; the slide itself labels only the 38.2% result.

Figure 5. Test comparison published by Wiwynn. The presentation labels a 38.2% reduction at 360 W/cm²; percentages for the first two rows are calculated from the table.

Four points matter when interpreting the results:

1. The 38.2% is a system-structure comparison. The microchannel geometry, removal of the TIM and replacement with diamond all change at once. The baseline cold-plate geometry was not disclosed, so the improvement cannot be attributed entirely to diamond as a material.
2. This is junction-to-inlet resistance, which includes heat picked up by the coolant itself. Using typical PG25 properties, I roughly estimate that at 3 kW and 2 L/min per kW, the coolant warms by about 8°C. That contribution is common to both solutions and is about one-sixth of the diamond solution’s 0.0157 °C/W. This is my estimate, not a reported measurement. An audience member suggested comparing cold-plate effectiveness based on NTU, precisely because this resistance metric can include such shared terms.
3. The 30°C inlet is below the 45°C warm-water cooling discussed in the industry. The speaker acknowledged this as a consideration for future work.
4. The test used a silicon thermal test vehicle, not a real AI chip.

6. The Gap Between 38.2% and 59.5%

The slide attributes the gap to interfacial thermal resistance caused by non-ideal bonding quality. The speaker said this was only a possibility and listed bond improvement as the first item for future study. He also connected the result to the 65–85% figure from the opening slide, suggesting room for improvement. But that percentage breakdown is illustrative, not measured in this experiment, and cannot be treated as a like-for-like gap.

For now, the interface explanation is a hypothesis. The talk provided no measured interface resistance or bonding-void fraction. Surface graphitization was also mentioned, leaving at least two possible factors that cannot be separated from the disclosed evidence. The presentation did not say whether simulation inputs matched the physical specimen; that is an additional question from my review.

For future diamond-component suppliers, the lesson is that heat still has to cross metallization and solder interfaces. High bulk conductivity does not automatically become system performance. The conditions for entry include machining microstructures, achieving stable metallization and bonding, and validating the final thermal resistance under consistent test conditions.

7. How Far Had Commercialization Progressed by October?

What can be confirmed is that Wiwynn had taken an SCD microchannel route to a defined geometry, a stated process sequence and comparative test results.

The talk and slides did not disclose pressure drop, pump power, thermal-cycle life, production yield, cost, or certification or purchasing by a named customer. Wiwynn also said verbally that single-crystal diamond is expensive and difficult to machine, and listed manufacturing scale-up, other diamond-based materials and fabrication methods as future directions. These remarks were spoken, not included on the slides.

The work should also be viewed alongside Wiwynn’s other cooling routes: a double-sided cold plate with liquid-metal TIM (the May release claimed a thermal-efficiency improvement of more than 30%) and topology-optimized microchannels developed with Corintis (in the October 12 release). Their improvement figures use different baselines and are not directly comparable.

The significance of this step is limited but real: a systems company has disclosed the form of a diamond component it is willing to evaluate—a microstructured single crystal that can be metallized and bonded. There is not yet evidence that it will become a procurement requirement.

If most of the remaining thermal-resistance gap sits at the bonding interface, should the solution come from the diamond material supplier, the machining company or the packaging supplier? The answer may say more about the distance to commercialization than the next thermal-conductivity figure.

Sources

1. Wiwynn, May 26, 2026: Computex announcement
2. Wiwynn, June 4, 2026: Diamond-composite thermal-solutions white paper
3. 2026 OCP APAC Summit, August 11–12, Taipei
4. Wiwynn, October 12, 2026: OCP Global Summit announcement
5. Nick Liu and Jake Hsieh, Investigation of Diamond-Based Materials for Direct Liquid Cooling of Next-Generation AI Chips, OCP Future Technologies Symposium, October 14, 2026, slides 2–10 and audience Q&A (transcript automatically generated).