In luxury watchmaking and precision glass manufacturing, precision spacer deposition is a mission-critical process where every micron directly impacts both aesthetics and functionality. Depositing high-viscosity adhesives – such as bi-component epoxy or UV-cure glues – onto curved, non-flat surfaces with micrometer accuracy (±2 µm) exceeds the capabilities of conventional dispensing technologies. Hummink’s HPCaP (High Precision Capillary Printing) technology, implemented via the NAZCA microprinting machine, solves this challenge at production scale. This use case details how Hummink enabled a leading watchmaker to achieve repeatable spacer deposition on sapphire glass bezels – reducing defect rates and eliminating manual rework.
Download the Full Use Case PDF – technical data, figures, and process parameters.
The Challenge of Spacer Deposition in Luxury Watchmaking
Assembling the glass on a luxury watch is far more complex than it appears. The sapphire crystal must be bonded to the bezel with an adhesive spacer that guarantees both structural integrity and optical cleanliness. In premium segments, tolerances leave no margin for error: the spacer must maintain a uniform gap, typically between 1 and 10 µm, across the entire bonding surface.
Several industrial constraints make this process particularly difficult. First, the bezel geometry is inherently non-planar: watch cases feature curved or faceted surfaces that standard flat-bed dispensing equipment cannot accommodate. Second, the adhesives best suited for this application – bi-component epoxies, UV-curing glues, silicone-based sealants – are high-viscosity materials, often exceeding 50,000 cP, which behave very differently from the diluted inks used in inkjet printing. Third, the esthetic requirements of luxury watchmaking are absolute: any excess adhesive, satellite droplet, or irregular bead is grounds for rejection. Functional sealing against dust and moisture adds a further layer of constraint.
These combined pressures – geometric complexity, extreme viscosity, micron-level tolerances, and zero-defect quality standards – systematically expose the limits of traditional dispensing methods.
Why Traditional Dispensing Methods Fall Short on Non-Flat Surfaces
Inkjet dispensing operates optimally with low-viscosity fluids (typically 1–50 cP). Materials above 1,000 cP cause nozzle clogging, inconsistent jetting, and satellite droplets that contaminate the bonding area. Inkjet heads cannot handle the epoxy formulations required in watch glass assembly.
Jet valve dispensing tolerates higher viscosities (up to 5,000–10,000 cP) but delivers minimum volumes in the nanoliter range, with positional accuracy of 50–200 µm – insufficient for sub-10 µm spacer control. On curved surfaces, the stand-off distance variation further degrades deposit consistency.
Screen printing and stencil dispensing are fundamentally incompatible with non-flat substrates. They require intimate contact between the stencil and the substrate, which is impossible on a three-dimensional bezel geometry.
Syringe-and-needle dispensing (contact dispensing) can handle high-viscosity materials but offers neither the positional precision nor the volumetric repeatability required for spacer deposition at the micron scale. Process control depends heavily on operator skill.
Micrometer Tolerances: The New Standard in Watch Glass Assembly
The tolerances demanded by Swiss-grade watchmaking for glass bonding are fundamentally different from standard industrial assembly. A spacer deposited with ±5 µm variability on a flat surface becomes a gap error of ±8–12 µm when projected onto a curved bezel – which may translate to visible unevenness or adhesion failure at the crystal edge.
The table below summarizes the gap between industry requirements and conventional equipment capabilities:
| Parameter | Industry Requirement | Conventional Systems | HPCaP / NAZCA |
|---|---|---|---|
| Positional accuracy | ≤ ±5 µm | 50–200 µm (jet valve) | < ±2 µm |
| Minimum deposit diameter | < 20 µm | > 100 µm (jet valve) | 4 µm |
| Viscosity range | > 10,000 cP | < 10,000 cP (jet valve) | Up to 250 000 cP |
| Non-flat surface compatibility | Required | Not supported | Supported |
| In-situ metrology | Recommended | External QC only | Integrated |
How HPCaP Technology Solves Precision Spacer Deposition
High Precision Capillary Printing (HPCaP) is a fundamentally different approach to micro-dispensing, based on the controlled exploitation of capillary forces rather than pressure-driven jetting or contact deposition. Developed from research conducted at the Institut Pierre-Gilles de Gennes (IPGG), École Normale Supérieure (ENS), CNRS, and PSL University, HPCaP was specifically engineered to bridge the gap between laboratory-scale precision and industrial production requirements.
Unlike jetting systems, HPCaP does not require fluids to be ejected through a nozzle under pressure. Instead, material is transferred via a precisely controlled capillary meniscus between the dispensing tip and the substrate. This mechanism is inherently compatible with high-viscosity materials: the higher the viscosity, the more stable the meniscus – and the more reproducible the deposit geometry. The NAZCA machine implements HPCaP at production scale, combining sub-micron XYZ positioning, integrated optical metrology, and full process traceability in a single compact platform.
For precision spacer deposition in watchmaking, HPCaP delivers three key advantages over conventional systems: (1) compatibility with adhesives up to several million cP; (2) deposit diameters from 4 µm to millimeter scale, fully programmable; and (3) in-situ characterization of every deposit, closing the QC loop without external measurement equipment. See our technology page for the full technical background.
The Science Behind Capillary-Based Precision Printing
Capillary printing exploits the interplay between surface tension, meniscus geometry, and contact angle dynamics to transfer defined volumes of fluid from a reservoir tip to a substrate. When the tip approaches the substrate to a controlled distance (the stand-off gap), a liquid bridge forms spontaneously. By controlling tip geometry, stand-off distance, dwell time, and retraction speed, the volume deposited can be tuned from picoliters to nanoliters with sub-percent repeatability.
This physics-based mechanism was pioneered at IPGG / ENS / CNRS / PSL and translated into the HPCaP process. Its key advantage for high-viscosity materials: viscosity stabilizes the meniscus during transfer, rather than disrupting it as in jetting. The NAZCA machine controls all relevant parameters in closed-loop, enabling microprinting of formulations that no conventional system can process.
Compatibility with High-Viscosity Materials: Epoxy Glues and UV Adhesives
HPCaP has been validated with a broad range of industrial materials, including:
- Bi-component epoxy adhesives (e.g., Araldite-type, 2K systems) – typically 20,000 to 200,000 cP
- UV-curing adhesives for optical bonding – 1,000 to 50,000 cP
- Silicone sealants and silicone-based spacers – 10,000 to 500,000 cP
- Silver inks and conductive pastes – from 10,000 cP to several million cP (see Figure 1)
- Precision greases and filled polymers for semiconductor packaging
The NAZCA machine processes these materials without applying destructive shear, heat, or ultrasonic agitation. The capillary transfer mechanism is material-agnostic within the viscosity range of 1 cP to 250 000 cP, making it the most versatile precision deposition platform available for micro-assembly applications.
Dot Size Control: From 4 µm to Millimeter-Scale Deposits
As demonstrated in Figure 1 (3D profilometry of silver ink bumps printed by HPCaP), the NAZCA machine achieves deposit diameters down to 4 µm with height-to-diameter aspect ratios well above standard dispensing limits. Deposit size is controlled by tip geometry, material properties, and process parameters – all programmable via the NAZCA software.
The system can print both isolated dots and continuous patterns (lines, rings, grids) with positional accuracy below ±2 µm. Figure 3 shows the height profile measured by the NAZCA’s integrated profilometer – the machine characterizes its own deposits in real time, enabling immediate process feedback and statistical process control (SPC).
Use Case: Spacer Deposition on Curved Watch Glass Surfaces
The following use case details a production challenge submitted by a Swiss luxury watch manufacturer. The complete technical data, process parameters, and metrology results are available in the downloadable PDF.
Customer Challenge: Assembling Sapphire Glass on Complex Watch Bezels
The customer manufactures high-end mechanical watches with sapphire crystal glasses mounted on polished steel bezels with three-dimensional geometry. The assembly process requires depositing a bi-component epoxy spacer on the inner bezel ledge to maintain a defined gap between the glass and the case during curing. Requirements: deposit diameter < 50 µm, height uniformity ±3 µm, full coverage of a curved 360° bonding path with no gaps or overlaps, and zero adhesive contamination on the optical surfaces.
Previous attempts with jet valve dispensing resulted in satellite droplets on the sapphire surface and height variability of ±15–20 µm – both unacceptable for series production. Manual dispensing was rejected due to cycle time and repeatability constraints.
Solution Deployed: NAZCA Machine Configuration for Watch Assembly
The solution deployed by Hummink used the NAZCA machine configured with an HPCaP head matched to the epoxy viscosity (approximately 80,000 cP at 25°C). As visible in Figure 2 (NAZCA machine during biocomponent epoxy glue deposition), the dispensing head maintains a controlled stand-off from the curved bezel surface.
The NAZCA process was configured as follows:
- Material: bi-component epoxy glue, mixed immediately before deposition via integrated micro-mixing
- Deposit pattern: continuous ring path, diameter 32 mm, 360° coverage
- Target dot diameter: 35 µm – achieved: 33–37 µm (±2 µm)
- Substrate compensation: active Z-axis correction for bezel curvature profile, measured by integrated profilometry before deposition
- Cycle time: < 45 seconds per watch case
The NAZCA’s integrated vision system was used to align the deposition path to the bezel geometry with sub-micron accuracy prior to each print cycle – a key advantage of the NAZCA platform versus standalone dispensing systems that rely on external fixturing.
Results: Micrometer Accuracy Achieved on Non-Flat Surfaces
Figure 3 (height profile of deposited spacer dots measured by NAZCA) confirms the results achieved in production conditions:
- Positional accuracy: ±1.8 µm across the full 360° bonding path
- Height uniformity: ±2.5 µm (vs. ±15–20 µm with jet valve dispensing)
- Satellite contamination: 0 incidents across 500 production cycles
- Defect rate reduction: from ~12% to < 0.5% at final assembly inspection
- Cycle time: 42 seconds per unit – compatible with series production
The in-situ characterization capability of the NAZCA was critical: by measuring each deposit immediately after printing – without removing the part from the machine – the customer eliminated a dedicated QC station and reduced total cycle time by 18%. Real-time height data feeds directly into the SPC system for process monitoring.
Extending the Application to Glass Manufacturing Beyond Watchmaking
The HPCaP process addresses any application requiring high-viscosity adhesive deposition with micrometer accuracy on non-flat substrates. While the watchmaking use case demonstrates the technology’s capabilities in a demanding B2B context, the same platform is directly applicable to a range of adjacent industries.
Optical Glass Assembly and Display Manufacturing
In optical glass assembly – lens bonding, AR coating deposition, prism cementing – HPCaP enables precise application of optical adhesives (e.g., UV-curing NOA-series, low-outgassing epoxies) with deposit diameters matched to the bonding area geometry. Tolerances in this sector are comparable to watchmaking: < 5 µm positional error, no adhesive on active optical surfaces.
For display manufacturing (OLED, µLED, miniLED assemblies), spacer deposition controls the air gap in optical bonding stacks. HPCaP can deposit spacers in arrays with pitches below 100 µm – beyond the reach of screen printing or stencil dispensing. See Hummink’s Applications page for display and semiconductor use cases.
Semiconductor Packaging: Precision Spacer Deposition at Wafer Scale
In advanced semiconductor packaging – underfill deposition, die attach, chip-to-chip spacer control, and wafer-level packaging – the HPCaP process offers sub-10 µm deposit accuracy at throughputs compatible with back-end manufacturing lines. Materials include silver sintering pastes, thermal interface materials (TIMs), anisotropic conductive films (ACF) precursors, and non-conductive adhesives in the 10,000–500,000 cP range.
The NAZCA platform’s wafer-scale motion control and integrated metrology make it directly transferable from watchmaking to semiconductor environments, with no architectural changes to the core dispensing technology.
NAZCA Machine: Technical Specifications for Precision Spacer Deposition
For engineers evaluating HPCaP as a solution for precision spacer deposition, the table below summarizes the key technical parameters of the NAZCA machine:
| Parameter | Specification |
|---|---|
| Viscosity range | 1 cP to several million cP (fluid-agnostic) |
| Minimum deposit diameter | 4 µm |
| Maximum deposit diameter | Millimeter scale (programmable) |
| Positional accuracy (XYZ) | < ±2 µm |
| Substrate compatibility | Flat, curved, structured surfaces – up to ±500 µm Z compensation |
| Integrated metrology | In-situ optical profilometry – real-time height and diameter measurement |
| Material mixing | Integrated micro-mixing for bi-component systems (2K epoxy, silicone) |
| Pattern capability | Dots, lines, rings, grids, arbitrary paths – CAD-driven |
| Throughput | Application-dependent – typically < 60 s for standard watch case patterns |
| Platform format | Compact benchtop (R&D and low-volume) – scalable to inline production |
Viscosity Range and Material Compatibility
| Material Type | Typical Viscosity | HPCaP Compatible |
|---|---|---|
| Low-viscosity UV adhesives | 1 – 100 cP | ✓ |
| Mid-viscosity epoxy systems | 1,000 – 10,000 cP | ✓ |
| High-viscosity 2K epoxy (watch assembly) | 10,000 – 200,000 cP | ✓ |
| Silver inks & conductive pastes | 10,000 – 1,000,000 cP | ✓ |
| Silicone sealants | 50,000 – 500,000 cP | ✓ |
| Thermal interface materials | Up to millions of cP | ✓ |
Positioning Accuracy and Minimum Feature Size
The NAZCA machine achieves < ±2 µm positional accuracy in XYZ – confirmed by in-situ profilometry (Figure 3). Minimum feature size is 4 µm diameter dots (Figure 1), with high aspect ratio bumps achievable for spacer applications requiring significant standoff height. The integrated Z-axis compensation accommodates substrate curvature up to ±500 µm without fixturing, making the NAZCA uniquely suited for non-flat surfaces in watchmaking and optical assembly.
Why Choose Hummink HPCaP Over Conventional Dispensing Systems
The table below compares HPCaP / NAZCA against the most common alternatives for precision spacer deposition:
| Technology | Viscosity Limit | Min. Deposit Size | Positional Accuracy | Non-Flat Surfaces | In-Situ QC |
|---|---|---|---|---|---|
| HPCaP / NAZCA | Up to millions of cP | 4 µm | < ±2 µm | ✓ (active Z comp.) | ✓ (integrated) |
| Jet valve dispensing | < 10,000 cP | > 100 µm | 50–200 µm | Limited | ✗ |
| Inkjet dispensing | < 50 cP | 20–50 µm | 20–50 µm | ✗ | ✗ |
| Screen / stencil printing | 1,000 – 100,000 cP | > 50 µm | 20–100 µm | ✗ | ✗ |
| Manual syringe dispensing | Unlimited | > 500 µm | > 500 µm (operator) | Manual adapt. | ✗ |
HPCaP vs. Jet Valve Dispensing: Precision and Viscosity Limits
Jet valve dispensing is the most common alternative for precision adhesive deposition in watchmaking. It handles viscosities up to ~10,000 cP – one to two orders of magnitude below the 2K epoxy systems used in watch glass bonding. Minimum volume is in the nanoliter range, with positional scatter of 50–200 µm. On curved surfaces, stand-off variation degrades both volume and position accuracy further. HPCaP operates with picroliter-scale volumes and < ±2 µm positional accuracy, across the full viscosity range required by watchmaking adhesives.
The Unique Advantage of In-Situ Characterization with NAZCA
Every NAZCA machine includes an integrated optical profilometer that measures deposit height, diameter, and volume immediately after printing – without removing the substrate from the machine. This eliminates the need for a separate QC station, reduces total cycle time, and enables real-time Statistical Process Control (SPC). If a deposit falls outside specification, the system flags it immediately and can trigger automatic rework – a capability unavailable on any conventional dispensing platform. This is a unique competitive differentiator of the NAZCA machine for production environments.
FAQ – Frequently Asked Questions on Precision Spacer Deposition
What is spacer deposition in watchmaking?
Spacer deposition in watchmaking refers to the precise application of an adhesive or polymer material between the sapphire glass crystal and the watch case bezel, creating a defined, uniform gap that ensures both structural adhesion and optical alignment. In luxury watchmaking, spacer heights are controlled at the micrometer level (typically 1–10 µm) to guarantee perfect glass seating, moisture resistance, and visual consistency across production batches.
Can high-viscosity adhesives be dispensed with micrometer precision?
Yes – with HPCaP technology. Conventional jetting systems (inkjet, jet valve) are limited to low-to-mid viscosity ranges and cannot deposit materials above ~10,000 cP with micrometer accuracy. HPCaP’s capillary mechanism is physically compatible with high-viscosity materials: viscosity stabilizes the meniscus rather than disrupting it, enabling deposits of bi-component epoxy and UV adhesives above 100,000 cP with positional accuracy below ±2 µm.
What viscosity range does the NAZCA machine handle?
The NAZCA machine processes materials from 1 cP to several million cP – covering aqueous solutions, UV adhesives, bi-component epoxies, silver pastes, silicone sealants, and thermal interface materials. This is the broadest viscosity range of any precision deposition platform on the market. Examples: bi-component epoxy (20,000–200,000 cP), silver ink (100,000–1,000,000 cP), UV adhesives (1,000–50,000 cP).
How does HPCaP compare to traditional adhesive dispensing systems?
HPCaP outperforms conventional systems on three critical dimensions: viscosity range (millions of cP vs. max ~10,000 cP for jet valves), precision (< ±2 µm vs. 50–200 µm), and in-situ quality control (integrated profilometry vs. external inspection). For non-flat surfaces – standard in watchmaking – HPCaP’s active Z compensation is a unique capability unavailable on any competing platform. Explore the NAZCA machine specifications.
Is precision spacer deposition applicable outside of watchmaking?
Absolutely. HPCaP precision spacer deposition applies directly to optical glass assembly (lens bonding, AR coatings), display manufacturing (OLED, µLED optical bonding stacks), semiconductor packaging (underfill, die attach, wafer-level bonding), and printed electronics (conductive paste deposition, antenna printing). Any application combining high-viscosity material, non-flat substrate, and micrometer tolerance is a candidate for HPCaP. See Hummink’s full application scope.
Conclusion: Redefining Micro-Assembly Precision with Hummink
Precision spacer deposition in watchmaking – and across all industries where micrometer accuracy meets high-viscosity materials – demands a technology that conventional dispensing systems cannot deliver. Hummink’s HPCaP process and the NAZCA machine address this gap directly: from 4 µm minimum deposit size to unlimited viscosity compatibility, from curved surfaces to real-time in-situ QC.
The results achieved in the watch glass assembly use case – ±1.8 µm positional accuracy, 0 contamination incidents, < 0.5% defect rate – demonstrate what is achievable when deposition technology is engineered to match the physics of the process. The same platform is immediately applicable to optics, displays, and semiconductor packaging, with no changes to core hardware.
Explore the complete technical data in the Use Case PDF, or browse the full Hummink Resource Library for additional application examples.
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