PCM Removes Many Constraints to Flow Channel Designs

Engineers and designers developing advanced heat exchanger systems are under constant pressure to increase thermal performance, reduce size and weight, and improve manufacturability—often simultaneously. As system architectures become more compact and thermally demanding, the design of internal flow channels plays a central role in determining overall performance. Photochemical machining (PCM), also known as chemical etching or photochemical etching, offers unique advantages for manufacturing precision flow channels in thin metal materials used in plate-type, microchannel, and laminated heat exchanger systems.

This article provides practical insights into how PCM can support high-performance flow channel design, why it compares favorably to stamping, laser cutting, and micro-milling, and what engineers should consider when designing etched flow plates.

Why Flow Channel Geometry Matters More Than Ever

In modern heat exchangers—whether used in aerospace environmental control systems, electric vehicle battery cooling, power electronics thermal management, or compact industrial chillers—thermal efficiency is tightly linked to flow channel geometry.

Engineers increasingly rely on:

• Microchannels to increase surface area-to-volume ratio
• Turbulence-inducing features to enhance convective heat transfer
• Complex serpentine or manifolded layouts for flow uniformity
• Thin-wall designs to minimize thermal resistance

Manufacturing these geometries using traditional methods introduces tradeoffs. Mechanical stamping can distort thin metals. CNC micro-milling increases cost and limits scalability. Laser cutting introduces heat-affected zones (HAZ) that may affect material properties or corrosion resistance.

Photochemical machining eliminates many of these constraints.

What Is Photochemical Machining?

Photochemical machining is a subtractive manufacturing process that uses photoresist imaging and controlled chemical etching to remove metal selectively from flat sheet materials. The process involves:

1. Laminating photoresist onto a metal sheet
2. Imaging the desired pattern via UV exposure
3. Developing the resist to expose selected areas
4. Chemically etching away unprotected metal
5. Stripping the resist to reveal the finished component

Because the process does not involve mechanical force or thermal energy, it is ideally suited for fabricating precision features in thin gauge metals without inducing stress, burrs, or distortion.

Key Advantages for Flow Channel Manufacturing

1. No Mechanical Stress or Distortion

Thin plates—often between 0.001″ and 0.040″ thick—are especially prone to distortion during stamping or forming. For heat exchangers relying on flatness for brazing or diffusion bonding, even slight deformation can compromise assembly integrity.

PCM applies no mechanical force, so parts remain flat and dimensionally stable. This is particularly valuable for laminated plate heat exchangers and stacked microchannel assemblies.

2. No Heat-Affected Zone (HAZ)

Laser cutting or EDM can create localized heating, altering microstructure or introducing recast layers. In heat exchangers operating in corrosive environments or high-temperature cycles, preserving base material properties is critical.

PCM is a room-temperature chemical process. There is no thermal distortion, no hardened edge, and no microcracking—ideal for materials such as:

• Stainless steels
• Nickel alloys
• Copper alloys
• Aluminum
• Titanium

Maintaining consistent metallurgy enhances corrosion resistance and long-term reliability.

3. Exceptional Precision for Complex Channel Geometries

Photochemical machining can produce highly detailed 2D channel geometries, including:

• Fine microchannels
• Intricate manifold patterns
• Cross-flow or counter-flow networks
• Mixing features and turbulators
• Integrated inlet and outlet ports

Feature sizes can be held to tight tolerances relative to material thickness, and repeatability across large production volumes is excellent.

Because PCM is driven by digital artwork, engineers can iterate channel layouts quickly without hard tooling costs. Design revisions require only phototool updates—not new dies or fixtures.

4. Ideal for Laminated or Stacked Plate Heat Exchangers

Many advanced heat exchangers use stacked plate construction, where individual etched layers are aligned and bonded through:

• Vacuum brazing
• Diffusion bonding
• Soldering
• Adhesive bonding (for lower-temperature systems)

PCM allows engineers to:

• Etch partial-depth cavities
• Create through-features for flow routing
• Integrate alignment holes and registration features
• Incorporate braze alloy preform patterns directly

This multi-layer approach enables 3D internal flow networks constructed from precision 2D sheets—often more economically than machining internal cavities from solid blocks.

5. Burr-Free Edges and Clean Internal Surfaces

In fluid systems, burrs are unacceptable. They can:

• Disrupt flow
• Increase pressure drop
• Generate particulates
• Compromise brazed joints

PCM produces burr-free features because metal is chemically dissolved rather than sheared. Edges are smooth and clean, minimizing secondary deburring operations.

This is especially important in:

• Aerospace fuel or environmental systems
• Semiconductor cooling loops
• Medical heat exchange systems
• High-purity chemical processing

6. Controlled Depth Etching for Microchannel Applications

In addition to through-etching, PCM can be used for half-etching (partial-depth etching). This enables:

• Microchannel cavities
• Flow restrictors
• Surface texturing
• Turbulence-promoting features
• Integrated sealing grooves

Engineers designing compact liquid cooling plates for power electronics can use half-etched flow paths that are subsequently capped with a cover plate and brazed. This approach often reduces machining time and material waste compared to CNC pocketing.

Design Considerations for Engineers

To maximize the benefits of PCM in flow channel manufacturing, several design principles should be considered.

Material Selection

PCM works exceptionally well with:

• Austenitic stainless steels (e.g., 304, 316)
• Copper and copper alloys
• Nickel alloys (e.g., Inconel)
• Aluminum alloys

Material thickness influences achievable feature size. As a rule of thumb, minimum feature width is proportional to material thickness due to isotropic etching behavior.

Etch Factor and Dimensional Control

Chemical etching removes metal isotropically, meaning it etches downward and laterally. Engineers should account for undercut when specifying channel widths and wall dimensions.

An experienced PCM supplier will provide design-for-manufacturing (DFM) guidance to optimize:

• Channel widths
• Land widths between channels
• Port dimensions
• Registration tolerances

Early collaboration during the design phase significantly improves yield and consistency.

Surface Finish and Flow Performance

The etched surface has a matte, chemically textured finish. In many heat exchanger applications, this can be advantageous, slightly increasing surface area and promoting turbulence.

If ultra-smooth surfaces are required for laminar flow or ultra-low pressure drop systems, secondary finishing processes may be considered—but often are unnecessary.

Scaling from Prototype to Production

One of PCM’s most compelling advantages is scalability. Because there is no hard tooling:

• Prototypes can be produced quickly
• Small production runs are economical
• High-volume production maintains consistency
• Tooling costs remain low

For emerging technologies such as hydrogen fuel cells or next-generation EV thermal systems, this flexibility supports rapid development cycles.

Comparison to Alternative Manufacturing Methods

For thin, layered heat exchanger architectures, PCM frequently offers the best balance of performance, cost, and design flexibility.

Emerging Applications

As thermal management demands intensify, PCM is increasingly used in:

• EV battery cold plates
• Hydrogen fuel cell bipolar plates
• Aerospace microchannel heat exchangers
• Two-phase cooling plates
• High-density power electronics cooling

The push toward miniaturization and higher heat flux makes precise microchannel control essential—an area where photochemical machining excels.

Final Thoughts for Design Engineers

For engineers and designers working on advanced heat exchanger systems, photochemical machining should be viewed not simply as a manufacturing alternative—but as a design enabler.

Its ability to produce intricate, burr-free, stress-free flow channels in thin metals opens the door to:

• More aggressive thermal designs
• Lighter assemblies
• Improved bonding reliability
• Faster prototyping cycles
• Lower overall system cost

The key to success lies in early collaboration with an experienced PCM supplier to align channel geometry, material selection, and bonding strategy with the realities of chemical etching.

In a market demanding greater thermal efficiency within smaller footprints, photochemical machining provides a powerful, scalable pathway to next-generation heat exchanger performance.