Folded and Zipper Fin Heat Sinks: Design and Cost
Short answer: A folded fin heat sink is made by bending a continuous strip of aluminium or copper into a corrugated fin pack and bonding it to a base; a zipper fin heat sink uses individually stamped fins with interlocking tabs that zip into a baseplate or into each other. Folded fins are the cheapest route to high fin density, typically 8–40 fins per inch, with tooling often under USD 1,500. Zipper fins cost more per part but allow variable fin height, mixed materials and a copper base with aluminium fins. Both are quoted by BQUQ in 12 working hours with flexible MOQ.
What Is a Folded Fin Heat Sink?
A folded fin heat sink starts life as a flat coil of metal strip — usually 0.3 mm to 1.0 mm aluminium, sometimes copper. A progressive die or a dedicated folding machine creases the strip into a continuous accordion or corrugated profile. The result is one unbroken piece of metal that forms dozens of fins without a single joint between them.
That continuity matters for two reasons. First, there is no thermal interface between adjacent fins, so heat spreads laterally along the fold rather than stopping at a bond line. Second, the fin pack is mechanically self-supporting — the folds act as ribs, which lets designers push fin height and fin density further than a loose stack of plates would allow.
Folded packs are then attached to a baseplate by one of three routes:
- Epoxy bonding — lowest cost, adequate for moderate heat fluxes.
- Soldering or brazing — better conductivity, higher process cost.
- Mechanical capture — the fin pack is crimped or swaged into a groove in the base.
The base itself is usually an extruded or CNC-machined aluminium plate. For a deeper look at how base geometry drives spreading resistance, see our guide to heat sink base thickness.
Where folded fins win
Folded fin heat sinks are the default choice when you need a lot of surface area in a small footprint at a low unit cost. Typical applications include LED drivers, telecom line cards, power supplies, inverter modules and compact enclosures where air is moved by a low-profile blower.
Because the fin pack comes off a continuous strip, the marginal cost of extra fins is small. A design that needs 22 fins per inch rather than 11 often costs almost the same to produce — you are simply changing the fold pitch on the same tool.
What Is a Zipper Fin Heat Sink?
A zipper fin heat sink is built from discrete stamped fins. Each fin is blanked from sheet metal with small tabs or barbs formed on one or both edges. Those tabs interlock — "zip" — into matching slots in the baseplate, or into the neighbouring fin, creating a rigid block without adhesive.
The name comes from the assembly motion: the fins are stacked and pressed together like closing a zipper. Once zipped, the pack can be soldered, brazed or left mechanically locked depending on the thermal requirement.
Why engineers specify zipper fins
Zipper fins solve problems that folded fins cannot:
- Variable fin height. Fins can be tall at the centre of a hot component and short at the edges, matching a non-uniform heat source.
- Mixed materials. A copper base with aluminium fins is straightforward, which is useful when spreading resistance dominates but weight and cost must stay low.
- Open fin geometry. Tabs can be positioned to leave clearance for mounting holes, screw bosses or a fan cutout.
- Tighter tolerance on fin pitch. Stamped fins are individually controlled, so pitch variation across a wide pack stays small.
The trade-off is tooling and assembly time. A zipper fin design needs a stamping die plus a baseplate with precision slots, and assembly is a discrete operation rather than a continuous fold.
Folded vs Zipper Fins: Direct Comparison
| Attribute | Folded fin | Zipper fin |
|---|---|---|
| Fin construction | Continuous folded strip | Individually stamped fins |
| Typical fin thickness | 0.3–1.0 mm | 0.2–0.8 mm |
| Fin density | High (often 8–40 FPI) | High, more uniform pitch |
| Base attachment | Epoxy, solder, crimp | Zip tabs + solder/braze or mechanical |
| Variable fin height | Limited | Yes, per-fin |
| Mixed Cu/Al | Possible but uncommon | Common |
| Tooling cost (indicative) | Lower | Higher |
| Unit cost at volume | Lowest | Moderate |
| Best fit | Cost-driven, uniform heat source | Performance-driven, complex geometry |
Both families sit between extruded profiles and skived or forged parts on the cost-performance curve. If you are comparing against a machined alternative, our heat sink skiving process article explains where skived fins beat both.
How Fin Geometry Drives Thermal Performance
Fin geometry is a balance between surface area, air flow and conduction. Three variables dominate.
Fin density and pitch
More fins mean more surface area, but also more flow resistance. Beyond a certain pitch, the boundary layers in adjacent channels merge and the extra fins stop contributing. For forced air at 2–4 m/s, pitches between 1.5 mm and 3 mm are common. For natural convection, wider pitches of 6–10 mm usually perform better because buoyancy-driven flow needs open channels.
Fin thickness and aspect ratio
Thin fins save weight and cost but increase conduction resistance along the fin. A useful rule of thumb: keep the fin aspect ratio (height ÷ thickness) below roughly 30:1 for aluminium and 40:1 for copper in forced-air applications. Beyond that, the fin tip runs noticeably cooler than the base and the fin is doing less work than its surface area suggests.
Base spreading
Folded and zipper fin packs are only as good as the base beneath them. A small die sitting on a large baseplate creates a spreading bottleneck that no amount of fin area can fix. This is where a copper base, a thicker aluminium base, or an embedded heat pipe earns its cost.
| Design goal | Practical lever | Typical effect |
|---|---|---|
| Lower thermal resistance | Increase fin density | Gains flatten past ~25 FPI |
| Lower pressure drop | Widen fin pitch | Reduces ΔP, may raise Rth |
| Lower weight | Thinner fins, shorter pack | Watch aspect ratio limit |
| Better spreading | Copper base or thicker base | Largest gain for small sources |
| Lower cost | Folded fins, epoxy bond | Sacrifices peak performance |
Manufacturing Route and Cost Structure
At BQUQ, folded and zipper fin heat sinks run alongside CNC machining, metal stamping, custom springs and heat sink production on four production lines in one Dongguan factory. That matters for this product family because a zipper fin heat sink is really a stamping job plus a machining job plus an assembly job — and keeping all three under one roof removes the tolerance stack-up that appears when three suppliers each hold their own datum.
Cost breakdown
| Cost element | Folded fin | Zipper fin |
|---|---|---|
| Stamping/folding tooling | Low, one folding setup | Higher, progressive die |
| Baseplate tooling | Extrusion die or CNC program | CNC program plus slot features |
| Material | Strip coil, minimal scrap | Sheet blanking, more scrap |
| Assembly labour | Low, continuous pack | Moderate, per-fin zipping |
| Bonding process | Epoxy or solder | Solder/braze or mechanical |
| Finishing | Anodise, chromate, bare | Anodise, chromate, bare |
The crossover usually happens around a few thousand pieces per year. Below that, folded fins almost always win on total cost. Above it, a zipper fin design with a well-optimised progressive die can close much of the gap while delivering better thermal margins.
Tolerances and finishing
CNC-machined baseplates at BQUQ hold ±0.005 mm where flatness and mounting-hole position matter. Fin packs themselves are held to normal sheet-metal tolerances, which is fine — the critical dimension is base flatness against the thermal interface, not fin position. For surface treatment choices that affect both emissivity and corrosion, see our comparison of anodised versus bare finishes.
Design Rules for Folded and Zipper Fin Heat Sinks
1. Define the heat source first. Footprint and watt density determine whether you need spreading help before you need fin area.
2. Pick fin pitch from the airflow mode. Natural convection wants open channels; forced air tolerates tight pitch.
3. Keep aspect ratios sane. Under 30:1 for aluminium, under 40:1 for copper.
4. Design the bond line deliberately. Epoxy is fine for moderate flux; solder or braze for high flux. Our article on fin bonding with epoxy covers the failure modes.
5. Leave room for the interface. A thin, well-controlled thermal pad beats a thick one.
6. Plan the mounting early. Fan mounting, screw bosses and board standoffs are cheapest when designed into the baseplate from the start.
When to Choose Which
Choose folded fins when the heat source is reasonably uniform, airflow is defined, and unit cost or tooling budget is the binding constraint. Typical winners: LED drivers, power conversion modules, industrial enclosures.
Choose zipper fins when the heat source is concentrated, when fin height must vary across the pack, when a copper base with aluminium fins is required, or when you need mechanical locking rather than adhesive. Typical winners: high-power electronics, IGBT assemblies, compact server and telecom hardware.
Choose neither when the geometry is a simple flat profile with generous space — an extruded heat sink will be cheaper. See our extruded heat sinks range for those cases, and our full heat sink portfolio for the complete comparison.
Getting a Quote
BQUQ quotes custom heat sinks in 12 working hours. Send a drawing or a STEP file with the heat load, airflow, ambient and mounting constraints, and we will come back with a manufacturable design, a material recommendation and indicative pricing at your volume. Flexible MOQ applies — prototype quantities are welcome, and the same tooling carries into production.
For machined baseplates and precision features, see CNC machined heat sinks.
Frequently Asked Questions
Q: What is the difference between a folded fin and a zipper fin heat sink?
A: A folded fin heat sink is formed from one continuous strip of metal bent into a corrugated fin pack, so there are no joints between fins. A zipper fin heat sink uses individually stamped fins with interlocking tabs that zip into a baseplate or into each other. Folded fins are cheaper and simpler; zipper fins allow variable fin height, mixed copper-aluminium construction and tighter pitch control.
Q: Which is cheaper, folded or zipper fin heat sinks?
A: Folded fins are almost always cheaper, especially at low to moderate volumes. The folding setup is simpler than a progressive stamping die, and assembly is a continuous operation rather than a per-fin stacking step. The gap narrows at high annual volumes, where a well-optimised zipper fin die can bring unit cost close to a folded design while delivering better thermal margin.
Q: What fin density is practical for folded fin heat sinks?
A: Typical production folded fin packs run between 8 and 40 fins per inch, with 0.3 mm to 1.0 mm strip thickness. For forced air at 2–4 m/s, pitches of 1.5 mm to 3 mm are common. For natural convection, wider pitches of 6 mm to 10 mm usually perform better because buoyancy-driven airflow needs open channels rather than tight ones.
Q: Can zipper fin heat sinks use a copper base with aluminium fins?
A: Yes, and this is one of the main reasons engineers choose zipper fins. Individually stamped aluminium fins can be zipped and soldered or brazed onto a copper baseplate, which gives strong spreading under a concentrated heat source while keeping weight and material cost down. The bond quality between copper and aluminium is the critical process variable.
Q: How fast can BQUQ quote a custom folded or zipper fin heat sink?
A: BQUQ issues quotes in 12 working hours. Send a drawing or STEP file plus your heat load, airflow, ambient temperature and mounting constraints. Because stamping, CNC machining and assembly all run on four production lines in one Dongguan factory, the quote covers the full process chain rather than a single operation, and MOQ stays flexible from prototype upward.
Related Resources
- About BQUQ and our Dongguan manufacturing footprint: /about/
- Full heat sink product range: /heat-sinks/
- Extruded heat sink profiles: /extruded-heat-sinks/
- CNC machined heat sinks: /cnc-machined-heat-sinks/
- Industry trends in thermal management: /industry-dynamics/
- Technical articles and engineering guides: /bquq-blog/
- Frequently asked questions: /faq/
- Case studies: /case/
- Contact the engineering team: /contact/
Authored by the BQUQ Engineering Team. BQUQ (Dongguan) runs CNC machining (±0.005 mm), metal stamping, custom springs, and heat sink production in one ISO9001 factory. Source-direct from Dongguan, China — quote in 12 hours: sc@bquq.com | WhatsApp +86 13713157787 | www.bquq.com
