Skiving needs a blade ground per pitch. Extrusion needs a die. A bonded fin needs a machined slot — which is why it is the one high-aspect fin field you can order as a single piece, and why the catalogue version quietly gives that advantage back.
Marketing pages for bonded fin heat sinks quote fin densities of 100 or more fins per inch and fin stock from 0.008 in. The catalogue tables published in the same industry tell a different story: a typical published bonded-fin base range runs a constant 1.3 mm fin at a pitch between 5.0 mm and 10.2 mm, on base plates 10.2 to 16.5 mm thick. That is roughly 2.5 to 5 fins per inch — an order of magnitude away from the headline figure, and no page anywhere reconciles the two.
Both numbers are real. They describe different things. The headline figure is what the process can reach when the fins, the slots and the bond are all made for one job. The catalogue figure is what a stocked base extrusion gives you, because the slot pitch was fixed when that die was cut. Buying from the catalogue means buying that die's pitch.
This is the whole reason the page exists. Bonded fin is a tooling-free process sold out of tooled catalogues. Machine the base instead of buying it, and the slot pitch, the fin height and the footprint all come off your drawing rather than off someone's die list — at quantity one, because there is nothing to amortise.
Bonded fin, folded fin, zipper fin and stacked fin are used interchangeably in enquiries and even in supplier copy. They are four different parts. The difference decides what you can order, in what quantity, and what it costs.
| Construction | How the fin is made | What sets the pitch | Tooling | Available at qty 1? |
|---|---|---|---|---|
| Bonded fin | Separate flat fins, each one a strip of rolled sheet, set individually into slots | The slots — machine them and the pitch is yours | None, if the base is machined | Yes |
| Folded fin | One continuous sheet corrugated back and forth, then attached to a separate base | The forming rolls | Forming tooling per pitch | Not economically |
| Zipper fin | Sheet progressively punched, then folded so each fin locks into the one before it | The punch set | Punch and die set | Not economically |
| Skived fin | A blade peels a layer off the solid block and folds it upright, still attached | The blade and fixture, ground per pitch | Blade + fixture per pitch | Blade cost does not spread |
Read the pitch column again, because it is the one that decides everything else. In three of these four constructions the fin pitch belongs to a tool. Only in bonded fin does it belong to the base — and a base is just a machined part. That is why bonded fin is the only high-aspect fin field you can have as a one-off, and it is also why the catalogue version loses the advantage: a stocked base extrusion has its slots already cut.
A skived or milled fin grows out of the base. There is no joint anywhere in the heat path. A bonded fin is a separate piece of metal standing in a slot, so every watt that leaves the base has to cross one interface before it reaches the fin. Nothing on this page is worth reading if that is glossed over, and most supplier pages gloss over it.
Two consequences follow that are worth stating plainly. Fin efficiency drops. Published figures for bonded assemblies put fin efficiency around 60–75 per cent, against up to about 85 per cent for an extruded fin of the same geometry — the joint is part of why. And an all-copper assembly is not epoxy bonded at all: copper fins into a copper base are brazed or soldered, which is a different process with a different cost and a different temperature ceiling. If your drawing says copper and bonded in the same sentence, one of those two words is doing something you did not intend.
Against that, the joint buys something no tooled process gives you: the fin field is decoupled from the base. Copper fins can stand in an aluminium base — the fins carry the conduction where it matters and the base carries the mass and the mounting, which is a pairing neither extrusion nor skiving can produce at all.
The same fin geometry gets built four different ways depending only on how many you order. Nobody publishes this, because for three of the four routes the honest answer sends the enquiry somewhere else.
| Quantity | Route that wins | Tooling you pay for | Why the alternatives lose here |
|---|---|---|---|
| 1 | Bonded fin on a machined base | None | A skiving blade and fixture are ground per fin pitch; a die is cut per section. Neither spreads across one part. |
| 2 – 50 | Bonded fin on a machined base | None | Still nothing to amortise. This is the band where skiving shops quote a 500-piece minimum and the enquiry stalls. |
| 50 – 500 | Bonded fin or skived, decided on the part | Blade grinding if skived | Thin copper fins start to favour skiving; the monolithic root is worth the blade once it spreads this far. |
| 500+ | Skiving, or extrusion if the section allows | Blade set, or an extrusion die | Bonded fin stops winning: the per-part labour of setting individual fins no longer beats amortised tooling. |
The sentence we hear almost word for word: "I need twenty pieces with 0.4 mm fins and every skiving shop wants a 500-piece minimum." That minimum is about the blade and the fixture, not about your fin. Bonded fin reaches the same fin density at quantity one, and we will tell you the crossover point where paying for the blade starts to make sense.
| Parameter | Range | What decides it |
|---|---|---|
| Fin thickness | 0.30 – 1.00 mm rolled sheet | Below 0.30 mm the fin bends under a thumb during packing. Thicker is always available and often better. |
| Aspect ratio | Past 50:1 | Nothing loads the fin during assembly, so height is limited by handling and by airflow, not by the process. |
| Fin pitch | Yours — the slots are machined | Below roughly 1.3 mm the slots and the bond line start to dominate the cost. |
| Base | Machined 6061-T6 or 6063 | Slot depth plus the metal that must remain under the roots. A bonded base is thicker than a milled fin field needs. |
| Fin material | 1050 or 6063 aluminium, C11000 copper | 1050 at about 229 W/m·K and 6063 at about 201 W/m·K; C11000 at about 388 W/m·K where the fin itself is the bottleneck. |
| Alloys that do not belong here | 7075-T6, stainless 304 | 7075-T6 carries about 130 W/m·K against 167 for 6061-T6 — thermally a step backwards, worth it only if the base is also a loaded structural part. Stainless 304 at about 16 W/m·K is out on conductivity before the process is even discussed. |
| Mixed pairing | Copper fins into an aluminium base | Available here and not from any tooled process. Dry air cooling only — there is no electrolyte, unlike a liquid loop. |
One limit deserves its own line because the industry answers it two different ways. Black anodising a finished bonded assembly is not a given. Some suppliers list it as routine, at least one states plainly that it is not possible on a bonded part. The practical answer is to decide the finish before the part is bonded rather than after: anodise the base and the fin stock separately and bond afterwards, or accept a chromate finish on the assembly. Put the finish on the drawing and it costs nothing; discover it after bonding and it costs the part.
Most bonded fin requirements are not our problem to solve, and saying so saves everyone a week.
| What you need | In the catalogue? | What we do about it |
|---|---|---|
| A standard bonded-fin base from a published profile list, in the pitch that profile carries | Yes — 20-odd base profiles are published, up to 60 fins | Buy it off the shelf. If your footprint matches a stocked base and its pitch suits you, that part is cheaper than anything we machine. |
| PC, gaming or server retail cooler | Yes — a whole retail industry | Not our market. Retail coolers have their own makers and their own prices. |
| Fin pitch that no published base profile carries | No — the slot pitch was fixed when that die was cut | Slots machined at your pitch, then bonded. No die, from 1 piece. |
| 0.30 mm fins, twenty pieces | No — skiving shops quote 500 minimum | Same fin density, no blade, no fixture, quantity 1. |
| Copper fins on an aluminium base | No — one tooled process makes one material | Fins and base chosen separately, then bonded. Dry air cooling only. |
| Fin field that stops around a fastener, or steps in height | No — a die makes one constant section | The slots go where you want them; a slot that is not cut is a fin that is not there. |
| Ten thousand a year of a constant-section finned bar | Yes — extrusion, and it will beat us | Go to an extruder. At that volume the die amortises and the piece price drops below anything we can reach. |
| All-copper assembly | Half — copper bonded parts exist but are not epoxy bonded | Brazed or soldered instead, quoted as the different process it is. |
Every supplier page in this category ends at a contact form without saying what it wants. Send these eight and the quote comes back inside 12 hours rather than after a week of questions.
No CAD is fine. A dimensioned sketch, a photo with a scale in it, or the old part in a box will do; we redraw it and send the drawing back for approval before anything is cut.
Not in service, and it is fair to ask because the whole part hangs on that joint. Being straight about the evidence: no supplier in this category publishes a pull-off force, a vibration profile or a thermal cycling regime for a bonded joint — the question is answered with reassurance across the entire industry, ours included. What we can tell you is what governs it: slot fit, surface preparation before bonding, and full coverage of the bond line rather than a bead down the middle. If your application has a qualification requirement, say so on the enquiry, because that changes the joint from bonded to brazed or soldered.
Yes, and anyone who tells you otherwise is selling. A skived or milled fin grows out of the base with no interface anywhere in the heat path; a bonded fin stands in a slot, so every watt crosses one bond line before it reaches the fin. Published figures put fin efficiency for bonded assemblies around 60 to 75 per cent against up to about 85 per cent for an extruded fin of the same geometry. That is the price of getting the fin field without tooling. Above roughly 500 pieces it stops being worth paying, and we say so.
Yes — this is the case bonded fin exists for. The 500-piece minimum is about the skiving blade and the fixture, which are ground for one fin pitch and cannot spread across twenty parts. A bonded fin needs neither: the slots are machined at your pitch and the fins are cut from rolled sheet, so quantity one costs what quantity one should cost. You give up the monolithic fin root, and we will tell you at what quantity buying the blade starts to pay.
Quantity decides it, not the drawing. At 1 to 50 pieces bonded fin wins because there is no tooling to amortise. From about 500 up, skiving wins because the fin root is solid metal with no interface and the blade cost has spread. Between 50 and 500 it is decided on the part: thin copper fins push toward skiving, an unusual pitch or a fin field that has to stop around a fastener pushes toward bonded. Send the quantity with the geometry and the answer is arithmetic rather than opinion.
Decide the finish before the part is bonded, not after. The industry answers this two ways — some suppliers list black anodising as routine on bonded assemblies, at least one states plainly that it is not possible — so the safe route is to anodise the base and the fin stock separately and bond afterwards, or to accept a chromate finish on the finished assembly. Put the finish on the drawing and it costs nothing. Discover it after bonding and it can cost the part.
Yes, and it is one of the few things bonded fin does that no tooled process can. The fins and the base are separate pieces of metal, so they do not have to be the same alloy: C11000 copper at about 388 W/m·K carries the conduction where it matters, while a 6061-T6 base at about 167 W/m·K keeps the mass and the mounting features. Air cooling only — there is no electrolyte in dry air, so the dissimilar pairing is not a galvanic problem the way it would be inside a liquid loop.
How the fin is made, and therefore what sets the pitch. A bonded fin is individual flat strips set into slots, so the pitch is whatever you machine. A folded fin is one continuous sheet corrugated back and forth before it is attached to a base, so the pitch belongs to the forming rolls. A zipper fin is sheet progressively punched and then folded so each fin locks into the one before it, so the pitch belongs to the punch set. Only the first one has a pitch you can specify freely, which is why it is the only one of the three worth quoting at quantity one.
No. A dimensioned sketch, a photo with something for scale in it, or the old part posted to us is enough to start. We redraw it and send the drawing back for approval before anything is cut. What we do need in writing is the heat load, the ambient the sink really sees, the airflow, the envelope and the quantity now against the quantity later — that last pair is what decides bonded against skived and it is the one most often left out.
Related: all fin processes compared · skived fin, once the quantity pays for a blade · extruded profiles and when not to pay for a die · fan-cooled assemblies
Send fin thickness, height and pitch, the base footprint, the airflow and the quantity. We reply within 12 hours — including when the honest answer is "buy the catalogue part".
// Route by quantity
1–50
Bonded fin
No blade, no fixture
50–500
Either
Decided on the part
500+
Bonded
Monolithic fin root
Response within 12h · Drawings kept confidential