Guides / Materials
Hard Anodize or Electropolish: Choosing a Finish for Semiconductor Hardware
September 21, 2026
Two finishes cover most machined semiconductor hardware. Hard anodize on aluminum, electropolish on stainless. Picking the wrong one is expensive in a specific way: the part passes dimensional inspection at the shop, then fails at your incoming dock or, worse, in the tool.
What each one actually does
Type III hard anodize grows an aluminum oxide layer on aluminum. It is hard, electrically insulating and it survives handling and wear. Typical thickness on semiconductor hardware is 25 to 50 microns. Type II clear anodize is thinner, around 5 to 25 microns. It is chosen when appearance and mild corrosion resistance matter more than wear.
Electropolish removes metal from stainless steel in an electrolytic bath. It takes the peaks off the surface, leaves a smoother and more passive skin and lowers the area available to trap gas and particles. Gas wetted surfaces in delivery lines are commonly specified around 8 Ra microinch, vacuum facing surfaces around 16 Ra.
They solve different problems. Anodize protects and insulates a soft metal. Electropolish makes an already corrosion resistant metal cleaner and easier to keep clean.
What it does to your dimensions
This is where most first articles fail.
| Finish | Dimensional effect | What to do on the drawing |
|---|---|---|
| Type II anodize | Grows roughly half in, half out. About 5 to 12 microns per surface | Call out masked features, state the thickness |
| Type III anodize | About 20 to 25 microns per surface at 50 microns thickness | Undersize before finishing, or mask threads and bores |
| Electropolish | Removes roughly 5 to 25 microns per surface, more on edges and corners | Allow for stock removal on tight features, expect softened sharp edges |
Threads are the classic failure. An unmasked M6 thread with a 50 micron hard coat will not accept a standard screw. O-ring grooves are the second. Electropolish rounds the groove corners and changes the seal geometry if nobody allowed for it.
Lead time and who controls it
Almost no machine shop in Vietnam runs a qualified anodize or electropolish line in house. The part leaves the shop, waits for a batch and comes back. That is why finishing, not milling, is usually what makes a four week job a six week job.
Three questions worth asking before the order:
- Which finisher, in which province and what is the normal turnaround
- What is the batch minimum, and what does a single urgent part cost
- Who inspects the part when it comes back, and who pays for rework
A shop that answers all three quickly has done this before. A shop that says “no problem, we handle everything” has usually not.
What drives the cost
Area drives the price of both finishes. After that, masking drives it: every masked feature is hand work, repeated per piece. Rack marks matter too, because the part has to hang somewhere and on a cosmetic or sealing surface that contact point has to be placed deliberately.
Small parts in small lots carry the worst cost per piece, because the bath, the rack and the handling do not get cheaper when the part gets smaller.
How to specify it so the quote is real
- Finish type and standard, for example Type III per MIL-A-8625 Type III Class 1, or electropolish to 8 Ra microinch maximum
- Thickness and whether it is per surface or total
- Which features are masked, on the drawing, not in an email
- Where rack marks are allowed
- What certificate you require with the shipment
Leave these out and each shop fills the gap differently, which is exactly why the cheapest quote is often the one that understood the least. The same logic applies to cleanliness and packing, which is covered in what cleanroom machining actually requires.
Have a drawing with a finish callout you are not sure about? Send the RFQ and we will match it with shops whose finisher already runs that spec.
Frequently asked questions
Does hard anodize change my dimensions?
Yes. The coating grows into the metal and out of it in roughly equal parts, so a 50 micron Type III coating adds about 25 microns per surface. On a bore that is 50 microns off the diameter. Either mask the feature or have the part machined undersize before finishing.
Can a part be both anodized and electropolished?
Not on the same surface. They are different base metals in practice: anodize belongs to aluminum, electropolish to stainless. A single assembly often has both, on different parts.
Who pays when a finish comes back wrong?
Settle that before the order. Most shops subcontract finishing and pass the risk on. Write into the purchase order who owns rework, and require the finish certificate with the shipment.
Need a quote for this part?
Send the drawing. We match you with up to 3 shops in Vietnam and reply within 24 business hours.
Get matched with a supplierMore on materials
- Choosing an Aluminum Alloy for Semiconductor Hardware
- ESD Requirements on Machined Semiconductor Hardware
- Machining PEEK, Vespel and Torlon for Semiconductor Hardware
- Stainless and Nickel Alloys in Semiconductor Hardware
All guides and the sourcing glossary.