Surface cleanliness
Residual rolling oil or particles create weak spots in the dielectric and raise dissipation factor. Foil must be annealed clean and stored dry.
Electronics foil
Aluminium Capacitor Foil for the Electronics Industry
Capacitor foil is thin aluminium used as the electrodes of capacitors. Film and paper capacitors use plain foil about 4.5 – 10 µm thick in 1050, 1060, 1100 or 1235, while electrolytic capacitors use etched high-purity anode foil and thinner cathode foil. Metline supplies plain capacitor foil and high-purity foil stock in slit rolls to capacitor and electrode makers worldwide.
- Alloys
- 1050 · 1060 · 1100 · 1235
- Plain foil
- about 4.8 – 10 µm
- Temper
- O (soft)
- Supply
- Slit rolls on cores
How aluminium foil is used in capacitors
Every capacitor stores charge on two conducting plates separated by a dielectric. In wound capacitors those plates are long ribbons of aluminium foil rolled up with the dielectric between them. Aluminium is used because it conducts well, rolls to a few micrometres without pinholes, and, in electrolytic types, grows its own insulating oxide film.
| Capacitor type | Role of the foil | Typical foil |
|---|---|---|
| Film / foil capacitor | Plain foil electrodes wound with polypropylene or polyester film | 1050, 1060, 1235, 1100 in O temper, about 4.8 – 10 µm |
| Paper and oil-impregnated power capacitor | Plain foil electrodes wound with capacitor paper or film | Similar plain foil, often 5 – 7 µm |
| Aluminium electrolytic – anode | Etched to multiply surface area, then anodised to form the Al2O3 dielectric | Purity 99.9 – 99.99 %+, roughly 70 – 130 µm; high cubic texture for high-voltage foil |
| Aluminium electrolytic – cathode | Etched foil that contacts the electrolyte | Commercial purity or Al-Mn / Al-Cu alloy, roughly 20 – 50 µm |
Metallised film capacitors replace foil with a vacuum-deposited aluminium layer only nanometres thick; foil electrodes are still chosen where high pulse current or high RMS current makes a solid foil conductor the safer option.
Alloys and aluminium content
| Alloy | Aluminium, min | Main limits (max, %) | Typical capacitor use |
|---|---|---|---|
| 1050 | 99.50 % | Si 0.25, Fe 0.40, Cu 0.05 | Plain electrode foil, cathode foil base |
| 1060 | 99.60 % | Si 0.25, Fe 0.35, Cu 0.05 | Plain foil where slightly higher conductivity is wanted |
| 1100 | 99.00 % | Si + Fe 0.95, Cu 0.05 – 0.20 | General foil with a little more strength |
| 1235 | 99.35 % | Si + Fe 0.65, Cu 0.05 | The most common thin-gauge foil alloy; good pinhole performance |
| High-purity (1A99 / 99.99 %) | 99.99 % | Very low Fe, Si and Cu | Electrolytic anode foil before etching |
For plain electrode foil, low iron and silicon reduce intermetallic particles that cause pinholes and breaks at very thin gauges. For anode foil, purity and crystal orientation control how evenly the etching tunnels form, which sets the capacitance per square centimetre.
Popular capacitor foil thicknesses
| Thickness (inches) | Thickness (mm) | Thickness (µm) | Approx. weight (g/m²) |
|---|---|---|---|
| 0.00019 | 0.0048 | 4.8 | 13.0 |
| 0.00020 | 0.0051 | 5.1 | 13.8 |
| 0.00025 | 0.0064 | 6.4 | 17.3 |
| 0.00030 | 0.0076 | 7.6 | 20.5 |
| 0.00035 | 0.0089 | 8.9 | 24.0 |
| 0.00040 | 0.0102 | 10.2 | 27.5 |
Supply details
- Temper
- O (fully annealed) for winding; H18 on request
- Width
- Slit to winding width, from narrow ribbons to full mill width
- Cores
- Aluminium, steel or paper cores to suit winding machines
- Surface
- Bright both sides or one side matt; clean, dry, free of rolling oil residue
- Edges
- Clean slit edges, free of burrs and edge cracks
What makes good capacitor foil
Low pinholes
At 5 – 7 µm a pinhole becomes a potential breakdown path. Alloy cleanliness and rolling practice control the count.
Thickness uniformity
Even gauge gives even capacitance along the winding and consistent roll diameter.
Straight, tight winding
Telescoping or loose rolls cause misalignment in the capacitor element. Rolls must be wound flat with controlled tension.
Clean slit edges
Burrs can pierce thin film and short the electrodes; edge quality is checked on each roll.
Consistent mechanical properties
Tensile strength and elongation must suit high-speed winding without breaks.
Handling and storage precautions
- Choose alloy and gauge from capacitance, voltage, current and temperature requirements, not price alone
- Handle rolls by the core, never by the foil face; dents and creases become electrical weak points
- Store in a dry, temperature-stable area in the original sealed packing to avoid condensation and white corrosion
- Use clean gloves and keep the winding area free of dust and metal particles
- Control static in the winding area; thin foil and film attract dust when charged
- Use foil in first-in, first-out order and record lot numbers for traceability
Applications
- Power electronics: DC-link, snubber and filter capacitors in inverters, drives and EV chargers
- Power factor correction: low-voltage and medium-voltage capacitor banks
- Pulse and energy discharge: capacitors for lasers, welding and pulsed power, where foil carries high peak current
- Motor-run and lighting capacitors: AC capacitors in motors, fans and ballasts
- Electronics: coupling and filter capacitors, and electrolytic capacitors for power supplies
Relevant standards
| Standard | Scope |
|---|---|
| ASTM B479 | Annealed aluminium and aluminium-alloy foil for flexible barrier and other applications |
| EN 546 (parts 1 – 4) | Aluminium foil: delivery conditions, mechanical properties, tolerances and surface requirements |
| JIS H4160 | Aluminium and aluminium alloy foils |
| IEC 60384-1 | Fixed capacitors for electronic equipment: generic specification |
| IEC 60384-4 | Sectional specification for aluminium electrolytic capacitors |
References and standards
- ASTM B479 – Annealed Aluminum and Aluminum-Alloy Foil for Flexible Barrier, Food Contact, and Other Applications
- EN 546 – Aluminium and aluminium alloys: foil
- IEC 60384-4 – Fixed capacitors for use in electronic equipment: aluminium electrolytic capacitors
- US Patent 4,474,657 – Single step electrochemical etch process for high volt aluminum anode foil
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits
Capacitor aluminium (aluminum) foil: FAQ
What thickness is capacitor foil?
Plain electrode foil for film and paper capacitors is usually about 4.8 – 10 µm. Electrolytic anode foil is much thicker, roughly 70 – 130 µm before etching, and cathode foil about 20 – 50 µm.
Which alloy is used for capacitor foil?
Plain foil is rolled from 1235, 1050, 1060 or 1100. Electrolytic anode foil needs high-purity aluminium of 99.9 – 99.99 % or more so that etching and forming give a uniform dielectric.
Why is electrolytic capacitor foil etched?
Etching dissolves microscopic tunnels into the foil, multiplying its surface area many times. Since capacitance scales with area, etched foil stores far more charge per square centimetre than smooth foil.
What is the difference between foil and metallised film capacitors?
Foil capacitors use separate aluminium foil electrodes and handle high pulse currents well. Metallised film capacitors use an aluminium layer vacuum-deposited on the film, which is smaller and self-healing but carries less peak current.
Do you supply capacitor foil outside India?
Yes. Metline ships slit capacitor foil rolls worldwide in sealed, moisture-protected packing with mill certificates.
Need foil for capacitor winding?
Tell us the alloy, gauge, width and core. We will confirm availability, certification and a delivered price.
