Tantalum Capacitor Polarity: How to Identify Positive and Negative
Last Updated: February 2026 | Reading Time: 8 minutes
Installing a tantalum capacitor backwards is not like installing an electrolytic backwards. An aluminum electrolytic with reversed polarity might bulge, leak, or pop its vent. A tantalum capacitor with reversed polarity can ignite. The tantalum pentoxide dielectric breaks down catastrophically under reverse bias, creating an internal short circuit that generates enough heat to cause thermal runaway and, in some cases, open flame on your PCB. There is no warning, no bulging, no gradual degradation --- just sudden failure. Getting polarity right is not optional with tantalum capacitors. It is the single most important step during installation.
The challenge is that tantalum polarity markings follow different conventions than aluminum electrolytic capacitors. Engineers and technicians who are experienced with electrolytics often assume the same rules apply, and that assumption leads to reversed parts and destroyed boards. This guide covers every tantalum package type, explains exactly where to find the polarity markings, and clarifies the differences from electrolytic conventions.
Tantalum capacitors use a thin layer of tantalum pentoxide (Ta2O5) as the dielectric, formed by anodizing a sintered tantalum powder anode. This oxide layer is designed to block current in one direction only. When voltage is applied correctly (positive to anode, negative to cathode), the dielectric holds and the capacitor functions normally.
When voltage is reversed, the oxide layer begins to conduct. Unlike aluminum oxide, which can partially reform under reverse bias, tantalum pentoxide breaks down irreversibly. The failure sequence is:
- Reverse voltage applied --- current flows through the dielectric
- Localized heating begins --- the manganese dioxide (MnO2) cathode material heats up
- Thermal runaway initiates --- the exothermic reaction becomes self-sustaining
- Catastrophic failure --- the component may short, crack, emit smoke, or catch fire
This entire sequence can occur in milliseconds. Solid tantalum capacitors with MnO2 cathodes are particularly prone to violent failure. Polymer tantalum types are somewhat safer (the conductive polymer cathode is less reactive), but reversed polarity will still destroy them.
Through-hole tantalum capacitors, sometimes called dipped tantalum capacitors because of their epoxy-dipped coating, mark the positive lead. This is the opposite of aluminum electrolytic convention, where the negative terminal is marked.
How to identify the positive lead:
- "+" sign printed near the positive lead on the body
- Stripe or band on the body near the positive lead
- Longer lead indicates positive (on new, untrimmed parts)
| Identification Method | Tantalum (Through-Hole) | Aluminum Electrolytic (Through-Hole) |
|---|
| Marking on body | + (positive) marked | - (negative) stripe |
| Longer lead | Positive (+) | Positive (+) |
| Stripe/band indicates | Positive (+) anode | Negative (-) cathode |
The critical difference is the stripe. On an electrolytic capacitor, the stripe with minus signs marks the negative terminal. On a dipped tantalum capacitor, the stripe or marking identifies the positive terminal. Confusing these conventions is the most common cause of reversed tantalum installations in mixed-technology boards.
Surface-mount tantalum capacitors use a molded rectangular package with a bar or stripe at one end. The bar marks the positive (anode) end.
Key identification features:
- Bar/stripe on the case --- marks the positive terminal
- The bar is on the same side as the anode pad on the PCB footprint
- Beveled or notched corner on some packages also indicates positive
This is, again, opposite to SMD aluminum electrolytic capacitors, where the bar or notch typically marks the negative (cathode) terminal.
Reading the PCB footprint:
Most PCB silkscreens for tantalum capacitors include a "+" symbol near the positive pad. If the silkscreen is missing or unclear, the bar on the component itself always indicates positive. Match the bar to the pad marked "+" on the schematic or assembly drawing.
SMD tantalum capacitors come in standardized case sizes. The polarity marking convention is the same across all sizes, but the bar can be harder to see on smaller packages.
| EIA Case Size | Dimensions (mm) | Polarity Bar Visible? | Notes |
|---|
| A (3216-18) | 3.2 x 1.6 x 1.6 | Yes, but small | Use magnification for inspection |
| B (3528-21) | 3.5 x 2.8 x 1.9 | Yes | Most common size, bar is clear |
| C (6032-28) | 6.0 x 3.2 x 2.6 | Yes | Easy to read |
| D (7343-31) | 7.3 x 4.3 x 2.9 | Yes | Largest standard size, very clear |
| E (7343-43) | 7.3 x 4.3 x 4.1 | Yes | Taller D case, bar on end face |
| V (7361-38) | 7.3 x 6.1 x 3.8 | Yes | Wide body, clear marking |
On all standard EIA case sizes, the bar is molded or printed on the positive (anode) end of the package. Some manufacturers also add a small "+" symbol near the bar, but the bar itself is the primary indicator.
Tip for A-case (3216) parts: The polarity bar on these tiny components can look like a manufacturing artifact or mold line. Always verify with a datasheet if there is any doubt. Under magnification, the bar is a distinct, uniform stripe across the full width of one end.
The severity of reverse-polarity failure depends on the applied voltage relative to the rated voltage and the cathode technology:
| Condition | MnO2 Cathode (Traditional) | Polymer Cathode |
|---|
| Reverse voltage < 10% of rating | May survive briefly, degraded life | May survive briefly |
| Reverse voltage 10-50% of rating | Likely short circuit, possible ignition | Short circuit, unlikely fire |
| Reverse voltage > 50% of rating | High probability of fire | Short circuit, cracking |
| Full rated voltage, reversed | Immediate thermal runaway and ignition | Immediate short, possible fire |
MnO2 cathode tantalum capacitors are the most dangerous. The manganese dioxide is an oxidizer that fuels the exothermic reaction once thermal runaway begins. The component can reach temperatures above 600 degrees C and produce open flame.
Polymer cathode tantalum capacitors (used in newer designs) fail more benignly. The conductive polymer cathode is not an oxidizer, so thermal runaway is less likely. However, the part will still be destroyed and may short the power rail, causing secondary damage downstream.
Mistake 1: Assuming the stripe marks negative (like electrolytics)
This is the number one error. Tantalum stripe = positive. Electrolytic stripe = negative. Always verify which component type you are handling before using the stripe to determine orientation.
Mistake 2: Relying on lead length after trimming
Once leads have been trimmed (common in rework or kit preparation), the longer-lead rule no longer applies. Use the body marking only.
Mistake 3: Ignoring polarity on low-voltage circuits
Even at 3.3V or 5V, a reversed tantalum capacitor can fail catastrophically. There is no safe low-voltage threshold for reverse bias on tantalum parts.
Mistake 4: Substituting tantalum for electrolytic without checking orientation
When replacing an aluminum electrolytic with a tantalum (or vice versa), the PCB silkscreen polarity markings may not match the component marking convention. Always verify positive-to-positive and negative-to-negative from the schematic, not from visual pattern matching.
Mistake 5: Hand-soldering SMD tantalum parts without magnification
The polarity bar on small case sizes (A, B) is easy to misread. Use a magnifying lamp or microscope when placing tantalum capacitors by hand.
Best practices:
- Verify polarity against the schematic before soldering
- Use incoming inspection to confirm marking orientation on reels
- On mixed boards, highlight tantalum locations in assembly instructions with a polarity warning
- Consider polymer-cathode tantalum capacitors for new designs to reduce catastrophic failure risk
| Feature | Tantalum | Aluminum Electrolytic |
|---|
| Through-hole body marking | Marks positive (+) | Marks negative (-) |
| Through-hole stripe indicates | Positive (anode) | Negative (cathode) |
| SMD bar/stripe indicates | Positive (anode) | Negative (cathode) |
| Longer lead (new parts) | Positive | Positive |
| Failure mode if reversed | Thermal runaway, fire | Bulging, venting, possible rupture |
| Severity of reversed polarity | Catastrophic (immediate) | Serious (usually gradual) |
The only marking convention that is the same between these two types is the longer lead indicating positive on new, untrimmed through-hole parts. Every other visual indicator is reversed.
On through-hole (dipped) tantalum capacitors, the positive lead is marked with a "+" symbol or a stripe on the body near the positive lead. The longer lead also indicates positive on untrimmed parts. On SMD tantalum capacitors, the positive (anode) end is marked with a bar or stripe across one end of the package.
The stripe on a tantalum capacitor marks the positive (anode) terminal. This is the opposite of aluminum electrolytic capacitors, where the stripe marks the negative (cathode) terminal. This difference is the most common source of polarity errors when working with tantalum components.
A reverse-biased tantalum capacitor can fail catastrophically. The tantalum pentoxide dielectric breaks down under reverse voltage, causing a short circuit and rapid heating. In parts with manganese dioxide cathodes, this can trigger thermal runaway with temperatures exceeding 600 degrees C, potentially causing fire on the circuit board. This failure can happen within milliseconds of power being applied.
No. Tantalum capacitors are strictly DC-polarized components and must not be used in AC applications. AC voltage would apply reverse polarity on every negative half-cycle, leading to rapid dielectric breakdown and catastrophic failure. For AC applications, use non-polarized capacitors such as film or ceramic types.
If the body markings are illegible, check the PCB silkscreen for a "+" symbol or polarity indicator at the component location. You can also reference the schematic or assembly drawing. On through-hole parts with untrimmed leads, the longer lead is positive. As a last resort, a careful visual inspection under magnification may reveal the molded polarity bar on SMD parts, as it is a physical feature of the case, not just printed ink.
- Tantalum stripe = positive --- the opposite of aluminum electrolytic capacitors
- SMD tantalum bar = positive --- the bar marks the anode end on all standard case sizes
- Reversed polarity causes immediate catastrophic failure --- including fire risk with MnO2 cathode types
- No safe reverse voltage --- even low-voltage circuits can trigger thermal runaway
- Always verify from the schematic --- do not rely on pattern matching between different capacitor types
- Polymer cathode types are safer --- but reversed polarity still destroys the component
Need help identifying tantalum capacitor polarity? Contact our technical team. With over 40 years in the capacitor industry, we can help you verify orientation for any tantalum part number --- and source replacements if a reversed part has already caused damage.
