Polymer capacitor

Polymer capacitors, are types of electrolytic capacitor with conductive polymer as solid electrolyte (cathode). These electrolytic capacitors with conductive polymer (PEDT for example) and polymerized organic semiconductor (TCNQ complex salt for example), rather than the more usual liquid electrolyte, are available since 1983. Names used for similar technologies are OS-CON (Sanyo trademark), Aluminum Organic Polymer Capacitors (AO-CAPS), Organic Conductive Polymer Aluminum Electrolytic Capacitor (OC-CON), Functional Polymer Capacitors (FPCAP).

Characteristics

• Equivalent series resistance (ESR), an important characteristic particularly for high-ripple-current and switching applications, is usually lower (better) than electrolytics of the same value. Unlike standard electrolytics ESR is stable with varying temperature. This allows polymer capacitors to handle higher ripple current. However, some high quality wet electrolytic types have ESR as low as polymer capacitors.

As of 2012:

• Some types have longer life than wet electrolytics, e.g. 50,000 hours life at 85 °C. Others are specified typically for guaranteed 1000 hours at 105 °C.
• Working voltage up to around 35 V.
• May be more expensive than wet electrolytic capacitors of the same capacitance and voltage; this may change with time.
• More restrictive range of capacitance and working voltage available than wet electrolytic capacitors.
• Typically electrically polarized, just like their conventional electrolytic counterparts.

Construction

• Cathode is aluminum or tantalum foil.
• A separator sheet is impregnated with electrolyte.
• Anode is aluminum or tantalum foil with an oxide layer.
• Often made in surface-mount packages; while standard electrolytics, more prone to needing replacement, are less frequently surface-mounted.

Sandwich is rolled and assembled into a leaded or surface-mount can. Polymer capacitors (with some exceptions) do not have vents; due to the lack of liquid electrolyte they will never make gas and explode under failure conditions.

Tantalum polymer capacitors (such as Sanyo's POSCAP) use a different construction: sintered tantalum with polymer electrolyte.

Reliability and failure modes

Polymer capacitors can fail by going open-circuit or short-circuit. If moisture is trapped in the capacitor during manufacture ESR may increase invisibly over time. However, failures are infrequent and reliability is good.

History

Sanyo OS-CON polymer capacitors went into production in 1983. They were used on server and workstation computer motherboards first, then on graphics cards, and in 2007 became more common for high-end consumer motherboards.

External links

• Sanyo OS-CON capacitors
• Polymer capacitor construction image