©2005 KEMET Electronics Corp.

May 2005

+20°C internal rise and an arbitrary figure in defining the

power capability for these devices.

This arbitrary rise

added to the ambient temperature creates the absolute in-

ternal temperature of the component. Since capacitors are

life tested under DC or static stress, there is no temperature

rise at the maximum rated temperature of the device. Only

by using the positive tolerance of +2°C at this temperature,

can we define a “tested capability” at this temperature ex-

treme. We then need to look at the difference between the

temperature extreme and the assigned or arbitrary rise of

+20°C, to calculate the point at which a power derating is

applied. For 150°C, and an allowable rise of +20°C, the

power derating must begin at 130°C. The power capabil-

ity (allowing a +20°C rise) for this device is the same from

-55°C through 130°C.

If the case power is defined as

150mW, then the power capability is defined as 150mW

for this temperature range. There is a linear reduction in

that power capability then applied from 100% at 130°C,

down to 15 mW (10% or 2°C/20°C) at 150°C. Figure 6

shows this delineation.

Figure 6. Power derating to maximum temperatures.

The allowable temperature rise is arbitrary and two

considerations must be weighed when choosing this figure.

First, the internal temperature rise plus the ambient must

never exceed the maximum temperature plus 2°C. To do

so would create an environment in which there is no reli-

ability data to justify this application.

Second, the rise

must be considered as a potential thermal shock condition

when the device is at ambient temperature and immedi-

ately after power is applied. Deltas in excess of +50°C

may lead to thermal gradients that could induce stresses

high enough to cause an internal fracture and failure.

It is evident from the plot of Figure 6 that the differ-

ence in these two types of capacitors creates entirely dif-

ferent power capabilities between 105°C and 125°C. For

example, the power dissipation for the standard tantalum

at 125°C is down to 10% of the case defined power capa-

bility, while the T498 shows a capability at this tempera-

ture of 100% of the case defined power. Consider that

these are two “D” case units and the actual power capabil-

ity here is 15 mW for the standard and 150 mW for the

T498. For devices of equal capacitance and ESR, the rip-

ple capability for the T498 would increase by a factor of

3.16 (square root of 10).

Application Areas

The ideal applications for these components begin

where the standard products’ end.

At temperatures be-

tween 115°C and 140°C, these applications would still al-

low a 10°C margin or better, between the rating and the

application. New under hood or in system applications

may be considered with the T498 that were previously

thought to be too precarious for the standard tantalum.

1

RoHS –“Restriction on the use of certain Hazardous Substances in

Electrical and Electronic Equipment” (European Union directive 2002 /

95 / EC)

2

J-STD-020C – IPC/JEDEC Joint Industry Standard – Moisture/Reflow

Sensitivity Classification

3

MIL-HDBK-217F – Notice 2, Reliability Prediction of Electronic

Equipment, Department of Defense, December 2, 1991, Washington,

DC.