CERAMIC CAPACITORS

131

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General characteristics

Page revised 06/20

On November the 9th 2011, the test set was completed without any problem to report.

!

III. CONCLUSIONS

These tests have shown the reliability of Temex-Ceramics capacitors in operation. Each

of the HiQ capacitors under test has been exposed during 4 months to their maximum

RF power signal rating, heated up to 125°C continuously and without any failure or

event to report.

This endurance test, along with the European Space Agency qualification (see ESA.

pdf on our website), the regular life test performed on standard production lots (see

Reliability_Data.pdf) and the MIL class R rating (see MIL.pdf) highlight, the high quality

and reliability associated with EXXELIA capacitors.

IV. APPENDIX

The capacitance of the capacitor under test may vary during the temperature ramp

up time. Additionally it may vary if there is a beginning of destruction process. If the

frequency was kept constant, the RF power coupled into the capacitor under test will

decrease. Hence the temperature control loop will increase the RF power.

This may lead to a situation where the temperature decreases when the RF power

cannot be increased any more. In order to cope with this, there is a second control

loop that varies the frequency in order to minimize the reflected power. So the RF

power amplifier stage will always be able to deliver the necessary power to keep the

temperature constant.

As PC board, a ceramic material from Rogers is used, the RO4350 material. Comparing

to the standard FR4 material the ceramic board has the following advantages: improved

heat conductivity; improved heat resistance and improved electrical strength.

Due to the improved electrical strength, it was possible to have a ground plane on the

bottom side of the board. The coupler bar rests on a PTFE insulation. It was meant to be

a heat insulation. However, during pre-tests, it became apparent that the PTFE material

spreads the heat more than expected. In order to improve the heat insulation towards

ground and the ambient air, the complete setup is now surrounded by a layer of glass

wool.

All these efforts led to the following results: the temperature difference between the

RF on time and the RF off time is less than 10°C and a total RF power of approximately

35 Watts is sufficient to heat the capacitors to 125°C. The capacitors under test are

soldered with a non lead solder, Sn95Ag4Cu1 which has an extended temperature

range also. Figure 4 shows the test setup.

Figure 4

Both control loops are realized by a micro controller. Additionally, the micro controller

provides an RS-232 interface to set some configuration values. A LC display shows

warning messages also and some status information like temperature, RF power, etc.

The test generator works completely self sustained. It controls the temperature, RF

power, frequency and all other parameters. The test generator takes also care that

it remains itself within safe limits like maximum cool plate temperature, maximum

forward power, maximum reflected power, frequency within a given bandwidth, etc. The

test generator is connected to a remote computer.

General Information