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I have a device that contains this capacitor: https://search.murata.co.jp/Ceramy/image/img/A01X/G101/ENG/GRM21BR71H104JA01-01.pdf

The rated temperature range was listed as -55°C to 125°C. However, in the section "Storage and Operation condition", it states "The performance of chip monolithic ceramic capacitors may be affected by the storage conditions. Store the capacitors in the following conditions: Room Temperature of +5℃ to +40℃ and a Relative Humidity of 20% to 70%."

I'm wondering why there is such a huge discrepancy. Does this mean that if I needed to keep the capacitor in a 80℃ environment, I need to keep the capacitor powered at all times? Or maybe the +5℃ to +40℃ values are specific to the pre-soldered state?

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Cold range:

Condensation , freezing and thermal cycles around 0'C with power off may cause stress forces if not packed to inhibit moisture to alter critical parameters.

For example if you start to see cracked ceramic caps post soldering during ICT , you may want to review the storage history to see if humidity or storage temp. was a problem that caused a "pop-corn effect" crack. Then bake the parts to remove any long term storage moisture.

Hot Range:

Metallurgic migration/diffusion of conductor molecules into dielectric crystals is a known characteristic usually minimized by gold wire bonds that can affect dielectric properties. This may be the mechanism that ought to be considered if planning on storing parts for a long time with aging rates increasing with temperature rise.

If you needed "space qualified" parts then you can afford gold plated terminals. but for commercial applications nobody produces high volume and quality better than Murata and TDK. enter image description here

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Yup, that section is about the pre-soldering storage. If the capacitor is stored in a humid environment, then it can absorb moisture, and that moisture will expand and pop during soldering. Also, the leads can oxidize (corrode), making the solder joint weak.

The context from that datasheet (p. 12) tells the story:

1-1. Store the capacitors in the following conditions:

Room Temperature of +5°C to +40°C and a Relative Humidity of 20% to 70%.

  1. Sunlight, dust, rapid temperature changes, corrosive gas atmosphere, or high temperature and humidity conditions during storage may affect solderability and packaging performance.

    Therefore, please maintain the storage temperature and humidity. Use the product within six months, as prolonged storage may cause oxidation of the terminations (outer electrodes).

  2. Please confirm solderability before using after six months.

    Store the capacitors without opening the original bag.

    Even if the storage period is short, do not exceed the specified atmospheric conditions.

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