Electronic Components & Devices

# FAQ

## Electronic components in general

I'd like to know about products that are out of production.
What is the status of component compliance with environmental regulations?
What are ISO/IATF certifications status?
How can I find the desired product from the application of each electronic
component?

## Power Devices

What is root-mean-square forward current? What does it mean?

It indicates the forward current tolerance in steady state.
*Transient current flows (overload current, short pulse surge current) are excluded.
When the root-mean-square forward current is within the guaranteed values in Specifications, it is usable.
However, even if the current is within the guaranteed values, it may not be possible to use due to heat generation in the heat radiation environment and usage conditions.

Which do various characteristic graphs show the typical values or the maximum
values?

All values except for the graph of Junction capacitance vs. Reverse Voltage of SBD products are maximum values, which are guaranteed. Graphs of Junction capacitance vs. Reverse Voltage show typical values (TYP). The curves of the average forward current rating are formed by connecting points where the junction temperature reaches 150℃.

How much is the difference between I2･t and I2･√t?

When considering dissipation with constant energy, I2･t is mainly used for fuses, high current products, and etc.
On the other hand, I2･√t is used when considering dissipation with constant temperature rise. In the case of semiconductors, thermal destruction does not occur when energy reaches a certain level, but it is thought that the phenomenon occurs when the temperature of the Si chip reaches a certain temperature. In that sense, I2･√t, calculating with specified temperature rise, is a more realistic and useful calculation method.
There is I2 in both methods, which means that the property of the semiconductor is lost in the large current region, it becomes a mere resistance, and if the resistance is r, the loss becomes I2r. In other words, I2 represents the loss. Therefore, it is a concept that I2･t defines the current resistance when the energy is constant, and I2･√t is to keep the temperature rise constant.

What do you think of and how do you calculate guaranteed value of average
rectified current?

It depends on duty of the current flow.
If it is a square wave with 2A peak current and the duty is 50% or less, the average current becomes 1A or less, which is within the range of our guarantee. But if the duty is more than 50% and the average current exceeds the guaranteed value, which is out of the guaranteed range and it is impossible to be used. Additionally, please make sure that the peak current shall not exceed the maximum surge forward current.

●Calculating average forward current of each waveform

1. Square wave　　　 IF(Avg.) = IFP × Duty
2. Half sine wave　　 IF(Avg.) = IFP × {(2×Duty)/π}
3. Triangular wave　　　 IF(Avg.) = (IFP/2)×Duty
IFP: Peak forward current
Duty: Forward current conduction time ratio in a cycle

What is MSL (Moisture Sensitivity Level)?

MSL standards are defined for SMDs to be reflow-soldered, and all our products are MSL: 1. (Unneeded damp proof packing)

What are storage conditions for power device products?

The followings are recommended storage conditions for our power device products:

[Before unpacking]
Storage temperature: 5 to 35℃ / Storage humidity: 45 to 70% RH

How can I judge whether or not the product is usable for the transitional surge
current. If the current pulse duration is shorter than the described condition,
is the larger surge current acceptable?

In past days, surge current capability of a discrete diode had been considered to follow the I2t-constant law, as is the case with current fusing phenomenon. However, for more accurate estimation, the I2√t-constant law is preferable.
Therefore, guaranteed values for higher current products like as diode modules are calculated by I2･t , and lower current products like as discrete diodes should be calculated by I2√t. Even in this case, the resistance does not increase without limit, and the value at 100 μs is considered as the upper limit value for energization of 100 μs or less. In the case of a few micro seconds of electricity energizing time and a large duty, a limit could be caused due to the root mean squared value.

●Calculating formula for allowable current:
I2√t =（IFSM／√2）2× √10ms
IFSM: Surge forward current resistance value shown in Specifications or catalogues
ｔ: Current pulse duration (100μs = 0.0001s at minimum)
The allowable current "I" can be obtained by substituting each value into the above formula. However, it would be corrected due to waveforms and energizing frequency.

Square waveform: I itself　　　　　Triangular waveform: I×√3　　　　　Half sine wave: I×√2

1. One shot current pulse: Current forcing only once in the circuit during the lifetime
The calculated value as above
2. A few current pulses in a day: Irregular and long-interval current pulses when the power turns on etc.
Half of the calculated value as above
3. Energizing continuously: Continuous energization
A quarter of calculated value as above

We are considering connecting products in parallel, what is the minimum
flow dividing ratio?

When connecting one-chip type elements such as axial type products or miniature SMD products, 1:0.6 (62.5% : 37.5%) would be an approx. value as a general theory. Since two-chip in an element such as represented by the TO-220 type is a package and has good heat balance, the good flow dividing ratio would be 1:0.8 (55.6% : 44.4%).

I want to use FRD products connected in series directly.
Is there anything I have to pay attention?

It would be difficult to secure voltage balance in two high-speed FRDs connected in series directly (Connection where voltage protection is not coordinated). Especially for the commutation surge voltage in high-speed switching, shared voltage varies largely due to difference in reverse recovery characteristics of the two devices. Thermal influence of other components and exoergic environment also affect the difference largely. Therefore, it is possible that 100% of voltage would be applied to one device.
In order to suppress such differences, it is necessary to add a voltage dividing capacitor to each device to share the differences. There is no specified capacitance value for such voltage dividing capacitors because the value varies depending on the operating conditions. It is necessary to make sure whether the voltage can be surely shared by the capacitors so that their capacitances could be between several tens pF and several hundreds pF.
Ripping can be suppressed by these capacitors. In order to divide the steady reverse voltage in half, resistors in parallel are also required.
That is to say, adding capacitors or resistors is an only way to balance voltage. The point is that adding a resistor or a capacitor is an only way to get the voltage balance.

What is the recommended mounting torque for screwed housing type products?

The recommended range of mounting torque is between 0.4 and 0.8 Nm.

How can I connect elements in parallel?

Please avoid connect them directly. It is necessary to devise the wiring pattern and to examine the connection method so that the equal wiring reactor and series resistance can be expected. Please use products of same characteristics, such as ones in a manufacturing lot or unit of purchase. Characteristics of a device are closely related to temperature, and temperature unbalance causes current unbalance on products connected in parallel. To avoid it, it is effective to attach them closely or attach them to the same fin to equalize the element temperature.

What does "RECT" mean in graphs in Specifications or catalogues?

RECT is initial letters of RECTANGLE and means square waveform. It represents the conduction angle when one cycle is 360 °.
e.g.) Duty 50% = RECT 180°, Duty 25% = RECT 90°

## SAW Devices

What is the specification of the electrostatic withstand voltage, or ESD (Electro-
Static Discharge) resistance?

It is 50 volts or more. (Cumulative failure rate: 10%)

What is the maximum input power?

The standard specification is +29dBm (at 50℃ for 5000 hours) with CW (Continuous Wave) at the transmitting side and Tx filter of SAW duplexers. For others, it is CW+13dBm (at 50℃ for 5000 hours).

What is MSL (Moisture Sensitivity Level) for SAW devices?

The MSL is 3 for all our SAW device products. (Needed damp proof packing)

What are storage conditions for SAW devices?
1. Not opened damp proof packing：Please store them under the normal temperature and humidity (-10 to +40℃ and 30 to 85% RH). As for products that have been stored over one year since they were shipped, their solderability could be deteriorated, so please be sure to evaluate their solderability before use them.
2. Unpacked damp proof packing: After opening, please make sure to mount them within 168 hours in an environment of 5 to 30℃ and 60% RH or less.
What are the baking conditions of the SAW devices stored exceeding the storage
period after opening the damp proof package?
1. Dry the packed and taped products one time for 10±1 hours at 60±2℃ and 10% RH or less.
2. Put the products in a heat-resistant container and dry it one time for 10±1 hours at 60±2℃ and 10% RH or less, for 8±1 hours at 70±2℃ and 10% RH or less, or for 6±1 hours at 80±2℃ and 10% RH or less.
How many time of reflows do the products go through?

We recommend up to three times.

What are other soldering conditions than reflow?

When soldering, please use a spot heater under the following conditions:
・Preheating: 150℃ +/- 10℃ for 60 seconds at minimum
・Warm air temperature: 280℃ +/- 10℃ for 30 seconds at maximum

Is it possible to use the products in a transfer molding method?

## Capacitors

Does the capacitance of ceramic capacitors change when a DC voltage is
applied to ceramic capacitors? Are there any points to keep in mind in regards
to capacitance change?

The capacitance of a capacitor changes depending on the DC voltage applied. Select a capacitor considering the DC voltage characteristics of the DC circuit in which the capacitor is used. The capacitance of ceramic capacitors might change sharply depending on the applied voltage. (See figure)

Confirm the followings in order to ensure desired capacitance.

1. Confirm whether the capacitance change according to the applied voltage is within an allowable range or not.
2. Regarding DC voltage characteristics, capacitance decreases as voltage increases, even if the applied voltage is below the rated voltage. Therefore, when a capacitor is used in a circuit with a narrow range of capacitance change allowance like a time constant circuit, it is recommended that the capacitance is within the allowable range under operating voltage.
What are the conditions to store ceramic capacitors?

The following storage conditions are recommended unless otherwise specified by the detailed specification.

• *Recommended temperature range: 5 to 40°C
• *Recommended humidity range: 20 to 70% RH
See JIS C 60721-3-1, class 1K2 for other climatic conditions.
1. High temperature and high humidity environment may affect capacitor's solderability because they accelerate terminal oxidization. They also deteriorate performance of taping and packaging. Therefore, the following storage periods are recommended.
1. For SMD capacitors, use within 6 months.
2. When capacitors are stored for a period longer than specified, confirm the solderability of the capacitors prior to use.
3. Store capacitors without opening their unit bags. Keep them in the same package as shipped.
4. Even though the storage period is short, do not exceed the specified atmospheric temperature and humidity conditions.
2. Corrosive gasses in the air or atmosphere may result in deterioration of the reliability, such as poor solderability of the terminal electrodes or lead wires of capacitors. Do not store capacitors where they will be exposed to corrosive gas (e.g. hydrogen sulfide, sulfur dioxide, chlorine, ammonia etc.).
1. In corrosive atmosphere, solderability might be degraded, and silver migration might occur to cause low reliability.
2. Due to the dewing by rapid humidity change, or the photochemical change of the terminal electrode by direct sunlight, the solderability and electrical performance may deteriorate. Do not store capacitors under direct sunlight or dewing condition.
Is there any problem to use ceramic capacitors with applied voltage over
specifiedrated voltage?

Voltage which is applied to the capacitor should not exceed the rated voltage given in the specifications.
When AC voltage is superimposed on DC voltage, the zero-to-peak voltage shall not exceed the rated voltage.
When AC voltage or pulse voltage is applied, the peak-to-peak voltage shall not exceed the rated voltage.

Applying overvoltage to a capacitor may cause dielectric breakdown and result in a short circuit.

The duration until dielectric breakdown depends on the applied voltage and the ambient temperature. Abnormal voltage (surge voltage, static electricity, pulse voltage, etc.)shall not exceed the rated voltage. When pulse voltage with a very short rising time or AC voltage of a high frequency is applied to capacitors, even though the voltage is less than or equal to the rated voltage, the reliability of the capacitor may be influenced.

What are points to keep in mind in reflow soldering process for ceramic
capacitors?

The soldering conditions (preheating temperature, soldering temperature and their durations) shall be within　the limits in the catalogs or product specifications.

When the capacitors are used exceeding the limits given in the catalogs or product specifications, cracks may occur in the capacitors and the reliability may deteriorate, especially the rapid temperature changes and partial heating during soldering may cause cracks.

Generally recommended temperature conditions for reflow soldering is as follows:

When the capacitors are soldered under long duration or high temperature, the dissolution of electrode (leaching), deterioration of adhesion (shear strength) and capacitance decrease may occur.

Take into consideration tombstone phenomenon (also called "Manhattan phenomenon") for 3216M size or smaller capacitors when the soldering is not proper.

The tombstone phenomenon can be avoided by taking the following measures:

• - reducing land dimensions
• - optimizing solder amount
• - ensuring accurate placement

- providing equal heating to both terminations during soldering

How is the capacitance of ceramic capacitors measured?

Measure the capacitance under the conditions specified in the product specifications.

Some measuring equipment may not be able to apply the required measuring voltage and the measured value will be underestimated, when capacitance is high. Measuring equipment with Auto Level Control (ALC) function is recommended.

Most of the causes of difference in measured capacitance among each measuring equipment result from difference in actual voltage applied by each measuring equipment even if the same measuring voltage is set up.

Since higher capacitance makes smaller impedance in capacitors, it shall not disregard the influence of the voltage drop by voltage divider with the output resistance of measuring equipment.

The measuring equipment, which has the function to adjust to the measuring voltage automatically, is recommended for the measurement of a high capacitance capacitor. And, when the measuring equipment without the ALC function is used, it is recommended to check and adjust the measuring voltage by a voltmeter.

Are there any points to keep in mind when manually repairing or reworking on
already mounted ceramic capacitors on a board?

Heat stress during rework may possibly be reduced by using a spot heater (also called a "blower") rather than a soldering iron.

General Instruction

When capacitors are reworked using soldering irons beyond the limits stated in the catalogs or product specifications, cracks may occur in the capacitors due to thermal stress and insulation resistance may deteriorate.
When lead-free solder which has a higher melting point (liquid phase temperature of over 200 °C) is used, the risk of cracks is higher due to the larger thermal stress in the capacitor induced if rapid cooling or heating and partial heating occur during reworking.
Do not touch the tip of a soldering iron to the termination electrode of a capacitor.
Reworking using a spot heater may suppress the occurrence of cracks in the capacitor compared to using a soldering iron. A spot heater can heat up a capacitor uniformly with a small heat gradient which leads to lower thermal stress caused by quick heating and cooling or localized heating.
Moreover, where ultra-small capacitors are mounted close together on a printed circuit board, reworking with a spot heater can eliminate the risk of direct contact between the tip of a soldering iron and a capacitor.

Repair Conditions

If the blower nozzle of a spot heater is too close to a capacitor, a crack in the capacitor may occur due to heat stress. Below are recommendations for avoiding such an occurrence.
Keep more than 5 mm between a capacitor and a spot heater nozzle.
The blower temperature of the spot heater shall be lower than 400 °C.
The airflow shall be set as weak as possible.
The diameter of the nozzle is recommended to be 2 mm (one-outlet type). The size is standard and common.
Duration of blowing hot air is recommended to be 10 s or less for 3225M size or smaller capacitors, and 30 s or less for 3216M size or larger capacitors, considering surface area of the capacitor and melting temperature of solder.
The angle between the nozzle and the capacitor is recommended to be 45 degrees in order to work easily and to avoid partial area heating.
As is the case when using a soldering iron, preheating reduces thermal stress on capacitors and improves operating efficiency.

Does the capacitance of ceramic capacitors change with time?
Are there any points to keep in mind in regards to capacitance change with time?

High dielectric constant ceramic material, when left in room temperature without any bias, has tendency to decrease its capacitance almost linearly to logarithmic time. This phenomenon is caused by the dielectric ceramics to transfer to more stable phase, and these are inevitable characteristics. Therefore, it is suggested to consider the capacitance change with time when using capacitors in circuits such as time constant circuit.

Most ceramic dielectrics used for ceramic capacitors have ferroelectric characteristics, and exhibit a curie temperature. Above this temperature, the dielectrics have a highly symmetric cubic crystal structure whereas below the curie temperature, the crystal structure is less symmetrical. Although in single crystals this phase transition is very sharp, in practical ceramics it is often spread over a finite temperature range. In all cases it is linked with a peak in the capacitance/temperature curve.

Under the influence of thermal vibration, the ions in the crystal lattice continue to move to positions of lower potential energy for a long time after the dielectric has cooled down below the curie temperature. This makes capacitance aging, whereby a capacitor's capacitance continually decreases. (Line A in the below graph) However, if the capacitor is heated to a temperature above the curie temperature, de-aging takes place and the capacitance lost through aging is regained. (B point in the below graph) The aging recommences when the capacitor cools down below its curie temperature. (Line C in the below graph)

This is a phenomenon of shifting to a lower energy state by which the ceramic dielectric becomes more stable.Therefore, take capacitance aging into consideration when using a capacitor with Class 2 or Class 3 ceramic dielectrics for a circuit with a narrow range of allowable capacitance change, such as a time constant circuit.

Since the effects of this aging can be reversed, a dielectric's capacitance can be returned to its original value by subjecting it to a higher temperature than its Curie point, e.g. 125°C for BaTiO3. The phenomena can been noticed immediately after soldering or after reworking/repair with a soldering iron.

Are there any products which do not comply with EU Directive
2015/863/EU (RoHS) in ceramic capacitor product line-up?
What is the specification of allowable ripple current

Although there is not a specification of ripple current for ceramic capacitors, it is recommended to confirm the following.
Confirm whether AC voltage and pulse voltage are continuously applied to the capacitor. Be sure to take into account self-heating when using DC capacitors for AC or pulse circuits. General capacitors are designed for DC use. When they are used in a circuit where AC or pulse voltage is applied, the current value may increase and the capacitors may short-circuited due to self-heating.

1. For capacitors of Class 2, it is necessary to maintain the surface temperature shall not increase more than 20°C.
2. For capacitors of Class 1, since the permitted temperature rise depends on the dielectric material, consult us about the details.

Note:

• Class 1 : Temperature compensating capacitor (C0G, NPO)
• Class 2 : High dielectric constant capacitor (X5R, X7R)

Self-heating of a capacitor depends on the dielectric material, the capacitance, the applied voltage, the frequency, the voltage waveforms and other factors. Moreover, the surface temperature may be affected by heat radiation related to the style of the capacitor, the mounting method to the equipment and the ambient temperature.
Since self-heating affects the characteristics of capacitors when ambient temperature changes, even under the same voltage conditions, perform the confirmation of self-heating at room temperature (25 °C).

Are there recommended land patterns?

Since the amount of solder (fillet size) for mounting a capacitor on a printed circuit board influences the capacitor directly, sufficient consideration is necessary. Confirm the suitable land pattern size in order to decide the suitable amount of solder.

When the amount of solder is too much, stress on a capacitor increases. It may cause a crack in the capacitor. When a land design of a printed wiring board is considered, it is necessary to set up the form and size of the land pattern so that the amount of solder is suitable.

When the amount of solder is too little, the adhesion (shear) strength of the terminal electrode may be insufficient, and the capacitor may drop off from the printed wiring board. The reliability of the circuit may also be affected.

Recommendation for land pattern size with which the amount of solder does not become excessive

How do I read Kyocera part number?

For AVX products, enter from here.

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