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1206N272J101PXTM

CERAMIC MULTILAYER CAPACITORS

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A P P L I C AT I O N

NOTES

CHIP SELECTION

Multilayer capacitors (MLC) are categorized by dielectric

performance with temperature, or “temperature coefficient”,

as these devices vary in behavior over temperature. The choice

of component is thus largely determined by the temperature

stability required of the device, i.e. type of dielectric, and the size

necessary for a given capacitance and voltage rating. The following

items are pertinent to chip selection:

DIELECTRIC TYPE

COG: Ultra stable Class I dielectric, with negligible dependence of

electrical properties on temperature, voltage, frequency and time.

Used in circuitry requiring very stable performance.

X7R: Stable Class II dielectric, with predictable change in properties

with temperature, voltage, frequency and time. Used as blocking,

de-coupling, bypassing and frequency discriminating elements. This

dielectric is ferroelectric, and provides higher capacitance than Class I

Z5U/Y5V: General purpose Class III dielectrics with higher dielectric

constant and greater variation of properties with temperature and

test conditions. Very high capacitance per unit volume is attainable for

general purpose applications where stability is not important.

CAPACITOR SIZE

Size selection is based primarily on capacitance value and voltage rat-

ing. Smaller units are generally less expensive; 0805 is the most eco-

nomical size. Because mass affects the thermal shock behavior of

chips, size selection must consider the soldering method used to

attach the chip to the board. Sizes 1812 and smaller can be wave,

vapor phase or reflow soldered. Larger units require reflow soldering.

TERMINATION MATERIAL

Nickel barrier termination, with exceptional solder leach resistance is

recommended for all applications involving solder. Silver palladium

termination is required for epoxy attachment, also for solder reflow

below 230°C . Silver termination, which is most ductile, yet leaches

readily in solder, is often preferred for units to be leaded, to minimize

thermal cycle stresses.

PACKAGING

Units are available in bulk, reeled or in waffle pack. Bar coding is

optional.

ATTACHMENT METHODS

Bonding of capacitors to substrates can be categorized into two

methods, those involving solder, which are prevalent, and those

using other materials, such as epoxies and thermo-compression or

ultrasonic bonding with wire.

SOLDERING

Soldering methods commonly used in the industry and recom-

mended are Reflow Soldering, Wave Soldering, and to a lesser

extent, Vapor Phase Soldering. All these methods involve thermal

cycling of the components and therefore the rate of heating and

cooling must be controlled to preclude thermal shocking of the

devices. In general, rates which do not exceed 100°C per minute

and a ∆T spike of 100°C maximum for any soldering process is

advisable. Other precautions include post soldering handling,

primarily avoidance of rapid cooling with contact with heat sinks,

such as conveyors or cleaning solutions.

Large chips are more prone to thermal shock as their greater bulk

will result in sharper thermal gradients within the device during

thermal cycling. Units larger than 1812 experience excessive stress

if processed through the fast cycles typical of solder wave or vapor

phase operations. Solder reflow is most applicable to the larger

chips as the rates of heating and cooling can be slowed within safe

limits.

Attachment using a soldering iron requires extra care, particularly

with large components, as thermal gradients are not easily

controlled and may cause cracking of the chip. Precautions include

preheating of the assembly to within 100°C of the solder flow

temperature, the use of a fine tip iron which does not exceed 30

watts, and limitation of contact of the iron to the circuit pad areas

only.

BONDING

Hybrid assembly using conductive epoxy or wire bonding requires

the use of silver palladium or gold terminations. Nickel barrier

termination is not practical in these applications, as an increase in

ESR results.

CLEANING

Chip capacitors can withstand common agents such as

water, alcohol and degreaser solvents used for clean-

ing boards. Ascertain that no flux residues are left

on the chip surfaces as these diminish

electrical performance.

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