08055C datasheet(19/20 Pages) AVX

19 / 20 page

Surface Mounting Guide

MLC Chip Capacitors

POST SOLDER HANDLING

Once SMP components are soldered to the board, any

bending or flexure of the PCB applies stresses to the sol-

dered joints of the components. For leaded devices, the

stresses are absorbed by the compliancy of the metal leads

and generally don’t result in problems unless the stress is

large enough to fracture the soldered connection.

Ceramic capacitors are more susceptible to such stress

because they don’t have compliant leads and are brittle in

nature. The most frequent failure mode is low DC resistance

or short circuit. The second failure mode is significant loss

of capacitance due to severing of contact between sets of

the internal electrodes.

Cracks caused by mechanical flexure are very easily identi-

fied and generally take one of the following two general

forms:

Mechanical cracks are often hidden underneath the termi-

nation and are difficult to see externally. However, if one end

termination falls off during the removal process from PCB,

this is one indication that the cause of failure was excessive

mechanical stress due to board warping.

COMMON CAUSES OF

MECHANICAL CRACKING

The most common source for mechanical stress is board

depanelization equipment, such as manual breakapart, v-

cutters and shear presses. Improperly aligned or dull cutters

may cause torqueing of the PCB resulting in flex stresses

being transmitted to components near the board edge.

Another common source of flexural stress is contact during

parametric testing when test points are probed. If the PCB

is allowed to flex during the test cycle, nearby ceramic

capacitors may be broken.

A third common source is board to board connections at

vertical connectors where cables or other PCBs are con-

nected to the PCB. If the board is not supported during the

plug/unplug cycle, it may flex and cause damage to nearby

components.

Special care should also be taken when handling large (>6"

on a side) PCBs since they more easily flex or warp than

smaller boards.

REWORKING OF MLCs

Thermal shock is common in MLCs that are manually

attached or reworked with a soldering iron. AVX strongly

recommends that any reworking of MLCs be done with hot

air reflow rather than soldering irons. It is practically impossi-

ble to cause any thermal shock in ceramic capacitors when

using hot air reflow.

However direct contact by the soldering iron tip often caus-

es thermal cracks that may fail at a later date. If rework by

soldering iron is absolutely necessary, it is recommended

that the wattage of the iron be less than 30 watts and the

tip temperature be <300ºC. Rework should be performed

by applying the solder iron tip to the pad and not directly

contacting any part of the ceramic capacitor.

Type A:

Angled crack between bottom of device to top of solder joint.

Type B:

Fracture from top of device to bottom of device.

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