Mounting, Soldering, Storage and
Mechanical Precautions
.033" wide by .050" in length. Opposing pads should be identical in size to preclude
uneven solder fillets and mismatched surface tension forces, which can misalign the
BONDING
Hybrid assembly using conductive epoxy or wire bonding requires the use of
device. It is preferred that the pad layout results in alignment of the long axis of the
chips at right angles to the solder wave, to promote even wetting of all terminals.
Orientation of components in line with the board travel direction may require dual
waves with solder turbulence to preclude cold solder joints on the trailing terminals of
the devices, as these are blocked from full exposure to the solder by the body of the
capacitor.
silver palladium or gold terminations. Nickel barrier termination is not practical in
these applications, as intermetallics will form between the dissimilar metals. The
ESR will increase over time and may eventually break contact when exposed to
temperature cycling.
CLEANING
The preheat ramp should be such that the components see a temperature rise of
1.5ºC to 4ºC per second as for reflow soldering. This is to maintain temperature
uniformity throughout the MLCC and prevent the formation of thermal gradients
within the ceramic. The preheat temperature should be within 120ºC maximum (100ºC
preferred) of the maximum solder temperature to minimize thermal shock. Maximum
permissible wave temperature is 270ºC for SM chips. Total immersion exposure
time for Sn/Ni terminations is 30s at a wave temperature of 260ºC. Note that for
multiple soldering operations, including the rework, the soldering time is cumulative.
The total immersion time in the solder should be kept to a minimum. It is strongly
recommended that plated terminations are specified for wave soldering applications.
PdAg termination is particularly susceptible to leaching when subjected to lead-free
wave soldering and is not generally recommended for this application.
Chip capacitors can withstand common agents such as water, alcohol and
degreaser solvents used for cleaning boards. Ascertain that no flux residues are
left on the chip surfaces as these diminish electrical performance.
HANDLING
Ceramics are dense, hard, brittle and abrasive materials. They are liable to suffer
mechanical damage, in the form of chips or cracks, if improperly handled.
Terminations may be abraded onto chip surfaces if loose chips are tumbled in
bulk. Metallic tracks may be left on the chip surfaces which might pose a reliability
hazard. Components should never be handled with fingers; perspiration and
skin oils can inhibit solderability and will aggravate cleaning. Chip capacitors
should never be handled with metallic instruments. Metal tweezers should never
be used as these can chip the product and may leave abraded metal tracks on the
product surface. Plastic or plastic coated metal types are readily available and
recommended — these should be used with an absolute minimum of applied
pressure. Counting or visual inspection of chip capacitors is best performed on
a clean glass or hard plastic surface. If chips are dropped or subjected to rough
handling, they should be visually inspected before use. Electrical inspection may
also reveal gross damage via a change in capacitance, an increase in dissipation
factor or a decrease either in insulation resistance or electrical strength.
Cooling to ambient temperature should be allowed to occur naturally, particularly if
larger chip sizes are being soldered. Natural cooling allows a gradual relaxation of
thermal mismatch stresses in the solder joints. Forced cooling should be avoided as
this can induce thermal breakage.
VAPOR PHASE SOLDERING CHIP CAPACITORS
Vapor phase soldering, can expose capacitors to similar thermal shock and stresses as
wave soldering and the advice is generally the same. Particular care should be taken
in soldering large capacitors to avoid thermal cracks being induced and natural cooling
should be use to allow a gradual relaxation of stresses.
TRANSPORTATION
Where possible, any transportation should be carried out with the product in its
unopened original packaging. If already opened, any environmental control agents
supplied should be returned to packaging and the packaging resealed.
HAND SOLDERING AND REWORK OF CHIP CAPACITORS
Avoid paper and card as a primary means of handling, packing, transportation
and storage of loose components. Many grades have a sulphur content that will
adversely affect termination solderability. Loose chips should always be packed with
sulphur-free wadding to prevent impact or abrasion damage during transportation.
Attachment using a soldering iron requires extra care and is accepted to have a risk of
cracking the chip. Precautions include preheating of the assembly to within 100°C of the
solder flow temperature and the use of a fine tip iron that does not exceed 30
watts. In no circumstances should the tip of the iron be allowed to contact the chip
directly. KPD recommends hot air/gas as the preferred method for applying heat for
rework. Apply even heat surrounding the component to minimize internal thermal
gradients. Minimize the rework heat duration and allow components to cool
naturally after soldering.
STORAGE
Incorrect storage of components can lead to problems for the user. Rapid
tarnishing of the terminations, with an associated degradation of solderability,
will occur if the product comes into contact with industrial gases such as sulphur
dioxide and chlorine. Storage in free air, particularly moist or polluted air, can result
in termination oxidation.
SOLDER LEACHING
Leaching is the term for the dissolution of silver into the solder, causing a failure of the
termination system, which causes increased ESR, tan δ and open circuit faults, including,
ultimately, the possibility of the chip becoming detached. Leaching occurs more readily
with higher temperature solders and solders with a high tin content. Pb-free solders can
be very prone to leaching certain termination systems. To prevent leaching, exercise
care when choosing solder alloys and minimize both maximum temperature and dwell
time with the solder molten. Plated terminations with nickel or copper anti-leaching
barrier layers are available in a range of top coat finishes to prevent leaching from
occurring. These finishes also include Syfer FlexiCap™ for improved stress resistance
post soldering.
Packaging should not be opened until the MLCCs are required for use. If opened,
the pack should be resealed as soon as is practicable. Alternatively, the contents
could be kept in a sealed container with an environmental control agent.
Long-term storage conditions, ideally, should be temperature controlled between
-5°C and +40°C and humidity controlled between 40ꢀ and 60ꢀ RH. Taped
product should be stored out of direct sunlight, which might promote deterioration in
tape or adhesive performance. Product, stored under the conditions recommended
above, in its “as received” packaging, has a minimum shelf life of 2 years.
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KNOWLES [ KNOWLES ELECTRONICS ]
