500R07S0R2AV4T Datasheet, PDF (1/3 Pages) Johanson Technology Inc. – APPLICATION NOTES FOR CERAMIC CHIP CAPACITORS

APPLICATION NOTES FOR CERAMIC CHIP CAPACITORS
GENERAL
Ceramic chip capacitors exhibit excellent reliability
characteristics providing that proper circuit design
techniques and controlled assembly processes are
utilized. Due to the ceramic capacitor’s crystalline
micro-structure these components are susceptible
when exposed to excessive thermal or mechanical
shock during circuit processing. It should be noted that
micro-cracks in ceramic can be difficult to detect with
normal post assembly visual and electrical testing and
can pose a significant threat to reliable field operation.
For this reason it is recommended that the assembly
qualification process employ suitable testing to expose
the presence of micro-cracking conditions.
CHIP CAPACITOR ATTACHMENT
LASERtrim^® CAPACITORS - Offered with gold
flashed nickel-barrier terminations only. Due to the
unique internal construction of the LASERtrim^®
it is recommended that a conservative reflow
temperature profile be used ( Fig. 1). Wave soldering is
discouraged.
HIGH FREQUENCY CAPACITORS & INDUCTORS
- Offered with standard tin plated nickel-barrier
terminations compatible with solder flow and reflow
processes.
MICROWAVE SINGLE LAYER CAPACITORS - Offered
with Titanium-Tungsten/Gold and Titanium-Tungsten/
Nickel/Gold thin-film termination as well as legacy
Platinum/Palladium/Gold terminations. Please refer to
the attachment compatibility table (page 31) specific to
these devices.
SOLDERING IRON
Ceramic capacitor attachment with a soldering iron
is discouraged due to the inherent limitations on
precisely controlling soldering temperature, heat
transfer rate, and time. In the event that a soldering
iron must be employed the following precautions are
recommended.
• Preheat circuit and capacitors to 150°C
• Never contact the ceramic with the iron tip
• 30 watt iron output (max)
• 280°C tip temperature (max)
• 3.0 mm tip diameter (max)
• Limit soldering time to 5 sec.
SOLDER PRE-HEAT CYCLE
Proper preheating is essential to prevent thermal shock
cracking of the capacitor. The circuit assembly should
be preheated as shown in the recommended profiles at
a rate of 1.0 to 2.0°C per second to within 65 to 100°C
of the maximum soldering temperature.
SMT SOLDERING TEMPERATURES
Solders typically utilized in SMT have melting points
between 179°C and 188°C. Activation of rosin fluxes
occurs at about 200°C. Based on these facts a
minimum peak reflow temperature of 205°C to 210°C
should be established. A maximum peak reflow
temperature of 225°C should be adequate in most
circumstances. Many reflow process profiles have
peaks ranging from 240°C to 260°C and while ceramic
capacitors can withstand soldering temperatures in
this range for short durations they should be minimized
or avoided whenever possible. Use of PCB mounted
multiple thermocouple M.O.L.E. profiling is advised for
accurate characterization of circuit heat absorption and
maximum temperature conditions.
REFLOW SOLDER
The general term “reflow” refers to several methods
used in heating the circuit so that solder paste reflows,
or “wetting” of the ceramic capacitor and PCB contacts
occurs. These methods include infra-red, convection
and radiant heating. The size of the solder fillet may be
controlled by varying the amount of solder paste that is
screened onto the circuit. Recommended temperature
limits for solder reflow are shown in Figure 1 for
LASERtrim® and in Figure 2 for standard capacitors.
VAPOR PHASE
A typical vapor phase soldering process consists of
several temperature zones created by saturated vapor
from a boiling liquid. As the circuit passes through the
zone the vapor condenses on the solder paste, pad,
and termination resulting in heat transfer and reflow
of the solder paste. Vapor phase reflow produces
consistent circuit heating with reflow occurring at a
relatively lower temperature that is determined by the
known boiling point of the liquid used, typically 215°C.
Recommended temperature limits for vapor phase
reflow are shown in Figure 3.
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