SL
3 SNOVACAP
2 NN A COMPANY
25111 Anza Drive, Valencia, CA 91355 e Tel (661) 295 5920 e Fax (661) 295 5928
www.Novacap.com E-mail: [email protected]
High Temperature Soldering Recommendations
Contents:
1. Capacitor Size
2. Termination Material
3. Soldering
4, Cleaning
5. Board Design Considerations
6. Solders
7. Reflow Process
1. Capacitor Size
Size selection 1s based primarily on capacitance value and voltage rating. 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.
2. Terminal Material
Nickel barrier termination, with exceptional solder leach resistance is recommended for
all applications up to 160°C involving solder. Novacap offers four versions of the nickel
barrier termination. The "N" termination is a nickel barrier with 100% matte tin for a lead
free capacitor. The "Y" termination is a nickel barrier with 90/10 tin/lead for military
applications. The “C” termination is a polymer base nickel barrier with 100% matte tin
and a “D” termination with a polymer base nickel barrier with 90/10 tin/lead. Silver
palladium termination is required for applications above 160°C.
3. Soldering
Soldering methods commonly used in the industry and recommended 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 120°C per minute and a AT spike of 100°C maximum for any
soldering process on sizes 1812 and smaller 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. In
general, rates that do not exceed 60°C per minute and a AT spike of 50°C maximum for
any soldering process on sizes larger than 1812 is advisable. 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 that does not exceed 30 watts, and limitation of contact of the iron to
the circuit pad areas only.
4, Cleaning
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.
5. Board Design Considerations
NOVACAP has adopted the IPC-SM-782 methodology for solder reflow land patterns.
The NOVACAP recommended solder pads brochure is available for reference on the
NOVACAP Website.
6. Solders
A wide variety of solders are available in the industry. All four nickel barrier
terminations (N, Y, C, and D) have exceptional solderability, leach resistance, and are
compatible with all leaded and lead free solders. Care should be taken with the palladium
silver (P) termination. The palladium silver termination can leach which is the
dissolution of the termination into the solder. The result is exposure of the underlying
ceramic surface that would cause poor solder fillets or no solder fillets at all. Reduced
capacitance or open circuit conditions could happen with excessive leaching. Tin is the
predominant leaching component in solder. The solder selection should have silver as
part of the composition.
7. Reflow Process
The soldering process involves four separate inputs (two surfaces, solder paste, and heat
source); therefore, no single temperature profile is ideal for all products and heating
methods. A good profile will meet or exceed the minimum times at the coolest spot on
the product while not exceeding the maximum times at the hottest point on the product.
Because of the variability of soldered devices and reflow equipment, it may be necessary
to deviate from the suggestions given here.
Preheat Soak Activation Reflow Cool down
— Peak
7 N Liquid
— Liquidus -
— Solidus Plastic
Solid
N
Temperature
Time
Preheat: Duration: 45 to 90 seconds. During preheat, low boiling point solvents and
moisture are evaporated slowly to prevent spattering. Temperature ramps up from
ambient (around 23°C) to 110°C at between %2° and 2°C per second.
Soak: Duration: 20 to 90 seconds. The soak stage is used to stabilize temperature across
the entire product and continue evaporation of low boiling point materials. Small and
thermally uniform parts do not need much soak, while boards with large components may
require over a minute. Temperature ramps up from 110°C to 140°C at between 2° and
2°C per second.
Activation: Duration: 10 to 90 seconds for alloys with solidus under 250°C but may take
up to 120 seconds for alloys with a higher solidus on thermally challenging products. The
flux transitions from a gel state to a fluid state, then cleans the surfaces to be soldered.
Excessive time in the activation range will use up available flux activity and may result in
non-wetting, de-wetting, and related solder defects. Temperature ramps up from 140°C to
the alloy solidus at between 72° and 2°C per second.
Reflow: Duration: 25 to 90 seconds for most alloys. Soldering begins upon reaching the
solidus temperature of the alloy being used. For maximum joint strength, a peak
temperature of 20° to 40°C above the liquidus must be reached. Rapid cooling can cause
stress-related damage. Temperature ramps up from solidus to a peak at 20° to 40°C above
liquidus and back down to solidus at between 1° and 3°C per second. The duration for
palladium silver terminations should be kept to the minimum time possible.
Cool down: Product is cooled down to safe temperatures prior to handling. Total Time:
100 to 360 seconds for most products and alloys, averaging 230 seconds.
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