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 Supplemental
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Processing Data
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SOLDERING
& CLEANING
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NKK,
a pioneer in the development of washable switches, is ahead
of its time as a manufacturer of process sealed switches, which
are increasingly in demand because of the advancements in automated
PC board processing. NKK's expansive family of washables includes
toggles, rockers, pushbuttons, keypads, rotaries, and keylocks
in avariety of sizes.
Over 45 years of quality design experience produced the first
washable switches to satisfy the process requirements of PC
board soldering and cleaning techniques. As the cutaway drawings
on our Distinctive Features pages illustrate, our process compatible
switches incorporate all the features necessary to accomplish
washability: epoxy sealed terminals, heat resistant resins,
interior rubber o-rings, seals, and sleeves, plus ultrasonic
welding. The following data has been developed from a comprehensive
study of test data, technical literature, and industry practice.
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NON-AUTOMATED
SOLDERING SPECIFICATIONS
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3
seconds max. @ 350°C max. for Hand Soldering only. Some of our
switches can be damaged if these specifications are exceeded.
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5 seconds max. @ 270°C max. for Solder Pot
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SUGGESTED
WAVE SOLDER PROCESSING
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Profile
1. Ramp up at 3°C per minute maximum to a soak temperature
between 85°C and 104°C. Preheat and soak temperatures
are critical and must be limited by some components and the
glass transition temperature (Tg) of the laminate.
2. Raise temperature to the Wetting Spike Zone. Peak temperature
should not exceed 210°C to 235°C for 10 seconds.
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Time above 188°C should be limited to between 20 and
40 seconds.
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Dwell time should be as short as possible to minimize thermal
damage.
3.
The quicker the solidification, the finer the grain. The finer
grain structure has better physical properties and ashiny
appearance.
4. Continue cooling to 38°C.
5. Clean, if necessary.
Temperature Stabilize
To minimize the thermal shock, switches should be allowed
to air cool to 38°C or to the temperature of the hand
or machine wash.
Flux
NKK recommends a no-clean (low residue) flux that can be either
left on the board or cleaned with a mild organic solvent.
A second choice is a synthetic flux that can be effectively
removed with an alcohol based solvent.
A water soluble flux is not recommended because of the corrosive
nature of the flux residue. The relative high temperature
and energetic washing methods needed to ensure complete removal
of all flux residues could also be hazardous to the switch.
Flux Removal
Washing should take place at a slightly elevated room temperature
of between 38°C and 52°C. Spray pressure should not
exceed 25 psi. Do not submerge the switch more than 2 inches.
The total time that is required for removing the flux and
cleaning the board should not exceed 5 minutes.
Drying
Drying time should be extended to one hour (bake) at 52°C
maximum. This step will eliminate any condensation.
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SUGGESTED REFLOW PROCESSING
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Profile
This profile is based on the use of a no-clean flux.
The boards should enter the reflow oven between 20°C
and 38°C. This profile represents a "straight ramp" profile
The first ramp should be 2°C to 40°C per second to
a short dwell zone of 30 to 60 seconds at approximately 150°C.
The second ramp can be steeper to a dwell at liquid state
(210°C to 235°C) for 20 to 60 seconds. Maximum timeat
peak temperature should be limited to 10 seconds.
Do
not expose the switch to more than one pass of the profile.
- This
profile represents a generally acceptable profile for our
switches, but it is not intended for all solder paste or
ovens. Some fluxes require a longer dwell at 150°C to
160°C for activation. IR ovens create larger temperature
differentials on the board surface; in this case, longer
times in the dwell zones allow the entire boards to achieve
thermal equilibrium. Tight parameters on time and temperature
must be observed to avoid component damage.
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