Multilayer Varistors
l The amount of adhesive shall be such that the
adhesive does not flow off or be out of alignment.
(2) Curing Conditions
l Adhesives for mountings can be cured by
ultraviolet or infrared radiation. In order to
prevent the terminal electrodes of the Varistors
from oxidizing , the curing shall be done at
conditions of 160 ¡C max., for 2 minutes max.
3.4 Soldering
3.4.1 Flow Soldering
In flow soldering process, abnormal and large
thermal and mechanical stresses, caused by
ÒTemperature GradientÓ between the mounted
Varistors and melted solder in a soldering bath,
may be applied directly to the Varistors, resulting
in failure and damage to the Varistors. So it is
essential that the soldering process shall be
controlled to stay within the following recommended
conditions and precautions. (See Fig. 6)
3.2 Chip Mounting Consideration
In mounting the Varistors/components on
a
printed circuit board, any bending and expanding
force against them shall be kept to a minimum to
prevent them from being damaged or cracked.
Following precautions and recommendations shall
be observed carefully in the process;
Fig.6 Recommended Soldering Temperature-Time
Profile (Flow soldering)
(1) Maximum stroke of the vacuum nozzle shall be
adjusted so that the pushing force to the printed
circuit board shall be limited to a static load of
1 to 3 N (100 to 300 gf). (See Fig.4)
(2) Maximum stroke of the nozzle shall be adjusted
so that the maximum bending of printed circuit
board does not exceed 0.5 mm. (See Fig.4)
Fig.4
(1) Application of Flux:
The soldering flux (3.3) shall be applied to
the mounted Varistors thinly and uniformly
by forming method.
(2) Preheating:
×
The mounted Varistors/Components shall be
preheated sufficiently so that the ÒTemperature
GradientÓ between the Varistors/components
and the melted solder shall be 150 ¡C or below.
(3) Immersion to Soldering Bath:
The Varistors shall be immersed into a solder-
ing bath of 240 to 250 ¡C for 3 to 5 seconds.
(4) Cooling:
The Varistors shall be cooled gradually to
room ambient temperature with the cooling tem-
perature rates of 8 ¡C/s max. from 250 ¡C to
170 ¡C, and 4 ¡C/s max. from 170 ¡C to 130 ¡C.
(5) Flux Cleaning:
(3) The printed circuit board shall be supported by
means of adequate supporting pins as shown in
Fig.5-(b).
Fig.5
(a) Improper
(b) Proper
When the Varistors are immersed into
cleaning solvent, it shall be confirmed that the
surface temperatures of devices do not exceed
100 ¡C. (See 3.5)
3.3
Soldering Flux and Solder
3.4.2 Reflow Soldering
(1) Soldering Flux:
In reflow soldering process, the mounted
Varistors/components are generally heated
and soldered by a thermal conduction system such
as an ÒInfrared radiation and hot blast soldering
l The content of halogen in the soldering flux shall
be 0.2 wt% or less.
l Rosin-based and non-activated soldering flux is
recommended.
systemÓ or
a ÒVapour Phase Soldering System
(2) Water soluble type Soldering Flux:
In case of water soluble type soldering flux
being applied, the flux residue on the surface of
P.C. boards may have influences on the
reliability of the components and cause
deterioration and component failure.
(VPS)Ó. Large temperature gradients such as a
rapid heating and cooling in the process may
cause electrical failures and mechanical damage
to the devices. It is essential that the soldering
process shall be controlled to stay within the follow-
ing recommended conditions and precautions.
(See Fig.7)
(3) Solder:
An eutetic solder (Sn63: Pb37) is recommended.
$ESIGN AND SPECIlCATIONS ARE SUBJECT TO CHANGE WITHOUT NOTICEꢀ !SK FACTORY FOR TECHNICAL SPECIlCATIONS BEFORE PURCHASE ANDꢁOR USEꢀ
7HENEVER A DOUBT ABOUT SAFETY ARISES FROM THIS PRODUCTꢂ PLEASE CONTACT US IMMEDIATELY FOR TECHNICAL CONSULTATIONꢀ
