chipv0102_reli-PRP5
chipv0102_reli_e-01
＊ This catalog contains the typical specification only due to the limitation of space. When you consider the purchase of our products, please check our specification.
For details of each product (characteristics graph, reliability information, precautions for use, and so on), see our Web site (http://www.ty-top.com/) or CD catalogs.
Precautions on the use of Multilayer chip varistors.
■ PRECAUTIONS
3. Considerations for automatic placement
Precautions
◆Adjustment of m
ounting machine
1. Excessive impact load should not be imposed on the varistors when mounting onto the PC boards.
2
. The maintenance and inspection of the mounters should be conducted periodically.
◆Se
lection of A
dhesives
1. Mounting varistors with adhesives in preliminary assembly, before the soldering stage, may lead to degraded varistor characteristics unless the following
fa
ctors are appropriately checked; the size of land patterns, type of adhesive, amount applied, hardening temperature and hardening period. Therefore, it is
im
perative to consult the manufacturer of the adhesives on proper usage and amounts of adhesive to use.
Te
chnical
co
nsider-
ations
◆Adjustment
of m
ounting machine
1. If the lower limit of the pick-up nozzle is low, too much force may be imposed on the capacitors, causing damage. To avoid this, the following points should
be c
onsidered before lowering the pick-up nozzle :
（1）
The lower limit of the pick-up nozzle should be adjusted to the surface level of the PC board after correcting for deflection of the board.
（2）
The pi
ck-up pressure should be adjusted between 1 and 3N static loads.
（3） To reduce the amount of deflection of the board caused by impact of the pick-up nozzle, supporting pins or back-up pins should be used under the PC
b
oard. The following diagrams show some typical examples of good pick-up nozzle placement :
Not recommended Recommended
Single-sided mounting
Double-sided mounting
2. As the alignment pin wears out, adjustment of the nozzle height can cause chipping or cracking of the varistors because of mechanical impact on the
varistors. To avoid this, the monitoring of the width between the alignment pin in the stopped position, and maintenance, inspection and replacement of the
pin should be conducted periodically.
◆Se
lection of A
dhesives
1. Some adhesives may cause reduced insulation resistance. The difference between the shrinkage percentage of the adhesive and that of the varistors may
re
sult in stresses on the varistors and lead to cracking. Moreover, too little or too much adhesive applied to the board may adversely affect component
pl
acement, so t
he following precautions should be noted in the application of adhesives.
（1） Required adhesive characteristics
a. The adhesive should be strong enough to hold parts on the board during the mounting & solder process.
b. The adhesive should have sufficient strength at high temperatures.
c. The adhesive should have good coating and thickness consistency.
d. The adhesive should be used during its prescribed shelf life.
e. The adhesive should harden rapidly.
f. The adhesive must not be contaminated.
g. The adhesive should have excellent insulation characteristics.
h. The adhesive should not be toxic and have no emission of toxic gasses.
（2） W
hen th
e amount of adhesive is inappropriate to mount varistors on a PCB, that may cause a problem in placement of the component.
Too li
ttle adhesive may cause the varistors to fall off the board during the solder process.
Too mu
ch adhesive may cause defective soldering due to excessive flow of adhesive on to the land or solder pad.
4. Soldering
Precautions
◆Selection of F
lux
1. Since flux may have a significant effect on the performance of varistors, it is necessary to verify the following conditions prior to use ;
（1）
Flux used should be with less than or equal to 0.1 wt% (equivalent to chlorine) of halogenated content. Flux having a strong acidity content should not be
a
pplied.
（2） When
so
ldering varistors on the board, the amount of flux applied should be controlled at the optimum level.
（3） When using water-soluble flux, special care should be taken to properly clean the boards.
◆S
oldering
1.
Temperature, time, amount of solder, etc. are specified in accordance with the following recommended conditions.
Te
chnical
co
nsider-
ations
◆Selection
of F
lux
1-1. When too much halogenated substance (Chlorine, etc.) content is used to activate the flux, or highly acidic flux is used, an excessive amount of residue after
so
ldering may lead to corrosion of the terminal electrodes or degradation of insulation resistance on the surface of the varistors.
1
-2. Since the residue of water-soluble flux is easily dissolved by water content in the air, the residue on the surface of varistors in high humidity conditions may
ca
use a degradation of insulation resistance and therefore affect the reliability of the components. The cleaning methods and the capability of the machines
us
ed should also be considered carefully when selecting water-soluble flux.
◆So
ldering
1-1.
Preheating when soldering
Heating :
Ceramic chip components should be preheated to within 100 to 130℃ of the soldering.
Cooling :
The temperature difference between the components and cleaning process should not be greater than 100℃.
Ceramic c
hip varistors are susceptible to thermal shock when exposed to rapid or concentrated heating or rapid cooling. Therefore, the soldering process
must be conducted with great care so as to prevent malfunction of the components due to excessive thermal shock.
Recommended co
nditions for soldering
[Reflow so
ldering]
Temperature pr
ofile
Caution
1. The ideal condition is to have solder mass (fillet) controlled to 1/2 to 1/3 of the thickness of the varistor, as shown below :
2. Because excessive dwell times can detrimentally affect solder ability, soldering duration should be kept as close to recommended times as possible.
