Adhesive Application - Murata GRM Manual

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Notice
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3. Board Design
When designing the board, keep in mind that the amount
of strain which occurs will increase depending on the size
and material of the board.

2. Adhesive Application

If you want to temporarily attach the capacitor to the board
using an adhesive agent before soldering the capacitor, first
be sure that the conditions are appropriate for affixing the
capacitor. If the dimensions of the land, the type of
adhesive, the amount of coating, the contact surface area,
the curing temperature, or other conditions are
inappropriate, the characteristics of the capacitor may
deteriorate.
1. Selection of Adhesive
1-1. Depending on the type of adhesive, there may be a
decrease in insulation resistance. In addition, there is a
chance that the capacitor might crack from contractile
stress due to the difference in the contraction rate of
the capacitor and the adhesive.
1-2. If there is not enough adhesive, the contact surface
area is too small, or the curing temperature or curing
time are inadequate, the adhesive strength will be
insufficient and the capacitor may loosen or become
disconnected during transportation or soldering.
If there is too much adhesive, for example if it overflows
onto the land, the result could be soldering defects, loss
of electrical connection, insufficient curing, or slippage
after the capacitor is mounted.
Furthermore, if the curing temperature is too high or the
curing time is too long, not only will the adhesive
[Relationship with amount of strain to the board
thickness, length, width, etc.]
= 3PL
3
Relationship between load and strain
2
2Ewh
: Strain on center of board (μst)
3
L: Distance between supporting points (mm)
w: Board width (mm)
h: Board thickness (mm)
E: Elastic modulus of board (N/m
Y: Deflection (mm)
P: Load (N)
P
L
When the load is constant, the following relationship can be established.
· As the distance between the supporting points (L) increases,
the amount of strain also increases.
→Reduce the distance between the supporting points.
· As the elastic modulus (E) decreases, the amount of strain increases.
→Increase the elastic modulus.
· As the board width (w) decreases, the amount of strain increases.
→Increase the width of the board.
· As the board thickness (h) decreases, the amount of strain increases.
→Increase the thickness of the board.
Since the board thickness is squared, the effect on the amount of strain
becomes even greater.
strength be reduced, but solderability may also suffer
due to the effects of oxidation on the terminations
(outer electrodes) of the capacitor and the land surface
on the board.
(1) Selection of Adhesive
Epoxy resins are a typical class of adhesive.
To select the proper adhesive, consider the following
points.
1) There must be enough adhesive strength to
prevent the component from loosening or slipping
during the mounting process.
2) The adhesive strength must not decrease when
exposed to moisture during soldering.
3) The adhesive must have good coatability and
shape retention properties.
4) The adhesive must have a long pot life.
5) The curing time must be short.
6) The adhesive must not be corrosive to the exterior
of the capacitor or the board.
7) The adhesive must have good insulation properties.
8) The adhesive must not emit toxic gases or
otherwise be harmful to health.
9) The adhesive must be free of halogenated
compounds.
2
=Pa)
Y
h
w
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