ใ 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.
ใ 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 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
ใEpoxy resins are a typical class of adhesive. To select the proper adhesive, consider the following points.
ใ1) There must be enough adhesive strength to prevent the component from loosening or slipping during the mounting process.
ใ2) The adhesive strength must not decrease when exposed to moisture during soldering.
3) The adhesive must have good coatability and shape retention properties.
ใ 4) The adhesive must have a long pot life.
ใ5) The curing time must be short.
ใ 6) The adhesive must not be corrosive to the exterior of the capacitor or the board.
ใ 7) The adhesive must have good insulation properties.
8) The adhesive must not emit toxic gases or otherwise be harmful to health.
ใ 9) The adhesive must be free of halogenated compounds.
(2) Use the following illustration as a guide to the amount of adhesive to apply.
ใ ใChip Dimension (L/W)ใCode:18/21/31
2-1. An excessive amount of flux generates a large quantity of flux gas, which can cause a deterioration of solderability,
ใ so apply flux thinly and evenly throughout. (A foaming system is generally used for flow solderring.)
2-2. Flux containing too high a percentage of halide may cause corrosion of the terminations unless there is sufficient cleaning. Use flux with a halide content of 0.1% max.
2-3. Strong acidic flux can corrode the capacitor and degrade its performance.
Please check the quality of capacitor after mounting.
3.Leaching of the terminations
Set temperature and time to ensure that leaching of the
terminations does not exceed 25% of the chip end
area as a single chip (full length of the edge A-B-C-D
shown at right) and 25% of the length A-B shown as