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1. Electromagnetic shielding effect

The electromagnetic shielding effect is specified as the sum of the absorption loss and reflection loss of electromagnetic waves, but it can simply be expressed as follows:



For example, when the intensity of the transmitted wave is reduced to one one-hundredth of the intensity of incident wave by some shielding material, the shielding effect of the shielding material is 40 dB.

The shielding effect levels and their corresponding quality are simply classified as follows:

Shielding effect

Quality

Application example
0 to 10 dB

Substantially no shielding effect
10 to 30 dB Minimum-shielding effect
30 to 60 dB

Average level shielding

Standard electronic equipment
60 to 90 dB Above-average level, excellent shielding Advanced electronic equipment
90 to 120 dB Shielding by the best available technology

Shield room


2. Electromagnetic shielding by electroless plating

As electromagnetic shielding measures for plastic components excluding conductive plastics, zinc spraying, aluminum evaporation, conductive coating materials, electroless plating and other methods have mainly been used. The method by plating among them features the production of a very high electromagnetic shielding effect even if the plating film is thin, because a continuous elemental metal thin film is formed with no contact resistance generated through the intervention of an insulator. It differs from the methods by conductive coating materials or conductive plastics in which metal particles or metal fibers are dispersed in the polymer. This method by electroless plating has recently been used extensively as a housing shielding method for cell phones and portable PCs.



3. Electromagnetic shielding ability by electroless plating

The electromagnetic shielding ability is introduced below by taking our experimental results as examples.
As shown by these results, it is expected that the method by electroless plating can bring about a stable electromagnetic shielding effect even under harsh environmental changes.

3-1 Plating adhesiveness
Material/Grade DURANEX (PBT resin) FORTRON (PPS resin)
3300 1140A62
Plating film composition Electroless copper (2.0 )/
Electroless nickel (0.5 )
Plating adhesiveness Matrix adhesiveness Initial
After heat resistance test
After heat resistance test
After thermal test
Remarks:

Heat resistance test condition :
     After 100 × 1000 hours
Moisture resistance test condition :
     After 80, 95% RH × 1000 hours
Thermal test condition :
     (-40 × 0.5 hrs - 120 × 0.5 hrs) × 500 cycles


3-2 Electromagnetic shielding effect

[Measuring method]

Measurement of near-field shielding effect by "shielding material evaluation system R2547" manufactured by Advantest Corp. (Shield box method)
[Plating film thickness] Electroless copper 1.0, 2.0




3-3 Durability of electromagnetic shielding effect

In the applications under demanding environmental conditions for use, such as automobiles, there is concern about the reduction in the shielding effect because of cracks, etc., since the plating film is subject to repeated tension due to the difference in the coefficient of linear thermal expansion between the resin and plating film especially with abrupt temperature changes. Accordingly, electroless plating was applied to DURANEX® (PBT resin) and FORTRON® (PPS resin) to conduct heat shock resistance tests to measure the changes in the surface resistivity of the plating film.

Heat shock condition:
(-40 × 30 min - 120 × 30 min)/cycle