Reduce cost to start shielding at the source
Jan van Tienhoven
Specialist in Electro Magnetic Compatibilty solutions and materials
Do you think EMC shielding at the source reduce the cost?
We can make covers&cans in any size within 1-2 days. and will be happy to send you a free sample: [email protected]
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How to create optimal EMI shielding
15?In general, a shield consisting of more layers or zones is cheaper to produce than a shield made out of 1 high-performance layer. It is easy to create 3 zones:
LEVEL I?The component on the PCB is shielded by a can. Shielding at the source (fig. 15.1)
LEVEL II?The entire PCB is shielded by foil, wraps or a box (fig. 15.2) or the PCB and all the cables connected to it are inside the shielded box
LEVEL III?Or the outer housing is shielded as well (fig. 15.3).
Figure 15.1: Shielding at the source
Figure 15.2: Shielding the entire PCB
Figure 15.3: Shielding in three levels, see tip 16 - 24
Shielding at the source
LEVEL I?16?Source
Shielding at the source is usually the most cost-effective solution. Generally speaking, the source of unwanted radiation can be produced by voltage and current through one or more components or interconnections on the PCB.
The application of shielding can reduce it directly at the source.
LEVEL I?17?Clip mounting
Shielding cans are mounted onto the PCB with SMD clips, which come in several sizes. After the re-flow, the can (a cover with walls attached) is placed into the clips and can subsequently be removed for adjustments. (fig. 17.1)
Figure 17.1: SMD clip for mounting PCB shielding cans
LEVEL I?18?Pin mounting
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There are also systems with pins for through holes or covers with integrated pins that can be soldered directly onto the PCB. (Fig. 18.1)
Figure 18.1: Pin mounting used to mount PCB shielding cans
LEVEL I?19?Shield layout
Cooling holes can be made in the cover or steps to prevent short circuits with the tracks on the PCB. (Fig. 19.1)
Covers can also consist of a fixed part on the PCB (fence) and a separate cover that is clipped on to this fence. (Fig. 19.2 and Fig. 19.3)
Figure 19.1: Example of a shield layout with holes and openings for cables
Figure 19.2: Fixed part on the PCB (2. fence) and a separate cover (1)
Figure 19.3: Fixed part (fence) with a to the housing sticked foam/foil cover
LEVEL II?20?Covering the entire PCB
Another option is covering the entire PCB in shielding material. This can be achieved either by means of small housing, custom-made to exactly the right shape, or by simply wrapping or sticking material around the PCB.
Foils, textiles, stretch material, and wrap shields, cut to the appropriate shape, are easy to apply. Since it is always important to prevent short circuits, all materials can be provided with insulation layers.
Cable shielding
LEVEL II?21?Cables inside the housing
Once the PCB is covered, the attached cables can also be shielded. The longer a cable, the higher it's potential for emitting lower frequencies. Shielding a wire inside the enclosure will also prevent cross-talk and will make the main enclosure act as a cavity, and thus amplify the radiation. To prevent this, the enclosure can be (partly) laminated with EM absorption material.?(Fig. 21.1)
Figure 21.1: Flat cables, round cables, bundles of cables and branches can be shielded
LEVEL II?22?For round and flat cables?we produce shields in the shape of sleeves, wraps, tubes, and textiles so that all types of cables can be shielded. Some cable shields need to be grounded at both ends, but it is usually best to ground at only one end to prevent common-mode currents.