EMI Shielding
As the data rates increase and devices become smaller, the high speed signals are placed in close proximity of each other and the probability of signal interference increases. Objective of effective shielding in high performance board to board connectors is to minimize this unwanted signal from components near by, interfereing with the desired signal in connector and also to keep most of the energy of desired signal well with in the connected channels without being radiated outwards and affecting the circuits in close proximity. Intra System Electromagnetic Compatibility -EMC is another phenomonan which is related with the EMI noise generated from timing and switching circuits with in an Integrated Circuit.
The ZenShield® is a 360-degree EMC/ EMI shielding metallic cover offered in NOVASTACK® series board to board connectors. This shielding design prevents electromagnetic noise radiation not only from the contact points of the plug and receptacle, but also from the board mounting part (SMT positions) of the signal terminals. In addition, both plug and receptacle shields are properly connected for grounding at multiple points when the connectors are mated and are properly grounded to the board. This ensures enough ground return paths for the current generated in the metal shields of the connector. This works to suppress the emission of electromagnetic noise from the shield itself. With ZenShield®, these connectors can be placed close to high frequency transmitters and antennas. Figure 1 shows the EMI field patterns in a generic connector with out metal shield as compared to the patterns in fully shielded I-PEX connector with ZenShield®. In case of unshielded connectors, more of high speed signals radiate from both connector and FPC or board trace as compared to the design that uses fully shielded connectors and shielded FPC channels and/ or Co-planer Waveguide type board lay outs.
Right: I-PEX connector with metal shell
These radiated signals from unshielded connectors and FPC channel interfere and get coupled on adjacent signal channel, which may or may not be shielded as compared to the signals travelling on fully shielded connectors. Magnitude of unwanted noise on adjacent channels is obviously reduced if they are using shielded connectors and interconnects like shielded FPC channels or CPW type board traces etc. Figure 2 shows a similar result for electric and magnetic fields in mated shielded and unshielded connectors at 10 Ghz frequency. Little coupling of Electric and magnetic fields on used pair of mated pins leads to smaller noise in case of shielded connectors unlike the connectors with out EMI shield.
| E-Field | H-Field | ||
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With Shielding |
10.0 GHz |
10.0 GHz |
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Without Shielding |
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Figure 2. Coupling of Electric and Magnetic Fields on Unused Channel of Shielded and Unshielded Connectors
Newer multi GHz applications like 5G cell phones have multiple antennas for WiFi, GPS, GSM and Bluetooth connectivity, all with in a close proximity of each other. The need for small, compact, well shielded board to board connectors becomes even more important in such devices since many sub systems are connected either via flexible circuits and connectors or directly just by using these board to board connectors. The high speed data signals can be affected by cross talk noise from traces on the flexible cable itself. Both shielded and Unshielded Flexible Printed Circuit and Flat Flexible Circuit cables can be used with NOVASTACK® series connectors for design flexibility. The EMI and cross talk noise increases with the higher frequencies and it is important to consider EMI shielding at the time of product design, not as after the fact problem. A lot of band aid solutions like microstrip and stripline miniature coaxial connectors combined with cable grounding and wire management solutions that were effective at lower data rates are no longer effective at higher frequencies and smaller form factors. NOVASTACK® series connectors offer ultra compact, cost effective, high performance solution with integrated EMI shielding for modern high speed systems.
EMI Considerations in 5G Systems
ZenShield®: High-Performance EMC Shielding Connectors
