Every now and then an unusual application for EMI/RFI shield configurations can arise which might require some lateral thinking to solve the problem.
Fig.1 shows an example of a circuit working in a 3.2GHz environment with multiple strip array filters, coupled together with a variety of processing circuitry. In this particular application, engineers needed to isolate discrete processing circuitry from each other and yet maintain a reasonable level of accessibility to each circuit module.
The most efficient mode of isolating modules in a tight circuit would be to design a tuner type integrated shield (Multi cavity). The problem with this solution is that partition seams between the circuits would have to be soldered or welded. Furthermore, the cover of an integral shield at such frequencies requires significant contact between partition and screen.
These shields yield excellent results in many applications, however in this series of circuits for this particular customer the results were not good enough. EMI/RFI engineers specified for a shield with absolutely no apertures and with availability of multiple access to each shielded module. This required an extremely easily removable cover from each module and yet provide adequate EMI/RFI integrity upon closure.
Our client specified a reverse drawn cover with spring fingers to snap on the frames. Drawn shields can only be fabricated via dedicated tooling, yet have the advantage of providing hermetic EMI/RFI integrity. Components ejected from the tool prove to be highly planar on the PC side of the frame which provides almost 100% solder borders on the PCB when put in a reflow Process.
Frames are produced with pick and place tabs, a must on automated assembly lines. These tabs can be easily removed with a small cutter should access to the circuit be necessary. Spring finger covers are a luxury when it comes to EMI/RFI shields and they also carry that extra expense, however our client specified all the shields on these boards with these covers.