Board Level Shield Design Features & Assembly
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Location pins for through hole attachment during wave soldering and securing the shield for manual soldering. If necessary, these pins can be given a ‘rounded’ profile. |
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SMT feet are effectively small pads for solder attach to a ground plane in a multi-layer construction. |
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Serrated base edge – Surface mount shields requiring solder attach along an entire wall can have base serrations incorporated to enable the solder to flow through the wall and equalize the solder fillet for optimum strength.
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SAM line – SAM is a Solder Anti-Migration feature, essentially a partially etched lateral line on the walls of a shield that discourages ‘wicking’ of the solder up the walls of the can that might scavenge material from the joint area.
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Pick and place lands can be provided, even on two-piece shields, to enable automatic handling and placement. Typically on a one-piece ventilated shield, an area on the top is left without perforations to enable vacuum manipulation. In a two-piece shields a special land is designed into the shield body. It can be easily removed with a simple twist after assembly and before the lid is finally positioned.
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Design features for attenuation and noise reduction‘Quiet’ Venting – As devices carry more power, they generate more heat and require ever more cooling. The addition of a shielding may raise the operating temperature of the device past the critical limit. Perforations have been made in shields for many years, the maximum permissible dimension being a function of the device frequency and the level of attenuation desired. Contact MAJR for optimization. Quiet venting can increase the open area of a shield for optimum cooling by perforating a pattern of very small holes, effectively a mesh, into both the walls and tops of shields. This process also reduces the ‘maximum linear dimension’ to improve attenuation performance and does not add significantly to the part cost of the shield. To perforate the walls of a ‘drawn’ can requires multi-stage tooling which can be costly. Quiet venting also has the additional benefit of enabling some vision systems to ‘look’ inside the can to check component existence and correct placement.
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Finger-clip Lids – The Finger-Clip lid design design for securing lids in two-piece and labyrinth shield types provides positive engagement of the lid with an etch line in the shield wall. The design gives maximum conductivity and a snap-fit that makes disassembly just as easy. This design offers excellent anti-rattle performance.
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