Step 1 – Consider Configuration Format
If the application requires the shielding of a small circuit or a component, then a basic can will always provide the most cost-effective solution. In cases where significant test or rework is foreseen, a removable cover single-cavity package would be most suitable. If there are multiple shields required, then a multi-cavity option would be worth exploring.
Step 2 – Consider Material Choice
For most applications, tin-plated mild steel offers adequate performance and cost effectiveness. In demanding environments or service conditions, Nickel Silver is recommended for its excellent corrosion resistance properties.
Step 3 – Consider Package Height
Examine your design to determine your minimum required internal height. Normally, this will be determined by the tallest component plus a desired amount of clearance.
Step 4 – Consider Shield Footprint
Most applications are rectangular in shape, but your needs may require something different. The best way of approaching this is to create an outline drawing or sketch showing the center-line of all required walls. Keep in mind that flexibility allows for non-standard shapes. Try to keep angles between walls to 45 or 90 degrees, since this will help reduce costs. For multi-cavity designs, consider the placement of any internal partitions as you would an outside wall.
Step 5 – Consider Engagement Tab Placement and Style
All shields benefit from the use of engagement tabs for placement on the PCB. A variety of styles are offered for your selection. Generally speaking, the larger the footprint, the more engagement tabs that should be employed. As a general rule, avoid placing tabs within 0.3” of any corner or intersection between walls. Position of engagement tabs on the footprint is up to the user.
Step 6 – Consider Trace or Component Relief
In most applications, there are traces or components that pass through walls or internal partitions. Relief notches can be provided at all locations where this occurs, with the width and height as required for the situation. Placement of these features is usually centered on the trace or component.
Step 7 – Consider Interconnects
If your application uses connectors, please consider and the assembly sequence closely. In some cases, connectors are assembled to the PCB before the shield, and in others after. The shape of the opening may require a particular configuration in order to facilitate assembly. For fences, this may result in a situation of structural weakness, which may require additional consideration in design.
Step 8 – Consider Tuning/Inspection Access/Thermal Relief
Even for applications with removable covers, it is worth considering the addition of openings for tuning, inspection or test. For thermally challenging applications, the cover can be generally perforated to provide thermal relief. In some cases, fences can be as well, but only with significant package heights.
Step 9 – Consider Multi-cavity Issues
There may be cases in multi-cavity solutions where some cavities are noisier or more sensitive than others. In such cases, it may be desirable to consider segmentation and grounding strategies for partitions separating such cavities. Strategies vary depending on the case, but the goal is generally to divide the aperture at the top of the partition into a smaller number of segments, each below a critical dimension.