How to Select the Right EMI Shield Can for Your PCB Design

Selecting the right EMI shield can for your PCB design involves balancing multiple engineering constraints: height clearance, footprint dimensions, assembly process compatibility, and rework access requirements. Incorrect shield selection can lead to EMC test failures per FCC Part 15, board respins, or costly assembly line changes. This guide covers the key decision factors for choosing between SMD and clip-type shields and sizing them appropriately for your application.

SMD vs. Clip Type: The Primary Decision

Shield cans are available in two fundamental attachment methods, each with distinct manufacturing and performance tradeoffs.

SMD (Surface Mount Device) shields are designed for reflow soldering with heights typically ranging from 0.9mm to 1.45mm. These shields integrate directly into automated pick-and-place assembly processes without requiring separate mechanical clip installation. SMD shields are often used in high-volume production where minimal Z-height is critical, such as wearables, IoT devices, and ultra-compact consumer electronics. However, SMD shields become permanent once reflowed, making component access or replacement more difficult.

Clip-type shields use mechanical retention clips for attachment and offer heights ranging from 1.4mm to 10mm. These shields can be installed post-reflow, either manually or through automated clip insertion systems. Clip-type shields provide removable access to shielded circuits, which may be valuable during product development or field service. Higher contact force from spring clips may also provide more consistent grounding compared to solder-only connections, though this advantage depends on proper clip design and installation.

Neither type is universally superior; selection depends on whether height constraints, rework access, or component clearance is the primary design driver. For designs requiring less than 2mm total clearance, SMD types may be the only viable option. For development builds requiring frequent circuit access or designs with tall passive components (5-8mm), clip types are often more practical.

Size Selection Process

Proper shield footprint sizing requires measuring the RF circuit boundary and adding appropriate margin for ground connections.

Step-by-Step Sizing Methodology

1. Identify the Circuit Boundary Determine the perimeter of RF-sensitive components requiring shielding. This typically includes RF transceivers, power amplifiers, oscillators, and their immediate support components (matching networks, filters, baluns).

2. Add Ground Margin Add 2-3mm on all sides for ground pad width and shield wall thickness. This margin ensures adequate solder fillet area for SMD types or clip retention pad geometry for clip types.

3. Select from Available Sizes Match your calculated footprint to available shield dimensions. POCONS shield cans range from 9.45mm (miniature single-chip applications) to 75.20mm (large multi-chip RF subsystems) in length.

4. Verify Coverage Ensure the selected shield fully covers all target components with margin intact. Undersizing may leave portions of circuits exposed, while oversizing wastes PCB real estate and increases BOM cost without performance benefit.

Shielding effectiveness depends primarily on material conductivity, grounding quality per IEEE 299, and aperture control — not shield volume. A precisely sized shield with proper grounding will typically outperform an oversized shield with inadequate ground connections.

Height Considerations

Shield internal height must accommodate the tallest component within the shielded area with at least 0.5mm clearance to prevent mechanical stress during installation.

For Ultra-Low-Profile Designs (< 2mm clearance): SMD shields offer heights from 0.9mm to 1.45mm. The PES1693 (0.9mm height) represents the smallest available option suitable for ultra-compact wearables or miniaturized RF modules. These ultra-thin shields may require specialized pick-and-place nozzles and precise placement control during assembly.

For Standard Designs (2-6mm clearance): Both SMD and clip types are available in this range. Clip-type shields like PES1179 (1.6mm height) provide removable access while maintaining low profiles. Standard clip heights of 6-8mm accommodate most discrete RF circuits with typical passive components.

For Tall Component Designs (> 6mm clearance): Clip-type shields ranging from 7.9mm to 10mm (PES1785, PES1507, PES1785) can accommodate larger inductors, transformers, or shielded sub-modules. At these heights, proper mechanical retention through clips becomes increasingly important to prevent shield detachment during handling or vibration testing.

Both SMD and clip types can provide effective shielding when properly grounded to a continuous ground plane. Contact quality affects high-frequency performance above 5 GHz, where clip-type shields with spring finger contacts may offer more consistent impedance to ground. At frequencies below 2 GHz, type selection is typically driven by mechanical constraints rather than electrical performance.

Practical Selection Example

Consider a WiFi module design for a consumer IoT device requiring FCC Part 15 compliance:

Design Requirements:

• RF IC footprint: 8mm × 8mm
• Tallest component (inductor): 2.5mm
• PCB assembly: High-volume reflow process
• Development access: Limited rework expected after DVT

Selection Process:

1. Type Selection: SMD shields are eliminated due to 2.5mm component height (SMD max height: 1.45mm). Clip-type shield required.

2. Footprint Calculation: 8mm × 8mm + 3mm margin on all sides = 14mm × 14mm minimum. Select PES1255 (14.90mm × 13.40mm) as the smallest clip-type shield that provides adequate coverage.

3. Height Verification: PES1255 provides 1.4mm internal height. This is insufficient for a 2.5mm component. Select PES1573 (34.30mm × 28.30mm × 8.8mm) instead, which accommodates the component height with margin and still covers the 14mm footprint requirement.

4. Clip Selection: Shield requires compatible retention clips from the Shield Can Clip category (23 clip options available, selected based on shield thickness and retention force requirements).

This example demonstrates how height constraints often drive the selection process more than footprint optimization alone.

Common Selection Mistakes

Key Takeaways

EMI shield can selection requires evaluating height constraints first, then footprint dimensions, assembly process compatibility, and development access needs. SMD types offer lower profiles and reflow integration but permanent installation. Clip types provide rework access and accommodate taller components but require separate clip installation.

For comprehensive guidance on EMI shielding design principles, including grounding techniques, material selection, and aperture management, see our complete EMI Shielding Guide. Application-specific considerations for consumer electronics shielding including FCC Part 15 compliance and CE marking are covered separately.

What This Doesn't Cover

This guide focuses on shield can type and size selection based on mechanical and assembly constraints. Topics explicitly not covered include:

• Material and plating selection (nickel, tin, stainless steel properties)
• Shield can clip selection and installation procedures
• PCB grounding design and via stitching patterns
• Shielding effectiveness measurement per IEEE 299
• Thermal management of heat-generating shielded components
• Custom shield can design for non-standard dimensions

Final validation of shielding effectiveness requires EMC testing per applicable standards (FCC Part 15, CISPR 32, or IEC 61000-4-3 depending on application). Selection guidelines provided here support initial design decisions but do not replace compliance testing.