EMI Shielding Engineering Handbook EMI Shielding - INSCO Group

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SHIELDING SOLUTIONS FOR WIRELESS COMMUNICATIONS EMI Shielding/Grounding Spacer Gaskets The integrated conductive elastomer/plastic spacer gasket is a low cost, easily installed system for providing EMI shielding and grounding in small electronic enclosures. EMI Spacer Gaskets The unique design of Chomerics’ EMI spacer gaskets features a thin plastic retainer frame onto which a conductive elastomer is molded. The elastomer can be located inside or outside the retainer frame, as well as on its top and bottom surface. EMI spacer gaskets provide a new approach to designing EMI gaskets into handheld electronics such as digital cellular phones. Board-toboard spacing is custom designed to fit broad application needs. Customized cross sections and spacer shapes allow for very low closure force requirements and a perfect fit in any design or device. Robotic Installation Spacer gaskets can be installed quickly by robotic application. Integral locater pins in the plastic spacer help ensure accurate positioning in both manual and pick-and-place assembly. Benefits include faster assembly and lower labor costs. 14 CHO-SEAL ® 1310 or 1273 Conductive Elastomers With EMI spacer gaskets, shielding and grounding are provided by Chomerics’ CHO-SEAL 1310 and 1273 conductive elastomers, specifically formulated for custom shape molded parts. They provide excellent shielding and isolation against electromagnetic interference (EMI), or act as a low impedance ground path between PCB traces and shielding media. Physically tough, these elastomers minimize the risk of gasket damage, in contrast to thin-walled extrusions or unsupported molded gaskets. Silicone-based CHO-SEAL 1310 and 1273 materials offer excellent resistance to compression set over a wide temperature range, resulting in years of continuous service. CHO- SEAL 1310 material is filled with silverplated-glass particles, while 1273 utilizes silver-plated-copper filler to provide higher levels of EMI shielding effectiveness. US Headquarters TEL +(1) 781-935-4850 FAX +(1) 781-933-4318 • www.chomerics.com Europe TEL +(44) 1628 404000 FAX +(44) 1628 404090 Asia Pacific TEL +(852) 2 428 8008 FAX +(852) 2 423 8253 South America TEL +(55) 11 3917 1099 FAX +(55) 11 3917 0817 Superior elongation and tensile strength help to prevent tearing in use due to mishandling. Typical properties for CHO-SEAL 1310 and 1273 material are shown on pages 33 and 32 respectively. High Shielding Performance CHO-SEAL 1310 material provides more than 80 dB of shielding effectivness from 100 MHz to 10 GHz, while CHO-SEAL 1273 material provides more than 100 dB. Low Volume Resistivity Both materials have exceptionally low volume resistivity, which makes them well suited for grounding applications in which a flexible electrical contact is needed. Low Compression Gasket Spacer gaskets are typically designed to function under low deflection forces. Chomerics uses design tools such as Finite Element Analysis (FEA) to accurately predict compression-deflection behavior of various cross section options. Refer to page16. LCP Plastic Spacer Liquid crystal polymer (LCP) spacers, including those made with Vectra A130 material, provide a Locator Pins CHO-SEAL 1310 or 1273 Conductive Elastomer (Inside) Plastic Spacer Around Outside or Inside Figure 1 Single Piece EMI Gasket/ Plastic Spacer for Accurate and Low Cost Installation
stable platform for direct, high precision molding of conductive elastomers. The Vectra A130 material described in Table 1 has excellent heat deflection temperature characteristics (489°F, 254°C). For weight considerations, the LCP has a specific gravity of only 1.61. This plastic is also 100% recyclable. Typical EMI Spacer Gasket Design Parameters The EMI spacer gasket concept can be considered using the design parameters shown in Table 2. Some typical spacer gasket profiles are shown below. ,,, ,,, ,,, ,,, ,,, ,,, ,,, ,,, ,,, ,,, ,,, ,,, Applications for EMI Spacer Gaskets The spacer gasket concept is especially suited to digital and dual board telephone handsets or other handheld electronic devices. It provides a low impedance path between peripheral ground traces on printed circuit boards and components such as: ■ the conductive coating on a plastic housing ■ another printed circuit board ■ the keypad assembly Typical applications for EMI spacer gaskets include: ■ Digital cellular, handyphone and personal communications services (PCS) handsets ■ PCMCIA cards ■ Global Positioning Systems (GPS) ■ Radio receivers ,,, ,,, ,,, ,,, ,,, ,,, ,,, ,,, ,,, ,,, ,,, ,,,,,, ,,,,,, = Plastic Spacer ,,,,,, ,,,,,, = Conductive Elastomer ,,,,,, Figure 2 Typical Spacer Gasket Profiles ■ Other handheld electronics, e.g., personal digital assistants (PDAs) ■ Replacements for metal EMI shielding “fences” on printed circuit boards in wireless telecommunications devices AN EMI SPACER GASKET APPLICATION CASE STUDY Design Problem A manufacturer of cellular telephone handsets needed to provide a low impedance connection from the underside of a keyboard assembly to the ground trace on a circuit board. Design Requirements ■ Provide 360° low impedance connection from conductive coating to circuit board ground trace ■ Low deflection forces available ■ Low cost solution needed ■ Sufficient EMI shielding of the handset needed to operate properly and meet commercial EMC regulations Chomerics Solution Three possible solutions were considered: 1. A small cross section conductive elastomer with conductive pressure-sensitive adhesive 2. A conductive, form-in-place elastomer 3. An EMI spacer gasket system was chosen, based on its ability to meet all of the manufacturer’s design requirements. It consisted of a Vectra LCP plastic spacer with Chomerics’ CHO-SEAL 1310 silver-plated-glass filled silicone elastomer injection molded onto the inside walls of the plastic frame. Table 1 Table 2 LCP PLASTIC SPACER TYPICAL PROPERTIES Property Test Procedure Vectra A130 LCP 1 Tensile Strength, yield, Type 1, 0.125 inch (3.2 mm), psi (MPa) ASTM D638 30,000 (207) Tensile Elongation, break, Type 1, 0.125 inch (3.2 mm), % ASTM D638 2.2 Flexural Strength, break, 0.125 inch (3.2 mm), psi (MPa) ASTM D790 37,000 (254) Flexural Modulus, 0.125 inch (3.2 mm), psi (MPa) ASTM D790 2,100,000 (15,000) Compression Strength, psi (MPa) ASTM D695 20,000 (140) Compression Modulus, psi (MPa) ASTM D695 1,700,000 (12,000) Izod Impact, notched, 73°F (23°C), ft-lb/in (J/m) ASTM D256 2.8 (150) HDT, 66 psi (0.45 MPa), 0.250 in., (6.4 mm), unannealed, °F (°C) ASTM D648 489 (254) Specific Gravity ASTM D792 1.61 Volume Resistivity, ohm-cm ASTM D257 10 x 10 15 UL 94V-0 Flame Class Rating, inch (mm) UL 94 0.018 (0.45) Limiting Oxygen Index (LOI), % 1 Celanese AG ASTM 2863 37 DESIGN PARAMETERS Maximum overall dimension 18 inch x 18 inch (45.7 cm x 45.7 cm) Minimum cross section 0.050 inch (1.27 mm) Minimum plastic cross section 0.020 inch (0.51 mm) Minimum elastomer cross section 0.015 inch (0.38 mm) Minimum plastic cross-sectional area 0.001 inch 2 (0.025 mm 2 ) Minimum elastomer cross-sectional area 0.0020 inch 2 (0.051 mm 2 ) Cross section tolerance (typical) ±0.003 inch (0.076 mm) Plan view tolerance (typical) ±0.005 inch (0.127 mm) US Headquarters TEL +(1) 781-935-4850 FAX +(1) 781-933-4318 • www.chomerics.com Europe TEL +(44) 1628 404000 FAX +(44) 1628 404090 Asia Pacific TEL +(852) 2 428 8008 FAX +(852) 2 423 8253 South America TEL +(55) 11 3917 1099 FAX +(55) 11 3917 0817 continued 15
Page 1 and 2: Chomerics is the world’s largest
Page 3 and 4: Contents COST-EFFECTIVE SOLUTIONS F
Page 5 and 6: Cost-Effective Solutions for Major
Page 7 and 8: As Lead Supplier, Chomerics... Prov
Page 9 and 10: Shielding Solutions for Wireless Co
Page 11 and 12: SHIELDING SOLUTIONS FOR WIRELESS CO
Page 13: Table 2 Table 1 *Copies of CHO-TM-T
Page 17 and 18: SHIELDING SOLUTIONS FOR WIRELESS CO
Page 19 and 20: gaskets will typically save 60% or
Page 21 and 22: Table 1 TYPICAL PROPERTIES OF CHO-F
Page 23 and 24: Optimizing the design of Cho-Form S
Page 25 and 26: Optimizing the design of Cho-Form S
Page 27 and 28: Conductive Elastomer Gaskets SECTIO
Page 29 and 30: Material Selection Chomerics’ arr
Page 31 and 32: Table 2 continued ELASTOMERS FOR TY
Page 33 and 34: Table 3 continued survivability bey
Page 35 and 36: Conductive Elastomer Extrusions...
Page 37 and 38: Bonded gaskets — Similar and diss
Page 39 and 40: Table 2 EXTRUSION MANUFACTURING GUI
Page 41 and 42: Standard Extrusion Sizes Table 7 ,,
Page 43 and 44: Table 8 continued HOLLOW O-STRIPS C
Page 45 and 46: Table 11 continued Chomerics P/N* M
Page 47 and 48: Table 15 A Chomerics P/N MIL P/N: M
Page 49 and 50: 19-09-12023-XXXX 19-08-12057-XXXX 1
Page 51 and 52: 19-09-15245-XXXX 19-09-15486-XXXX 1
Page 53 and 54: 19-05-E328-XXXX 19-08-F676-XXXX 19-
Page 55 and 56: CONDUCTIVE ELASTOMERS Co-Extruded S
Page 57 and 58: 19-18-15351-XXXX 19-18-M391-XXXX 19
Page 59 and 60: Table 2 STANDARD SHEET STOCK SIZE A
Page 61 and 62: CONDUCTIVE ELASTOMERS Molded Shapes
Page 63 and 64: CONDUCTIVE ELASTOMERS Molded D- and
Page 65 and 66:
Table 3 continued Table 3 continued
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CONDUCTIVE ELASTOMERS Waveguide Gas
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Table 2 continued Frequency Range (
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Table 4 Note: Raised portion will b
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temperatures to 125°C, and CHO-SEA
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Jam Nut EMI Seals MIL-C-38999, MIL-
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CONDUCTIVE ELASTOMERS Molded-In-Pla
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Table 1 * Where two values are show
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Load, lb./inch Load, lb./inch 30 20
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Stress Relaxation As important as C
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Heat Aging The primary aging mechan
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CONDUCTIVE ELASTOMERS Part Number I
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19-06-11223-XXXX . . . . . . .Hollo
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SOFT-SHIELD® Low Closure Force, Fo
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LOW CLOSURE FORCE, FOAM CORE EMI GA
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Table 3 ORDERING INFORMATION Referr
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Table 6 74046 APPROX. ACTUAL SIZE R
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Table 1 Material 4000 4002 4004 400
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Page 103 and 104:
Page 105 and 106:
Metal EMI Gaskets, Clip-on Gaskets
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METAL EMI GASKETS MESH STRIP MESH
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METAL EMI GASKETS MESH STRIP MESH
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METAL EMI GASKETS SPRINGMESH ® SPR
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Fabricated COMBO GASKETS: Select th
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METAL EMI GASKETS SHIELDMESH SHIEL
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Table 2 SINGLE EMI/EMP FRAME GASKET
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Table 2 POLASHEET COMPOSITE GASKETI
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METAL EMI GASKETS METALASTIC ® MET
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METAL EMI GASKETS METALKLIP ® META
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SHIELDING EFFECTIVENESS Figures 8-1
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PITCH 0.095 (2.41) PITCH 0.165 (4.1
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PITCH PITCH 0.187 (4.75) PITCH 0.25
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METAL EMI GASKETS SPRING-LINE ® Ta
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Conductive Compounds Adhesives Seal
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CONDUCTIVE COMPOUNDS CHO-BOND ® Co
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Table 1 continued SPECIFICATIONS AN
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Silicones and Flexible Polyisobutyl
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• CHO-SHIELD 4900 silver-filled a
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Engineered Laminates & Grounding Pr
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Ordering Procedure CHO-MASK II tape
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Table 1 Property Test Method Typica
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LAMINATES & GROUNDING PRODUCTS EMI
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Table 1 SPECIFICATIONS Property Tes
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LAMINATES & GROUNDING PRODUCTS CHO-
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SPRING-LINE ® “Pick and Stick”
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EMI Shielded Vents SECTION CONTENTS
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Customization Options • Alternati
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EMI SHIELDED VENTS CHO-CELL Shield
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Round SHIELD CELL and OMNI CELL Pan
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EMI SHIELDED VENTS SLIMVENT Shield
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EMI SHIELDED VENTS Common Parts Tab
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EMI Shielded Windows & Contrast Enh
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Figure 2 Shielding Effectiveness fo
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Insertion Loss (dB) WIN-SHIELD Wind
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Cable Shielding SECTION CONTENTS PA
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BEADS ON LEADS Impedance-Frequency
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Table 5 continued Dimensions - Inch
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FLAT SPLIT CABLE CORE Impedance-Fre
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CABLE SHIELDING CHO-DROP ® EMI Abs
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Table 2 STRAIGHT LENGTHS inch (mm)
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Connector Boots and Cable Transitio
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CABLE SHIELDING CHO-JAC ® Flat Cab
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EMI Shielding Theory & Gasket Desig
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E i Current on front wall due to re
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Figure 6 Absorption Loss Nomograph
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,, ,,, ,, ,,, ,, ,,, ,, ,,, G G G E
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Table II Group Material Groupings*
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Non-Conductive Sealing Gasket Volum
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enclosure, or by using an insert si
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Gasket Mounting Choices Our various
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Actual deflection vs. distance betw
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percentage increase required to sat
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Figure 28d Section B-B from Figure
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Formulas (see definition of terms a
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in the unit price of the gasket. Bo
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Wire Mesh EMI Gasket Selection Guid
Page 219 and 220:
Relative Conductivity: Conductivity
Page 221 and 222:
Global Compliance Testing Page 222
Page 223 and 224:
FCC, CSA, CISPR, VCCI, AUSTEL, EN T
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THERM-A-GAP TM Thermally Conductive
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EMI Shielding Engineering Handbook EMI Shielding - INSCO Group

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