最新-EMI屏蔽材料應(yīng)用設(shè)計-(2)-PPT課件

1、EMI屏蔽材料應(yīng)用設(shè)計 常用屏蔽材料1:導(dǎo)電布( Fabric Over Foam: FOF)Fibric +foam+ PSA or Clip常用屏蔽材料2導(dǎo)電泡棉(Conductive Foam: CF)導(dǎo)電泡棉襯墊(CF)制成的板料,方形條,及用于電腦接口的I/O屏蔽襯墊常用屏蔽材料3:金屬簧片 (Finger Stock)由特殊合金鈹青銅制成的指形簧片，能夠解決起它襯墊不能在剪切方向受力問題，形變范圍大，低頻段和高頻段屏蔽性能優(yōu)勢常用屏蔽材料4:導(dǎo)電橡膠 Conductive ElastomersHigh shielding effectivenessProvides environm

2、ental sealingExtruded, molded, and die-cutVariety of compounds and fillersBest for miniature devices.常用屏蔽材料4:導(dǎo)電橡膠 Conductive ElastomersHollow P25-50%Hollow D 20-50%Hollow O 0-50%Solid D 5-20%Solid O20-25%Flat strip 5-10%常用屏蔽材料5: 點(diǎn)膠 Form-In-Place ElastomerApplied to die-cast metal or metalized plasti

3、c parts.Can be applied to non-planar surfaces.Can be applied with standard application machinery常用屏蔽材料6: Board Level Shielding常用屏蔽材料: -總匯 填充在縫隙中的導(dǎo)電材料,提供連續(xù)的低阻抗的連接。必要條件是”彈性+導(dǎo)電” FOF導(dǎo)電布CF 導(dǎo)電棉BLS屏蔽合Finger Stock金屬簧片屏蔽條 金屬絲網(wǎng)屏蔽條：金屬絲網(wǎng)屏蔽條充分利用了紡織Monel,BeCu合金絲網(wǎng)的導(dǎo)電性能與橡膠優(yōu)良壓縮形變特性，它是將雙層或多層紡織金屬絲網(wǎng)包裹在橡膠芯上特制而成。Elastome

4、r 導(dǎo)電橡膠：導(dǎo)電橡膠是將微細(xì)導(dǎo)電粒均勻分布在硅橡膠中的方法制成。它既保持住橡膠原有水汽密封性能和彈性，同時有高導(dǎo)電性。Waveguide 蜂巢式：通風(fēng)口是電磁干擾主要泄露之一，機(jī)箱板上開小孔或加金屬網(wǎng)的常規(guī)通風(fēng)方法，但其屏蔽性能很難達(dá)到期望水準(zhǔn)。波導(dǎo)通風(fēng)板則可兼顧兩者。Tape 屏蔽膠帶：導(dǎo)電布屏蔽膠帶是由鍍銀紡織物組成，并帶有高導(dǎo)電性的背膠，該種膠帶有極好的柔韌性，適合于各種表面，并能承受高達(dá)200的高溫FIP 點(diǎn)膠：導(dǎo)電膠是在硅樹脂中摻銅鍍銀顆粒精致而成，具有優(yōu)良導(dǎo)電性和粘接強(qiáng)度，通過點(diǎn)膠方法直接成型于機(jī)殼上，它最適合小型化需求。應(yīng)用EMI襯墊考慮之 1 - 襯墊的彈性與變形EMI襯墊都

5、克意設(shè)計有柔軟的彈性，該回彈壓緊能形成面與面的緊密全面接觸,以兗分發(fā)揮導(dǎo)電性能.同時也是開開關(guān)關(guān)的需要.因此,彈性是一個關(guān)鍵因素。為了在任何情況下都能獲得良好的電氣接觸，并適應(yīng)機(jī)箱尺寸微少變化，壓縮到一定量值是必要的,一般30-50%. 襯墊的壓縮能改善接觸阻抗，可以使屏蔽具有更高的效能。但襯墊釋放的壓力過大也會導(dǎo)致機(jī)箱尺寸變化.特別是塑殼和薄金屬殼.殘余形變(compress set)會影響接觸.軟軟彈性和少少的殘余形變是我們所追求的。 襯墊在推薦壓縮量時所需的壓力類 型壓力（磅/英尺）壓縮比（%）導(dǎo)電布 FOF4.83 good30鈹銅指形簧片 (Be Cu)20.00 good30不銹鋼

6、50.0030蒙乃爾金屬絲網(wǎng)(橡膠管芯)42.0030蒙乃爾金屬絲網(wǎng)（發(fā)泡芯）49.5030D形橡膠條7.50 good30應(yīng)用EMI襯墊考慮之 2 - R - C%-Force壓縮量:壓力電阻:壓縮量5ConnectionElectrolyteAnode( + )Cathode( - )EMF1.10 VoltsZincCorrosionSilver應(yīng)用EMI襯墊考慮之 3 - 電化學(xué)穩(wěn)定性 當(dāng)兩個金屬電極被浸在電觸液中時，電子就被從一個電極流向另一個電極。電子的流動的建立，又支持電流的流動，施主電極(anode)就慢慢被腐蝕。 不同的金屬呈現(xiàn)這個效應(yīng)有不同的程度，通過此較它們的電位差，就可

7、以分級。 材料中任何兩個金屬之間得出的電壓，是表中材料電壓之間的電位差。從耐腐蝕的觀點(diǎn)看，襯墊和接觸表面都用相同或相近的金屬或合金制作，接金屬電位差一般不大于0.3.應(yīng)用EMI襯墊考慮之 4 -襯墊工作受力形式受正壓力受單剪切力受單剪切力/倒溝受90壓力雙向受的剪切力EMI襯墊在安裝條件下受力后的尺寸H: 襯墊壓后高度W: 襯墊壓后寬度應(yīng)用EMI襯墊考慮之 5 -塑性變形,無恢復(fù)變形塑性變形,殘余變形,無恢復(fù)變形(圖例中)=無恢復(fù)變形量0.0048/壓入量0.120= 0.0048/0. 120= 4%. .120.200應(yīng)用EMI襯墊考慮之 6 -SE對比Qualitative Shield

8、ing EffectivenessFive Popular Gasket Types120 - 100 - 80 - 60 - 40 - 20 - 0 -dB | | | | | | | 10k 100k 1M 10M 100M 1G 10G Frequency (Hz)BeCu Metal GasketsBeCu Mesh GasketsBeCuFabric Over Foam GasketsElastomer GasketsMonel Mesh Gaskets應(yīng)用EMI襯墊考慮之 7 - EMI襯墊的固定方法卡扣短縫溝槽雙卡壓敏膠/導(dǎo)電膠鉚,焊,螺SNAP-INWELDRIVETRITE

9、TRAKSNAP-IN RIVET TRAKCLIP-ONOTHERSSOLDERSLOT MOUNT PSA-金屬簧片 安裝應(yīng)用EMI襯墊考慮之 8: UL RateLaird Technologies FOF UL ratings driven by foam and adhesive layerHB 80/20 Blend of TPE/DSM Foam w/ Polyethylene AdhesiveFR Urethane Foam w/ Polyester Adhesive V0100% DSM TPE Foam w/ Polyethylene AdhesiveFR Urethane

10、 Foam w/ FR Polyester Adhesive對比Five Popular Gasket Types ParameterdB Falloff, 10k-10G VariabilityCompression Range Closure Pressure Usable in Shear Compression Set Flame Retardant Fluid Seal Surface Area Weight Gas PermeableBeCu FingerNo0 - 6 dB20 - 80%,45 20 #/Lin Ft0,3 kg/cmYesNoneYesNoMinimumLig

11、htNoBeCu MeshYes (Hi Freq)6 - 18 dB15 - 75%,4510 #/Lin Ft0,15 kg/cmNoNoneYesNoMediumLightNoMonel MeshYes (Hi Freq)6 - 18 dB5 - 15%,1020 #/sq in1.41 kg/sq cmNoMediumYesNoMaximumMediumNoFabric o FoamYes (VHiFreq)0 - 10 dB20 - 60%,4510 #/Lin Ft0,15 kg/cmLimitedLowYesNoMediumLightYesAg Filled ElastYes (

12、LowFreq)40 - 60 dB5 - 20%,1250 - 100 #/sq in3,5 - 7 kg/sq cmNoHighestYesExcellentMediumHeaviestYes應(yīng)用EMI襯墊時應(yīng)綜合全面考慮以下17因素Area of Interference: Location of interferenceShielding Required: How many dB at what range (90dB at 2GHz)Conductivity , R: include Material R & Contact RUsage Environment: Outdoor

13、/Indoor/ Dusty/ Waterproof Contact surface: Material or finishing. Chromium, Tin or Zinc plated Compression : (Recommended compression 30%)Force required : impact for deformationFire Rating : UL94V0, UL94HB, UL94HF-1, No rating Resistance to Abuse: times?Corrosion Resistance: -Galvanic -OxidationSpring / Compression Set: soft ?Profile/Shape Selection: standard or custom design ?Operating Temperature : 10% , 60 Deg