屏蔽材料应用设计

,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,EMI屏蔽材料应用设计,Winson Ma,(马万幸),2,Laird Technologies (SZ),1,常用屏蔽材料1:导电布,( Fabric Over Foam: FOF),2,Fibric +foam+ PSA or Clip,3,常用屏蔽材料2,导电泡棉,(,Conductive Foam: CF),导电泡棉衬垫(CF)制成的板料,方形条,及用于电脑接口的I/O屏蔽衬垫,4,常用屏蔽材料3:金属簧片,(Finger Stock),由特殊合金铍青铜制成的指形簧片，能够解决起它衬垫不能在剪切方向受力问题，形变范围大，低频段和高频段屏蔽性能优势,5,常用屏蔽材料4:,导电橡胶 Conductive Elastomers,High shielding effectiveness,Provides environmental sealing,Extruded, molded, and die-cut,Variety of compounds and fillers,Best for miniature devices.,6,常用屏蔽材料4:,导电橡胶 Conductive Elastomers,Hollow P25-50%,Hollow D 20-50%,Hollow O 0-50%,Solid D 5-20%,Solid O20-25%,Flat strip 5-10%,7,常用屏蔽材料5: 点胶 Form-In-Place Elastomer,Applied to die-cast metal or metalized plastic parts.,Can be applied to non-planar surfaces.,Can be applied,with,standard application machinery,8,常用屏蔽材料6:,Board Level Shielding,9,常用屏蔽材料,: -总汇,填充在缝隙中的导电材料,提供连续的低阻抗的连接。必要条件是”弹性+导电”,FOF导电布,CF 导电棉,BLS屏蔽合,Finger Stock金属簧片屏蔽条,金属丝网屏蔽条：金属丝网屏蔽条充分利用了纺织Monel,BeCu合金丝网的导电性能与橡胶优良压缩形变特性，它是将双层或多层纺织金属丝网包裹在橡胶芯上特制而成。,Elastomer 导电橡胶：导电橡胶是将微细导电粒均匀分布在硅橡胶中的方法制成。它既保持住橡胶原有水汽密封性能和弹性，同时有高导电性。,Waveguide 蜂巢式：通风口是电磁干扰主要泄露之一，机箱板上开小孔或加金属网的常规通风方法，但其屏蔽性能很难达到期望水准。波导通风板则可兼顾两者。,Tape 屏蔽胶带：导电布屏蔽胶带是由镀银纺织物组成，并带有高导电性的背胶，该种胶带有极好的柔韧性，适合于各种表面，并能承受高达200的高温,FIP 点胶：导电胶是在硅树脂中掺铜镀银颗粒精致而成，具有优良导电性和粘接强度，通过点胶方法直接成型于机壳上，它最适合小型化需求。,10,应用EMI衬垫考虑之 1 -,衬垫的弹性与变形,EMI衬垫都克意设计有柔软的弹性，该回弹压紧能形成面与面的紧密全面接触,以兖分发挥导电性能.同时也是开开关关的需要.因此,弹性是一个关键因素。,为了在任何情况下都能获得良好的电气接触，并适应机箱尺寸微少变化，压缩到一定量值是必要的,一般30-50%. 衬垫的压缩能改善接触阻抗，可以使屏蔽具有更高的效能。,但衬垫释放的压力过大也会导致机箱尺寸变化.特别是塑壳和薄金属壳.,残余形变(compress set)会影响接触.,软软弹性和少少的残余形变是我们所追求的。,11,衬垫在推荐压缩量时所需的压力,类 型,压力（磅/英尺）,压缩比（%）,导电布 FOF,4.83 good,30,铍铜指形簧片 (Be Cu),20.00 good,30,不锈钢,50.00,30,蒙乃尔金属丝网(橡胶管芯),42.00,30,蒙乃尔金属丝网（发泡芯）,49.50,30,D形橡胶条,7.50 good,30,12,应用EMI衬垫考虑之 2 - R,- C%-Force,压缩量:压力,电阻:压缩量,13,5,Connection,Electrolyte,Anode,( + ),Cathode,( - ),EMF,1.10 Volts,Zinc,Corrosion,Silver,应用EMI衬垫考虑之 3 - 电化学稳定性,当两个金属电极被浸在电触液中时，电子就被从一个电极流向另一个电极。电子的流动的建立，又支持电流的流动，施主电极(anode)就慢慢被腐蚀。,14,不同的金属呈现这个效应有不同的程度，通过此较它们的电位差，就可以分级。 材料中任何两个金属之间得出的电压，是表中材料电压之间的电位差。从耐腐蚀的观点看，衬垫和接触表面都用相同或相近的金属或合金制作，接金属电位差一般不大于0.3.,15,应用EMI衬垫考虑之 4 -,衬垫工作受力形式,受正压力,受单剪切力,受单剪切力/倒沟,受90压力,双向受的剪切力,16,EMI衬垫在安装条件下受力后的尺寸,H: 衬垫压后高度,W: 衬垫压后宽度,17,应用EMI衬垫考虑之 5 -,塑性变形,无恢复变形,塑性变形,残余变形,无恢复变形(图例中),=无恢复变形量0.0048/压入量0.120,= 0.0048/0. 120,= 4%.,.120,.200,18,应用EMI衬垫考虑之 6 -SE,19,对比Qualitative Shielding Effectiveness,Five Popular Gasket Types,120 -,100 -,80 -,60 -,40 -,20 -,0 -,dB,| | | | | | |,10k 100k 1M 10M 100M 1G 10G,Frequency (Hz),BeCu Metal Gaskets,BeCu Mesh Gaskets,BeCu,Fabric Over Foam Gaskets,Elastomer Gaskets,Monel Mesh Gaskets,20,应用EMI衬垫考虑之 7 -,EMI衬垫的固定方法,卡扣,短缝,沟槽,双卡,压敏胶/导电胶,铆,焊,螺,21,SNAP-IN,WELD,RIVET,RITE TRAK,SNAP-IN RIVET TRAK,CLIP-ON,OTHERS,SOLDER,SLOT MOUNT,PSA,-金属簧片,安装,22,应用EMI衬垫考虑之 8:,UL Rate,Laird Technologies FOF UL ratings driven by foam and adhesive layer,HB,80/20 Blend of TPE/DSM Foam w/ Polyethylene Adhesive,FR Urethane Foam w/ Polyester Adhesive,V0,100% DSM TPE Foam w/ Polyethylene Adhesive,FR Urethane Foam w/ FR Polyester Adhesive,23,对比,Five Popular Gasket Types,Parameter,dB Falloff, 10k-10G,Variability,Compression Range,Closure Pressure,Usable in Shear,Compression Set,Flame Retardant,Fluid Seal,Surface Area,Weight,Gas Permeable,BeCu Finger,No,0 - 6 dB,20 - 80%,45,20 #/Lin Ft,0,3 kg/cm,Yes,None,Yes,No,Minimum,Light,No,BeCu Mesh,Yes (Hi Freq),6 - 18 dB,15 - 75%,45,10 #/Lin Ft,0,15 kg/cm,No,None,Yes,No,Medium,Light,No,Monel Mesh,Yes (Hi Freq),6 - 18 dB,5 - 15%,10,20 #/sq in,1.41 kg/sq cm,No,Medium,Yes,No,Maximum,Medium,No,Fabric o Foam,Yes (VHiFreq),0 - 10 dB,20 - 60%,45,10 #/Lin Ft,0,15 kg/cm,Limited,Low,Yes,No,Medium,Light,Yes,Ag Filled Elast,Yes (LowFreq),40 - 60 dB,5 - 20%,12,50 - 100 #/sq in,3,5 - 7 kg/sq cm,No,Highest,Yes,Excellent,Medium,Heaviest,Yes,24,应用EMI衬垫时应综合全面考虑以下17因素,Area of Interference: Location of interference,Shielding Required: How many dB at what range (90dB at 2GHz),Conductivity , R,: include Material R & Contact R,Usage Environment: Outdoor /Indoor/ Dusty/ Waterproof,Contact surface: Material or finishing. Chromium, Tin or Zinc plated,Compression : (Recommended compression 30%),Force required : impact for deformation,Fire Rating : UL94V0, UL94HB, UL94HF-1, No rating,Resistance to Abuse: times?,Corrosion Resistance,: -Galvanic -Oxidation,Spring / Compression Set,: soft ?,Pro Selection: standard or custom design ?,Operating Temperature : 10% , 60 Deg C,Mounting Method: Stick on, Clip on, Rivet on, Slot in, etc,Dimension of gap and space: Height, Width, Length of gap or I/O,Criteria to follow: Mil Spec, FCC, CE,Cost per Performance: not cost consideration only,25,