SMD焊接作业简.docx

SMD焊接作业简.docx

《SMD焊接作业简.docx》由会员分享，可在线阅读，更多相关《SMD焊接作业简.docx（12页珍藏版）》请在冰豆网上搜索。

SMD焊接作业简

SMD焊接作业

1.Keepthecircuitboardclean.Isopropanolorwoodalcoholissuitableforremovinglightoilsandgrease.PCB'sshouldalwaysbewashedunderwarmwater,thenovendriedat60degreesCelsiusfor10to15minutes.HandlethePCBbytheedgeonlyandavoidtouchingcopperwithyourbarehands.

线路板保持干净,轻微的油渍可以使用酒精去除,冲洗PCB板务必要使用温水,然后在摄氏60度下烘干10到15分钟,过程中务必只能手触板边,绝对不能手摸铜箔,尤其是裸铜.

2.Usetherightsolderingironforthejob.Youdon'tneedtopurchaseatemperaturecontrollediron,specialSMTtiporSMThotgasreflowstation.Thesetoolsmightbeusedinindustry,butonlytosavetimeandincreasereliability.

使用正确的烙铁,一般SMD并不需要特殊的烙铁,温控,SMD专用烙铁头,或者是热气式的焊枪,这些一般常见于工业生产用,这些工具只是可以节省时间及增加焊点可靠性,但并非是非用不可的工具.

AllsortsofSMTsolderingjobscanbedonewiththecommonWellerworkstation.Theimportantpointisselecttherighttip（i.e.:

haveseveraltipsonhand）.Aswithanysolderingjob,thegeneralideaistohavethejointuptotemperatureandsolderedinafewseconds.Thinkabouthowmuchofa"heatsink"thejointwillbeandchoosethetipbasedonthat.Useoflargertipsshouldbelimitedtoareasoflargesolidcopperplane（i.e.:

groundplane）.Foralljobsexceptveryverysmallparts,Iuseasmalltipasshownabove.Withpractice,youwilllearnwhattipsuitsyoubest.

一般的烙铁就可以做SMD的焊接,重点不在烙铁,而是烙铁头,进行锡焊接的要点在于接点的温度及焊接的时间,因此首先要想到的是焊接点上的吸热,并且继而想到要选用什幺样的烙铁头,一般会选用大烙铁头无非是有很大的裸铜或者是接地面上的焊点,只要有够多的经验并且注意细节,你很快就可以自己选用合适的烙铁头.

UseL.M.P（LowMeltingPointSolder）ifyouareexperimenting.LMPsolderisverysimilarto60/40solder,exceptthatitcontains2%Silver.ThisSilver"loading"hastwoeffects.Itlowersthemeltingpoint（afewdegrees）anditreducestherateatwhichcomponentmetalisationleechesintothesolderitself.

使用低融点锡,这种锡与60/40锡相同,只是另外加有2%的银,增加银有二个作用,一是降低融点,另外一个作用是增加锡融解后的延展度.

SMTresistors,capacitors,ferritebeads,etc.allmakethereelectricalconnectionsviametalisedpadsdepositedonasubstrate（Alumina,ceramic,ferrite,etc）.ThemetalusedisoftenNickelorarelatedalloy.Oneproblemwithsolderingthesamejointseveraltimes,isthateachtimethejointisheated,someoftheNickelleavesthecomponentandjoinsthesolder.Theiscalled"leeching".Leechingisonlyaproblemwhenthesolderjointofametalisedcomponentisheatedseveraltimes.Leechingoccursatafasterratewithstandard60/40solderthanwhatitdoeswithLMPsolder.

不论是电阻电容或电感,这些SMD型式的零件,都是采用金属介质成为端点,使用的金属介质包含镍合金等,这些零件端点上的镍合金经过多次焊接后,镍会游离出来在焊点上,这称为LEECHING,一般使用60/40锡时很容易产生LEECHING,使用低熔点锡,可以降低零件焊点上的LEECHING效应.

ThedownsideofLMPsolderisthatitisabout3timesthepriceof60/40solderandhardertoobtain,althoughsourcesofsupplyhavebeenquotedatthebackofthisarticle.

使用低融点锡的问题点在于价格,这种锡的价格大约是标准60/40锡的3倍,同时也不很普遍.

Ifakitwasbeingbuilt,wherethecomponentvaluesareknown,then60/40solderwillbefine.Ifcomponentchangesareoftenandlikely,thenLMPwouldbemoreadvantagesforalongtermreliablesolderconnection..

假如制程中的零件是就定位的,而且也不会常因为更换零件而做焊点的融接,则可以使用60/40锡,假如焊点异动频繁,则以低熔点锡较佳.

Somepeopleuse"soldercream"soldbyvariousshops.Theadvantageofsoldercream,isthatithasmorefluxthanregularsolder.Thesoldercreamismadeupofveryfineballsofsoldermixedwithawaterbasedflux.

有些人会使用锡乳膏,锡乳膏的优点就是它含有较多的助焊剂,通常锡乳膏是由很小的锡球与助焊剂混合而成.

Unfortunately,soldercreamwasneverintendedtobeusedwithasolderingiron.Infact,becausethesoldersitsinawaterbasedfluxsolution,thecreamneedstobe"dried"out（i.e.:

thewaterhasbeendrivenoff）beforethesoldercanbemelted.Thiscanbedonebymovingtheirontipclosetothejointforafewsecondspriortomovingontothejoint.

很可惜的是,锡乳膏通常不用于烙铁作业,事实上,锡乳膏是呈液态状,因此锡乳膏制程需要烘干作业,也就是要在小锡球溶解前必须烘干,这用在烙铁作业时,可以先将烙铁头靠近焊点几秒钟,先烘干锡乳膏,然后再将烙铁头碰触焊点.

Inexperimentationquantities,soldercreamisonlyavailableas60/40mix.Inmyopinion,theSMTexperimenterwouldbebetterofftouseLMPsolderandextraflux（fromatubeorapen）ratherthansolderpaste.Itisamatterofpersonalpreference.Ifyoulikeusingthepaste,thengoforit!

一般而言,适合实验用的的锡乳膏只有60/40,但使用于实验桌上还是以低熔点锡乳膏较佳,同时还需外加助焊剂.

Usesolderfluxwherepossible.OneofthebiggestproblemswithsolderingSMTpartsisthattheamountoffluxwithinthesoldercoreisnotsufficientforthejoint.ProfessionalSMTmanufacturersuse"soldercream"andcontrolledtemperatureovens.However,solderingirontemperaturesarefarlesscontrolledandoftenthefluxhasevaporatedbeforethejointhassolidified,leadingtodryjointwhichisoftendullincomplexion.

可能的话,尽量使用助焊剂,焊接SMD零件的最大问题点之一,在于焊接点上的助焊剂量往往不足,专业SMD制程往往使用锡乳膏作业,并且使用温控回焊炉,采用烙铁的缺点,就是温度不容易掌控,而且往往在焊点尚未就绪前,助焊剂已发挥殆尽,这就容易造成焊点的假焊.

Solderfluxhasotheradvantages.Becauseofitsliquidnature,itincreasestheconductionofheatfromtheirontiptothejoint.Italsoincreasesthesurfacetensionofthemoltensolderwhichhelpstoachieveareliablejointandminimisesthechanceofbridgingfinelyspacedpins.

使用助焊剂还有其它好处,因为助焊剂呈现出液态状,它有助于将烙铁头的温度传导到焊点上,而且也可以将焊点上的表面涨力扩大,这可以提升焊点的可靠性.

Fluxhasthedisadvantagethatitisgenerallysticky,andcanrequirespecialfluxremoverstoremove.Soapywaterandultrasonicbathsareonesolution,butthisrequiresasecondwashinfreshwaterandabakeintheoven.Fluxcanalsocarrycontaminantswhichmayeffectcircuitsoperatinginthemicrowaveregionorcircuitswithveryhighimpedance's,especiallyinVCOs.Somefluxescontainleadbasedchemicals,anditiswisetouseglovestoavoiddirectskincontact.

助焊剂也有缺点,那就是沾粘,而且还需要助焊剂清除剂才能清洗干净,通常清除助焊剂是使用加入泡剂的水用超音波清洗,之后再用清水冲洗,然后烘干,另外助焊剂也有碍于微波讯号的传递,尤其是碰到高阻抗讯号路径等.因为有些助焊剂内含有铅化合物,因此处理作业上,要避免用手直接接触.

Fluxisavailablefromseveralhobbyshopsandotheroutletsinsyringe（seeFig4）andpenapplicationform.Ingeneral,theuseofextrafluxmakesSMTsolderingmucheasierandincreasessolderjointreliability.However,youmaynotneeditatall.

店面上贩售的助焊剂,有条状有笔型,SMD焊接有赖于外加助焊剂,这不但有助于焊接的流畅性,也有助于焊点的可靠性.

Useagoodmagnifyinglamporothermagnificationsource.SMTpartsareverysmall.SMTsolderjointsareatleastfourtimessmalleragain.Sinceitsthesolderjointthatshouldconcernyoumost（especiallyifyouwanttobuildsomethingreliable）itisusefultohaveasourceofmagnification.SomeexamplesareshowninFig5.

SMD零件很小,而且其焊点可能比零件小上4倍,针对SMD焊接作业,你的关注焦点应该是在焊接点上,这幺微小的焊点,可能需要放大镜来帮你详细检查焊点.

Mostpeoplewithreasonableeyesightshouldbeabletosolderwithoutmagnificationandcheckthejointundermagnificationlater.Forthosewhohaverelativelypooreyesight（likemyself）,special"jeweller'seyes"thatsitontheheadcanhelp.Goodlightingisessential.

大多数人用裸眼就可以初步检视SMD焊点,但是要彻底检查还是要藉助于放大镜,当然够亮的灯光环境也是必须的.

Dontworkinaclutteredspace.Giveyourselfroomtomovearound,andorientatethePCBsoitseasytoreachthejointyourtryingtosolder.

不要在碍手碍脚的环境中作业,要让身处环境自由自在,同时PCB板的移动或转动也必须要流畅,这才方便SMD焊接作业.

Buyagoodpairoftweezers.YouwillbeamazedhowmucheasierSMTsolderingbecomes.Infact,outofalltheequipmentIhavesuggested,Ifeelthisisthemostimportant.Bothsolderinganddesolderingwillinvolveyourtweezers,sotheyareaworthwhileinvestment.Ifpossible,getaqualitysetwherethetwoendsmeettogetheraccurately.

聂子也是不可少的工具,好的聂子可以让SMD作业如行云流水般流畅,我认为聂子可能是所有SMD焊接作业中最重要的工具,不论是焊接上零件或是焊锡除零件,都必须使用聂子,要选用精品级的聂子,选用时候要检查聂子尾端的结合性,越精确越好.

ThefollowingtechniqueshouldbeusedforsolderingsmallSMTpartssuchasresistors,capacitors,inductors,transistors,etc,withasolderingiron.

以下是焊接电阻电容电感晶体管等SMD零件的要点:

1.）Addasmallamountoffluxtothearea（ifrequired）andaddasmallamountofsoldertoonepad.

先在必要的地方施加助焊剂,然后在零件单端加上少量锡.

2.）Pickupcomponentintweezersmakingsurecomponentishorizontal.Alternatively,justmovethecomponentuntilitisclosetothefinalposition.

用聂子夹起零件,注意要水平摆放,移到就位处.

3.）Whilstholdingthecomponentwithyourtweezers,meltthesolderonthepadandmovethecomponentintoposition.

一边用聂子让零件就位,一边用烙铁让零件单端焊接固定.

4.）Removeyourironbutcontinueholdingthecomponentuntilthesolderhassolidified.ChecktoseethatthecomponentissittingflatonthePCB.Ifnot,re-meltsolderwhilstpushinggentlyontopofthecomponentwithtweezers.

先移开烙铁但是聂子还不能动,让温降下来后才移开聂子,在等待时可以先检是零件是不是平贴线路板,如果没有,要双手并用,烙铁与聂子协调好,直到零件平贴.

5.）Soldertheothersideofthecomponent.

焊接零件另一端或其它端

6.）Re-meltthefirstsolderjointandletsolidify.Thisensuresbothjointarestableduringsolidification.

烙铁回到第一个焊点上,让零件接脚可以正常舒展,以防接点断裂.

7.）Checkyourworkundermagnification.

使用放大镜检视这些焊点.

8.）Thejointshouldbeshinyandconcave.Ifyouaddedtoomuchsolder,wickupwithsmallsolderwickandtryagain.SeefollowedFig.forjointquality.

检视焊点应该光亮且呈现完美的弧度,如下图中间位置.

IC'srequireasimilarbutslightlydifferenttechnique.

以下是SMDIC的焊接技巧:

1.）AddfluxtothepadswheretheICistobesoldered.

在所有IC接脚的裸铜上追加助焊剂.

2.）Addasmallamountofsoldertooneofthecornerpinpads.

在IC的端脚裸铜位置加少量锡.

3.）LineuptheICwiththepadsonthePCB.DoublechecktheICorientation.

检视IC的方向有无摆错,并对齐方向.

3.）MeltthesolderwithyourironandmovetheICintopositionwithyourtweezers.Letthesoldersolidify.

固定IC的第一个脚,同时注意其斜对角上的脚位置是不是也对齐.

4.）Solderthediagonallyoppositepin.Checkundermagnificationthatallpinslineupwiththererespectivepads.

焊接斜对角上的脚,如果这两脚精密对齐,其余脚位置也应该是对齐的.

6.）Soldertherestofthepinsandcheckworkundermagnification.

焊接其余IC脚.

De-solderingSmallSMTComponents

拆解小型SMD零件

1.Addexcesssoldertoonesideofthecomponent.

先在其中施加一些锡,这可以让烙铁离开后能维持更长的高温时间.

2.Whilstthesidewithexcesssolderremainsmolten,moveyourirontotheotherjointandgentlypushthecomponentoffthepads.

迅速把烙铁移到另一端,用聂子把零件移开.

3.Cleanuppadswithsolderwick.

请除零件移开后在焊点上留下的锡渣

Note:

Thetrickhereismakeonesideofthecomponentalargerthermalmassandheatthats