NJIRA YOPHUNZITSIRA MOUNT

Reflow soldering ndiyo njira yomwe imagwiritsidwa ntchito kwambiri polumikizira zida zapamtunda pama board osindikizidwa (PCBs).Cholinga cha ndondomeko ndi kupanga ovomerezeka solder olowa ndi choyamba chisanadze Kutentha zigawo zikuluzikulu / PCB / solder phala ndiyeno kusungunula solder popanda kuwononga ndi kutenthedwa.

Zinthu zazikulu zomwe zimapangitsa kuti pakhale njira yabwino yopangira reflow soldering ndi izi:

1. Makina oyenera
2. Mbiri yovomerezeka yobwereza
3. PCB/gawo footprint Design
4. PCB yosindikizidwa mosamala pogwiritsa ntchito stencil yopangidwa bwino
5. Kuyika kobwerezabwereza kwa zigawo zokwera pamwamba
6. Zabwino PCB, zigawo zikuluzikulu ndi solder phala

Makina Oyenera

Pali mitundu yosiyanasiyana yamakina opangira ma reflow omwe akupezeka kutengera liwiro la mzere wofunikira ndi mapangidwe / zida zamisonkhano ya PCB yoti ikonzedwe.Uvuni wosankhidwa uyenera kukhala wakukula koyenera kuti ugwire ntchito yopangira chotengera ndi malo.

Liwiro la mzere litha kuwerengedwa monga momwe zilili pansipa: -

Liwiro la mzere (ochepera) =Mabodi pamphindi x Kutalika pa bolodi
Load Factor (danga pakati pa matabwa)

Ndikofunika kulingalira kubwereza kwa ndondomekoyi kotero kuti 'Load Factor' nthawi zambiri imatchulidwa ndi wopanga makina, kuwerengera komwe kuli pansipa:

Kuti athe kusankha olondola kukula reflow uvuni ndondomeko liwiro (tafotokozedwa pansipa) ayenera kukhala wamkulu kuposa osachepera mawerengedwe liwiro mzere.

Liwiro la ndondomeko =Uvuni chipinda mkangano kutalika
Processing nthawi

Pansipa pali chitsanzo cha kuwerengera kuti mutsimikizire kukula koyenera kwa uvuni: -

Wophatikiza wa SMT akufuna kupanga ma board a mainchesi 8 pamlingo wa 180 pa ola limodzi.Wopanga phala la solder amalimbikitsa mphindi 4, mbiri ya masitepe atatu.Kodi ndifunika kuunika kwauvuni kwautali wotani kuti ndikonze matabwa?

Mabodi pamphindi = 3 (180/ola)
Utali pa bolodi = mainchesi 8
Load Factor = 0.8 (2-inch space pakati pa board)
Nthawi Yokhala Nthawi = Mphindi 4

Weretsani Liwiro la Mzere:(3 matabwa/mphindi) x (8 mainchesi/ bolodi)
0.8

Liwiro la mzere = 30 mainchesi / mphindi

Chifukwa chake, uvuni wa reflow uyenera kukhala ndi liwiro la mainchesi 30 pamphindi.

Dziwani kutalika kwa chipinda chotenthetsera cha uvuni ndi liwiro la equation:

30 mu/mphindi =Uvuni chipinda mkangano kutalika
4 mphindi

Kutalika kwa uvuni = mainchesi 120 (mamita 10)

Dziwani kuti kutalika konse kwa ng'anjo kudzapitilira mapazi 10 kuphatikiza gawo lozizirira komanso magawo onyamula onyamula.Kuwerengera ndi kwa HEATED LENGTH - OSATI ONSE OVEN ULENGTH.

2. Kutsekedwa kotsekedwa kwa liwiro la mafani a convection - Pali mapepala ena okwera pamwamba monga SOD323 (onani kuyika) omwe ali ndi malo ochepa okhudzana ndi misala omwe amatha kusokonezeka panthawi ya reflow.Kuwongolera liwiro lotsekeka la mafani a msonkhano ndi njira yovomerezeka pamisonkhano yogwiritsa ntchito magawo oterowo.

3. Automatic control of conveyor and center-board-support widths - Makina ena ali ndi kusintha kwa m'lifupi mwamanja koma ngati pali misonkhano yambiri yosiyana yomwe iyenera kukonzedwa ndi ma PCB osiyanasiyana, ndiye kuti njirayi ikulimbikitsidwa kusunga ndondomeko yokhazikika.

Mbiri Yovomerezeka Yobwereranso

Pofuna kupanga reflow mbiri thermocouples olumikizidwa kwa chitsanzo msonkhano (nthawi zambiri ndi mkulu kutentha solder) m'malo angapo kuyeza osiyanasiyana kutentha kudutsa PCB.Ndibwino kuti mukhale ndi thermocouple imodzi yomwe ili pamtunda wopita m'mphepete mwa PCB ndi thermocouple imodzi yomwe ili pamtunda wolowera pakati pa PCB.Moyenera ma thermocouples ochulukirapo akuyenera kugwiritsidwa ntchito kuyeza kuchuluka kwa kutentha kudutsa pa PCB - yotchedwa 'Delta T'.

Mu mawonekedwe a reflow soldering nthawi zambiri pamakhala magawo anayi - Preheat, soak, reflow and cooling.Cholinga chachikulu ndikusamutsa kutentha kokwanira mumsonkhano kuti asungunuke solder ndikupanga zolumikizira popanda kuwononga zida kapena PCB.

Preheat- Mu gawo ili zigawo, PCB ndi solder zonse zimatenthedwa kuti zilowerere mwapadera kapena kutentha kwapang'onopang'ono kusamala kuti zisatenthe mwachangu (nthawi zambiri osapitilira 2ºC/sekondi - onaninso phala la solder).Kuwotcha mwachangu kwambiri kungayambitse zolakwika monga zigawo kuti ziphwanyike ndi phala la solder kuti splatter ipangitse mipira ya solder panthawi yobwereranso.

Zilowerere- Cholinga cha gawoli ndikuwonetsetsa kuti zigawo zonse zikufika pa kutentha kofunikira musanalowe mu reflow stage.Kulowetsedwa nthawi zambiri kumakhala pakati pa masekondi 60 ndi 120 kutengera 'kusiyana kwakukulu' kwa msonkhano ndi mitundu ya zigawo zomwe zilipo.Kutentha kotentha kwambiri panthawi yonyowa kumafunika nthawi yochepa.

Ngati mawonekedwe a reflow ali ndi kutentha kosakwanira komwe kumagwiritsidwa ntchito panthawi ya reflow padzakhala zolumikizira zogulitsa zomwe zikuwoneka ngati zithunzi pansipa: -

solder osapangidwa fillet ndi lead

Osati mipira yonse ya solder inasungunuka

Cholakwika chodziwika bwino cha soldering pambuyo pa kusefukira ndi kupanga mipira yapakati pa chip solder / mikanda monga momwe tawonera pansipa.Njira yothetsera vutoli ndikusintha kapangidwe ka stencil -zambiri zitha kuwoneka apa.

Kugwiritsiridwa ntchito kwa nayitrogeni panthawi yobwezeretsanso kuyenera kuganiziridwa chifukwa cha chizolowezi chochoka ku phala la solder lomwe lili ndi ma fluxes amphamvu.Nkhaniyi sikuti ndi kuthekera kobwereranso mu nayitrogeni, koma kuthekera kobwereranso pakapanda mpweya.Kutentha solder pamaso pa okosijeni kumapanga ma oxides, omwe nthawi zambiri amakhala osagulitsidwa.

Kuziziritsa- Iyi ndi nthawi yomwe gulu lazizirira koma ndikofunikira kuti musazizire mofulumirirapo - nthawi zambiri kuzizirira kuyenera kusapitirire 3ºC/sekondi.

PCB/Component Footprint Design

Pali zinthu zingapo zamapangidwe a PCB zomwe zimakhudza momwe msonkhano udzayendera.Chitsanzo kukhala kukula kwa njanji zolumikizana ndi chigawo chotsatira - ngati njanji yolumikizira mbali imodzi ya chigawocho ndi yayikulu kuposa inayo izi zitha kupangitsa kuti gawolo likhale 'mwala wamanda' monga momwe zikuwonekera pansipa:-

Chitsanzo china ndi 'copper balancing' - mapangidwe ambiri a PCB amagwiritsa ntchito madera akuluakulu a mkuwa ndipo ngati pcb itayikidwa mu gulu kuti ithandizire kupanga zingayambitse kusalinganika kwa mkuwa.Izi zitha kupangitsa kuti gululo lisunthike panthawi yobwereranso ndipo njira yabwino ndikuwonjezera 'copper balancing' pazinyalala za gululo monga momwe zikuwonekera pansipa:-

Mwaona'Design for Manufacture'kwa malingaliro ena.

PCB yosindikizidwa mosamala pogwiritsa ntchito stencil yopangidwa bwino

Njira zoyambira mkati mwa msonkhano wa mount Mount ndizofunikira kwambiri kuti pakhale njira yabwino yopangira reflow soldering.Thesolder phala kusindikiza ndondomekondikofunikira kuti mutsimikizire kusungitsa kokhazikika kwa solder phala pa PCB.Cholakwa chilichonse panthawiyi chidzatsogolera ku zotsatira zosafunika ndipo kotero kulamulira kwathunthu kwa ndondomekoyi pamodzi ndikamangidwe kothandiza ka stencilchofunika.

Kuyika kobwerezabwereza kwa zigawo zokwera pamwamba

Kusintha kwa magawo

Kuyika kwa zida zokwera pamwamba kuyenera kubwerezedwanso motero makina odalirika, osamalidwa bwino ndi ofunikira ndikofunikira.Ngati mapaketi a zigawo saphunzitsidwa m'njira yolondola angayambitse makina owonera masomphenya kuti asawone gawo lililonse mwanjira yomweyo ndipo kusiyanasiyana kumawonedwa.Izi zidzatsogolera ku zotsatira zosagwirizana pambuyo pa ndondomeko ya reflow soldering.

chigawo makhazikitsidwe mapulogalamu akhoza analenga ntchito sankhani ndi malo makina koma ndondomeko si zolondola monga kutenga centroid zambiri mwachindunji PCB Gerber deta.Nthawi zambiri izi centroid deta zimagulitsidwa kunja kuchokera PCB kapangidwe mapulogalamu koma nthawi zina palibe ndipo koterontchito yopanga fayilo ya centroid kuchokera ku data ya Gerber imaperekedwa ndi Surface Mount Process.

Makina onse oyika zida azikhala ndi 'Placement Accuracy' yotchulidwa monga: -

35um (QFPs) mpaka 60um (tchipisi) @ 3 sigma

Ndikofunikiranso kuti mphuno yolondola isankhidwe kuti ikhale yamtundu wa chigawocho - mitundu ingapo yamitundu yosiyanasiyana yoyikamo imatha kuwonedwa pansipa:

Zabwino PCB, zigawo zikuluzikulu ndi solder phala

Ubwino wa zinthu zonse zomwe zimagwiritsidwa ntchito panthawiyi uyenera kukhala wapamwamba chifukwa chilichonse chosakhala bwino chidzabweretsa zotsatira zosafunikira.Malinga ndi kupanga ndondomeko ya PCB ndi momwe iwo akhala kusungidwa mapeto a PCB a zingachititse osauka soderabilty pa ndondomeko reflow soldering.Pansipa pali chitsanzo cha zomwe zitha kuwonedwa pamene kutha kwa PCB kumakhala koyipa komwe kumabweretsa chilema chotchedwa 'Black Pad': -

UTHENGA WABWINO PCB FINISH

Chithunzi cha PCB

Solder ikuyenda ku gawo osati PCB

Momwemonso ubwino wa chigawo chokwera pamwamba ukhoza kukhala wosauka kutengera njira yopangira ndi njira yosungiramo.

Ubwino wa solder phala amakhudzidwa kwambiri ndikusunga ndi kusamalira.Phala losakwanira la solder ngati litagwiritsidwa ntchito lingapereke zotsatira monga momwe zikuwonekera pansipa: -