QFN thiab DFN cov khoom
Lub cev me me thiab qhov taw qhia tsis yog qhov tsuas zoo rau QFN. Qhov tsawg tshaj plaws ntawm cov pob khoom no xaus nrog cov kab mob luv luv. Qhov no pub rau cov teeb meem kev txhim kho thiab cov thermal khoom zoo. Feem ntau QFN thiab DFN qhov chaw muaj hlau loj hu rau hauv qab no, hauv sab cov kab sib chaws sib txuas, raws li muaj nyob hauv daim duab saum toj no.
Lub silicon tsuav sits ntawm lub thermal ncoo, li no rau qee qhov kev ua haujlwm thermal impressive. Kuv tau pom 3hli x 3 hli QFNs uas tau tso tawm 5V ntawm 800mA, uas siv los ua kom tau ib lub hnab loj TO 220 thiab ib lub heatsink.
Qhov kev kawm ntxiv no los nrog tus nqi, ho. Hauv qhov no, tus nqi qis dua hauv qhov chaw ntawm cov khoom tsim tawm, uas yog li cas peb kev sib tham rov los rau kuv hnub ua haujlwm. Ntawm Screaming Circuits , peb tau kawm dab tsi ua rau QFN cov teeb meem thiab yuav ua li cas tiv thaiv cov teeb meem no. Nws nqis mus rau qhov muab cov khoom siv khom hnyav uas muab tso rau hauv thiab qhov sib txawv ntawm thaj tsam ntawm lub thermal loj thiab cov neeg sib txuas.
Looj caum muab tso rau saum roob los ntawm ib txoj kab kev lo lo ntxhuav los sis nrog ib lub tshuab luam ntawv laub luam dav hlau. Nyob rau hauv txoj kev ntsuas kev lo lo ntxhuav, ib qho qauv stainless-steel solder stencil yog tsim los ntawm laser txiav kev qhib rau tag nrho ntawm qhov chaw ntom ntom. Cov stencil no ces muab tso rau saum lub rooj sib tham ntawm daim ntawv cog lus (PCB) thiab muab tshuaj khi rau siv los tso nrog tus cwj mem. Cov txheej txheem no yog ze li ntawm cov tswvyim ua ib lub hnab looj ntsej muag khov.
Muaj ntau lub khw, kuv muaj, kuj siv ib lub tshuab luam ntawv muab luam dav hlau los siv qhov muab tshuaj txhuam. Qhov no muaj qhov kom zoo dua rau kev cia kev hloov kho yooj yim ntawm tus qauv muab tshuaj rau ntawm yoov. Nws disadvantage yog tias cov tshuaj muab tshuaj tso nws nws siv tsis muab qhov kev nkag siab xav tau los ntawm qee qhov tshiab tshiab qhov chaw me me.
Ib hom kab laug sab stencil yuav yog 3 lossis 4 mils (0.067 to 0.100mm) tuab. Saib cov duab QFN saum toj no, koj tuaj yeem pom tias qhov piv ntawm cheeb tsam mus rau 4mil stencil thickness loj heev rau lub qhov chaw hauv plawv tab sis ntau me me rau cov neeg nyob sab ntug.
Thaum lub lauj kaub muab tshuaj khi melts hauv lub qhov cub ci rov qab, cov duab ntawm cov laug cog hauv dej yuav hloov. Kuv yuav tsis mus rau hauv cov kua hluav taws xob ntawm qhov teeb meem, tab sis qhov tshwm sim yog tias, yog qhov chaw hauv ncoo muab ib qho tshuaj poom kua txig poom, feem ntau yuav ntab rau hauv plawv thiab ib txhia lossis tag nrho cov neeg sib cuag feem ntau yuav tsis tshuav, raws li qhia hauv daim duab hauv qab no:
QFN float (Source: Duane Benson)
Lub stencil qhib yog tswj los ntawm CAD cov ntawv qhia. Hmoov tsis, lub hneev taw ntawm QFN thiab DFN yam hauv CAD cov tsev qiv ntawv yuav luag txhua zaus hauv qhov no. Lawv muab ib lub cav zom zaws qhib uas yog tib yam loj li lub tooj ncoo. Tsis tsuas yog lawv yeej ib txwm tsis ncaj ncees nyob rau hauv CAD software, tab sis lawv yuav luag tas li raws li nquag pom incorrectly nyob rau hauv kev tivthaiv datasheet.
Tsis yog qhib qhov rooj loj, qhov stencil yuav tsum tau segmented kom muab 50 txog 75% muab tshuaj rau qhov chaw hauv plab raws li hauv qab no:
QFN segmented stencil (Source: Duane Benson)
Cov ntaub ntawv rau cov khoom siv zom zaws stencil (los yog cov txheej txheem dej khoov rau lub dav hlau) yog teev nyob rau hauv stencil txheej - qee zaum hu ua "paste layer" los yog "cream layer" - hauv koj cov software CAD. Ntau cov ntawv sau kab mob tuaj yeem tsim cov stencil txheej thaum koj tso lub ntim roob saum npoo.
Qhov no yog ib feem ntawm qhov teeb meem. Feem ntau, cov software ua ib qho kev sib tw qhib txuam txawm yog qhov tooj liab loj npaum li cas. Qhov tseeb tias qhov cuab yeej ua tau qhov no txhais tau hais tias ntau cov neeg siv nyob rau hauv lub tswv yim tias lawv tsis tas yuav xav txog qhov no, tab sis lawv ua tiag tiag, vim hais tias - rau ib tug loj QFN tshav kub taub hau - nws yuav zaum tsis ncaj ncees lawm.
Kho cov hneev taw yog ib txoj hauj lwm yooj yim zoo nkauj, tab sis yuav ua li cas koj thiaj paub tias koj yuav tsum kho txhua yam tshwj tsis yog qee lub koomhaum PCB ua haujlwm rau koj? Koj ntshe tsis xav, yog li ntawm no kuv yog, qhov ranting ntawm koj.
Cov tshuaj, raws li kuv hais, yog yooj yim zoo nkauj. Zoo, nws yog ib qho yooj yim yog tias koj paub txog tus txheej txheem tsim los yog kho cov kev hla hauv koj cov software CAD. Kuv mam li tawm qhov kev qhia ntawd rau koj, tab sis yog tias koj paub tias ua li cas, los sis thaum koj tau kawm li cas, Kuv mam li qhia koj seb yuav ua li cas.
Nyob rau hauv koj lub footprint editor, tua qhov tsis siv neeg paste txheej thiab tes kos nws. Cov txheej txheem yuav txawv raws li cov hauj lwm ntawm koj tus ntawv luam kab, tab sis qhov koj yuav tsum ua yog tib yam. Xyuas kom tus stencil txheej tsis yog tsim los ntawm lub neej ntawd, thiab tom qab ntawd kos nws hauv qhov txheej txheem stencil. Daim duab hauv qab no qhia txog ib qho piv txwv ntawm nws yuav tsum zoo li cas.
QFN solder paste stencil txheej piv txwv (Source: Duane Benson)
Tua rau ntawm 50 thiab 75% cov kab uas siv tshuaj yaj yeeb; piv txwv tias, cov tshuaj txhuam hniav yuav tsum npog 50 mus rau 75% ntawm lub ncoo tooj liab. Yog tias muaj lwm txoj kab hauv ncoo, tsis txhob muab tshuaj txhuam rau saum toj ntawm lawv. Vias yuav tsum tau muab capped nrog daim npog qhov ncauj, lossis ntim thiab muaj phaj tshaj. Yog tias koj tawm hauv kev qhib vias, lub kiv yuav tawm mus thiab nyob rau sab nraud ntawm lub rooj tsavxwm. Qhov no kuj tsis yog ib qho zoo tshaj plaws tshwm sim.
Ib yam ntxiv: Nws puas yog 50% los yog nws 75%? Hauv lub ntiaj teb los sis lub ntiaj teb tsawg tsawg, qhov twg hauv qhov ntawd muaj qhov zoo ntawm txoj kev vam meej. Yog tias koj tabtom tsim ib qhov khoom loj, koj yuav xav ua haujlwm nrog cov kws tsim khoom tsim ntawm lub tuam txhab tsim koj cov laug cam. Lawv yuav pib ua qhov ntawd thiab tweak tus qauv stencil kom ua tiav cov txiaj ntsig zoo tshaj plaws rau lawv cov kab tsim.
QFNs yuav ua tau kom ntshai, tab sis lawv nyob ntawm no mus nyob. Nrog saib xyuas me ntsis ntxiv, koj tuaj yeem ua tau zoo nrog lawv. Tej zaum koj yuav muaj peev xwm qeeb koj pawg thawj coj me ntsis thiab txuag tau qee qhov khoom lag luam.