cac khai niem co ban trong thiet ke pcb

HC VIN CNG NGH BU CHNH VIN THNG

KHOA K THUT IN T 1

Nhng khi nim c bn v thit k PCB

Cc khi nim c bn trong thit k PCB

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Gii thiu PCB- Printed Circuit Board Thit k PCB cn c s hiu bit v kh nng sp xp v tr ca hng trm linh kin v hng nghn ng dy thnh mt thit k hon chnh tha mn ng thi cc yu cu vt l v in. Thit k PCB hp l l mt phn rt quan trng ca mt bn thit k. Thit k PCB l mt qu trnh sng to ca mi c nhn. Mt s li khuyn v quy tc chnh thit k v i dy PCB. tng thit k

Thit k mch nguyn l

Cn chnh sa

M phng, kim tra hot ng ca mchHot ng tt

Hot ng cha tt

Thit k PCBHon thin

Mch inQuy trnh thit k mch in t2


Ni dung GII THIU THIT K V SP T LINH KIN CC LP KHC THIT K CHO VIC CH TO


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GII THIU Mch nguyn l H chun v h mt Lm vic vi Grid (khung li) Lm vic t mt trn Track Dy ng Pad L ng Via L xuyn mt Polygon Lp ph ng Clearances - Khong h/khong cch v in


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Mch nguyn l Trc khi bt u layout PCB, bn PHI c mt s mch nguyn l chnh xc v hon thin. Mt thit k PCB l mt phin bn ca mch nguyn l, v vy thit k PCB chu nh hng ca mch nguyn l gc. Mch nguyn l r rng, logic v sng sa th chc chn vic thit k PCB s d dng hn. Cc phn in t quan trng cn c v mt cch chnh xc, cc nh thit k s quan tm ti chng i dy trn PCB. Nh vic t cc t cnh linh kin m chng h tr ( nh lc ngun). Cc ghi ch trn mch nguyn l gip cho vic i dy rt hiu qu. V d , chn ny yu cu mt dy bo v ti tn hiu t, vit cc ghi ch r rng gip cho ngi i dy bng mch bit c phng. Thm ch nu bn l ngi thit k mch v v mch nguyn l, cc ghi ch khng ch nhc nh bn khi i dy bng mch, m cn rt hu dng cho ngi duyt thit k.Cc khi nim c bn trong thit k PCB5

H chun v h mt H chun (inch, thou, mil) Do qu kh, v do phn ln thit b in t c ch to vi khong cch gia cc chn o theo tiu chun (imperial). Trong thit k PCB s dng n v mil hay thou. 1 mil = 1 thou = 1/1000 inch (1 mili inch)

S dng mil cho cc track, pad, cc khong cch v cc mt li, hu ht c trong cc yu cu sp xp v thit k c bn.

H mt (mm) S dng mm cho cc yu cu c kh v sn xut nh kch thc l v kch thc bng mch.

Chuyn i gia n v chun sang n v h mt: 100 thou (0.1inch) = 2.54mm 1mm = 39.37 thou (inch) 100 mil l im tham chiu c bn cho tt c cc khong cch ca thit k PCB, v khong cch linh kin thng l bi s hoc phn s ca n v c bn . 50 mil v 200 mil l nhng n v in hnh.Cc khi nim c bn trong thit k PCB6

Lm vic vi Grid (khung li) grid cn chnh, ging nh con tr ca bn, cc linh kin v cc dy s cn chnh trn cc v tr grid c nh. Khng cn phi nh tt c kch thc ca grid m ch cn nh kch thc c bn. 100 mil l mt grid tiu chun c bn cho cng vic to l, 50 mil lm chun cho vic i dy, nh chy cc dy gia cc l xuyn qua. i vi nhng thit k t m hn bn c th s dng grid cn chnh 25 mil hoc nh hn na.

Ti sao mt grid cn chnh th li quan trng? N s gi cho cc linh kin ca bn ngn np v cn i; em li s d chu v mt thm m. Gip cho cc cng vic: chnh sa, ko th, di chuyn v cn l cc dy, cc linh kin v cc khi linh kin tr nn d dng hn khi kch thc v phc tp ca vic i dy tng.Cc khi nim c bn trong thit k PCB

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Lm vic vi Grid (tip) sp xp PCB tt bn cn bt u vi grid th l 50 mil v tng dn mn ca grid cn chnh nu thit k ca bn thiu khong trng. Gim xung n 25 mil v 10 mil cho cc ng i nh v sp t khi cn. m bo grid mn hn bn chn mt c s ph hp ca 100 mil. Thng l 50, 25, 20, 10, hoc 5 mil. Cc loi grid trong chng trnh thit k PCB: grid cn chnh nh c ni trn, grid nhn thy c, l mt grid tu chn trn mn hnh theo chc nng ca khi hoc cc ng nt, hoc cc im. N hin th nh mt phng nn pha sau bn thit k v h tr vic sp t cc linh kin v cc dy. Grid in, khng nhn thy, nhng n gip cho con tr cn chnh vo chnh gia ca cc tip xc in nh cc dy v cc l, khi t con tr gn. N cc k hu ch cho vic i dy, hiu chnh v di chuyn cc i tng thc hin bng tay. Grid linh kin, lm vic ging nh grid cn chnh, nhng ch dnh cho vic di chuyn linh kin. Grid ny cho php cn chnh linh kin trn mt grid khc. N l bi s ca grid cn chnh m bn s dng. Cc khi nim c bn trong thit k PCB8

Lm vic t mt trn Thit k PCB lun c quan st t mt trn ca bng mch, nhn xuyn qua cc lp ging nh chng trong sut. Ch cn nhn bng mch t mt di kim tra hoc ch to. Phng php through the board xuyn qua mch ny c ngha l bn s phi c ch trn b mt lp y nh mt nh gng.


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Track Dy ng Khng c tiu chun quy nh cho kch c dy. Kch c dy s ph thuc vo yu cu v in ca thit k, khong trng ng i, v quyt nh bi chnh s thch ca ngi thit k. Mi thit k s c mt tp cc yu cu v in khc nhau, cc yu cu ny c th thay i tu vo cc dy trn bng mch. Tt c cc thit k khng gii hn c bn s s dng nhiu kch c dy. Ni chung, dy cng ln cng tt. Cc dy ln hn c tr khng DC thp hn, t cm thp hn, nh ch to c th khc axit d dng hn v r hn, d kim tra v sa li. Gii hn di ca rng dy s ph thuc vo t l track/space dy/khng gian m nh sn xut PCB c th p ng. V d, mt nh sn xut a ra t l track/space l 10/8, c ngha l cc dy khng th c rng nh hn 10 mil, v khong cch gia cc dy (hoc cc pad, hoc bt c b phn bng ng no) khng th nh hn 8 mil. T l thc t l 10/10 v 8/8 cho cc bng mch c bn. Chun IPC khuyn ngh 4mil l gii hn di. T l track/space cng nh, nh sn xut cng phi cn thn hn khi cn l v khc axit ln bng mch. H s tnh c chi ph , v vy m khng nn lm nh hn nhng g mnh cn. Cc khi nim c bn trong thit k PCB10

Track Dy ng (tip) Ngi mi bt u thch s dng la chn 25mil cho cc dy tn hiu, 50mil cho dy ngun v t, v 10-15 mil i dy gia IC v cc chn linh kin. Nhiu nh thit k thch cc track tn hiu nh hn nh 10 hoc 15 mil, trong khi nhiu ngi khc li thch cc track to hn. Thc t th mt thit k tt l gi cho cc track cng to cng tt, sau chuyn thnh cc track nh hn ch khi cn tha mn cc yu cu khong trng. Vic thay i kch thc track t to sang nh ri sau khi phc kch thc ban u c gi l c, hay tht c. S dng khi bn phi i dy gia cc chn IC hay cc chn linh kin. Cho php c c cc track to p v tr khng nh, nhng vn gi c tnh mm do khi i gia cc ch hp. Trn thc t th rng cc track c quyt nh bi dng in chy qua n v nhit ln nht m track c th chu ng c. Cc track c tr khng nht nh nn n s to nhit ging nh mt in tr. Track cng ln th tr khng cng nh. dy ca lp ng trn bng mch cng to nhit mt phn. Cc khi nim c bn trong thit k PCB11

Pad L ng Kch c, hnh dng v kch thc pad khng ch ph thuc vo cc linh kin s dng, m n cn ph thuc vo phng php sn sut lp rp bng mch. Mt thng s quan trng l t l pad/hole (l ng/l khoan). Mi nh sn xut s phi a ra thng s k thut ti thiu cho t l ny. Mt quy tc n gin l ng knh ca pad t nht phi ln gp 1.8 ln ng knh ca hole, hoc t ra phi rng hn 0.5mm. iu cho php dung sai cn chnh gia my khoan v hnh nh minh ho trn cc lp top v bottom. T l ny cng quan trng hn i vi cc pad v hole c kch thc nh, v n c quan h cht ch ti cc via.

Mt s thi quen ph bin: cc pad bao quanh chn cc linh kin nh in tr, t v IC c ng knh l 60mil, pad cho diode l 70 mil. Hu ht cc linh kin hn dn s dng cc pad hnh ch nht. Cc linh kin khc th da vo s lng cc chn, nh cc conector v cc khi in tr SIP, vn lun da theo quy tc chn 1 hnh ch nht. Cc pad hnh bt gic t c s dng, v hu nh nn trnh. Quy tc chung l s dng cc pad hnh trn hay hnh bu dc khi khng s dng pad hnh ch nht. Cc khi nim c bn trong thit k PCB12

Via L xuyn mt Cc via kt ni cc track t mt mt ny ti mt khc ca bng mch, bng cch i qua mt hole trn bng mch. Cc via c to ra vi nhng hole c m kim loi dn in, gi l cc l xuyn mt (PTH Planted Through Holes). PTH cho php ni in gia nhng lp khc nhau trn bng mch. Vy s khc nhau gia via v pad l g? Thc t chng khng khc nhau nhiu lm, chng u l cc hole c m in. Nhng c mt s im khc nhau khi chng cng i vi cc b thit k PCB. Cc pad v cc via nn nghin cu theo cch khc nhau. Cc hole trong cc via thng nh hn so vi cc pad mt cht, ph bin l 0.5-0.7mm. S dng mt via kt ni hai lp thng c gi l mi khu, ging nh bn khu c hai lp li vi nhau mt cch hiu qu, nh mt kim xu ch xuyn qua xuyn li mt vt liu.Cc khi nim c bn trong thit k PCB13

Polygon Lp ph ng Mt polygon t ng ph mt lp ng ln mt vng mong mun, nhng ch chy vng quanh v tch bit vi cc pad v cc track khc. Chng rt c ch cho vic t nhng vng tip t. Cc polygon c t sau khi hon thnh vic sp t cc pad v cc track. Polygon c th l mt trong hai cch ph kn thnh di ng hoc ph mt li an bi cc track ng. Cch ph kn thng c a chung hn, cch ph mt li th c hn.

ph kn ph mt li Cc khi nim c bn trong thit k PCB

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Clearances - Khong h Khong cch v in l mt yu cu quan trng cho mi bng mch. Mt khong cch qu st gia cc track v cc pad c th dn ti cc chp mch ng mnh nh si tc v kh khc axit trong qu trnh sn xut. iu ny c th gy kh khn cho vic tm ra li khi lp rp bng mch. ng vt cc gii hn ca nh sn xut tr khi bn phi lm vy, c gng thc hin ngh ca h v khong trng nh nht nu c th. 15 mil l mt gii hn khong cch nh nht cho cc thit k hole c bn, vi 10 mil hoc 8 mil c s dng cho cc sp t c nhiu linh kin hn dn. Vi cc in p ln 240V trn PCB c rt nhiu yu cu, v bn cn tham kho cc tiu chun c lin quan nu bn ang thc hin cng vic ny.Cc khi nim c bn trong thit k PCB15

Clearances - Khong h


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THIT K V SP T LINH KIN Routing c bn Hon thnh cc chi tit Thit k mt mt Thit k hai mt


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Routing c bn Khi nim: Routing l qu trnh t cc dy kt ni cc linh kin trong bng mch. Mt kt ni in gia hai hay nhiu pad c gi l mt net. Gi cho cc net cng ngn cng tt. Tng chiu di mt track cng di, th tnh tr, dung, cm cng ln => gy mt n nh. Cc track nn c cc gc l 45 . Trnh s dng gc vung, v cc trng hp s dng gc ln hn 90 . Cc chng trnh PCB s c ch di chuyn 45 . Khng nn i nhng dy vng v sp t chng kh v chm chp hn, nn bm theo cc gc 45 . i dy im ti im c v n gin cho nhng ngi mi bt u, nhng c mt vi l do khin bn khng nn s dng chng. Th nht l n xu, mt nhn t quan trng trong thit k PCB! Th hai l n khng c nhiu cc khong trng ph hp khi bn mun chy nhiu dy trn cc lp khc.


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Routing c bn (tip) Cho hin grid in bi n c dng tham kho nh mt chc nng cn chnh vo gia hoc cn chnh gn nht. Lun gi cho track chnh gia pad, ng bao gi cho track v pad ca bn tnh trng ch tip xc. C mt s l do. Th nht, n th hin s cu th v khng chuyn nghip. Th hai, chng trnh ca bn c th s khng ngh rng track tip xc in vi pad. S dng grid cn chnh v grid in ng quy tc s trnh c nhng vn .

Ch s dng mt track, khng dng nhiu track cng nhau t im ti im. Cc track phi ng gia cc pad v linh kin, khng b lch v bn no c. S dng grid cn chnh ph hp s m bo bn lun i dy ng. Ch to mt track gia cc pad 100 mil. Ch vi cc thit k ln v dy c th bn nn cn nhc hai track gia cc pad. i vi dng cao, s dng nhiu via khi i dy gia cc lp. iu ny s lm gim tr khng cho track v tng n nh. Khng ko cc track thnh cc gc khc 45 .Cc khi nim c bn trong thit k PCB19

Routing c bn (tip) Gim khong cch gia cc track n mc c th. V d. mt track 10 mil qua 2 pad 60 mil to ra mt khong h 15 mil gia track v pad. Nu c nhiu track ngun v t, u tin hy c t chng vo mch . ng thi, hy lm cho cc track ngun cng ln cng tt. Gi cc track ngun v t cng cch xa nhau cng tt, ng chng ngc hng nhau xung quanh bng mch, s lm gim t cm trong h thng ngun. Gi cho mi th i xng. S i xng trong sp t track v linh kin thc s lm tng tnh thm m v chuyn nghip ca thit k. ng cc lp ng trng thi khng ni vo u c (thng gi l ng cht), hy ni t chng hoc b chng i. ng t cc via bn di cc linh kin. Khi mt linh kin c hn th bn s khng th tc ng n l via hn ng dn xuyn qua c (trng hp cc via khng c m l). C gng s dng cc chn linh kin xuyn l ni cc track lp trn v cc track lp di. iu ny s ti thiu s lng via. Nn nh rng mi via s ng vi hai mi hn trn bng mch ca bn. Cng nhiu mi hn, th bng mch ca bn cng tr nn thiu tin cy. Cha k n vic n s lm cho vic ch to lu hn. Cc khi nim c bn trong thit k PCB20

Routing c bn (tip)

i dy ngun tt

i dy ngun xu

i dy tt

i dy xu21


Hon thnh cc chi tit Khi hon thnh vic i dy, bng mch c th cha c kh lm, nn c mt s pht dnh cho kim tra v hon thin cc tip xc (chi tit). Nu c cc track mnh ( thit k gn hn. S lp trong cc bng mch thng chn, ph bin l 4, 6, v 8 lp.


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Cc k thut thit k tn s cao Khi thit k tn s cao cn xem xt nh hng ca cm khng, dung khng v tr khng ca vic b tr PCB. Nu tn hiu qu nhanh v track qu di, th track c th nh hng n c tnh ca ng truyn. Nu khng s dng ng k thut ng truyn theo tiu chun th bn s gp s c vi nhiu ca cc tn hiu khc. Track di gii hn l mt track trong thi gian truyn ca tn hiu bt u dn t n chiu di ca track. Trn cc bng mch ng FR4 tiu chun, mt tn hiu s di chuyn khong 6 inches/ns. Trong thit k tc cao, mt t l c s cho vic bo v tnh ton vn ca cc tn hiu, v cng gim cc pht x EMI. N cho php to ra cc dy tr khng c iu khin, nh vic ghp ngun in v ti. N cng cho php bn gi cc tn hiu c ghp cht vi ng hi tip (t) ca chng. C nhiu cch to cc ng truyn tr khng c iu khin trn mt PCB. Nhng c hai cch c bn v ph bin nht c gi l Microstrip v Stripline. Mt Microstrip n gin l mt dy lp trn, vi mt mt ngun bn di. Tnh ton lin quan tm kim tr khng c trng ca mt Microstrip l tng i phc tp. N c da trn rng v dy ca dy, chiu cao so vi mt t, v hng s in mi tng i ca vt liu PCB. iu ny gii thch ti sao gi mt t gn mt lp trn cng li quan trng nh vy. Cc khi nim c bn trong thit k PCB35

Cc k thut thit k tn s cao (tip) Mt Stripline tng t vi Microstrip, nhng n c mt mt t thm vo phn trn ca dy. V vy trong trng hp ny, dy s phi mt trong cc lp bn trong. Ci tin ca stripline trn microstrip l hu ht pht x EMI s c cha cng cc mt t. C nhiu chng trnh v cc bng tnh min ph s tnh ton tt c cc s bin thin ca Microstrip v Stripline. Mt vi thng tin hu dng v cc quy tc chnh cho thit k tn s cao l: Gi cc dy tn hiu tn s cao cng ngn cng tt. Trnh chy cc dy tn hiu tn s cao chun trn bt k vt ct no trong mt t. iu ny gy ra s gin on trong ng hi tip tn hiu, v c th dn ti cc vn EMI. Trnh cc vt ct trong mt t ni no c th. Mt vt ct khc vi mt mt tch, n l tt v c cung cp bn gi cc dy tn hiu tn s cao trn mt lin tc c lin quan. C mt t tch ring ra trn mi chn ngun. Nu c th, dy t chn ngun IC ti t trn u tin, v sau ti mt ngun. iu ny s gim nhiu chuyn mch trn mt ngun ca bn. Vi cc thit k tn s rt cao, t chn ngun trc tip ti mt ngun cung cp tr khng thp hn, c th thu c nhiu thp hn trn mt ca bn. Cc via s gy ra cc s gin on trong tr khng c trng ca mt ng truyn. cc tiu xuyn m gia hai dy trn mt mt t, phi cc tiu ho khong cch gia mt v dy, v cc i ho khong cch gia cc dy. Cc via ng knh nh c t cm k sinh thp hn, v c u tin cao hn trong tn s bn c. Khng kt ni connector u vo ngun chnh trc tip ti cc mt ngun, thc hin kt ni thng qua cc t lc chnh.


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B tr linh kin hai mt B tr cc linh kin trong c hai mt ca mt PCB c th c nhiu li ch. Thc t, n l mt la chn cn thit v ph bin khi i dy trn mt bng mch. C hai h s iu khin quyt nh thc hin b tr hai mt. L do u tin l kch thc bng mch. Nu bn yu cu mt kch thc mch c th, v tt c cc linh kin ca bn khng va trn mt mt, khi cn b tr linh kin trn hai mt bng mch. L do th hai l n tha mn c cc yu cu v in. Vi nhiu linh kin hn dn tc cao t trn mt bng mch, khng c khong trng cho nhiu t trn c yu cu, hoc chng khng th c t qu gn nhau. Cc thit b BGA l mt linh kin m thu c t vic c cc t trn mt di ca bng mch. Thng thng tm thy cc bng mch b tr hai mt vi cc t trn c dn trn mt ngc. iu ny cho php cc t trn t gn vi chn ngun thit b vt l.


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THIT K CHO VIC CH TO Panelisation Panel ho Tooling Strips Cc i tng gia cng Nhng im chun Tn nhit Hn mch Ch to PCB c bn Cc hon thin b mt Kim tra in Ch k Trnh by thit k ca bn vi nh sn xut


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Panelisation Panel ho Nu bn ang xem bng mch c sp xp mt cch t ng vi mt my la chn v sp t, th n cho php t nhiu bng mch trn mt panel nh bn cn. Mt panel n gin l mt PCB rng cha nhiu bn copy bng mch ca bn. Mi ln thc hin t mt bn mch vo mt v tr trn mt my la chn v sp t, v vy nhiu bng mch bn c th b tr mt ln, mang li hiu qu chi ph trong vic sn xut. Mt panel cng s cha tooling strips ti mt trn v mt di, cho php x l t ng panel. Nhng nh sn xut khc nhau c th to ra cc kch thc panel cc i khc nhau. Mi bng mch ring l c th c i dy bn ring v c nhp vo vi cc ng ngn cch. Bn cn phi tham kho b tr bng mch quyt nh cc yu cu v kch thc panel ti u.


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Cc i tng gia cng Tooling Strips l cc ng gia cng phn trng mt trn v di ca bng mch. N bao gm cc l gia cng (Tooling holes), cc im chun (fiducial marks), v cc thng tin sn xut khc nu cn. Cc l gia cng tiu chun l cn thit cho vic iu khin t ng ho bng mch. 2.4mm v 3.2mm l 2 tiu chun cc kch c hole. Bn l gia cng trn panel l , mi gc mt ci. Cc l gia cng kt ni ti bng mch bi cc di ngn cch hoc cc ng kha hnh ch V.


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Nhng im chun im chun l nhng phng tin tr gip cho vic sp t trc quan trn PCB. Chng c s dng bi cc thit b la chn v xc nh v tr t ng canh l cho bng mch v tm cc im tham kho. Mt camera trn my c th nhn dng trung tm ca fiducial marks v s dng cc im nh mt tham chiu. Trn mt panel c 3 im chun, gi l chun ton cu. Cc gc di tri/phi v nh tri. Khong cch ti thiu ca n ti cc cnh bng mch t nht l 5mm. Chng c th c t trn tooling strips. im chun nn l mt pad trn trn lp ng vi ng knh tiu chun 1.5mm. im chun khng b che bi mt n hp kim, v mt n bao quanh cch im chun t nht 3mm. Pad c th c v bc hoc khng c v bc ging nh pad bnh thng. Hai chun khu vc (mt trong cc gc i din) c yu cu tip theo mi gi thit b hn dn trn bng mch.


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Tn nhit Nu bn kt ni trc tip mt pad ph b mt vi mt b mt ph ng, th b mt ng s c tc dng nh mt tm tn nhit hiu qu. N s dn nhit t pad ca bn khi hn. N c th lm kh cc mi ni v cc vn lin quan n vic hn. Trong cc trng hp ny, mt kt ni tn nhit bao gn mt s (thng l 4) cc track nh hn ni pad n mt ng. Vic s dng tn nhit c th t ng to ra trong nhiu chng trnh.


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Hn mchC 3 k thut hn c bn: - hand, - wave, - reflow.Hn nng chy SMD

Hn sng SMD

Hn sng xuyn l43


Kim tra in Kim tra in: C th kim tra PCB hon thnh v s lin tcv ngn dng trong thi gian sn xut. N kim tra s lin tc ca cc track ph hp vi file PCB. N c th tn thm cht chi ph, nhng l rt cn thit i vi cc bng mch nhiu lp. Nu bn c mt li ch to nhng lp bn trong, th rt kh sa.

Ch k: Ging nh bt k hot ng ngh thut no, bng mchhon thnh lun c tn hoc ch k ca bn trn !


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cac khai niem co ban trong thiet ke pcb

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