CHAPTER – 1 INTRODUCTION
A printed circuit board (PCB) mechanically supports and electrically connects electronic connects electronic components using components using conductive tracks, conductive tracks, pads and other features etched from etched from copper sheets laminated onto laminated onto a non-conductive substrate. substrate. PCBs can be single sided (one copper layer), double sided (to copper layers) or multi-layer (outer and inner layers). !ulti-layer PCBs allo for much higher component density. Conductors Conductors on different layers are a re connected ith plated-through holes called vias called vias.. Advanced Advanced PCBs may contain components capacitors, resistors or active devices - embedded in the substrate. "#-$ glass "#-$ glass epo%y is the primary insulating substrate upon hich the vast ma&ority of rigid PCBs are produced. A thin thin layer of copper foil is laminated to one or both sides of an "#-$ panel. Circuitry interconnections are etched into copper layers to produce printed circuit boards. Comple% circuits are produced in multiple layers. Printed circuit boards are used in all but the simplest electronic products. Alternatives to PCBs include ire rap and rap and point-to-point point-to-point construction. PCBs construction. PCBs re'uire the additional design effort to lay out the circuit, but manufacturing and assembly can be automated. !anufacturing circuits ith PCBs is cheaper and faster than ith other iring methods as components are mounted and ired ith one single part. "urthermore, operator iring errors are eliminated. hen the board has only copper connections and no embedded components, it is more correctly called a printed iring board (PB) or etched iring board. Although more accurate, the term t erm printed iring board has fallen into disuse. A PCB populated ith electronic components is called a printed circuit assembly (PCA), printed circuit board assembly or PCB assembly (PCBA). he *PC preferred *PC preferred term for assembled boards is circuit card assembly (CCA), and for assembled backplanes assembled backplanes it it is backplane assemblies. he term PCB is used informally both for bare and assembled boards .
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"ig + PCB
1.1
Design
A board designed in /0 the seeping curves in the traces are evidence of freehand design using self-adhesive tape *nitially PCBs ere designed manually by creating a photomask a photomask on on a clear mylar mylar sheet, sheet, usually at to or four times the true si1e. 2tarting from the schematic diagram the component pin pads ere laid out on the mylar and then traces ere routed to connect the pads. #ubondry ondry transfers of common component footprints increased efficiency. e fficiency. races ere made ith self-adhesive tape. Pre-printed non-reproducing grids on the mylar assisted in layout. o fabricate the board, the finished photomask as photolithographically as photolithographically reproduced reproduced onto a photoresist photoresist coating coating on the blank copper-clad boards. 3oadays PCBs are designed ith dedicated layout softare, generally in the folloing folloing steps4 . 2chematic capture through an electronic design automation (56A) automation (56A) tool. 7. Card dimension dimensionss and template are decided decided based on re'uired re'uired circuitry circuitry and case of the PCB. 8. he positions positions of the the compon components ents and and heat sinks are sinks are determined. $. 9ayer stack stack of the PCB is decided, decided, ith ith one to tens tens of layers dependin depending g on comple%ity. :round and poer and poer planes are decided. A poer poer plane is the counterpart to a ground plane and behaves as an AC AC signal signal ground hile providing 6C poer to the circuits mounted on the PCB. 2ignal interconnections are traced on signal planes. 2ignal planes can be on the outer as ell as inner layers. "or optimal 5!* 5!* performance performance high fre'uency signals are routed in internal layers beteen poer or ground planes. ;. 9ine impedance is impedance is determined using dielectric layer thickness, routing copper thickness and trace-idth. race separation is also taken into account in case of differential signals. !icrostrip !icrostrip,, stripline stripline or or dual stripline can be used to route signals. . Component Componentss are placed. hermal hermal consideratio considerations ns and geometry geometry are taken into account.
1.2 Manufacturing PCB manufacturing consists of many steps. 2
1.2.1 PCB CAM
!anufacturing starts from the PCB fabrication data generated by CA6. he :erber or 5%cellon files in the fabrication data are never used directly on the manufacturing e'uipment but alays read into the CA! (Computer Aided !anufacturing) softare. CA! performs the folloing functions4 . *nput *nput of of the the :erbe :erberr data data 7.
utput >utput of of the digital digital tool toolss (copper (copper patterns, patterns, solder resist image, image, legend image, image, drill files,, automated optical inspection data, files data , electrical test files, files,...)
1.2.2 Paneliati!n
Paneli1ation is a procedure hereby a number of PCBs are grouped for manufacturing onto a larger board - the panel. ?sually a panel consists of a single design but sometimes multiple designs are mi%ed on a single panel. here are to types of panels4 assembly panels - often called arrays - and bare board manufacturing panels. he assemblers often mount components on panels rather than single PCBs because this is efficient. he bare board manufactures alays uses panels, not only for efficiency, but because of the re'uirements the plating process. hus a manufacturing panel can consist of a grouping grouping of individual PCBs or of arrays, depending on hat must be delivered. he panel is eventually broken apart into individual PCBs0 this is called depaneling. 2eparating the individual PCBs is fre'uently aided by drilling or routing perforations along the boundaries of the individual circuits, much like a sheet of postage stamps. stamps . Another method, hich takes less space, is to cut <-shaped grooves across the full dimension of the panel. he individual PCBs PCBs can then be broken apart along this line of eakness. oday oday depaneling is often done by lasers hich cut the board ith no contact. 9aser paneli1ation reduces stress on the fragile circuits.
1.2." C!##er #atterning
he first step is to replicate the pattern in the fabricator@s CA! system on a protective mask on the copper foil PCB layers. 2ubse'uent etching removes the unanted copper. (Alternatively, a conductive ink can be ink-&etted on a blank (non-conductive) board. his techni'ue is also used in the manufacture of hybrid circuits.) circuits.) 3
. 2ilk screen printing uses printing uses etch-resistant inks to create the protective mask. 7. Photoengraving uses Photoengraving uses a photomask and developer to selectively selective ly remove a ?<-sensitive photoresist coating and thus create a photoresist mask. 6irect imaging techni'ues are sometimes used for high-resolution re'uirements. 5%periments ere made ith thermal resist. 8. PCB milling uses milling uses a to or three-a%is mechanical milling system to mill aay the copper foil from the substrate. A PCB milling machine (referred to as a @PCB Prototyper@) operates in a similar ay to a plotter a plotter , receiving commands from the host softare that control the position of the milling head in the %, y, and (if relevant) 1 a%is. $. 9aser resist ablation ablation 2pray 2pray black black paint onto onto copper copper clad laminate, laminate, place into C3C C3C laser laser plotter. he laser raster-scans the PCB and ablates (vapori1es) the paint here no resist is anted. (3ote4 laser copper ablation is rarely used and is considered e%perimental.) he method chosen depends on the number of boards to be produced and the re'uired resolution. 9arge volume •
2ilk screen printing + used for PCBs ith bigger features
•
Photoengraving + used hen finer features are re'uired.
2mall volume •
Print onto transparent film and use as photo mask along ith photo-sensiti1ed boards. (i.e., pre-sensiti1ed boards), then etch. (Alternatively, use a film photoplotter)
•
9aser resist ablation.
•
PCB milling.
obbyist •
9aser-printed resist4 9aser-print onto toner transfer paper, heat-transfer ith an iron or modified laminator onto bare laminate, soak in ater bath, touch up ith a marker, then etch.
•
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"ig + 7 he to processing methods used to produce a double-sided P6 ith plated through holes
1.2.$ C%e&ical etc%ing Chemical etching is usually done ith ammonium persulfate or ferric chloride. "or P (plated-through holes), additional steps of electroless deposition are deposition are done after the holes are drilled, then copper is electroplated to build up the thickness, the boards are screened, and plated ith tinlead. he tinlead becomes the resist leaving the bare copper to be etched aay. he simplest method, used for small-scale production and often by hobbyists, is immersion etching, in hich the board is submerged in etching solution such as ferric chloride. Compared ith methods used for mass production, the etching time is long. eat and agitation can be applied to the bath to speed the etching rate. *n bubble etching, air is passed through the etchant bath to agitate the solution and speed up etching. 2plash etching uses a motor-driven paddle to splash boards ith etchant0 the process has become commercially obsolete since it is not as fast as spray etching. *n spray etching, the etchant solution is 5
distributed over the boards by no11les, and recirculated by pumps. Ad&ustment of the no11le pattern, flo rate, temperature, and etchant composition gives predictable control of etching rates and high production rates. As more copper is consumed from the boards, the etchant becomes saturated and less effective0 different etchants have different capacities for copper, ith some as high as ; grams of copper per litre of solution. *n commercial use, etchants can be regenerated to restore their activity, and the dissolved copper recovered and sold. 2mall-scale etching re'uires attention to disposal of used etchant, hich is corrosive and to%ic due to its metal content.
1.2.' (a&inati!n
"ig + 8 Cut through a 26#A!-module, a multi-layer PCB.
1.2.) Drilling
"ig + $ 5yelets
oles through a PCB are typically drilled ith small-diameter drill small-diameter drill bits made bits made of solid coated tungsten carbide. carbide. Coated tungsten carbide is recommended since many board materials are very abrasive and drilling must be high #P! and high feed to be cost effective. 6rill bits must also remain sharp so as not to mar or tear the traces. 6rilling ith high-speedsteel is simply not feasible since the drill bits ill dull 'uickly and thus tear the copper and ruin the boards. he drilling is performed by automated drilling machines ith machines ith placement controlled by a drill tape or drill file. 6
CHAPTER – 2 PCB CHARACTER*TIC*
!uch of the electronics elec tronics industry@s PCB design, assembly, ass embly, and and 'uality control follos standards published by the *PC *PC organi1ation. organi1ation.
2.1 T%r!ug%+%!le tec%n!l!g,
"ig + ; hrough-hole(leaded)register
he first PCBs used through-hole technology, mounting electronic components by leads leads inserted inserted through holes on one side of the board and soldered onto copper traces on the other side. Boards may be single-sided, ith an unplated component side, or more compact double-sided boards, ith components soldered on both sides. ori1ontal installation of through-hole parts ith to a%ial leads (such as resistors, capacitors, and diodes) is done by bending the leads degrees in the same direction, inserting the part in the board (often bending leads located on the back of the the board in opposite directions to improve the part@s mechanical strength), soldering the leads, and trimming off the ends. 9eads may be soldered soldered either either manually or by a ave soldering machine. hrough-hole PCB technology almost completely replaced earlier electronics assembly techni'ues such as point-to-point as point-to-point construction. construction. "rom the second generation of computers in computers in the ;s until surface-mount surface-mount technology technology became popular in the late =s, every component on a typical PCB as a through-hole component. hrough-hole manufacture adds to board cost by re'uiring many holes to be drilled accurately, and limits the available routing area for signal signal traces on traces on layers immediately belo the top layer on multi-layer boards since the holes must pass through all layers to the opposite side. >nce surface-mounting came into use, small-si1ed 2!6 components ere used here possible, ith through-hole mounting mounting only of components unsuitably unsuitably large for surface7
mounting due to poer re'uirements or mechanical limitations, or sub&ect to mechanical stress hich might damage the PCB.
"ig + hrough-hole devices mounted on the circuit board of a mid-=s home computer
2.2 *urface+&!unt tec%n!l!g,
"ig + / 2urface mount components, including resistors, transistors, and anintegrated circuit
2urface-mount technology emerged in the s, gained momentum in the early =s and became idely used by the mid-s. Components Components ere mechanically redesigned to have small metal tabs or end caps that could be soldered directly onto the PCB surface, instead of ire leads to pass through holes. Components became much smaller and component placement on both sides of the board became more common common than ith through-hole mounting, alloing much smaller PCB assemblies ith much higher circuit densities. 2urface mounting lends itself ell to a high degree of automation, reducing labor costs and greatly increasing production rates. Components can be supplied mounted on carrier tapes. 2urface mount components can be about one-'uarter to one-tenth of the si1e and eight of 8
through-hole components, and passive components much cheaper0 prices of semiconductor surface mount devices (2!6s) devices (2!6s) are determined more by the chip itself than the package, ith little price advantage over larger packages. 2ome ire-ended components, components, such as 3$$= 3$$= small-signal small-signal sitch diodes, are actually significantly cheaper than 2!6 e'uivalents.
"ig + = PCB in computer mouse
2." Circuit #r!#erties !f t%e PCB 5ach trace consists of a flat, narro part of the copper foil foil that remains after etching. he resistance, determined by idth and thickness, of the traces must be sufficiently lo for the current the conductor ill carry. Poer and ground traces may need to be ider than signal traces. *n a multi-layer board one entire layer may be mostly solid copper to act as a ground plane for plane for shielding and poer return. "or microave microave circuits, circuits, transmission lines can lines can be laid out in the form of stripline stripline and and microstrip microstrip ith ith carefully controlled dimensions to assure a consistent impedance impedance.. *n radio-fre'uency and fast sitching circuits the inductance inductance and and capacitance capacitance of of the printed circuit board conductors become significant circuit elements, usually undesired0 but they can be used as a deliberate part of the circuit design, obviating the need for additional discrete components.
2.".1 Materials
5%cluding e%otic products using special materials or processes all printed circuit boards manufactured today can be built using the folloing four materials4 . 9amin aminat ates es 7. Copper Copper-cl -clad ad lamina laminates tes 9
8. #esin #esin impreg impregnat nated ed B-stag B-stagee cloth cloth (Pre-preg (Pre-preg)) $. Copp Copper er foil foil 2.".2 (a&inates
9aminates are manufactured by curing under pressure and temperature layers of cloth or paper ith thermoset resin resin to to form an integral final piece of uniform thickness. he si1e can be up to $ by = feet (.7 by 7.$ m) in idth and length.
T%icness
T%icness
IPC (a&inate
T%icness
T%icness
in inc%es
in &illi&eters
Nu&-er
in inc%es
in &illi&eters
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7.8
CHAPTER – " ENTERIN/ THE *CHEMATIC INTO E0PRE***CH 10
. >pen 5%press2C 5%press2C to create create a fresh fresh schematic schematic.. he first time time you you start start 5%press2C 5%press2C you ill get a dialog bo% ith a link link to a 'uick start guide for 5%press2C. his can be useful if you ant to get a general overvie for the tool. >nce you are ready to start, close the dialog bo% to vie the empty schematic.
7. Click on on >p-Amp-li >p-Amp-like ke symbol symbol to place compon components. ents. o place place the resistors, resistors, select select DPassive-#esistorE in the te%t bo% in the upper right corner.
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8. hen click click on the the schematic schematic for the $ resistor resistorss (not includin including g the photores photoresistor istor or potentiometer) in roughly the location you you ant them to display. hen 1oom in using the magnifying glass tool (or the heel on the mouse) and pan the display (using the sliding bars) to improve i mprove your vie.
$. 3o you you need need to give each each of the resistor resistorss uni'ue uni'ue identifier identifiers. s. #ight click on a resistor and choose D2et component component properties.E *n the Component Component Properties bo%, under DComponent *6,E *6,E select DAuto assign Part *6.E he program should should assign this resistor to be #. 2et its value k in the DPart 3ameE field and hit >F. >F. #epeat this process to identify and label #7 (k), #8 (k), and #$ (k).
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;. #otate #$ #$ by right right clicking clicking on it, it, selecting selecting D#otate D#otate componen componentE tE and then then DBody DBody left GE
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. 3o add the the capacitor, capacitor, potentiom potentiometer, eter, compar comparator, ator, and transistor transistor to the the circuit by first first clicking back on the component placement tool (the red op-amp symbol) and using the component names DPassive-Capacitor polari1ed,E DPassive- Potentiometer,E D*C + 3ational - 9!8 + Comparator + 6*P-=,E and D2emiconductor D2emiconductor + ransistor ransistor 3P3.E ?se Dset component propertiesE to assign all of these parts Part *6s, label them and position them (using the arro tool) in a logical manner. manner.
/. 3o e need need to add add some compon components ents (the photor photoresistor esistor and and the bu11er) bu11er) that donHt donHt e%ist in the library. library. 9etHs start ith the photoresistor. he easiest ay to make make ne parts is to start ith a symbol thatHs already close to hat hat you ant and modify it. Place a regular resistor on the layout (using the placement tool ith IPassive + #esistorH). :o to the selection tool tool (the arro), choose that that resistor and go to the the DComponentE menu at the top and select D?ngroup componentE
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=. ?sing the the circle shaped shaped tool tool from the the tool menu, menu, dra dra a circle around around the the resistor. resistor.
. 2elect the the hole hole ob&ect (using (using the the arro tool), tool), and and choose choose DComponen DComponentE tE -J D:roup D:roup to make componentE
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. *n the component properties bo% that appears, assign the photoresistor a uni'ue uni'ue part *6, such as DP#E.
. "or future use, save this this as a custom component component by selecting DComponentE DComponentE -J D2ave custom componentE and then in the dialog bo% that appears give the component a name such as Dphotoresistor.E Dphotoresistor.E (*f someone else has already completed the tutorial on this computer, the part may already e%ist, in that case you should either save this component ith a uni'ue name, or save your component on top of the one already e%isting)
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7. !ove the photoresistor to the spot you ant it in the circuit. 8. 3o e ill ill create the bu11er. bu11er. he bu11er is a polari1ed device, so a good starting point is a polari1ed capacitor. :o to the component selector, choose a polari1ed capacitor, ungroup the capacitor, and then add a circle to the symbol to distinguish it as a bu11er. :roup the entire ob&ect as a component ith part *6, DBK,E and and label DC5P-777$E and save the component component as a DBu11erE under custom components. At the last step, youHre display ill be as follos4
$. 3o e need to add our connections to poer and ground. ground. 9etHs start ith ground. :o to the Dsymbol or signal labelE tool, hich looks like a ground, and select DPoer + groundE from the te%t bo% in the upper right.
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;. Place ; grounds into the circuit, at the bottom of #7, #7, near pins and $ of the 9!8, 9!8, near the bottom of the capacitor, at the emitter of the BL, and at the bottom of the potentiometer.
. #epeat this process, but using DPoer +
/. 3o letHs add in our our battery connection. Place a battery into the circuit, using D!isc + Battery.E Battery.E Assign the battery battery the part *6 DBE and give it the label D<. D<.E hen, use the symbol tool to add a ground connection and a M< netork connection (this ill link the positive terminal of the battery ith every other point in the circuit that should go to
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=. 3o select the ire tool, and ire your circuit together. together. he left-click starts the ire and sets a bend, and the right click ends a ire. After iring, the schematic should appear as follos4
. 2ave your ork, using D2ave As..E to create a uni'ue uni'ue filename. 7. Check your file for netlist errors using D"ileE -J DCheck schematic schematic for netlist errorsE
7. he pins inside of of the BL are not not specified (this is because pin assignments assignments vary for different BLs) so you ill probably ill get an error message, like that shon belo4 20
77. it DcancelE on the error message, and then as that message suggested, select the part and choose DComponentE and then then D?ngroup Component.E his e%ample uses the 7n/ BL in the little tin can (the >-8 >-8 package). "or this package the base is pin 7, the emitter is pin , and the collector is pin 8. o set this in the schematic, double click on &ust the collector pin, and assign it to pin 8.
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78. *n a similar fashion, assign D7E to the base, and DE to the emitter. hen select the entire component (this takes a lot of shift-clickingNbe sure to get all the little parts), choose D:roup to make componentE from the Component menu, and assign the part *6 to be O.
7$. *f youHre going to be using the the transistor again, itHs probably a good good idea to then click on it, select DComponentE -J D2ave custom componentE and save it as the transistor name, hich in this case is 7n/.
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7;. 3o check your your file for netlist errors again, using D"ileE -J DCheck schematic for netlist errors,E you might get an error like that shon shon belo (if not skip to 7= 7=))
7. he cause of this error is that the ire isnHt really connected. he Dsnap-to-gridE function has prevented prevented you from making a connection. it continue to e%it the netlist check. hen toggle the Dsnap-to-gridE function off, off, select the errant line end(s) and move it (them) into the correct position. #epeat this process until all the lines are properly connected.
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7/. #eattempt #eattempt the netlist error error check. 7=. >nce the netlist error check runs clean, you ill be asked to save your your file, hich you should definitely do. he final schematic should look like this4
7. Print your schematic to reference as you you ork on on your layout. At this point, you should revie your your schematic carefully to check for errors. >nce you are satisfied that the schematic is correct, close 5%press2C.
Creating the 9ayout in 5%pressPCB
hen doing the layout, it is particularly useful to have the actual components andor in front of you, along ith a ruler or set of calipers (the ruler and calipers are unnecessary for this tutorial).
. >pen 5%pressP 5%pressPCB. CB. hen you first first open open the program, program, a dialog dialog bo% bo% appears appears ith ith links links to the Ouick 2tart :uide and a PCB 6esign ips file. *f you have time, both of these links can be instructive. >nce youHre ready to continue, continue, hit >F to go to a ne file.
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7. ?nder D"ileE select D3e file.E file.E Choose Choose the 7-layer 7-layer board, board, ith ith 6efault 6efault via I.; I.;EE round via ith .7E holeH. Change both default default clearances for the filled planes to .; (the ma%imum alloed). it >F and again >F on the arning that appears in the ne%t indo.
he yello line on the screen shos the boundary boundary for the PCB. he default boundary is 8.= % 7.; 7.; inches, hich matches the the e%press PCB miniboard service. his demo ill use the entire boardNhoever for our class pro&ect you should only use half the board (.E % 7.;E) so that e can double double up designs. Also, be aare that no copper copper (pads or traces) can be placed closer than .7;Q to the perimeter of the board.
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8. he first first thing you you need to to do is to place place all of your your componen components ts onto the layout. layout. 9etHs start ith the resistors. 2elect the component placing placing tool, hich looks looks like a little *C, and from the pull-don menu on the upper right choose D#esistor-.7; att (lead spacing .$ inch).E (his description matches the small resistors in #i-7$). Put $ resistors on the schematic.
$. 3o double double click click on each each of the resistors resistors to to bring up the compon component ent properties properties bo%, bo%, and assign the resistors ith part *6s #, #7, #8, and #$.
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;. he 9!8 9!8 for for this e%ample e%ample is in an =-pin =-pin 6*P package package,, so you place place the comparator comparator using the component component D6ip =-pin.E 3otice ho the s'uare pad denotes pin . .
. 6ouble-click 6ouble-click on the the component component and assign assign the the part ith ith the the part *6 D?E
/. 3o add add the folloin folloing g component componentss (this assumes assumes that each each of these these component component descriptions match the components in the circuitNitHs good to confirm this ith a 27
ruler hen you go to build your on circuitNmatching lead spacings are particularly important)4 a. A capacitor capacitor ith the the description description DCap DCap + radial radial electrolytic electrolytic + 9ead spacing spacing .7 .7 inchE and give it part *6, DCE (notice ho the s'uare pad denotes the positive lead) b. A transistor ith the description D2emiconductor + >-8E >-8E and give it part *6, DOE c. A potentiomet potentiometer er ith the the description description DPotenti DPotentiometer ometer + Bourns Bourns series 88=E 88=E and give it part*6, D#;E
=. 2av 2ave you yourr or ork. k. . 3o e e need need to build the compon components ents that that arenHt arenHt already already in the the library4 library4 the photoresistor, and the bu11er. 9etHs start ith the photoresistor. photoresistor. he photoresistor dimensions are as follos (you could get this either from the data sheet or by measuring the actual component ith calipers)4
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9ike before, the easiest ay to build a ne component is to start ith one that is similar. 2o e look through the component options for a to-pin component component ith a .E lead spacing. A good choice is DCap + lead spacing . inch.E inch.E Place this component on the diagram, and 1oom in so that you can get a better vie.
. 3o select the component and choose DComponentE DComponentE -J D?ngroup PCB ComponentE ComponentE to break the component don into parts.
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. #emove the boundary around the part, and then dra in a circle using the arc tool. hen double click on the circle to set its properties, and set the radius to .=7;, and the layer to the silkscreen layer (the yello layer).
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7. 2elect the entire part, and then choose DComponentE -J D:roup to make PCB componentE
8. 6ouble click on the ne component, component, and give it the part *6 DP#E to match the photoresistor *6 from your circuit schematic.
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$. o use this component again, save your component component using DComponentE -J D2ave custom component,E and save the component as DphotoresistorE (if you use this in your design later, be sure that your photoresistor matches these dimensionsNif not you ill need to create a ne part).
;. 3o e ill repeat this process for the bu11er, hich hich has the dimensions shon belo (given in mm)4
o create this part, e ill start ith a capacitor base again, this time ith a lead spacing of . inch (; mm). mm). *tHs best to use a polari1ed polari1ed capacitor, as the bu11er is 32
polari1ed. 9etHs use use DCapacitor + A%ial electrolytic + 9ead spacing . . inch.E After placing this part, the display ill be as follos4
. ?ngroup the component, component, delete the rectangle, and add a circle in the silkscreen layer that has a radius of .; inches. !ove other components components out of the ay if they are too too close. Rour Rour display ill then look as follos4
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/. 3o e need to check that the pads are large enough enough for the bu11er, hich hich has fat leads. 6ouble click on one of the pins to pull up its properties4
he holes have a diameter of .8;E, hich corresponds corresponds to .= mm. his could be a little tight for our bu11er, here the pin diameter is specified as .= .= M- . mm. Pull don on the Dpad typeE menu and select I.E s'uare pad ith .$E holeH hich gives us a little clearance. (Rou need to make the pad and hole large enough that it the part ill fit considering tolerances on pin dimension and placement, but if you you make the holes too big it ill be harder to solder the part in place --- a beginner should err on the side of making the hole too large).
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=. #epeat this process ith the other pad to make it I.E round round pad ith .$E holeH
. 2elect all the parts of the bu11er, group it as a component, component, and give the component part *6 DBKE to match the schematic. 2ave your component as Dbu11erE to use again later. (*f someone else has already completed the tutorial on this computer, the part may already e%ist, in that case you should either save this component ith a uni'ue name)
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7. "inally, e need to add in the battery, battery, hich is going to be connected by a battery strap to the circuit, and therefore re'uires only to pads (the battery ill lie off of the board). his is a good opportunity for for us to create a part from scratch. ?se the pad tool to place a pad ith the description I.;E s'uare s 'uare pad ith ./E holeH to be the positive battery lead.
7. !ake this pad correspond to pin for the battery battery by choosing it ith the select tool, and assigning it to be pin . 36
77. Create another pad, this time round, using the the description, I.;E round round pad ith ./E hole,H near the first pad, and assign it to be pin 7. hen select both pads, and group them to make a component. 9abel the component component ith the Part *6 DB.E 2ave the part as Dbattery strap connectionE in the component library.
78. 3o ("inallyS) e have all the components on on the board. Rou can no link in the schematic file. o do this, select D"ileE -J D9ink schematic to PCBTE 37
7$. 2elect your schematic file. Rou Rou should should then get a message like this4
7;. 3o if you select the net tool, and click on a pin, pin, 5%press PCB ill highlight all of the pins that should connect to that pin. "or e%ample, select the net tool and click on the M terminal of the battery, you should see something like this4
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Click on some of the other pins to check your ork and to get a sense of ho the parts ill connect. 7. 3o, e ant to arrange our components in a logical fashion. Rour goal is to minimi1e the length of connecting ires. Rou also ould ould like (ideally) to have a single ground plane on the back and all of other connections on the front surface, hich means that you ant to avoid having to cross ires over one another (this canHt alays be avoided). o rotate a component, right click on it and select the desired rotation. "or e%ample, here it might be nice to rotate #$4
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7/. #otate the transistor and arrange the other parts until your board looks like this4 this4
7=. 3o its time to dra in connection lines. >ne thing that you must consider hen draing connector lines is the the current capacity of the lines on on the board. ere are some general rules of thumb on line idths from the 5%pressPCB eb site4
.Q .8 Amps .;Q .$ Amps .7Q ./ Amps .7;Q . Amps .;Q 7. Amps .Q $. Amps .;Q . Amps
!ost of our circuits ill not dra more than mA, so any line idth should be acceptable. oever, if your circuit uses a component that dras a significant current, such as a motor, than you should err toards larger line idths.
9etHs begin ith the M< lines. ?se the net tool to highlight the M< net on your board. hen click on the ire tool and select the upper metal (red) layer, and a .E trace idth (this is overkill, but itHs a good habit to make the poer lines fat). Connect the M terminal of the battery to the top of the bu11er4 40
7. 3o connect to the other M< points in the circuit.
8. he potentiometer (#;) is a little close to the one poer poer connection, so rotate rotate it and shift it over4 41
8. 3o create the signal connections. ighlight the unconnected pin pin of the photoresistor ith the net tool, then select the iring tool and a .7;E .7;E line idth, and connect the photoresistor to the potentiometer as shon4
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87. Complete the connections and and repeat this process for the other other signal nodes in the the circuit. hen you get to #$, #$, you may notice that the component component ould be more easy to ire if it ere flipped, you can right-click on the component to accomplish this4
88. After all the signal lines are completed, your circuit should look look as follos (only the grounds are unconnected)4
8$. 3o for the the ground plane. 2elect the DPlace a filled planeE tool, hich is the the green tool right above the circle tool. 2ay >F to the informational message on the tool that 43
pops up, and then create a bo% that encompasses encompasses the entire circuit on the bottom layer of the chipNbut leaving a boundary of at least .7;E from the board edge. o do this, choose the green layer from the top bar, then click near the upper left corner of the board (at least .7;E from both boundaries). boundaries). Click again near the upper right cornerTat this point your display looks something like this4
8;. Continue don to the bottom right right corner and then to the bottom left corner. corner. hen right-click to end the bo%. Rour display should no look like this4
3otice ho there is a space around each pad in the layer. he idth of that space is controlled by Board Properties, under the D9ayoutE menu, and e set that at the largest possible si1e hen e started this process (in step 7).
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8. 3o e need need to make make our ground ground connections. ?se the netork tool to highlight the ground connections. connections. #ight-click on the ground pad for the battery. 2elect DBottom layer pad shapeE and then Dhermal pad to filled plane.E his ill link that pad to the ground plane. he thermal pad has some thermal isolation beteen it and and the rest of the plane, hich ill make it easier to solder later.
8/. #epeat this for all of the ground pads in your layout. Rour our layout should no look like this4
8=. "or your on circuit, you should also add your initials in an unused corner corner of the chip. 6o these initials in the top metal (red) layer rather than in the silkscreen (yello) layer, because if e use mini-boards, the silkscreen layer is not included. o add te%t, select the te%t tool, select the layer here you ant the te%t to appear, and enter the te%t in the bo% on the upper right. right. hen click on the layout to place place the te%t4 45
8. Carefully inspect your circuit board. ?se the layer visibility tools in the bottom left corner to turn off and on layers. layers. Koom in to check for connections. ighlight all of the pads ith the netork netork tool on to verify that they are correctly correctly connected. Print out your circuit and confirm that every connection specified in the schematic is present. ith circuit boards, you you definitely ant to measure tice and cut once. At this point, you ould be ready to submit the circuit.
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