PCB_MF

3.8 Double Sided PCB DesiRequirementused when a large no. of comounted on one printed cirThe conductor paths are disof the board and are intercomounting holes

ignomponents are to bercuit board.stributed on both sidesonnected by component





The following should be obs1. Two layouts are required, onefor the bottom. Components ar2.The conductor paths are distrthe PWB.3.The conductor paths on the compothe body of the axial lead componencomponents, some space will be givecomponent and the PWB.

servede for the top side and onere mounted on the top side.ributed along both sides ofonents side can be routed undernts. While mounting theen between the body of the

4.Heat sinks, metal transistor camaterial should be mounted wepaths to avoid short circuits.5.Each component lead must haon the top and on bottom layouconnection can be make througand bottom pads must be align

ases or other conductive ell away, from conductor ave its mounting pad both uts, so that the electricalgh the PTH. In all these, topned.

3.9 Wave Solderin Component leads are solderby travelling at a predeterminedof molten solder.Wave soldering is the most wsoldering components to printe

ng : red to a printed circuit board d rate of speed through a wavewidely used method for ed circuit boards





.There are cost savings becaus1.Hand soldering is more work2.There is reduced inspectionthat every joint is soldered un3.There is reduced scrap which boards with soldering iron.4.There is the reduced possibi

se : k than wave soldering time because of knowledgender identical conditions. h would result from burningility of vapor or flux entrapment

. 5.The actual soldering tome p extremely short because of t conditions, the fast circulatio heating of the board, as it tra across the solder wave surfac

per solder joint isthe excellent heat transferon of solder and the pre-avels through the solderce

Fig.:Basic wave soldering machConveyor moves P.along wave solder

hineP.W. assembly system.





3.10 Reflow SolderingScreen Printing :In reflow soldering, primarily ussolder paste is forced through ametallic or polymeric squeeze. T& flux.

gsed for SMD components,a metal stencil by either a The paste contains both solder





Pick and place:After screen printing the boarplace machines were they are pMost SMDs are usually deliveeither paper or plastic tubes. Soare delivered in static free traysNumerical control pick and plfrom the tapes, tubes or trays a

rds then proceed to the pick &placed on a conveyor belt.ered to the production line inome large integrated circuitss.lace machines remove the partand place them on the PCB.





Reflow soldering:The boards are then conveyedoven.They first enter a pre-heat zonthe board & all the components The boards then enter a zonehigh enough to melt the solder.

d into the reflow solderingne, where the temperature ofs is gradually, uniformly raised.e where the temperature is.





3.11 SMT TECHN high degree of automatio greatly increasing produc manufacturers components are mounted boards The components as ‘surfa (SMDs)

NOLOGY on reducing labour cost ction rates for d onto the surface of the ace mount devices’

WHY IS SMT PREFERREDAdvantages of SMD:1.it’s faster for automatic machin2. Has a smaller physical size for3.Less parasitic(unwanted ) effec4. Parts are cheaper

D? nes to place r the same electrical function cts

Disadvantages of SMD:1- Manual prototype assembly or cdifficult2-SMDs cannot be used directly wi3-SMDs' solder connections may bcompounds going through thermal4- SMT is unsuitable for large, highfor example in power circuitry.5-SMT is unsuitable as the sole attcomponents that are subject to fre

component-level repair is more ith breadboardsbe damaged by potting l cycling. h-power, or high-voltage parts, tachment method forequent mechanical stress

SMT COMPONENTS:TRANSISTORS AND DIODES•small outline transistors’ (SOT)Eg.SOT23,SOT223INTEGRATED CIRCUIT PACKAGESSOIC (small out-line integrated circuitTSOP (thin small outline package)SSOP (shrink small outline package)TSSOP (thin shrink small out-line packPLCC (plastic leaded chip carrier)

ts)kage)

IC’S



UNLAYOUT P

NIT 4PLANNING

4.1 GENERATION OFBefore starting your layout desifollowing information from cust•Circuit diagram (schematic diag•Size & Type (S/S,D/S or MLB)•Component specification (mec•Equipment specification (ventiPCB).

F DESIGNign, designer should collect thetomergram)chanical size, values codes. Etc)ilation, view place for fixing

LAYOUT DESIGNTransition of circuit diadesign (Task of the des

agram into the layoutsigner)

Definition : Layout design is thecomponents and copperwhich are interconnectecomponents within the s

e sketch of outline ofr conductor routings,ed the respectivespecified area of PCB.