PCB_MF

SIGNAL COUPLING AT HIGH FRCROSS TALKHigh frequency electrical signalradiate energy. When energy isEMI: When energy is radiatecalled Electro magnetic interf

REQUENCIES:ls generate electric fields that coupled to a near by circuit.ed to the environment, it is ference (EMI).

4.10 SKIN EFFECT :The skin effect is the result offorce high frequency currents toAs the frequency of the signathe conducting “Skin” decreaseincreases.

:f self inductive effects that o the surface of a conductor.al increases. The thickness ofes and the DC resistance

4.11 Solder MaskProtects the circuit board fromThe solder resistant (liquid reon the circuit boards after etchitechniques and photo printing t

m the atmospheric corrosionesist or dry film resist) coated ing by screen printing techniques.

4.12 LEGEND PRINTSILKSCREEN :The silkscreen layer is also knoIt is the layer on the top of ththat contains component outlinand free text which helps in assThe legend can be added to atechniques.

TING OF own as “TOP OVER lay”.he PCB (and bottom if needed) nes and designators (R1,C1. Etc) sembly of PCB. a PCB using a screen printing





White is a standard colorKeep all your component desioriented in the same directionsEnsure that all polarized comppin 1 is identified

ignators the same text size ands.ponents are marked and that

4.13 GRID SYSTEM :A grid is a two dimensional rereproduced on paper or vinyl glguide for layout drawing.Precision grids on glass or polindustrial applications.Less accuracy grids are printefor experiments.

:ectangular pattern when lass that can be used as a lyester films are used ined on paper and generally used





4.14 General rules for PCBdouble sided PCBConductor routing practiceIn double sided PTH board runthe y co-ordinate directionIn solder side the conductor decomponent side.Distribute max no. of conductoof the conductors in the compo

B design for es. n the conductor on one side in ensity will be more than ors on the solder side and restonent side.

In both sides of the conductordielectric material as a capacitoDue to soldering, IC’s like heardestroyed easily so IC bases areThe sharp internal bending ofmore than 90oConductor forming sharp interavoided

rs are in same axis, it acts as aor.r sensitive components can bee provided. the conductors should bernal angles of 90o must be

If the bending is less than 90ospikesIf the angle is less than 90o somdeposited may not get removedconductors may get corroded e

they will act as an electricalme chemicals, which ared while cleaning. So theeasily.





Minimum spacing between thconductors:It is based on the cross talkIt is based on the breakdown

he parallel voltage

Cross talk : The min. spacing between tw 0.5mm The min spacing between tw

wo parallel conductors iswo solder pad is 0.4mm.

4.15 Component Placemen1)Line spacing based on B voltage.Less than 45v445-80V80-150v150-250vFor AC mains < 250v.

nt, Ground PlanBreak down 0.3mm 0.4mm 0.6mm 1.0mm 3.0mm

(2) Components placeIn a highly sensitive circuit, thplaced and also in such a mannthe critical conductorsIn a less critical circuit distribuorder of signal flow so as to reqinterconnecting length

ementhe critical components are firstner as to require min. length for ute the components as per thequire the shortest

3)Components holeIn the PCB any component leathe hole of a appropriate diameTotal Clearance - 0.2Hole dia= Effective lead Total clearan PTH thicknes

e diameter.ad should be fitted only intoeter.2 to 0.5mmd dia (+)ncess

3)Pad Diameter for doublethe width of the Annul ring shpreferably more. A solder pad diameter is appthe drilled hole diameter.The conductor width should apad diameter, but preferably ab

sided PCB’should be at least 0.5mm butproximately 2.5 to 3 times ofalways be less than the solderbout one third

Pad dia = Hole dia + 2 (widthExample :For : 1.0mm lead dia(3 times) 3.0mm = 1.3mm +(2.5 times) 2.5mm = 1.3mm

h of Annular ring)2(0.85)+ 2(0.6)

UNIBOARD CLEAN PATTERN T

IT:5NING BEFORETRANSFER

5.1 PATTERN TRANFER:The generation of the patternfilm on to a copper or other meThe fabrications of PCB, Therethe pattern from the Photograp1. Photo printing process2. Screen printing processBefore going to transfer the pshould be free from oil, dust, grforeign particles.

n from artwork or Photographicetal clad laminate.e are two methods to transferphic film to the laminate.pattern on to the laminate, itrease, the finger print and

5.2 ORGANIC SOILS:Possible sources causing contequipment used for shearing, dThe air from the air compresssolutions for such equipment. Itsuitable solution or solvent.

tamination could be thedrilling, punching.sor or contaminated cleaning t can be degreased with a

5.3 METALLIC SOIL:Metallic soils are mainly oxidethe copper surface caused by atmospheric attackpoor rinsing and drying.

es and corrosion products onk and residuals remains after