PCB_MF

7.8 Tin Plating :Here tin is the most commfor printed circuits.The advantages are goodcontrol the process.

monly used plated finish solderability and easily

7.9 Gold PlatiGold is plated on edge co1) Low contact resistance2) High wear resistanceits customary to plate 5µ2.3µm,gold over a nickel

ing:onnector tabs to provideeµm gold over copper orl under coat of 4µm.





7.10 Nickel PlatingNickel is the most often ugold act as a barrier over to coincrease the wear resistancereducing the minimum gogiven application.

gused as a undercoat foropper migration as well as e of the coatingold deposit needed for a

UNIETCH

IT – 8HING

ETCHINselective removal of t

NGthe unwanted copper





8.1Etchants S1. Alkaline Ammoni2. Cupric Chloride E3. Ammonium Pers4. Ferric Chloride E5. Chromic Acid Etc

Solutions:- ia Etching Etching sulphate Etching Etching ching

8.2 Equipments and Te Etching techniques ahave evolved four basic meth 1. Immersion Etching 2. Bubble Etching 3. Splash Etching 4. Spray Etching

Techniques:-and the equipment used today hods.

8.3 TYPES OF E IMMERSION ETCHING: The PCB is immerseetching is complete it requires long procfactor in large quantity p Heating the etch solusome form speed up th This method is suitabof small or prototype bo

ETCHINGed in the solution untilcess time, and intolerable production.ution and agitation ofhe action. ble for laboratory etchingoards.





BUBBLE ETCHIN modified form of immers Air is bubbled through thbeing etched. Air passing through the s• It ensures the availabisurface and rinse away diss• It provides oxygen whioxidizing power and regpressure up to 2psi is used. EX:- Ammonium persulp

NG:sion etchinghe solution and past the work solution has two functions.ility of fresh etchant at thesolved metal. ich increases the additionalgenerating the etchant. Air .phate & chromic Acid etchant.





SPLASH ETCHING: Splash etching offers distincetching with regard to evennesundercut. few pieces only etch at a tim A large volume reservoir isto minimize solution replaceme The etch solution is pickeddriven shaft and thrown by cenbeing etch. Speed of shaft rotation andamount and force of solution co

: ct advantages over bubbless of etch and minimization of ime built in to the bottom of the tankent. up in a cup attached to a motorntrifugal force towards the boardsd cup design determine the oming in contact with the board.

SPLASH ETCHING SYSTE

EM WORK PIECE SPRAYING TUBE ACTIVE MEDIUM

SPRAY ETCHING Spray etching is the most co it is fast well suited to high pfine line definition. Spray etching techniques insided etching with either horizowork. the etchants is pumped undpipe networks to the nozzles anthe boards.

G: ommon method production and capable of verynclude the single and doubleontal or vertical positioning of theder pressure from the pump via nd from there gets splashed on to

 Spray etching machineetching uniformity and to a

es can offer very highfast etching rate.



JETS( FREEORMOVING)WORK PIECE TRANSPORTED ACTIVE MEDIUM

8.4FERRIC CHLORIDE used in small scale P In high volume prodnot much importance bregeneration and it attaetch resists.[Tin &Tin Le

E ETCHANT:PCB productionoduction ferric chloride isbecause it can hardly be acks the common metal ead].

8.5 CUPRIC CHLOR Cupric chloride can replaceetching print & etch type board Cupric chloride can be easidisposal and higher copper disgm/ltr) and no sludge formation -

RIDE ETCHANT:e ferric chloride in large scaleds ily regeneratability, easilyssolving capacity (up to 150n.

8.6 CHROMIC ACID Chromic acid etching is usuSulpuric acid, hence it is alsetching. It is widely used because of• its higher corrosiveness whmetal resist• fast etching rate with little u Chromic acid etchant is hihealth hazard, so it is not reco

D ETCHANT: ually carried out with addition of so called chromic Sulpuric acid f hich works well with all kind ofunder etching ighly toxic, heavy pollution and ommended.

8.7 ALKALINE AMMON Alkaline etching with the amhas found increased acceoperation compatibility with most mespecially solder minimum under cut high capacity for dissolved

NIA ETCHANT: mmonium hydroxide complexioneptancy owing to continuousmetallic and organic resist and copper and fast etch rate

UNIMECHANICA OPERA

IT-7AL MACHININGATIONS

9.1 INTRODUCTION:Laminate machining consprocesses by which circuit bvital chemical processes of IEtching. Such processes as cuttingshaping have major effectsprinted board.

sists of the mechanicalboards are prepared for the Image Transfer, Plating andg to size, drilling holes and on the final quality of the

9.2 PUNCHING HOLES (pieIt is possible to pierce holFR2 and paper Epoxy FR3 m By using the punch and D Always pierce with the coThey are for use where inrough-Quality holes.

ercing): les to the paper phenolicmaterialDie, Holes can be pierced. opper side upnspection standards permit