Friday, March 23, 2012

PCB from scrach



INTRODUCTION

A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board (PWB) or etched wiring board. A PCB populated with electronic components is a printed circuit assembly (PCA), also known as a printed circuit board assembly or PCB Assembly (PCBA). Printed circuit boards are used in virtually all but the simplest commercially produced electronic devices. The credit goes to Arthur Berry in 1913 patented a print-and-etch method in Britain.


 Printed Circuit Board (PCB)

MATERIALS

Conducting layers are typically made of thin copper foil. Insulating layers dielectric are typically laminated together with epoxy resin prepreg. The board is typically coated with a solder mask that is green in color. Other colors that are normally available are blue, black, white and red. There are quite a few different dielectrics that can be chosen to provide different insulating values depending on the requirements of the circuit. Some of these dielectrics are polytetrafluoroethylene (Teflon), FR-4, FR-1, CEM-1 or CEM-3.

 Ferric Chloride (FeCl3) available in Indian market.

PATTERNING (ETCHING)

The vast majority of printed circuit boards are made by bonding a layer of copper over the entire substrate, sometimes on both sides, (creating a "blank PCB") then removing unwanted copper after applying a temporary mask (e.g., by etching), leaving only the desired copper traces. A few PCBs are made by adding traces to the bare substrate (or a substrate with a very thin layer of copper) usually by a complex process of multiple electroplating steps. The PCB manufacturing method primarily depends on whether it is for production volume or sample/prototype quantities. Double-sided boards or multi-layer boards use plated-through holes, called vias, to connect traces on either side of the substrate.

CHEMICAL ETCHING

Chemical etching is done with ferric chloride, ammonium persulfate, or sometimes hydrochloric acid. For PTH (plated-through holes), additional steps of electroless deposition are done after the holes are drilled, then copper is electroplated to build up the thickness, the boards are screened, and plated with tin/lead. The tin/lead becomes the resist leaving the bare copper to be etched away.

 Ferric Chloride (FeCl3) solution in a plastic tray.

The simplest method, used for small-scale production and often by hobbyists, is immersion etching, in which the board is submerged in etching solution such as ferric chloride. Compared with methods used for mass production, the etching time is long. Heat and agitation can be applied to the bath to speed the etching rate. In bubble etching, air is passed through the etchant bath to agitate the solution and speed up etching.

METHOD WE USE

Laser-printed resist: Laser-print onto transparency film, heat-transfer with an iron or modified laminator onto bare laminate, touch up with a marker, then etch. 

 Step1: Pattern created using EAGLE CAD software.

Pattern created using CAD tools.

             Step 2: Creating impression on the Copper Clad board using Heating Iron.


             Step 3: Redrawing the tracks using a corrosion resistant paint.
 
            Step 4: Immersing in a FeCl3 solution to remove exposed copper. See this video to get more elaborated idea.

PCB etching in FeCl3 Solution.

DRILLING

Holes through a PCB are typically drilled with small-diameter drill bits made of solid coated tungsten carbide. Coated tungsten carbide is recommended since many board materials are very abrasive and drilling must be high RPM and high feed to be cost effective. Drill bits must also remain sharp so as not to mar or tear the traces.

  Fixing PCB on a wooden board.

Drillers and shaping tools i used to drill holes.

Drilling with high-speed-steel is simply not feasible since the drill bits will dull quickly and thus tear the copper and ruin the boards. The drilling is performed by automated drilling machines with placement controlled by a drill tape or drill file. These computer-generated files are also called numerically controlled drill (NCD) files or "Excellon files". The drill file describes the location and size of each drilled hole. These holes are often filled with annular rings (hollow rivets) to create vias. Vias allow the electrical and thermal connection of conductors on opposite sides of the PCB.

DESIGN

Printed circuit board design was initially a fully manual process, where an initial schematic diagram was converted into a layout of parts, then traces were routed between package terminals to provide the required interconnections. Pre-printed non-reproducing mylar grids assisted in layout, and rub-on dry transfers of common arrangements of circuit elements (pads, contact fingers, integrated circuit profiles, and so on) helped standardize the layout. The finished layout "artwork" wash then photographically reproduced on the resist layers of the blank coated copper-clad boards.

You can use a Layout edited CAD software to design the PCB layout. Here is the software that i used.
The whole document in PDF format is here Download full PDF



 

1 comment:

  1. This is one of the most incredible blogs I have read in a very long time. Your blog is great for anyone who wants to understand this subject more. Great stuff.
    Flexible PCB

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