This document discusses the outputs and files generated during the electric circuit design and PCB manufacturing process. It describes: 1. The different types of outputs like assembly drawings, pick and place files, composite drawings, and reports. 2. The fabrication files and outputs used in the manufacturing process like composite drill drawings, Gerber files, and NC drill files. 3. The differences between artwork files used for PCB etching and Gerber files used for PCB milling. It provides details on the PCB etching and milling processes.

1. ELE 2573
Electric Circuit Design andPCB
Manufacturing

2. Fabrication files - outputs
Assembly Outputs
Assembly Drawings - component positions and orientations for each side of the board.
Pick and Place Files - used by robotic component placement machinery to place components onto the board.
Documentation Outputs
Composite Drawings - the finished board assembly, including components and tracks.
PCB 3D Prints - views of the board from a three-dimensional view perspective.
Schematic Prints - schematic drawings used in the design.

3. Fabrication files - outputs
Fabrication Outputs
Composite Drill Drawings - drill positions and sizes (using symbols) for the board in one drawing.
Final Artwork Prints - combines various fabrication outputs together as a single printable output.
Gerber Files - creates manufacturing information in Gerber format.
NC Drill Files - creates manufacturing information for use by numerically controlled drilling machines.
ODB++ - creates manufacturing information in ODB++ database format.
Power-Plane Prints - creates internal and split plane drawings.
Solder/Paste Mask Prints - creates solder mask and paste mask drawings.

4. Fabrication files - outputs
Report Outputs
Bill of Materials - creates a list of parts and quantities (BOM), in various formats, required to manufacture the
board.
Report Single Pin Nets- creates a report listing any nets that only have one connection.
Electrical Rules Check - formatted report of the results of running an Electrical Rules Check.

5. Fabrication files – artwork vs Gerber
There are various methods used to transfer a specific pattern on a blank PCB.
The two most used methods are etching and milling, therefore the fabrication files you generate must match the
technique used to manufacture the PCB.
Generally the associations are:
Artwork file <-> etching
Gerber file <-> milling

6. PCB Etching
Definition: a selective removal of material from the surface of a PCB by means of the chemical action of an
etchant (or etching agent).
Etching usually removes the copper areas which are not desired on the finished PCB.
Steps to be executed in order to fabricate a PCB using etching technique:
1. PCB Layout
The PCB layout is a mirrored positive one - black on white. Mirrored as viewed from the silkscreen top (component)
side. The PCB layout is printed 1:1 on a transparent substrate by means of a laser printer or a laser plotter.

7. PCB Etching
2. PCB Preparation
The copper surface of the PCB needs to be thoroughly cleaned and covered with a photoresist polymer. The
photoresist will change structure when exposed to UV light and will dissolve in a basic solution therefore exposing
the copper to be removed by the etching agent while the areas not exposed will be insulted thus will remain
unaffected.
There are two methods to cover the PCB with photoresist:
Dipping – PCB is dipped in a photoresist tank -> a thin layer will stick to the copper
Film deposit – a photoresist film is attached to the PCB under specific temperature and pressure conditions (much
like a paper film laminator)

8. PCB Etching
3. PCB UV Exposure
The protective plastic layer (if any) is removed from the photosensitive PCB.
The toner side of the transparent film layout is placed on the copper of the PCB. Captured air-bubbles are gently
pressed away from underneath the layout.
The PCB with the layout is covered with an appropriate sized windowpane and placed on a piece of plain
polished surface.
Three to four minutes 300W bulb UV exposure from a distance of 30-40 cm will do the photo transfer

9. Place layout with toner side on copper of the PCB
Cover PCB and layout
with window-pane
Exposure

10. PCB Etching
4. PCB Developing - The PCB is developed with a 1% solution of sodium hydroxide NaOH. Use a brush or a tank
agitator to speed up the developing process. The developing process takes about 1 minute.
This process will remove the photopolymer cover previously exposed to UV thus exposing the copper layer.
Gently brush the PCB
Almost developed, some traces are not clear yet clear

11. PCB Etching
5. PCB Etching
The developed PCB is etched with a 220 g/l solution of ammonium peroxydisulfate (NH4)2S2O8 a.k.a.ammonium
persulfate.
Theoretically it should be possible to etch slightly more than 60 grams of copper with 1 liter etching solution.
Assuming an 50% efficiency, about 30 grams of copper can be removed. Considering a 35 µm copper thickness on
your PCB this covers a copper area of about 1000 cm2.
Etching at ambient temperature might take over an hour, it is better to heat up the etching solvent to about 35-45
degrees Celcius.

12. Rock the etching tray The PCB substrate becomes visible Almost finished
Finished

13. PCB Milling
Printed circuit board milling (also: isolation milling) is the process of removing areas of copper from a sheet of
printed circuit board material to recreate the pads, signal traces and structures according to patterns from a
circuit board plan known as a layout file.
Similar to the more common and well known chemical PCB etch process, the PCB milling process is subtractive:
material is removed to create the electrical isolation and ground planes required. However, unlike the chemical
etch process, PCB milling is typically a non-chemical process and as such it can be completed in a typical office
or lab environment without exposure to hazardous chemicals.
In the case of PCB milling, the quality of a circuit board is chiefly determined by the system's true, or weighted,
milling accuracy and control as well as the condition (sharpness, temper) of the milling bits and their respective
feed/rotational speeds.
By contrast, in the chemical etch process, the quality of a circuit board depends on the accuracy and/or quality
of the photomasking and the state of the etching chemicals.
The mechanics behind a PCB milling machine are fairly straightforward and have their roots in CNC milling
technology. A PCB milling system is similar to a miniature and highly accurate NC milling table.
XY axis - The mechanics behind a PCB milling machine are fairly straightforward and have their roots in CNC
milling technology. A PCB milling system is similar to a miniature and highly accurate NC milling table.
Z-axis drive and control are handled in several ways. The first and most common is a simple solenoid that
pushes against a spring. High accuracy control of Z axis is however achieved using a stepper motor
NOTE: One of the major challenges with milling PCBs is handling variations in flatness.

14. PCB Milling
Tooling
PCBs may be machined with conventional endmills, conical d-bit cutters, and spade mills.
Engraving V bit
Drill bits
End mill

15. PCB Milling
The biggest challenge in this DIY process is getting a correct and consistent cutting depth.
The V-bits yield a wider cut the deeper you go, effectively robbing you of precious engraving resolution. If you do
not tune in just the right depth, some traces will come out too thin and frail.

16. Isolation Milling Drilling Cut out