After properly aligning films on the photoresist laminated board, the board is
exposed by a UV light on both sides in the UV exposure unit.
The exposed board is developed in a spray developer unit. The developer solution is sprayed on both sides of the board by a spray rotating system. Afterwards the rest of the non‐exposed laminate is removed by a rinsing process, whereas the exposed laminate is etch resistant and thus protects the circuit pattern against etching
In that process the UV nonexposed copper is etched. Afterwards the etch resistant
material over the tracks, pads of PCB is rinsed by means of a solvent attack.
Solder resist masking/Legend printing (optional)
In our lab this is done manually by screenprinting process.
A. OVERALL GUIDELINES (SUMMARY )
Maximum PCB size which can be fabricated: 10 inches x 12 inches
Minimum PCB size which can be fabricated: 3 inches x 2 inches
Maximum track width possible: 100 mil
Minimum track width possible: 8 mil
Minimum clearance required for perfect plot: 8 mil
B. DETAILED GUIDELINES FOR PCB JOB ORDER
B.1 Pad dimension requirements
Inner diameter is 33 mil minimum. Higher values will automatically be mapped to nearest hole drill bit available. Must be at least 4 mil greater than component lead
diameter to allow considerations for minimum copper plating thickness in the hole.
Outer diameter is 55 mil minimum and an integer values thereafter.
Differencebetween inner diameter and outer diameter must be 20 mil minimum to ensure good copper area for soldering. This also applies to those footprints which
have been specially created for the purpose by the designer. For SMDs, the standard pad size specified by the component manufacturer may be used.
B.2 Via requirements
Inner diameter is 24 mil minimum to ensure correct feedthrough. Outer diameter is 40 mil minimum.
B.3 Fill requirements
Copper fills for power planes need to be created with basic blocks of squares of thefollowing dimensions: blocks of sizes 10 mil to 100 mil in steps of 5 mil; blocks of
sizes 100 mil to 200 mil in steps of 10 mil. Considerable overlapping between these building blocks is necessary to ensure no visible gaps in the photo plot.
B.4 Maximum primitive dimension
The photoplotter at PCB fab facility, IIT Kanpur can accept and plot aperture sizes up
to 100 mil. So the designer might take this into consideration before designing the
PCB. If any dimension higher than this is needed, he/she might have to use some
basic primitives. For example, if a track of 150 mil is required, a 100 mil track and a
55 mil track can be placed side by side with a 5 mil overlap to get a 150
B.5 Hole drill bits available at the facility
78.70 mil (2.0 mm), 62.99 mil (1.6 mm), 51.18 mil (1.3 mm), 39.37 mil (1.0 mm), 35.43 mil
(0.9 mm), 31.49 mil (0.8 mm), 27.56 mil (0.7 mm), 23.62 mil (0.6 mm), 19.69 mil (0.5 mm)
118.11 mil (3.0 mm), 59.06 mil (1.5 mm), 51.18 mil (1.3 mm), 43.31 mil (1.1 mm), 39.37 mil
(1.0 mm), 35.43 mil (0.9 mm), 31.49 mil (0.8 mm), 27.56 mil (0.7 mm), 23.62 mil (0.6 mm)
78.70 mil (2.0 mm), 39.37 mil (1.0 mm), 15.75 mil (0.4 mm),7.87 mil (0.2 mm), 5.91 mil
B.6 Solder Masking/Legend Printing Facility: Available on request
B.7 Copper thickness on board
Single layer: Options of 1.38 mil (35 microns) with a board thickness of 62.99 mil (1.6
mm) and 2.76 mil (70 microns) with a board thickness of 94.49 mil (2.4 mm) are
available. Board material is Glass Epoxy or Paper Phenolic.
Double layer: Options of 1.38 mil (35 microns) and 0.67 mil (17 microns) both with a
board thickness of 62.99 mil (1.6 mm) are available. Board material is Glass Epoxy
C. Basic PCB Design Issues
IIT Kanpur PCB Design Guide Sheet Page 23 of 26
The designer can use auto‐route tools of the PCB design software he/she is using.
But care must be taken that all dimensions are of integer values. Usually the designer
can restrict the auto‐route tool to use only integer dimensions by setting design rules
for the PCB. It must also be ensured to keep outer most layer, a little larger in
dimension than the actual board. A mechanical layer called ‘Mechanical Layer 4’
showing the actual dimensions of the board must be incorporated. This helps the
fabricator to correctly use the CNC machine for drilling holes into the PCB. The origin
of the PCB dimensions must also be set a little far, diagonally from the left bottom
corner of the board. Please refer to the documentation of the PCB design software
used for further information.
The PCB design name must also be mentioned either on the top layer or the bottom
layer for a dual layered PCB. The text placement tool of the concerned PCB design
software can be used. It is a good practice to make sure that the name of the file
which contains the PCB design represents the PCB design very closely
D. Recommended CAD Software
Altium Protel DXP Suite 2004
Note: If DXP 2004 is being used, please ensure that the .PCBDOC file is exported to
PCB Version 4 Binary format (.PCB file) before ordering the PCB. The file which
results due to the export must be directly sent to PCB fab for processing. Opening
this file in DXP again could result in problems with the existing procedure .
Note: Please send only the final PCB file while ordering .
E. Ordering, Fabrication and Delivery
The final file required for fabrication must be submitted in the PCB Lab after filling up
the PCB job order form The process might result in delivery periods of 2‐3 weeks for
normal PCBs and 3‐4 weeks for PCBs with green masking and legend printing.
These times may vary a bit depending on the queue pending at the facility and
the process conditions of the PCB. Single layer PCBs will be delivered in less than 2
weeks time. PCB fabrication is a time and resource consuming process and hence is
done with utmost care. Any complaints regarding the PCB fabrication and quality
may directly be addressed to the PCB fabrication facility in charge
F. Glossary of terms
Footprint : The pattern and space on a board taken up by a component.
Clearance : The spacing required between two entities on a PCB to ensure safe
Photoplotter: ( also “vector plotter”, or “Gerber photoplotter” after Gerber Scientific
Co., which built the first vector photoplotters for commercial use). It plots images
from a CAD database on photographic film in a darkroom by drawing each line with a
continuous lamp shined through an annular‐ring aperture, and creating each shape
(or pad) by flashing the lamp through a specially sized and shaped aperture.
Gerber File : Data file used to control a photoplotter. Named after Gerber Scientific
Co., who made the original vector photoplotter .
Aperture: An indexed shape with a specified x and y dimension, or line‐type with a
specified width, used as a basic element or object by a photoplotter in plotting
geometric patterns on film. The “apertures” are thin trapezoidal pieces of plastic
which are mostly opaque, but with a transparent portion that controls the size and
shape of the light pattern passing through it.
Track : Besides its usual definition of a strand of conductor, wire on a printed board
also means a route or track .
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