GERBER ANALYSIS
Gerber Analysis is required for
1. DFM - Design for Manufacturability
2. DFA - Design for Assembly
3. DFT - Design for Testability
4. DFS - Design for Suitability for Servicing and repairing
** General consideration for PCB design suitable for meeting this requirement.
1] DFM – DESIGN FOR MANUFATURABILTY
Design consideration points.
1. PCB Instruction Files - It should be required with PCB Gerber file. It must consist of
PCB part number, Part name, Revision number,
Required Layers,
Board Thickness,
Solder Mask whether it is on Top side, Bottom side or both Side,
Solder Mask colour (generally Green but sometime we use RED masking),
Legend Colour (generally White but may be Black if necessary),
Information about Penalization (if required with size and Array size),
Requirement of UL logo on PCB in to legend layer on each PCB.
2. All Gerber Files with require layers. - There is requirement for Gerber files with
following Layer.
TOP layer - C.PHO
BOT layer - S.PHO
TOP Legend - CI.PHO
BOT Legend - SI.PHO
TOP Mask - SI.PHO
DRILL DRAWING - DR.PHO
NC DRILL - DR.DRL
(All above layer is required for double sided PCB, but if Single sided PCB is
required, there is minimum 2 files (top legend and Bot route is required with drill files) are
usable.
3. All PCB manufacturing consideration should be done as per requirement by
manufacturing capability of Manufacturer. It includes PCB size [ maximum or
minimum], PCB shapes (It may be regular or as per require by Engineering
Department), Minimum Trace width, minimum spacing between two nearest traces,
minimum spacing between two drills, minimum spacing between PADS or Vias,
minimum spacing of traces with PADS, Vias, drilling etc., Copper pouring with
minimum clearances, required minimum Legend text size.
[ All this design consideration are checked by PADS design software and
verified by respective PCB manufacturer. All this points are verified and validated by
manufacturer and labelling BBT OK sticker or marking on PCB].
2. DFA - DESIGN FOR ASSEMBLY
PCB assembly is mostly important, time consuming and expensive process, so
to avoid the assembly rework DFA is very important. There are many consideration pointes
for DFA but some points are mostly important.
1. Matching of PCB PADS with SMD components
2. Component marking and identification should be clear and accurate.
3. Suitable Foot prints of Components with required PAD size, PAD shape, Drill size.
4. Legend Text should clear. Reference designator for components should be clear
and readable.
5. Suitable Drill holes required for TH components
6. Thermal relief applicable to components PADs.
7. Requirement of Fiducial point. It should be required minimum three fiducial point
for PCB (It may be single PCB or PANEL). If not possible minimum 2 Fiducial point
is necessary.
8. Checking of possibility of Penalization of PCB.
9. Checking PCB connector position is suitable for Housing, avoiding unnecessary
length of Cables, Mounting Holes position, required minimum spacing of
Components from mounting Holes, Checking fitments of PCB with proper
arrangement
** The Gerber Analysis point done by PADS VX2.3 Software are follows.-
10. All components should be placed with suitable distance. So that soldering and
rework process will do properly.
11. Requirement of minimum annular ring for PADS and Vias. Or required for specially
manufactured component.
12. Vias should be keep suitable distance from pads of component. It may be on PAD
sometime if design made for HIGH Frequency circuit. In this case Via will be on
PAD to avoid increase in trace length.
13. Board Edge clearance - There is required sufficient board edge clearance for
components. For Components it should be on 2.54mm, For Trace it should be 1
mm and drill it should be 2.54 mm. It may be varying as per PCB components
density and circuit design requirement.
3. DFT - DESIGN FOR TESTABILTY
1. All test point should be easily accessible.
2. It should be maintaining minimum distance from one test point to another.
3. Size of Test Point is suitable for placing terminal for multimeter or testing
instrument.
4. Position of Testing points - It should be outside of PART outlines.
5. Special TEST points - Test points which is very important and required regularly
for testing instruments. [ e.g. at GND net]
4. DFS - DESIGN FOR SERVICING AND REPAIRING PURPOSE
1. PCB should be easily Accessible when open the housing.
2. PCB assembly should be clearly identified by blocks easily.
3. Polarity of components should be easily understandable.
4. Pin 1 marking for IC should be clearly noted for IC.
5. PCB wiring should be easily & identifiable by noting number or colour code.
