pcb design rule
TRANSCRIPT
-
7/28/2019 PCB Design Rule
1/43
http://s653.photobucket.com/albums/uu259/rockc4/FanLED/?action=view¤t=mat_1-Copy.png -
7/28/2019 PCB Design Rule
2/43
Cu lc bNghin Cu Khoa Hc Khoa in in t
-
7/28/2019 PCB Design Rule
3/43
Many PCB designers like to think of PCB layouts as
works of art
It is, however, quite difficult to try and teach
PCB design It is like trying to teach someone how
to paint a picture.
apart from that PCB design is a highly creative
and individualprocess.
-
7/28/2019 PCB Design Rule
4/43
These standards are controlled by the former
Institute for Interconnecting and Packaging
Electronic Circuits IPC(www.ipc.org).
The major document that covers PCB design is
IPC-2221, Generic Standard on Printed Board
Design
-
7/28/2019 PCB Design Rule
5/43
you MUSThave a complete and accurate
schematic diagram.
Place notes in Schematic.
i.e. this track should be as short as possible (ASPS-
rule)
putting bypass capacitors next to the component
Your schematic really should be drawn with the
PCB design in mind.
-
7/28/2019 PCB Design Rule
6/43
Imperial and Metric
you should always use imperial units (i.e.
inches)
A thou ( /a/), also known as a mil, is the
verbalized abbreviation for "thousandth(s) of
an inch
Whatever you have to do in PCB design youll
need to become an expert at imperial to
metric conversion, and vice-versa.
http://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_English -
7/28/2019 PCB Design Rule
7/43
Imperial and Metric
100 mils = 0.1 inch = 2.54 mm
50 mils = 0.05 inch = 1.27 mm
1 pitch = 1 inch
i.e. 0.1 pitch pin spacing
-
7/28/2019 PCB Design Rule
8/43
Imperial and Metric
Use mils (thous) for tracks, pads, spacings and grids,
which are most of your basic design and layout
requirements.
Only use mm for mechanical and manufacturing
type requirements like hole sizes and board
dimensions.
-
7/28/2019 PCB Design Rule
9/43
4. Snap Grids
Lay out your board on a fixed grid
Standard placement grid: 100 mils
For finer routing and placement: 50 25 20 10 5
Dont use anything else, youll regret it.
-
7/28/2019 PCB Design Rule
10/43
5. Visible Grid
Most common: 100 mils visible grid
-
7/28/2019 PCB Design Rule
11/43
6. Component Grid
Snap grids your PCB designs will be
one step closer to being neat and
professional.
-
7/28/2019 PCB Design Rule
12/43
7. Tracks
Track size depend on:
Electrical requirements
Routing spaceClearance
Your own personal preference
The bigger the track width, the better
-
7/28/2019 PCB Design Rule
13/43
7. Tracks
The bigger the track
width, the better!
keep tracks as big aspossible, and then to
change to a thinner track
only when required to
meet clearance
requirements.
-
7/28/2019 PCB Design Rule
14/43
7. Tracks
The thickness of the copper on the PCB: is nominally
specified in ounces per square foot, with 1oz copper
being the most common. Other thicknesses like0.5oz, 2oz and 4oz.
Required track width based on the current and the
maximum temperature rise.
-
7/28/2019 PCB Design Rule
15/43
7. Track width vs. Current
-
7/28/2019 PCB Design Rule
16/43
8. Pads
The pad should be at least 1.8 times the diameter of
the hole, or at least 0.5mm larger.
Pin 1 of the chip sould always be a different pad
shape, usually rectangular (square).
Most SM components use rectangular pads (R,C,),although surface mount SO package ICs should use
oval (oblong) pads. Again, withpin 1 being
rectangular.
-
7/28/2019 PCB Design Rule
17/43
8. Pads
-
7/28/2019 PCB Design Rule
18/43
9. Vias
Vias connect the tracks from one side of
your board to another, by way of a hole in
your board.
Holes in vias are usually a fair bit smaller
than component pads, with 0.5-0.7mm
being typical.
Use vias as less as possible!
-
7/28/2019 PCB Design Rule
19/43
10. Polygons
Copper Pour, Copper Area
Solid vs. Hatched
Make sure youplace polygons after you
have placed all of your tracks and pads.
-
7/28/2019 PCB Design Rule
20/43
11. Clearances
At least 15 mils is a good clearance limit
for basic through hole designs.
10 or 8 mils clearance for SMD layout.
Be careful with HV on board.
(i.e. 315mils (8mm) for 240V tracks and signal tracks)
-
7/28/2019 PCB Design Rule
21/43
11. Clearances
-
7/28/2019 PCB Design Rule
22/43
Set snap grid, visible grid, and default track/pad sizes.
Throw down all the components onto the board.
Divide and place your components into functional building
blockswhere possible.Identify layout critical tracks on your circuit and route them
first.
Place and route each building block separately, off the board.
Move completed building blocks into position on your main
board, route the remaining signal and power connectionsbetween blocks.
Do a general tidy upof the board.
Do a Design Rule Check.
Get someone to check it
12. Component Placement
-
7/28/2019 PCB Design Rule
23/43
Your components should be neatly lined up.
i.e. ICs in the same direction, resistors in neat columns,
polarised capacitors all around the same way, and connectorson the edge of the board.
Digital and analogjust do not mix, and will need to be
physically and electrically separated.
High frequency and high current circuits do not mix with
low frequency and low current sensitive circuits.
12. Component Placement
-
7/28/2019 PCB Design Rule
24/43
12. Component Placement
If you have placed your componentswisely, 90% of your work will be done.
-
7/28/2019 PCB Design Rule
25/43
13. Basic RoutingSome basic routing rules:
Keep nets as short as possible.
Tracks should only have angles of45 degrees.
Snake your tracks around the board, dont just go
point to point.
Always take your track to the center of the pad,
dont make your track and pad just touch.
-
7/28/2019 PCB Design Rule
26/43
13. Basic RoutingSome basic routing rules:
Only take one track between 100 mils pads unlessabsolutely necessary.
Only one large and very dense designs should you
consider two tracks between pads.
For high currents, use multiple vias when going
between layers.
-
7/28/2019 PCB Design Rule
27/43
13. Basic RoutingSome basic routing rules:
Neck down between pads where possible.If your power and ground tracks are deemed to be
critical, then lay them down first.
Also, make yourpower tracks as BIG as possible.
Keep power and ground tracks running in closeproximity to each otherif possible, dont send them
in opposite directions around the board.
-
7/28/2019 PCB Design Rule
28/43
13. Basic Routing
-
7/28/2019 PCB Design Rule
29/43
13. Basic Routing
-
7/28/2019 PCB Design Rule
30/43
13. Basic Routing
Some basic routing rules:
Dont leave any unconnected copper fills (also called
dead copper), ground them or take them out.
-
7/28/2019 PCB Design Rule
31/43
14. 2-Layer Routing
Do not place vias under components.
Try and use through hole component legs to connecttop tracks to bottom tracks. This minimises the
number of vias.
Use as less vias as possible
SMDs are always better than leads components!
-
7/28/2019 PCB Design Rule
32/43
15. Finishing Touches
If you have thin tracks
(
-
7/28/2019 PCB Design Rule
33/43
15. Finishing Touches
Check that you have any required mounting
holes on the board. Keep mounting holes well
clear of any components or tracks. Allow roomfor any washers and screws.
-
7/28/2019 PCB Design Rule
34/43
15. Finishing Touches
Minimise the number of hole sizes. Extra hole sizes
cost you money.
Double check for correct hole sizes on all yourcomponents.
Nothing is more annoying than getting your
perfectly laid out board back from the manufacturer,
only to find that a component wont fit in the holes!This is a very common problem, dont get caught
out.
-
7/28/2019 PCB Design Rule
35/43
15. Finishing Touches
Minimise the number of hole sizes. Extra hole sizes
cost you money.
Ensure that all your vias are identical, with the
same pad and hole sizes. Remember yourpad to
hole ratio.
-
7/28/2019 PCB Design Rule
36/43
15. Finishing Touches
Check that there is adequate physical
distance between all your components.
Watch out for components with exposed
metal that can make electrical contact
with other components, or exposed
tracks and pads.
Add teardrops to all your pads and vias.
-
7/28/2019 PCB Design Rule
37/43
16.Silk Screen Layer
Silk Screen Layer (SSTOP, SSBOT): contains your
component outlines, designators (C1, R1 etc), and free
text.
Make sure that you keep all your component
designators the same text size, and oriented in the
same direction.
Make sure that you add a component overlay that
reflects the actual size of your component.
-
7/28/2019 PCB Design Rule
38/43
16.Silk Screen Layer
Ensure that all polarised components are marked,
and that pin 1 is identified.
Ensure that no part of the silkscreen overlaps a bare
pad.
As a general rule, dont put component values onthe silkscreen, just the component designator
(but)
-
7/28/2019 PCB Design Rule
39/43
17. Solder Mask
Solder Mask Layer (SMTOP, SMBOT):
The solder mask typically covers everything exceptpads and vias.
The gap it leaves between the pad and the solder
mask is known as the mask expansion.
-
7/28/2019 PCB Design Rule
40/43
18. Other Layers
The mechanical layer is used to provide an outline
for your board, and other manufacturing instructions.
Keepout
The keepout layer generally defines areas on your
board that you dont want auto or manually routed.
This can include clearance areas around mounting holepads or high voltage components for instance.
-
7/28/2019 PCB Design Rule
41/43
Auto Tool
Auto Route
Real PCB designers dont auto route!
Artificial intelligence and neural based technology are
some of the marketing buzz words used, but no matterhow smart an auto router is, it simply cannot replace
a good human PCB designer.
Auto Placement
Professional PCB designers do not use Auto Placement
tools. Dont rely on the Auto Place feature to select the
most optimum layout for you. It will neverwork!
-
7/28/2019 PCB Design Rule
42/43
References
[1] PCB Design Tutorials David L. Jones
[2] wikipedia.org
-
7/28/2019 PCB Design Rule
43/43