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Schematic Layout Tips
What we hope to achieve with this page and the PCB Design Tips page is a resource to help people get started in schematic and PCB layout.
If you would like to help this resource to grow please send your advice to tips@blackstick.co.uk and we will add it into this page.
Learn about:
Flow Annotation Decoupling Power Junctions Critical Signals Component Notes
Flow:
A well laid-out and documented schematics will save time and reduce possible problems.
We generally keep the flow as "inputs at the left of the page and outputs on the right". This makes the design much easier to follow, but we understand that it is not always possible.
Annotation:
We try to include as much relevant information as possible in the schematic rules, or even just a piece of text.
e.g.
- "This net will carry 3 amps"
- "This bus should be 50 Ohms"
- "Length match nets to within 10 thou"
- "These Nets are 100ohm differential pairs"
- "Keep these devices close to the processor U1" etc...
These are just examples but a well marked-up schematic can greatly improve and speed up the whole design.
Decoupling:
It makes much easier reading if the decoupling for specific devices is placed on the same sheet as (or preferably next to) the device it is intended for. Where a great deal of decoupling is needed, and space is an issue, then we sometimes use a separate sheet with some text indicating which device the decoupling is for. General board decoupling is marked as such.
Power:
Where a creapage and clearance gap is needed, an indicative line showing the split will make the placement stage much easier.
Marking high power devices that will require large heat dissipation areas.
Showing current and voltage where deemed relevant.
Where an analogue/digital ground split is required, marking where the two are tied (if at all) is always advisable.
Where various ground or powers connect together and a star point junction is required, indicating the junction point will be helpful to the PCB layout engineer.
Component Notes:
Where a specific device has PCB layout notes, a link to the data sheet and a note indicating is useful.
Junctions:
Steering clear of cross-junctions will help eliminate possible misunderstandings.
e.g.
we don't |
we do |
 |
 |
Critical Signals:
Marking any critical signals will greatly speed up layout.
We find that schematics with the maximum additional information tend to yield better results at design and production stages.
