Fabrication Methods
Become familiar with practical knowledge about PCB fabrication and production. This
leads to more complex PCB designs than are necessary. For instance, a common problem
is orthogonal trace bends on tight grids. Not every PCB fabricator has the ability
to produce that type of design with acceptable results. You may be able to cut costs
and improve reliability if you choose a larger grid, larger via sizes, or elimination
of blind, or buried vias.
Don’t Avoid the Schematic
It’s tempting to skip a schematic if the board is relatively simple. The schematic
forms a visual representation of your circuit. It lets you arrange components near
their functional counterparts, regardless of where they will be physically placed.
When each pin on each component is depicted in the schematic symbols, a disconnect
is easy to recognize. They help you determine if basic circuit design rules have
been followed by visualizing the design. Building your layout from a complete schematic
gives provides a reference and helps make sure that all of your layout connections
will be complete.
Over-Reliance on Auto-router Tools
Most PCB CAD tools include an auto-router function. It’s a great time saver as a
first pass or sanity check, but it is important that you also know how to route
traces without it. Auto-router parameters require precise setup which must be changed
from job to job and sometimes even between modules within a single PCB design.
Current Flow Considerations & Board Layout
Current flow can be impacted by bottlenecks and pinch points in your Printed Circuit Board (PCB) Design.
Avoid such roadblocks, like:
- a 90-degree bend when two 45 degrees could serve the same purpose
- bendsgreater than 90 degrees, and switchback shapes.
These features can have the effect of slowing down signal propagation or unnecessarily
increase thermal issues.
Avoid Potential Slivers
Narrow wedges of copper or solder mask produced during the PCB manufacturing process
can generate slivers which become a big problem during fabrication. They are created
during the etching process and can happen
- When an extremely long, thin feature of the copper or solder mask is etched away.
Sometimes it detaches beforefully dissolving and can float around in a chemical
processing bath and eventually land on another board, adding unintended connections.
- When a section of the PCB design is too narrow or too deep. If an etched section
is narrow enough or the etching is deep enough, a sliver of material can completely
or partially detach, either producing a floating sliver or a peeled-back sliver.
Slivers can be avoided by designing sections with minimum widths, minimizing the
chances of producing slivers.
Design Rule Checkers (DRC)
It is a good idea to think through and craft a set of design rules that standardizes
PCBs to manage costs and maximize yields. They also make assembly, inspection, and
test more consistent. These can also help create more consistency in purchasing.
Pricing for the manufacture of boards is consistent, possibly enabling reduction
in the number of specialized PCB manufactures required. .
To support this effort, many PCB design software platforms have a Design Rule Checker
(DRC), or constraint manager built in. This tool will call out design rule outliers
right while you are editing. They usually err in the direction of reporting an error,
but then let you decide if it is really a violation. This is worth doing as it may
save you from a failure or be an indication that trace placement should be reconsidered.
Know Your Fabricator
In order to set up DRCs correctly, youneed to know the capabilities of the intended
PCB fabricator. If you’ve chosen a good partner, they will offer help and advice
on how to craft your design to keep down the number of iterations, make debugging
easier, and improve the quality of outputs overall.
Each manufacturer has its own specifications
- minimum trace width
- spacing
- number of layers, etc.
You need to understand your requirements and find an appropriate Printed Circuit Board Manufacturer.
These requirements should includethe grade of the material required. Grades range
from FR-1 (paper-phenolic mixture) to FR-5 (glass cloth and epoxy). The choice of
materials will impact the board’s strength, moisture absorption, flame resistance,
and durability.
If you have a good understanding of the PCB manufacturing process, you will be better
positioned to make smart design decisions. You should know exactly which processes
and methods will be used by the manufacturing partner that you select.
By keeping these points in mind, as you work on your design, you’ll improve your
chances for reliable PCB designs and shorter overall time-to-market for new product
introductions.