This document describes the preferred interface for design engineers working
with Small Systems Company. These procedures apply to the design of
electronic PCB assemblies and systems. (We also do mechanical design.)
Note "preferred". This is the default. Other working relationships are negotiable. We can do some portion of this work for you, for example -
bring your finished schematics through PCB layout to photoplot. We recommend
that you review this document so we can each begin with the same expectations
and then discuss variations as needed.
Design Procedures at Small Systems
The Design Engineer provides -
- A schematic and/or netlist, in pencil or digital form.
- A comprehensive Bill of Materials for the design, which includes -
- The complete nomenclature of the part, with the
manufacturer's prefixes and suffixes, sufficient to
specify the component to a vendor.
- The package type of the component to used.
- The quantity of the component used.
- Copies of the data sheets for each component. These may be
partial copies as long as the following information is provided -
- The front page including the name of the component
and general description.
- The component nomenclature - the manufacturer's naming
matrix which shows the meaning of the choices in
the various sections of the component name.
- The pin-out. The table which shows which signal is
on which pin. If there are swappable pins or
gates, this data should be shown here.
- The mechanical specifications of the package to be
used. These must be sufficient to create a
"decal" or footprint for the component in the
PCB design library. The height of the package
may be a concern as well.
Specifications of signal timing and electrical parameters
may be omitted from these copies, and probably should be
when extra pages are involved.
This BOM should be provided at the outset of the design
process or ASAP, because purchasing cannot begin until this
information is submitted, and purchasing is usually the
longest task to complete. A decision on the quantity of assemblies
to be built on the first run should be made as soon as the BOM is
prepared, again, so purchasing can begin.
A pencil schematic should be drawn by any means suitable to
the engineer. The schematic should show signal names
attached to every pin of every component in the design.
Drawn wires are optional. A netlist, in any human-readable
form, may be substituted for a schematic, as long as it is
Block diagrams are helpful, but not required.
Notes should be included with the schematic or netlist which
specify any special treatment required on any signals, such
as maximum or matched lengths, reduced capacitance,
inductance, or noise, etc.
Bypass capacitors should be included in the design, with
indications of how many should be adjacent to which component.
An effort should be made to use components in the design
which already exist in your company's manufacturing
When the design is completed, the engineer should complete a
paper APSS (approved parts specification sheet) for each new
component specified. Part names and part numbers will be
assigned according to your company's part naming convention.
However, our system has certain constraints and preferences which
are documented on pages one and two of
"Electronic Part and Signal Naming Conventions for Use with Schema
and PADS PCB Software" , Hileman, 1989.
Small Systems Engineering Services will provide -
- The capture of the schematic/netlist to digital form. This includes
the generation of library items for all new components.
- The PCB layout, including design of decals for all new
components. The culmination of this process is photoplotting to film.
Gerber and drill files are supplied on disk.
- Purchase of all components and management of inventory for
the first assembly run. Entry of all component purchasing
information into a manufacturing database. The database and a
complete kit for the first run are the results here.
- Management of the fabrication of the first PCBs. The product is
bare boards, aka "fabs".
- Management of assembly of the first run. The output of this process
is a delivered set of assemblies ready for testing by the design
- Documentation of all of the above sufficient for turn-key
quotes from assembly houses.
The engineer is responsible for -
- informing the design with appropriate market information.
- the performance of the design.
- the cost-of-goods decisions made in the design process.
- testing the finished assemblies of the first run.
- providing a testing methodology for manufacturing.
ssdesign.html 7/18/97 R L Hileman
Index to design pages -