Complete Electronic Hardware Design Package
Electronic Hardware, Electronic Hardware Design Package, Hardware Design
Introduction
I’d like to recognize the valuable input to this Device Tip from Tom Lupfer, John Fox and Jackie Neal of Clarity Design, Inc. where Tom is CEO, John is Vice President of Engineering and Jackie is Senior PCB Designer. Clarity Design has been turning great ideas into amazing products since 1991. Offering design, prototyping, and manufacturing services, Clarity Design has helped hundreds of customers bring thousands of products to market.
I have done several projects over the past fifteen years that had at their root shortcomings in the completeness of the design documentation for the electronic hardware of a product. In my experience this was caused by:
- an incomplete knowledge of what constitutes a complete Electronic Hardware Design Package; and/or
- not requiring specific documents and files as part of the deliverables from internal or contract hardware design resources
The 1st situation often occurs when the individual overseeing or directing the electronic hardware design does not have detailed knowledge of the electronic design and manufacturing process.
The 2nd situation often occurs when documentation is not made a specific deliverable, while physical deliverables such as prototypes or functioning units are.
The goal of this device tip is to address both of these situations by providing a checklist that can be used to ensure that a complete Electronic Hardware design package is delivered. This checklist can also be used to determine whether one actually has possession of an electronic hardware design (not just possession of functioning units).
Here’s the tip:
Always use the checklist when specifying the deliverables for electronic hardware design.
So here’s a checklist of a complete Electronic Hardware design package:
- Hardware Block Diagram
- Hardware-Software Interface Specification
- Electronic Hardware Specification
- Electronic Sub-system Specifications
- Theory of Operation(s)
- Schematic Design File(s)
- PCB Design Files
- PCB Fabrication Files (Gerbers)
- PCB Fabrication drawing(s)
- PCB Assembly drawing(s)
- PCB Bill(s) of Material
- Interconnect drawings(s)
- cables
- wiring harnesses
- flex circuits
- Electronic Component Specification(s)
- Design Note(s)
For each item listed, the package should contain the original design file as well as PDF’s of the design files. (Ex: OrCad schematic design file and PDF of schematic; AutoCad PCB Fabrication Drawing and PDF of Fabrication Drawing). The reason for the PDF files is for ease of viewing and review by someone who doesn’t have the design package software installed on their PC.
Some designs may not require every item listed, but can easily be determined to be “not applicable” for a given design. The point is to ask whether they are applicable.
The more complete an Electronic Hardware Design package is:
- the more likely the design will work the 1st time without requiring major changes;
- the shorter the overall development time will be; and
- the lower the total cost will be to sustain the design throughout the product lifecycle.
More Info
Unless the electronic hardware design is a single circuit with a single, simple function, a Hardware Block Diagram provides a high- level breakdown of the major functional sub-circuits of the design. This would include interconnects if applicable. The Hardware Block Diagram is one of the most important documents for long-term ease of sustaining a design, and for quickly transferring the “big picture” of the design to manufacturing, service and sustaining staff.
If the Hardware will have Software running on it, the Hardware-Software Interface Specification is the key document to communicate design decisions between Hardware and Software Engineers. This document defines the hardware resources dedicated to software features and functions, the I/O assignments, and the performance specifications that the Hardware must meet in order to provide those software features and functions. A good Software Interface Specification makes software development easier (and faster), and can save days, weeks and even months of time during software-hardware integration. The Hardware-Software Interface Specification is additionally valuable when troubleshooting both hardware and software.
An Electronic Hardware Specification is essential for any hardware design, and defines the features and functions of a system that must be provided by the hardware. It includes the physical, functional and performance aspects, and can even include cost requirements, especially in cost-sensitive designs. Without an Electronic Hardware Specification there is virtually no chance the hardware design will work as needed.
If an overall Electronic Hardware design comprises electronic Sub-systems to be designed and/or manufactured by separate individuals or entities, the Electronic Sub-system Specifications provide similar value as the Electronic Hardware Specification. And similar to a Hardware-Software Interface Specification, the Electronic Sub-system Specifications document the design decisions between different portions of the hardware. Similarly, the Electronic Sub-system Specifications document the design decisions between different Hardware Engineers.
Theory of Operation(s) are possibly the most under-represented, yet most important documents an engineer can write. Theory of Operation (TOO) documents document how specific circuits work, why certain components were chosen, and what the critical specifications are for specific components. They can be used for Design Reviews, during development, during software-hardware integration, during design verification, as well as when the design is transferred to manufacturing and service.
I like to refer to them as the “Individual Retirement Account” for engineers because they allow engineers to “retire” from a given design or project. When new people come to the engineer (sometimes years later) and ask how a given design works or why certain components were chosen or what the critical specifications are for a component, it’s nice for that engineer to hand (or email) them a document and say “here’s your answer(s)”. They don’t even have to still work there if the Theory of Operation(s) documents are organized and put in an accessible location.
Schematic(s) are the common bridge between the circuit design, components, PCB design, PCB Assembly and interconnects. Realistically one cannot do hardware design without a schematic, so it’s amazing when schematics are not part of the package for a hardware design. Interconnects are probably the most common situation where the schematic is often replaced with a “wiring table” (cables) or “wire list” (harnesses), and I suppose it can be acceptable. I still think it’s easier to visualize the interconnects with a schematic. Some electronic and electromechanical components (such as transformers and motors) are leftoff the schematic, which can lead to a lot of energy spent trying to figure out how they’re wired.
Another potential pitfall is when the PCB design package uses a different schematic tool (or has its own schematic capture tool) than the original design. This is usually not a problem if the netlist from the original schematic is used to design the PCB. But problems can be created when changes are made to the schematic design during the PCB design process. When this occurs, it is critical to keep the original schematic updated to identically match the circuit in the PCB design.
PCB Fabrication Files (Gerbers) are one of the two key sets of files to have if one wants to actually possess a PCB design. It’s amazing how many companies pay to have PCB designs done by outside services, yet never actually get the Gerbers. This can occur when the PCB design service sends the Gerbers directly to the PCB Fabrication Supplier (aka Fab House), or when the PCB design service provides the bare PCB’s (aka ‘Fabs’) or PCB Assemblies.
The second key file(s) to have is the PCB Design File(s), which are generated by the PCB design tool (PADS, Altium, Allegro, etc.). These are often huge files, but if you ever want to change anything in the PCB design, you need to have the PCB Design File(s), not just the. Having the PCB Design File(s) not only allows one to make changes to the PCB design, but also have those changes done by a different PCB design service, provided the new PCB design service uses the same PCB design tool.
PCB Fabrication Drawing(s) (aka “Fab drawing(s)”) are used by the bare PCB fabrication manufacturer (aka “Fab House”) to manufacture the bare PCB from the Gerbers. The Fab drawing typically provides:
- A Drill Table that specifies the drill sizes and/or finished hole sizes
- A PCB stack-up drawing showing the thickness of individual layers and the order they go in
- Notes that specify materials used, including the bare copper thickness, metal plating, solder mask, silkscreen, impedance requirements, etc.
- Notes that specify inspection, testing, packaging and other requirements
- A Note that references the Gerber files to be used to fabricate the PCB (typically this is a ZIP file containing all the individual Gerber files), with a specific filename, date and time stamp.
- A net list created in the appropriate software tool ( i.e. IPC-D-365A).
PCB Assembly Drawing(s) (PCBA) are used by the company that assembles the components onto the bare PCB to create the finished PCB assembly. The PCB Assembly drawing typically provides:
- A Note that references the Bill of Material (BOM) file that lists all the components to be used to assemble the PCBA
- Notes that specify the soldering process and cleaning process to be used including the solder itself, cleaning solvents, etc.
- Notes that specify inspection, testing, packaging and other requirements
- A pick and place file for automated part placement.
- Gerber Array files from board fabrication manufacturer to make paste mask stencil.
The PCB Bill(s) of Material (PCB BOM) is typically a list of the PCB components in tabular form. For each component, the PCB BOM typically lists the BOM item number, component description, component manufacturer, manufacturer’s part number, PCB reference designators (locations of the component on the PCBA) and component quantity. The PCB BOM may also list the Customer’s internal component part numbers, component distributor, and component cost, although component distributor and component cost are quite variable and are usually not included.
Interconnect drawings(s) can include cables, wiring harnesses and flex circuits. Often these are not included in the “hardware design” document package, but I can say from many years of troubleshooting that these can be some of the most important documents in the hardware design. I prefer interconnect drawings(s) to include a “schematic view” showing traces from pin x on connector 1 to pin y on connector 2, as well as a “physical view” that shows that the “trace” from pin x on connector 1 to pin y on connector 2 is actually, say a yellow wire. Interconnect drawings(s) also typically include dimensional information, wire gauge, insulation specification, and connector details, as well as item numbers that refer to a Bill(s) of Material (BOM) for that interconnect.
Electronic Component Specification(s) are documents that specify technical details about components such as those on a PCBA or Interconnect assembly. Since the vast majority of electronic components are off-the-shelf parts manufactured by component manufacturers, a company’s Electronic Component Specification typically defines one or more manufacturer’s components, that correspond to the company’s internal part number. Complete Electronic Component Specification(s) also specify, among the numerous specifications for a given component, what are the key specifications for that component as used by the company for that specific internal part number.
Design Note(s) are documents that help others understand key and/or subtle aspects of an electronic design, including technical reasons for certain component selection, certain PCB component layout aspects, or certain circuit design choices. Design Notes can operate in conjunction with Theory of Operation documents to describe both how various circuits work, as well as important aspects of the design not readily apparent in the other documents within the hardware design document package.
If you strive to include as many of the above elements as are applicable for a given hardware design, my experience is that every hour and dollar invested in producing these documents, pays for itself 10X or more in cost savings between design, manufacturing and service.