Hardware Design

Once the requirements have been defined, we can proceed with hardware design, including:

component engineering

First, we determine what key components we’ll need in the design. We select components based on:

• Performance

• Cost

• Availability

• Manufacturability

One of the advantages of using a company that designs a lot of boards is that we have a lot of experience with components. Some we love, some we hate. We have several thousand components in our library already, but if we don’t have the component we need then we’ll create it, including:

• Schematic symbol

• Supplier Link

• PCB Footprint

• 3D model

The last part is important - the 3D model allows us to verify the footprint with the actual part. Most errors on boards are incorrect footprints, so we follow the IPC guidelines in designing footprints.

Schematic Capture

I always thought this was a funny term for drawing the schematic, as if the schematic was running around in the wild and we had to trap it somehow. This step entails doing the calculations on the design and drawing the schematic diagram. There are different philosophies about how much information to put on the schematic, but we will generally try to put all calculations and links to notes on the schematic so they’re easy to find and verify later. This step is really “where the rubber hits the road” and is the key to the rest of the design. We will also compare our design with the chip manufacturer’s reference design and ask them questions as needed. Schematics should show:

• How components connect together

• Calculations

• Part numbers, for active components

• Notes to make it easy to review

PCB Layout

We will use the completed schematic to layout the components on the board. We will work with your mechanical designer to identify the mechanical constraints (board shape, component keep out areas, etc.) Then we will place the components and route the connections. Once the routing is done then we’ll take a look at the board and see if there are any more test points or labels that would be useful.

“90% of good layout is getting the placement right”

We’ll first place the components to ensure that they’re correct. We’ll often change pin assignments and adjust the schematic to make routing easier. As a result we will often end up lowering the cost of the printed circuit board. We’ve also done more exotic PCB designs, including:

• Metal clad substrate, for better heat dissipation

• High Density Interconnect (HDI) included buried vias, via-in-pad, etc.

• Tight tolerance (<5mil)

• Lots of layers (too many to count)

manufacturing documentation

After the board is complete we will create the manufacturing documents. We work closely with the contract manufacturers to supply them with the information they need. We are somewhat passionate about manufacturing drawings and have spent many hours researching optimal notes for PCB fabrication and assembly. See blog post on this topic.