PCB Component Selection
A meticulous review of all a PCB component’s specifications is crucial to avoid engineering change orders (ECOs). Initially the PCB designer may routinely check out electrical and engineering data as well as end of life and availability. But when a component is in the early stages of market introduction, all the critical specifications may not yet be available on the data sheet. The reliability data currently available may not be extensive or sufficiently detailed when the component has been on the market for only a few months or is available only in small sample quantities. Consequently, there may not be a sufficient amount of reliability and quality assurance data on field failures, for example.
It’s important not to accept the spec sheet at face value, but to contact the component vendor to learn as much as possible about a component’s characteristics and how these characteristics relate to the design. An example is the expected maximum current flow or voltage the component will need to handle. If the component is not selected for sufficient current or voltage, the component may burn out.
Performing extra analysis and calculations is also highly important in component selection, for instance, calculating current or voltage during peak performance. A component might be specified at a certain peak temperature and current level.
The responsibility rests with the engineer to not only perform calculations on a single component, but consider that component’s relation to other components used in that particular design. For example, calculations are especially important for analog components generating a high level of heat. Let’s say a number of analog components are placed next to each other on one side of the board. Those are creating considerably more power and thereby generate more heat compared to the other side of the board, which is digital in nature. In such a case there is a possibility of solder mask de-lamination occurring on the heavily populated analog component side.
Analog portions of the component’s circuitry can generate a lot of heat. Overheating can create delaminating of the solder mask or in a worst case scenario, it could burn and damage the components.
Design and layout engineers need to work together on component placement at the layout stage to avoid placing the component too close to the board’s edge or next to another component without allowing sufficient spacing. Component placement can be easily designed on the computer, but if component footprints are not created accurately in layout, the pick and place machine might not be able to place them perfectly next to each other.