Part Attrition Calculations

SMT pick&place machines are not perfect, and during the assembly process some parts will get lost or rejected. Additionally, the mechanical construction of the tape feeders requires a certain length of tape (the "leader") to be present before parts can be picked up automatically.

This results in part attrition, also known as part wastage. Attrition rates vary depending on the particular component, packaging, pick & place machine, production batch size, and many other factors.

PartsBox allows for defining attrition on a per-component level. There are two parameters:

• Percentage-based: this number represents the percentage of components that are expected to be lost. Rates usually vary between 0.1% and 3% for production runs.
• Quantity-based: the minimum number of extra components that always needs to be reserved, even if percentage-based calculation would indicate otherwise. This is usually related to the length of leader required to feed a reel into a machine.

These parameters can be set either individually, or for many parts at once.

When building or pricing Projects/BOMs, PartsBox will take part attrition into account, so that the number of components actually taken from stock or ordered will be higher than what is strictly required.