What is part overage?

In PCB assembly, part overage is the extra parts in addition to what is required to complete the PCB assembly. Part overage accounts for manufacturing parasitic loss and errors.

Why is part overage necessary?

There is a potential for component or part loss in a couple different areas of the PCB assembly process.

Mycronic feeder cartridge loaded on a My200 pick and place.

Mycronic feeder cartridge loaded on a My200 pick and place.

The first occurs when loading our automated SMT placement machines with components. The feeders (tooling that holds and advances the parts to the machine) require a certain amount of exposed tape during setup. This exposed part section is called the leader section on the SMT tape. Modern SMT placement machines are very efficient in minimizing the amount of leader needed while older machines used to require almost 2 feet of extra leader!

Chip components (0402 and 1206) packaged in tape form.

Chip components (0402 and 1206) packaged in tape form.

If the component is a part we have not used before there is a component training phase the SMT placement machine needs to go through to learn the new component. This generally requires only two extra overage parts. One part to train the machine and one to verify the information.

Machine teaching for picking up a part out of tape feeder.

Machine teaching for picking up a part out of tape feeder.

Training the machine by test placing an LED package.

Training the machine by test placing an LED package.

Checking the orientation after training a new diode on the pick and place machine.

Checking the orientation after training a new diode on the pick and place machine.

During assembly of the PCBs there is a chance of a mispick by the SMT placement machine which can cause the vision inspection system to reject the part. For larger parts this is fine as the machine operator can remove the part from the reject bin on the machine but for chip size resistors and capacitors it is hard to identify individual parts.

Reject bin on the pick and place after a manufacturing run.

Reject bin on the pick and place after a manufacturing run.

If a part was lost due to the above problems and an exact number of parts was ordered this would cause a manufacturing delay in the PCB assembly process. To reduce manufacturing delays part overage is a necessary part of the logistics process.

Transparency for part overage.

Here at MacroFab, we want you to know exactly what you are ordering. The Bill of Materials workspace of your PCB assembly design displays the additional quantity and price of part overage required for each individual line item.

MacroFab PCB interface displaying the overage for a line item.

MacroFab PCB interface displaying the overage for a line item.

Learn how to Manage your PCB Bill of Materials with the MacroFab Platform.

Turnkey parts overage.

You do not have to worry about part overages for turnkey sourced parts. MacroFab will automatically calculate the overage required and order the parts for you. This reduces overall manufacturing delays by making sure all the parts arrive on time and there are no part shortages during assembly or your PCBs.

Consignment parts overage.

When shipping components to MacroFab for consignment parts it is required to ship part overage. The MacroFab platform will calculate how much overage you will need to send in. Failure to send in part overage will result in manufacturing delays with your order and could cause the cancellation of the order. Learn more about consignment parts.

Do I get my leftover overage after my order is complete?

If the part is a turnkey sourced part these are generally scrapped at the end of the order. Consignment parts are returned to you when the order is shipped out.