Definition of Tolerance for Manufacturing

Manufacturing tolerances are the amount of variation that is allowed in a measurement or other characteristic of an object.

Ref: Collins English Dictionary

We continue with our series on Understanding Tolerances on a PCB with our 4th guide:

Slot Size Tolerances

The definition of a slot is “a narrow-elongated slit or aperture”.

We define a slot or cut-out as an aperture inside of the PCB profile but differentiate between them from a production point of view.

A slot is simply an elongated hole whereas a cut-out, is another hole of any shape, see image below.

Slots are very common on PCB’s and like holes they can be plated (PTH) or non-plated (NPTH).

The purpose of slots varies, the most common use is for component mounting.

Other uses are for cable pass throughs, ventilation, electrical isolation etc.

The Finished Slot Size like holes are influenced by various factors during the manufacturing process as below:

  • Type of Slot – Plated or Non-Plated.
  • Nominal Slot Size vs available tool sizes.
  • Tool Size Tolerance.
  • Tool Wear during use.
  • Slot Cleaning (Desmear).
  • The Plating Process and Copper Balance.
  • The Final Surface Finish of the PCB.

We use our knowledge of the PCB manufacturing process to ensure that the finish slot size is within the accepted tolerance.

We produce all our boards according to the IPC-A-600 Acceptability of Printed Boards (Industrial products).

To read more and view our video on how and why these factors influence the finished hole size on a PCB simply click on the button below.