Nail Heading

Nail Heading Evaluation

Nail Heading is a phenomenon that occurs in the drilling of multilayer PCB's. The normal copper inner layers are drawn out or extruded by the drill which forms a nail head like shape on the hole wall.

• The inner hole wall is inspected by cross-section, the copper layer is measured where the nail head is formed. The nail heading value is expressed as a percentage according to the thickness of the inner layer copper as shown in the figure below.
• If the evaluation using stack drilling has been done, all the panels are measured.
• The maximum nailheading points are measured around final hit counts.

The inner layer copper thickness is measured from the average position of the "roughed" surface of the copper layer.

Nail Head[%]= b/a x 100 a: Copper layer thickness [µm] b: Nail head width [µm]