Device and method for measuring thickness of dielectric layer in circuit board

A method for measuring a thickness of a dielectric layer in a circuit board comprising:

• providing the circuit board comprising at least the dielectric layer and at least two circuit layers, the dielectric layer being between the circuit layers, the circuit board further comprising a test area that comprises a test pattern and a through hole, the test pattern having at least one first conductor and at least two second conductors, the first conductor being between and connecting to the two second conductors, the second conductors being parts of the circuit layer, the first conductor penetrating the dielectric layer, wherein a distance between a side of the through hole and the second conductor is less than a distance between the side of the through hole and the first conductor;
• providing a measuring device comprising a conductive pin and a sensing element, the sensing element having a sensing end, a linking portion and an insulation, wherein the linking portion connects to the sensing end, and the insulation wraps around the linking portion;
• powering the conductive pin, one end of the conductive pin electrically connecting to the second conductor;
• and
• moving the sensing element along the through hole to obtain a sensing curve, so as to calculate the thickness of the dielectric layer calculated via variations of the sensing curve.