Reverse Engineering PCB Layout Scheme for Impedance Test

Reverse Engineering PCB Layout Scheme from physical Printed circuit board target can provide great convenience for Impedance Test in the upcoming PCB card cloning and PCB re-manufacturing process;

Slight variations in impedance coupon design will depend on the probing method used for measurement. The items listed below for Printed circuit board recreation purpose are general guidelines for both normal and differential impedance measurements that can be adapted for different types of probing. The differences and descriptions of these different probing techniques are covered in the measurement techniques section of this document.

• · Trace geometry must replicate the design requirements. Structures must include ground shielding around the test trace if they are used in the design in order to comprehend the effects of ground shielding on impedance and etch variation.

• · Traces with ground shielding must both reference their corresponding plane, either VSS or VCC.
• · Traces should be single ended with no pad or via at the end of the line to avoid perturbations from the reflected TDR pulse.

• · Route the traces straight, without no bends. Bends can induce ringing on the TDR pulse reducing measurement accuracy when printed circuit board modification.

• · Required coupon line length is dependent upon the type of probing and equipment used for measurements:

 Handheld probe with ground spanner:

– minimum of 3 inches long (Tektronix*/Hewlett Packard*)

– minimum of 6 inches long (Polar* with IP50 probe)

– minimum of 4 inches long (Polar* with IP28 probe)