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Measuring Circuit Board Sublaminate Registration Using a Capacitance Bridge

IP.com Disclosure Number: IPCOM000036893D
Original Publication Date: 1989-Nov-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Canfield, DH: AUTHOR [+5]

Abstract

Disclosed is a technique for measuring the registration of sublaminate layers in a printed circuit board using a capacitance bridge to detect misalignment between a reference layer and other layers. It can be used prior to, or after, lamination.

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Measuring Circuit Board Sublaminate Registration Using a Capacitance Bridge

Disclosed is a technique for measuring the registration of sublaminate layers in a printed circuit board using a capacitance bridge to detect misalignment between a reference layer and other layers. It can be used prior to, or after, lamination.

This measurement uses a pattern of lines or other appropriate shapes placed in unused areas on each layer of the board. In the figure, two sinusoidal drive voltages, one at quadrature with respect to the other, are applied to drive lines 1 and 2. The alignment in one direction of the underlying sublaminate layer is determined by measuring the capacitive current from sense line 3 to ground. This current is zero if alignment is perfect. The patterns are duplicated and rotated by 90 degrees for measuring alignment in the other direction. Signals are coupled into or out of the board using plated through holes or by capacitive coupling.

In order to test the alignment of a power or ground plane sandwiched between adjacent layers containing drive and sense line patterns, a hole is drilled or etched in the power plane and the plane is grounded, thereby acting as an electrostatic shield to capacitive coupling between the drive lines on one adjacent layer, and the sense line on the other adjacent layer. Alignment of the power/ground plane is accurately measured as long as the relative alignment of the adjacent layers is known.

The measurement may also be pe...