Test Point Design Guidelines for Bed of Nails Fixtures
Test point designs require 0.80 mm targets on 1.27 mm pitch with bottom-side placement to maximize fixture alignment and maintain strain under 500 microstrain.
Target Diameter
Geometric Designator
Specified circular dimensions for conductive land pads define the acceptable target area for mechanically or laser-drilled holes in multi-layer board fabrication. The selection of the target diameter directly affects the reliability of the copper barrel to pad connection by providing enough metal to form a secure electrical joint. Designers must balance pad sizes with spacing rules to maintain layout density.
Drill Alignment
Drill wander occurs when the CNC spindle deviates from the programmed coordinates during the drilling operation. If the target diameter is too small, any drilling inaccuracy can cause the hole to breakout of the copper pad edge, which is known as pad breakout. This defect reduces the conductive cross-section and can lead to trace failure from thermal contraction or vibration during product operation.
Electrical Clearance
Annular ring requirements dictate the minimum amount of copper that must remain around the perimeter of the finished hole. Maintaining a larger target diameter ensures that even with maximum drill deviation, the board fabricator can meet the performance class requirements of IPC standards. Fabricators measure the remaining copper border after the plating process to verify that the plated through hole is structurally sound, as thin or broken annular rings are highly prone to cracking when the boards undergo wave or reflow soldering.