Best Guideline for Testing ZIG in PCB Design

In this tutorial, we are going to learn about the Guideline for Testing ZIG in PCB Design.

  • Place the Components and Test points minimum 3.2 mm (.125Inch) from board outer and preferred 3.8mm or 0.150Inch.
  • Use minimum two mounting holes with 3.2 mm (0.125Inch) diameter tooling holes, That’s should be   opposite corners, and at least minimum gap 3.2 mm annular area  around them all free of components and test points.
  • When place the components make the keying which pattern so boards can’t be inserted backwards.
  • When we design the PCB then try to design single sided because double sided Fabrication &  testing ZIG is more expensive rather than single sided ,Always make circuit  design in bottom side and also use the test point at bottom sided because top sided, because through holes components mounting easy on top side. Always probe sites should be Top-side, use top only for non-critical nets. Make the points for clocks, control pins, programming pins, serial data and also boundary scan (BST) on bottom.
  • Always try to make the test point should be through-hole leads, which are related to pads or small diameter Via’s, and avoid test points on surface mount lands or gold-plated edge fingers. Please don’t use larger via hole of diameters as test probe sites. Which Via hole size have 0.36 mm (.014inches) or less try to use test point.
  • If there is requirement of 100% testability, In case we should  provide at least one test pad for each net & use two pads on nets which will be tied to critical low impedance devices.
  • First use 2 to 10 probes that’s are use for testing of primary power, and minimum two test points each for isolated power and grounds. Always try to make the maximum test point of probe should be for primary ground and minimum one test point for every twenty grounds.
  • For Probe sites then it should be at least with 1.0 mm (.040Inches) pad diameters are preferred, 0.9 mm (.035Inches) is acceptable, and 0.8 mm (.031Inches) can be used when the tooling holes are available for alignment, if else small size  diameters will reduce contact repeatability , Minimum space of probe sites at least 2.5 mm (.100 Inches) apart, center-to-center. In reality, 0.9 mm .035 Inches) pads spaced 1.8 mm (.070 Inches).
  • Place the big size of components on the side which is not probed. The platen has to be cut out in places If  components are over 6.4 mm (.255inches) tall on the probed side then platen should be cut out in this situation  test points at least 5.0 mm (.200Inches) away.
  • If components taller than 2.6 mm (.100inches), In case minimum 2.0 mm (.080) clearance be should edge- to-edge, and also for other components, keep test pads at least 1.0 mm (.040 Inches) from component body, edge-to-edge.
  • If Component like Through-holes are used for test probe locations, make sure leads are robust enough for compressive force (be careful using LEDs or some types of transformers) and the  PTH leads will be present on all versions of assembly

When the design is panelized, Use at least one tooling hole on each board which are used in the rail of the PCB panel

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