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The Superconductive Circuit Board

4 Circuit Board Design Mistakes to Avoid

Posted by Paul Jackson on Sat, Jun 30, 2012 @ 02:03 PM

cream circuit board 9 11 crop sizeAvoid these four circuit board design mistakes

1) Stipulating a minus tolerance on small (micro) via holes

This might cause limitations on panel size due to pad/hole ratios. High current densities might plate the hole down. Reworking the vias to unplug the holes is time consuming. Specify if vias can be filled or designate tolerances as a "+" allowance only or specify that vias may be plugged or filled

2) Nonfunctional pads on inner layers

Routing traces too close to plated through holes. In designing a board minimum spacing is an important consideration. Often, this spacing does not take into account manufacturing tolerance buildup (i.e. maximum allowable mis-registration combined with maximum etch back). A trace routed between plated through holes on a layer with the nonfunctional pads removed can actually short out during an electrical test resulting in a scrapped unit.

If pads do have to be removed (as is the case in flex or rigid/flex boards) it is advisable to let the manufacturer take care of this.

3) Edge Tolerances

Ground planes (and traces) should end approx 0.010" from the edges of the board to ensure against accidental shorting with metal chassis and cases.

4) Copper thicknesses

Often designers request 1 ounce of copper as a finished thickness whether they intend for a copper thickness of that dimension or not. A total of 1 ounce of copper would not ensure adequate plating in the holes. Being specific as to the parameters that you require will ensure that your design will not fail. The common designation for the finished thickness of copper is 1 or 2 ounces per sq ft.

Photo by SD Jackson Photography. All rights reserved.

Tags: PCB copper thickness, printed circuit board design

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