6-1
SECTION 6 – APPLICATION NOTE
QUESTION ABOUT PLANE SHORTS
For full details on using the PLANE SHORTS range refer to Section 4.3.
Even if I can find the location of a short on a multi-layer board, will I be able to repair it?
Most shorts on multi-layer boards have similar causes to those on single or double-sided boards — solder
bridges, track bridges, bent components, etc. These usually occur on the surface of the board and can be
rectified as normal.
The displayed reading is different when the same point is probed several times.
Check that you are not touching the probe tip as this will interfere with the measurement.
When I move a probe 10mm away from the short the reading is lower than another point that is closer to
it!
This is caused by variations in the physical shape and resistance characteristics of the plane. Once you
are close to the short, probe all appropriate points in the area and look for the lowest reading.
I cannot obtain a reading less than 10.0.
The actual short may be some distance from the points being probed. Example #2 in Section 4.3
describes a situation where the short occurs at the Vcc pin of an integrated circuit, but the user is
stimulating (and therefore probing) the ground plane. If you are unable to obtain under 10.0 it may be
necessary to remove components around the area of the lowest reading to locate the short. Visually
inspect the area as a hard short is usually caused by a solder or track bridge, or bent component lead.
What is a “hard short”?
A hard short is one whose resistance is under 200mΩ, typically caused by a solder or track bridge or bent
component lead. If the short resistance exceeds 1Ω, it is probable that a defective component is the
cause of the fault.
What if the short resistance is greater than 30
Ω
?
If the resistance of the short is high, the resolution of the 950 is reduced. Moving the Plane Stimulus leads
to stimulate a smaller area of the board will help compensate for this. This may be repeated as
necessary.
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