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— Electrical Test For PCBs —
Precoplat Precision Conductive Plates Technology (PCP)
decided for the Expensive Necessity |
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Demands for quality controls
mean additional production
costs. In the common interest of customers and
manufacturers, the question
of optimal testing is
repeatedly posed in the production process.
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The Dilemma is obvious: |
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The days of the first “printed circuits” which could
be checked simply with the naked eye
are over. Today, high-tech equipment is necessary for a thorough
PCB test.
Optical checks with the aid of conventional micro-scopic equipment are sufficient for one
sided
and relatively simple double-sided PCBs. Residues, constricted conductors and
subcorrosions can
be discovered which would otherwise lead to PCB failure after a
number of operational hours.
An electrical test is needed to check the actual functions of a PCB. It is an essential if
inner
layers need to be tested, as is the case with multi-layers.
In two position measure-ments all connections in the PCB are checked for stoppages and short circuits.
All SMD
pads and plated through holes are checked. The electrical test can be conducted
as a
parallel
or finger test.
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Parallel test: |
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For the parallel test a control adaptor is constructed, consisting,
e.g. of several synthetic
sheets positioned above each other and fitted with control pins.
An adaptor programme must be written to reflect the actual holes in each individual
synthetic
layer of the adaptor. The pin positions are identical to the control points
enabling an overall
PCB test within seconds.
The control adaptors are all the more expensive the higher the density and the lower
the grid
distances between control points. The adaptors can also only be used for one
specific type of
PCB which explains the high set-up costs for the test.
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Finger Test: |
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As PCB series are not always produced in mass, the finger test was
developed as an
alternative solution for small or medium-sized series. Manoeuverable probes move
to
the control points without necessitating an adaptor. As the points are checked
individually,
the time required for a complete check depends on the number of control
points. In extremely complex
layouts the test can take up to 30 minutes.
Electrical testing of PCBs is costly and time intensive.
However, it is obvious that testing
is necessary. Just consider the consequences of a defective
PCB discovered only after
assembling is completed!
As purchasers are generally unable to conduct tests themselves, there is
no alternative to the electrical test.
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