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|  The graph compares the
electrical performance of 100-25
Series probes with beryllium copper
and steel plungers with gold plating.
Eight probes from each of the
two types were cycle tested together.
There is a slight but measurable
difference in the average resistance
between the two base materials.
The steel plungers average 5 or
6 milliohms higher resistance
than the equivalent plungers made
of BeCu. Note that the bulk electrical
resistance of BeCu is .08 micro-ohm-meters
at 20° C, while the steel is .18
micro-ohm-meters. |
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Although steel
has about twice the bulk resistance
of BeCu, the difference it makes
in probe resistance will not affect
the vast majority of test applications.
The hardness of steel plungers
typically ranges between 58 and
60 on the Rockwell C scale, versus
38-42 for beryllium copper. Steel
plungers will, therefore, remain
sharp longer than BeCu plungers,
but note that the superior machinability
of BeCu means that BeCu plungers
generally start out sharper.
A summary of the average resistance
appears in the table below. |
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| 100-PRP2508H |
BeCu |
Gold |
14.3 |
| 100-PRP2508H-S |
Steel |
Gold |
20.0 |
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In cases of heavy sideloading
over many cycles, testing shows virtually
no difference in wear between BeCu and
steel plungers. Sixteen pieces each of
100-PRP2524S and 100-PRP2524S-S were run
for 500,000 cycles at two-thirds travel
against a contact surface angled 30° from
horizontal. There was no difference in
life between BeCu and steel.
Electrical resistance was
measurably different (again, due to the
difference in bulk resistance), but the
difference is not significant for most
applications. Electrical performance for
the sideload test is summarized in the
table below. Notice that the 4mOhms difference
in average electrical resistance is similar
to that found in the preceding cycle test.
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Plunger Mat'l |
Minimum |
Maximum |
Average |
Std. Dev. |
| BeCu |
7mOhms |
16 |
11 |
1.22 |
| Steel |
10 |
24 |
15 |
2.35 |
For QA Technology probes,
there is no significant difference in
electrical resistance or mechanical life
between plungers made with beryllium copper
versus those made with steel. There is
approximately a 5mOhms difference in average
electrical resistance, due to the higher
bulk resistance of steel. Probe life,
even under cases of extreme sideloading,
is the same. Steel plungers have a hardness
advantage, which will allow delicate tips
to remain sharp longer than the equivalent
beryllium copper tips in the same application.
This is particularly true in cases where
plungers are bottomed-out, abraded or
otherwise mistreated during use. Beryllium
copper, on the other hand, has a cost
advantage over steel. |
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