Ken
How long is a piece of string? What flux are you using? What cleaning
method (if any) are you using? What kind of assembly are you making?
What are the climatic conditions under which it will be working? What
reliability are you wanting?
With all the best will in the world, it is impossible to answer your
question. Contrary to the all MIL specs and other similar standards, the
famous figures of 1.5 to 1.6 ug/cm2 eq. NaCl is meaningless, stupid and
ridiculous. In the first place, they were derived empirically from
loosely populated boards with large through-hole components, using one
specific wave-soldering high-solids liquid flux and one specific
cleaning process with one specific solvent. Secondly, they take no
account of the conditions under which the assemblies will be used.
Thirdly, do you want the same reliability for a toy as with a satellite?
There is only one person who can answer your question. YOU! You
manufacture, say, 20 assemblies, using a method that you know will
satisfy the required reliability criteria and everything else. You
measure their residual contamination. You calculate the arithmetic mean
and standard deviation. That is your benchmark for ONLY that particular
assembly made using ONLY that particular process. Any major and
consistent change, in either direction, means that your process has gone
off the rails. By "major", I mean, say, 20% or more falling outside the
mean +/- 1/2 SD; the new mean changing by more than about 10% or the SD
widening.
In short, 0.3 ug/cm2 eq. NaCl may be insufficient for some applications
and 2.5 ug.cm2 eq. NaCl may be far too tough for others. Absolute
figures are meaningless, IMHO. And I say this as the original conceptor
of the Contaminometer, although the same applies to ther two Alpha
instruments and every other similar one.
Brian
Ken Patel wrote:
>
> Guys,
> What is the acceptable Ionic contamination limit for Omegameter 600 and
> Inograph 500 both made by Alphametals?
>
> re,
> ken patel
>
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