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Description / Abstract:
INTRODUCTION
Of the various methods for the determination of ionic residues,
the method of choice is ion chromatography, which determines both
the type of ionic residue and the amount present. The IPC method
for ion chromatography is IPC-TM-650, Method 2.3.28. For surface
insulation resistance (SIR) testing, the most modern test method,
involving frequent or continuous monitoring, is IPCTM- 650, Method
2.6.3.7.
The difficulty with any of these test methods is that there are
no generic pass fail levels which can be levied against all test
data to differentiate "good/acceptable" from "bad/unacceptable".
There are far too many variables involved. What is acceptable for
consumer electronics may be inadequate for life-sustaining medical
equipment. High frequency assemblies may have different critical
parameters than those for power supplies. Assemblies which function
in the harsh environment of space may have different requirements
than those which function in a harsh industrial gas atmosphere.
There are a variety of test vehicles in the electronics industry
that have been used to examine materials compatibility or materials
interactions, such as the IPC-B-24 standard test board used to
examine SIR performance of fluxes and solder pastes. All of the
available test boards leave something to be desired as there is
often a dramatic difference in materials between these standard
test vehicles and produced assemblies. As an example, the IPC-B-24
test board is a single sided, FR-4 laminate vehicle with no solder
mask and bare copper metallization, and no through-holes. It is
often a difficult task correlating the results from such a vehicle
to an assembly made of polyimide laminate, liquid photoimageable
solder mask, and mixed technology mounting pads, with immersion
silver finish.
Consequently, a test vehicle was needed which could be used for
both ion chromatography and SIR testing, that would be more
representative of mainstream manufacturing materials and processes.
The IEC-TB-57 test board, designed by the National Physical
Laboratory and Gen3 System Ltd., both in the United Kingdom, was
the result. In a subsequent effort between NPL, Gen 3, and Rockwell
Collins, the IPC-B-52 test board, mirroring many of the features of
the IEC-TB-57, was produced. As developmental work continued on the
IPC-B-52 board, the IEC-TB-57 was modified accordingly, with a goal
of having a world standard for process characterization and
qualification. Version 8 of the IEC-TB-57 is identical to the
IPC-B-52 standard test assembly.
The IPC-B-52 test vehicle can be used to evaluate and optimize a
manufacturing process, or to provide objective evidence that a
chosen manufacturing material set and manufacturing process are
compatible, from a cleanliness standpoint. This latter use is often
considered as a "process qualification", suitable for international
specifications such as IPC J-STD-001 or IEC-1189-5. Such efforts
are not trivial, and often an engineering analysis is required to
determine the meaning of the resulting data set.
This Users Guide was developed to assist the process
professional in evaluating a candidate manufacturing process and
determining acceptability guidelines for that process. It has also
been written as a companion document to IPC-9202.