Authored By:
Mike Konrad
Aqueous Technologies
Corona, CA
Summary
At its peak between 98-117 AD, the Roman Empire At its peak between 98-117 AD, the Roman Empire the Roman civilization can be credited with many technical and societal inventions, perhaps among the most important was the construction of aqueducts (Figure 1).
Rome is famous for its bath houses. With available clean water, residents of Rome were able to bathe regularly. In fact, bathing became a cultural ritual with public baths for the masses and even private baths for the wealthy.
In 476 AD, the last of the Roman emperors in the west was overthrown. As Rome fell, many of the inventions of the Romans were lost to history. This included the cultural embracement of personal hygiene. Personal cleanliness was no longer pursued and, in many cases, available. Many anthropologists believe the decline in post-Roman personal hygiene led to the spread of the great plagues of the middle ages.
Conclusions
As miniaturization (both board and components) continues to progress, the amount of residue tolerable on and within an assembly continues to decline. Modern assemblies can tolerate less residue than their older counterparts. Today’s assemblies must be cleaner in in order to prevent ECM in all of its manifestations.
The term “Harsh Environment” is relative. Through-hole circuit assemblies from many years ago could tolerate considerably more residue than a typical modern circuit assembly. Additionally, our industry transitioned from a clean strategy to a no-clean strategy. Formerly, circuit assemblies were cleaned. Not only was the flux removed, all other residue species were removed in the process. While flux is the intended target in a cleaning application, many other residues species are also removed. Residues from board fabrication, component fabrication, the assembly process, and human contamination combine with flux to create the total residue content on a circuit assembly (Figure 15).
When the electronic assembly industry stopped removing flux, it stopped removing everything. Because of the wide adoption of no-clean processes and the reduction of residue tolerance, we now witness a perfect storm of ECM possibilities.
When the electronic assembly industry stopped removing flux, it stopped removing everything. Because of the wide adoption of no-clean processes and the reduction of residue tolerance, we now witness a perfect storm of ECM possibilities.
IPC recently amended J-STD 001G2 to mandate a combination of Surface Insolation Resistance (SIR) testing under bias with heat and humidity to qualify an assembly process and Resistivity of Solvent Extract (ROSE) testing to verify contamination levels. The combination of SIR under bias with heat and humidity and ROSE testing will ensure the assembly is clean enough for the intended use.
The removal of just one required factor for the creation of ECM (conductive residues), will prevent ECM related failures. Our industry has two choices, provide more space between conductors or a cleaner space between conductors. As our industry steams toward an historic expansion of electronic products as a result of IOT, wearables, and the increasing electrification of automobiles, the removal of residues and the resulting increase of reliability seems likely to bring cleaning back into a conventional wisdom status.
While there are several cleanliness quantification techniques, sometimes, one simply has to rely on the “sound of clean”. Consider what your “sound of clean” is.
Initially Published in the SMTA Proceedings
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