ROSE testing, as the only measure of ionic contamination, should be considered an obsolete practice.

The issue of how to measure ionic contamination of a printed assembly, and the question of how clean is clean enough for a particular application, has plagued the industry for decades. For most manufacturers, resistivity of solvent extract (ROSE) testing, developed in the 1970s for high-solids rosin fluxes (e.g., RMAs) and chlorofluorocarbon (CFC) cleaning, has been used to address these questions.

Military standards, such as MIL-STD-2000, and commercial standards, such as J-STD-001, have mandated use of ROSE testing as a differentiator between “acceptably clean” and “unacceptably dirty,” using a metric of 1.56μg of sodium chloride equivalence per square centimeter of surface area. Numerous pieces of automated test equipment have been developed around this test and acceptance metric. But, as many have found to their detriment, this dividing line between “good” and “bad” is no longer reliable, as the chemical nature of the fluxes and cleaning chemistries is completely different from the 1970s.

Research presented at IPC and SMTA conferences has illustrated that a manufacturer can no longer rely on ROSE testing alone for product acceptance. In 2015, the leadership of the IPC J-STD-001 committee, recognizing these facts, tasked a small group of subject matter experts (SMEs) to rewrite J-STD-001 chapter 8 (on ionic cleanliness) and define what the next generation of ionic contamination testing would be. As there was a perceived high level of misunderstanding of this test, the experts were asked to generate educational material that would explain the new protocol in layman’s terms. I was privileged to lead this group of SMEs, shown in TABLE 1.

Table 1. Ionic Contamination Subject Matter Experts

This group presented its recommendations to the J-STD-001 committee. The new protocol has become J-STD-001, Revision G, Amendment 1, Section 8, and IPC membership is currently voting on its acceptance. Under the auspices of IPC, this group also published a white paper (IPC-WP-019) explaining the new approach, paragraph by paragraph. That white paper was being revised based on minor changes agreed upon at the IPC Apex meetings in February 2018, and should be available by the time this article is published. In addition, as part of the IPC “Wisdom Wednesday” offerings, a 30-min. overview of the approach was recorded and is available on YouTube.

A three-hour workshop on the new protocol was presented at IPC Apex, and it is anticipated it will be presented again at the SMTA/IPC-sponsored Cleaning and Coating Conference in November in Chicago. Those involved with either cleaning or coating in their facility are encouraged to attend this conference (smta.org/cleaning), which is held every other year.

Rather than trying to summarize the new protocol, which the white paper does very well, here are four main points an electronics assembler should be aware of:

• Use of ROSE testing as the only measure of ionic contamination should be considered an obsolete practice.
• Use of ROSE testing as a process control tool is perfectly valid and encouraged, but the numbers have to mean something.
• The new protocol addresses both clean and no-clean assembly processes.
• The new protocol centers on the concept of a qualified manufacturing process with supporting objective evidence.

The IPC committees are also working on updating other documents, such as ROSE and SIR test methods, that relate to the new approach. It is recognized this will be a massive undertaking to change how the world benchmarks and controls ionic contamination. But, just as the mandated elimination of CFCs in the 1990s forced us to understand fluxes and residues much better than we had previously, these new changes too will help us understand what levels of ionic residues equate to reliable assemblies in the field.

Doug Pauls is principal materials and process engineer at Rockwell Collins (rockwellcollins.com); doug.pauls@rockwellcollins.com.

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