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IPC-WP-019
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IPC-WP-019 2017 Edition, August 1, 2017 An Overview on Global Change in Ionic Cleanliness Requirements
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Description / Abstract:
Overview
For many years, military (e.g., MIL-STD-2000) and commercial (e.g., IPC-J-STD-001) manufacturing standards have required manufactured circuit card assemblies (CCAs) to meet an ionic cleanliness requirement of 1.56 microgram (μg) of sodium chloride (NaCl) equivalence per square centimeter (cm2) of extracted surface, using Resistivity of Solvent Extract (ROSE) testing per IPC-TM-650, Method 2.3.25. It is the position of the IPC committees that the value of 1.56 μg NaCl equivalence per square centimeter should be considered as obsolete for the following reasons:
• This test methodology was originally developed in the 1970s; it was never intended to be used as a cleanliness test, nor as a test for product acceptability, it was only intended to be used as a process control method • The use of the ionic contamination value as a measure of product acceptance was the result of a US Department of Defense desire to implement a pass/fail criteria.
• This ionic contamination value, and those derived from them, were originally developed for high solids (35% solids) rosin fluxes and ozone depleting chemical (ODC) cleaning. The flux chemistries and cleaning solutions used today are completely different from those used when the ROSE limits were established.
• Modern assemblies are simply too complex in terms of residues to have a single ‘‘one size fits all’’ cleanliness criterion.
• There is mounting evidence that as CCA component density increases, so does the sensitivity of the circuit to ionic contamination. Modern circuit assemblies have far greater component densities than found in the 1970s. This also means that residues that had minimal impact on 1970s component technologies can now have a significant impact on component reliability.
• For many assemblies, ROSE testing is no a longer sufficient test regimen to adequately predict acceptable levels of ionic residues. IPC has compiled a list of technical presentations showing the inadequacy of ROSE to predict ionic residues for high performance electronics (see last page of the document).
• It is recognized that ionic residue testing is critical for reliable circuit function and so the ROSE test has continued in use until a more suitable alternative can be identified and implemented.
IPC Technical Report 583 (IPC-TR-583, 1995) documents an extensive review of the ionic contamination testers on the market at that time. In general, it was found that the automated ROSE testers suffered from a lack of repeatability and reproducibility, even within the same make and model of tester. One of the conclusions was that the established ‘‘equivalency factors,’’ allowing comparison of values generated by different ionic cleanliness testers, were also invalid. The Executive Summary of IPC-TR-583 is included with this document as Appendix A. The full technical report is available from the IPC.
It should be noted that the TR-583 conclusions refer to the ionic testers of that era (1990s). Many of the more modern configurations of the ionic testers have been shown to be repeatable and reproducible. See Reference [36] as an example of testing modern instruments for repeatability and reproducibility. However, many of the instruments from that era are still in service today, so the TR-583 conclusions are still pertinent for older equipment.
Many of the other references in the Bibliography section can assist the reader in understanding the history of the ROSE test, as well as some of the shortcomings of using ROSE as a measure of product acceptance
For many years, military (e.g., MIL-STD-2000) and commercial (e.g., IPC-J-STD-001) manufacturing standards have required manufactured circuit card assemblies (CCAs) to meet an ionic cleanliness requirement of 1.56 microgram (μg) of sodium chloride (NaCl) equivalence per square centimeter (cm2) of extracted surface, using Resistivity of Solvent Extract (ROSE) testing per IPC-TM-650, Method 2.3.25. It is the position of the IPC committees that the value of 1.56 μg NaCl equivalence per square centimeter should be considered as obsolete for the following reasons:
• This test methodology was originally developed in the 1970s; it was never intended to be used as a cleanliness test, nor as a test for product acceptability, it was only intended to be used as a process control method • The use of the ionic contamination value as a measure of product acceptance was the result of a US Department of Defense desire to implement a pass/fail criteria.
• This ionic contamination value, and those derived from them, were originally developed for high solids (35% solids) rosin fluxes and ozone depleting chemical (ODC) cleaning. The flux chemistries and cleaning solutions used today are completely different from those used when the ROSE limits were established.
• Modern assemblies are simply too complex in terms of residues to have a single ‘‘one size fits all’’ cleanliness criterion.
• There is mounting evidence that as CCA component density increases, so does the sensitivity of the circuit to ionic contamination. Modern circuit assemblies have far greater component densities than found in the 1970s. This also means that residues that had minimal impact on 1970s component technologies can now have a significant impact on component reliability.
• For many assemblies, ROSE testing is no a longer sufficient test regimen to adequately predict acceptable levels of ionic residues. IPC has compiled a list of technical presentations showing the inadequacy of ROSE to predict ionic residues for high performance electronics (see last page of the document).
• It is recognized that ionic residue testing is critical for reliable circuit function and so the ROSE test has continued in use until a more suitable alternative can be identified and implemented.
IPC Technical Report 583 (IPC-TR-583, 1995) documents an extensive review of the ionic contamination testers on the market at that time. In general, it was found that the automated ROSE testers suffered from a lack of repeatability and reproducibility, even within the same make and model of tester. One of the conclusions was that the established ‘‘equivalency factors,’’ allowing comparison of values generated by different ionic cleanliness testers, were also invalid. The Executive Summary of IPC-TR-583 is included with this document as Appendix A. The full technical report is available from the IPC.
It should be noted that the TR-583 conclusions refer to the ionic testers of that era (1990s). Many of the more modern configurations of the ionic testers have been shown to be repeatable and reproducible. See Reference [36] as an example of testing modern instruments for repeatability and reproducibility. However, many of the instruments from that era are still in service today, so the TR-583 conclusions are still pertinent for older equipment.
Many of the other references in the Bibliography section can assist the reader in understanding the history of the ROSE test, as well as some of the shortcomings of using ROSE as a measure of product acceptance