New test standards for electronics manufacturing – and the need for objective evidence…

Author : Andy Naisbitt | CEO | GEN3

01 September 2021

Gen3_New Test Standards
Gen3_New Test Standards

Why do we test and set standards in the electronics industry? Using a system ensures that there is a common global measurement platform that helps catch technical errors and determines whether manufacturing output meets quality compliance, thereby reducing risk when bringing new products to market.

This article was originally featured in EPDT's H2 2021 Electronics Outsourcing supplement, included in the September 2021 issue of EPDT magazine [read the digital issue]. And sign up to receive your own copy each month.

Here, Andy Naisbitt, CEO at electronics industry test & measurement expert, GEN3 introduces new revised test methods that manufacturers will need to hold themselves accountable to in order to reduce electro-chemical failure risk and increase reliability…

Objective evidence is defined by lawyers as “evidence that is not subject to bias, and is quantifiable and able to be independently confirmed and verified using analytical or other tools”. In other words, objective evidence is based on facts that can be independently examined, evaluated and verified. So what are the current international standards for electronics manufacturers – and what kind of objective evidence do they provide?...

The resistivity of solvent extract (ROSE) test, developed in the early 1970s, measures the presence and average concentration of soluble ionic contaminants on, for example, a printed circuit assembly. When it was developed, as a means of process monitoring, it corresponded with design rules, process materials and operating environments typical of that period. The test result was expressed as a single pass-fail value, in terms of a sodium chloride equivalence that related to the whole assembly, and was not necessarily representative of its actual cleanliness level.

But technology moves on: line widths and spaces decrease, as do component stand-off heights. Fluxes and solder paste formulations change. Printed circuit assemblies are expected to reliably withstand harsh operating environments. Consequently, new standards for cleanliness testing have been developed. And although it can still be used for process monitoring, the ROSE test is no longer considered appropriate for process qualification; alternative methods must be used to determine meaningful cleanliness levels and to provide objective evidence that residues left on an assembly will not lead to failure under conditions of temperature, humidity and voltage bias – typically as consequences of electromigration or dendritic growth.

Several new revised International Standards now form part of the IEC 61189-5 Series: Test methods for electrical materials, printed boards and other interconnection structures & assemblies:

•  IEC 61189-5-501:2021 is used to quantify the deleterious effects of flux residues on surface insulation resistance (SIR) in the presence of moisture.

•  IEC 61189-5-502:2021 is used for evaluating changes to the surface insulation resistance of a pre-selected material set on a representative test coupon, quantifying the deleterious effects of improperly used materials and processes that can lead to decreases in electrical resistance.

•  IPC J-STD-001 describes materials, methods and verification criteria for producing high-quality soldered interconnections. The latest revision is J-STD-001H, which has a new section on cleanliness and residue testing.

Gen3_New Test Standards_Objective Evidence
Gen3_New Test Standards_Objective Evidence

The aim is to establish a qualified manufacturing process, in the knowledge that different types of assembly will have different critical cleanliness requirements, and assess how well it is controlled. A manufacturing process cannot be qualified through chemical analysis alone, and must be determined by testing using temperature/humidity/voltage-bias techniques.

Testing therefore now has to include objective evidence to indicate whether any of the chemical species remaining on the assembly will affect its electronic reliability in environments where it is subject to temperature differences or humidity differences. Ionic cleanliness testing in itself is effectively only a chemical test. But provided it can be related to the electromigration of the ionic species causing harmful effects, it can be used as a route to creating objective evidence to qualify a process.

Any substantial change in the process will require re-qualification, with objective evidence based on data derived from tests to demonstrate that residual chemical species do not adversely affect the reliability of the assembly. The data could be generated using SIR testing, in combination with ionic cleanliness testing or other functional testing, as agreed between user and supplier. Typical major changes could include flux, solder, cleaning agent, solder mask type, solderable finish, change of PCB supplier, and so on.

Objective evidence will also be required to qualify changes in such process settings as reflow profiles and cleaning parameters that are outside the process windows defined in the qualification of the process.

Sampling frequency and control limits for process monitoring will have been established as part of the process qualification procedure, and these should be statistically-based. Traditionally, ROSE testing was used for process monitoring. A contemporary development of this test, process ionic contamination testing (PICT), as detailed in IEC 61189-5-504, provides a fast and effective method of process control.

SIR testing of assemblies can provide the necessary objective evidence required by the recently published IPC-J-STD-001 Revision H, and the accompanying white paper, WP019B. This revision removed the sole requirement of <1.56µg/cm2 of NaCl equivalent of the old ROSE test, marking a fundamental change in approach. This SIR test is augmented by a modified ROSE test, better known as PICT, as detailed in IEC 61189-5-504. This test method provides the fastest and most effective method of process control, taking less than 15 minutes.

An assembly process involves a number of different process materials, including solder flux, solder paste, solder wire, underfill materials, adhesives, staking compounds, temporary masking materials, cleaning solvents, conformal coatings and more. The test employs two different test conditions: 85 °C and 85% relative humidity (RH), preferred for a process that includes cleaning; or 40 °C and 90% relative humidity (RH), preferred for processes where no cleaning is involved.

Gen3_Objective Evidence_Image 2
Gen3_Objective Evidence_Image 2

Testing is material (set) and process/equipment specific. Qualifications should be performed using the actual production equipment, processes and materials.

GEN3 President, Graham Naisbitt was the IEC TC91 Maintenance Leader for these new test standards, and commented: “These documents reflect the latest developments of measurement technology that we have been evolving with our peers over the past 25 years. The new test method IEC 61189-5-502, used for process characterisation of assemblies, is the latest revision, derived from research conducted by National Physical Laboratory (NPL) between 1999 and 2006.

“For more than 25 years, the industry largely relied on a now defunct criteria of the weight of ionic contamination. This redundant concept has been replaced in a step change improvement by pivoting iconic contamination measurement to be used as a process control method. With industry experts, we have developed a new standard, ‘Process Ionic Contamination Testing (PICT), IEC 61189-5-504’, published in 2020. This test method provides the user with control evidence in less than 15 minutes.

“This is the culmination of more than six years of research, bringing the very latest in test and measurement methodology. Introduced between 2020 and 2021, IEC have now provided the electronics industry with the tools to provide the required objective evidence.”

The documents comprise:

•  IEC TR 61189-5-506 – a Technical Report evaluating differing conductor spacings

•  IEC 61189-5-501 – surface insulation resistance (SIR) testing of solder fluxes

•  IEC 61189-5-502 – surface insulation resistance (SIR) testing of assemblies

•  IEC 61189-5-504 – process ionic contamination testing (PICT)

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