What is Objective Evidence?
It is required by IPC-J-STD-001 - Cleaning and Residue Requirements – For Qualifying a Manufacturing Process.
However, even if you don't build to standards, Objective Evidence is VERY important!
Well, there are two answers to this.
1. If you work to IPC J-STD-001 you will need to qualify your manufacturing process by producing data demonstrating compliance with the standard.
You may remember the ROSE test which had the number 1.56µg/cm² as the pass/fail limit. This test has now been removed and is no longer a requirement for quality. OE is the replacement.
2. There are two ways to achieving Objective Evidence.
The primary objective is to mitigate the phenomenon of Electro-Chemical Migration (ECM). ECM affects all board manufacturers whether they clean or not!
The first part is to initially demonstrate that your assembly meets the requirements of OE. J-STD-001 states to use SIR or Ion Chromatography
The second part is to demonstrate that you are meeting your OE requirements continuously i.e every day of the week or every week of the year. For this, it is recommended to use Process Ionic Contamination Testing (PICT).
Jstd001 does not detail how OE is met on a day to day basis. It tells you how to do it once, but not repeatably.
To meet the requirements of OE repeatably, the use of SIR, IC and PICT should be applied in the following way:
Obtain the OE, using the SIR technique. If the circuit assembly fails the SIR test, then an investigation using IC can be used to help identify the offending chemistry and likely source.
Once the OE has been achieved with the SIR test, boards from the same batch can be used to establish a PICT level for this board. The PICT value for actual assembly board can be measured when the process has been transferred from the SIR test board to an actual production board. These PICT values can be used in Industry 4.0 context with regular sampling from the production line.
This question is answered in the section 'Why is OE an issue today?'.
It is very important to note that it cannot be assumed that a no-clean assembly process avoids the requirements set out in Section 8 of J-STD-001 because ECM affects all electronic assemblies.
Of course, the final operating environment might minimise this effect, but latest research is showing that ECM might develop far longer into the service life than expected.