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Determining acceptable cleanliness demands significantly more investigation than has historically been the case. Until recently, the industry has been too reliant on the use of a “cleanliness” level of2NaCl equivalence. That has been removed from the venerable IPC-J-STD-001 now in Revision H.
With increasing packaging density, coupled with hostile operating conditions, the incidence of circuit failure has increased. Such failures are, most likely, the result of adverse electrochemical migration. Dendrites are the result.
Today’s non-negotiable requirement is to produce objective evidence. The two tools that have been proven to be up to the task, are SIR followed by PICT. What can also be seen is the plethora of issues that must be addressed.
For far too many years, the industry had been using the term “cleanliness,” which was particularly unsuitable because:
- Cleanliness assumes you have tested all possible contaminants on the board. You can’t do this.
- Process control assumes you are removing the same contaminants every time. You can do this reliably and reproducibly.
As explained in the new IPC WP019B, the requirement is to use SIR. This technique measures changes to insulation resistance by examining a representative example of the intended end-product from an electro-chemical standpoint.
To read this entire article, which appeared in the June 2021 issue of SMT007 Magazine, click here.